The Halogen Bond

Abstract

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

Figure 1

Schematic representation of the halogen bond.

Figure 2

Ball-and-stick representation (Mercury 3.3) of the Br₂···O(CH₂CH₂)₂O (top) and Br₂···C₆H₆ (bottom) adducts. Both adducts contain infinite chains formed by dibromine as the bidentate XB donor and dioxane, or benzene, as the bidentate XB acceptor. Color code: carbon, gray; oxygen, red; bromine, light brown. XBs are dotted black lines. Hydrogen atoms are omitted for clarity. CSD Refcodes are reported. Reprinted with permission from ref (63). Copyright 2015 Springer.

Figure 3

Ball-and-stick representation (Mercury 3.3) of the halogen-bonded infinite chains containing 1,4-diiodotetrafluorobenzene as the bidentate XB donor and n-Bu₄N⁺Br^– (OHOWAQ),n-Bu₄N⁺Cl^– (OHOVUD), and n-Bu₄N⁺SCN^– (AHAJEZ) as XB acceptors. Quite similar infinite chains are obtained when n-Bu₄P⁺Br^–, Me₄N⁺Br^–,n-Bu₄P⁺Cl^–, and Me₄N⁺Cl^–  are used. Cations are omitted for clarity. Color code: carbon, gray; nitrogen, blue; bromine, light brown; chlorine, light green, sulfur, dark yellow; fluorine, yellow. XBs are dotted black lines. CSD Refcodes are reported.

Figure 4

Ball-and-stick representation (Mercury 3.3) of the halogen-bonded infinite chains containing 1,4-diiodotetrafluorobenzene as the bidentate XB donor and neutral Lewis bases as bidentate XB acceptors. The selected Lewis bases are 4,4′-dipyridine (QUIHBEO),N,N,N′,N′-tetramethyl-p-phenylendiamine (MOFFUI), dioxane (DIVDAO), 1,4-benzoquinone (ZARFUV), thiourea (NUSBUZ), and triphenylphosphine selenide (ZEBJUN). Quite similar infinite chains are obtained when other nitrogen-centered nucleophiles,^−, oxygen-centered nucleophiles, and sulfur-centered nucleophiles are used. Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; sulfur, dark yellow; phosphorus, orange; selenium, dark orange; fluorine, yellow. XBs are dotted black lines. Hydrogen atoms are omitted for clarity. CSD Refcodes are reported.

Figure 5

Number of papers per year having “halogen bonding” in the title and/or abstract (source SciFinder, search performed in November 2015).

Figure 6

Short and directional XBs existing in halonium salts. Phenyl[2,2-dimethyl-4-(diethylphosphono)-2,5-dihydro-3-furyl]iodonium perchlorate (VOYXEM): one oxygen of the phosphonate residue and one oxygen of the perchlorate anion work as XB acceptors. [2-Ethoxy-2-oxo-1-(triphenyl-λ⁵-phosphanylidene)ethyl]phenyliodonium tetrafluoroborate (IWUKEQ): the carbonyl oxygen of the carbethoxy residue and a fluorine atom of the fluoroborate anion work as XB acceptors. Bis(pentafluorophenyl)bromonium tetrafluoroborate (HOHJUJ): BF₄^– works as a bidentate XB acceptor as the XB donor ability of Br is increased by strong electron-withdrawing residues. Hydrogen atoms have been omitted, XBs are dashed lines, and the numbers are the C–X···nucleophile angles (deg) and lengths of the halogen bonds (Å). Color code: carbon, gray; oxygen, red; iodine, purple; chlorine, light green; phosphorus, orange; fluorine, yellow; boron, pink. XBs are dotted black lines. Hydrogen atoms are omitted for clarity. CSD Refcodes are reported.

Figure 7

Selected examples of σ-hole interactions. Short and directional chalcogen bonds formed in the solid state by the sulfur atom of two derivatives of thiamin, a vitamin of the B complex, on the elongation of one (THIMHC) or both (MEMKEU) of its covalent bonds. Pnicogen bonds formed by arsenic atoms in 2-chloro-1,3-bis(4-methoxyphenyl)-2,3-dihydro-1H-bisthieno[3,2-e:2′,3′-g][1,3,2]benzodiazarsole (BAYREA) and arsenic trichloride dipyridyl (ASCDPY). Hydrogen atoms are omitted for clarity, chalcogen and pnicogen bonds are dotted lines, and the numbers are the angles (deg) and lengths of the chalcogen and pnicogen bonds (Å). Color code: carbon, gray; nitrogen, blue; oxygen, red; chlorine, light green; sulfur, dark yellow; phosphorus, orange; arsenic, violet. CSD Refcodes are reported.

Figure 8

Calculated B3PW91/6-31G** electrostatic potentials of SCl₂ (A), As(CN)₃ (B), and SiCl₄ (C, D) computed on the 0.001 electron/bohr³ contour of the electronic density. (A) SCl₂: the sulfur is in the foreground, and the chlorines are at the back. Color ranges (kcal/mol): purple, negative; blue, between 0 and 8; green, between 8 and 15; yellow, between 15 and 20; red, more positive than 20. (B) As(CN)₃: the arsenic is in the middle, toward the viewer. Color ranges (kcal/mol): red, greater than 45; yellow, between 30 and 45; green, between 15 and 30; blue, between 0 and 15; purple, less than 0 (negative). (C, D) SiCl₄: electron density views of different orientations of the molecule. In the (C) view three chlorine atoms are toward the viewer, and the σ-hole, due to the Cl–Si bond to the fourth chlorine, is in red in the center and on the extension of that Cl–Si bond. In the (D) view two chlorine atoms are toward the viewer. Color ranges (kcal/mol): purple, negative; blue, between 0 and 8; green, between 8 and 11; yellow, between 11 and 18; red, more positive than 18. Panel A adapted with permission from ref (143). Copyright 2008 Springer. Panel B adapted with permission from ref (133). Copyright 2007 John Wiley and Sons. Panels C and D adapted with permission from ref (6). Copyright 2008 Springer.

Figure 9

Electrostatic potential calculated at the M06-2X/aug-cc-pVTZ computational level on the 0.001 au molecular surface of PF(CH₃)(CN). Phosphorus is in the middle facing the viewer, the cyano group is to the left, the methyl group is to the top right, and fluorine is to the bottom right. Color ranges: red, greater than 1.26 V; yellow, from 1.26 to 0.65 V; green, from 0.65 to 0 V; blue, less than 0 V (negative). Reprinted with permission from ref (144). Copyright 2015 Springer.

Figure 10

Laplacian distribution for the (100) plane of solid chlorine, solid contours denoting negative values for the gradient of electron density. Reprinted with permission from ref (156). Copyright 1995 International Union of Crystallography.

Figure 11

Structural scheme for type I (left) and type II (right) halogen···halogen short contacts. X = halogen atom, and R = C, N, O, halogen atom, etc. Type II contacts are XBs.

Figure 12

Histogram of I···I contacts and assignment of type I and type II geometries. Adapted from ref (160). Copyright 2014 American Chemical Society.

Figure 13

Scatterplot derived from a CSD search reporting the C–X···N angle (deg) versus the X···N distance (Å) for crystal structures containing X···N contacts. Color code: blue rhombuses, I···N contacts; pink squares, Br···N contacts; green triangles, Cl···N contacts. Only error-free and nonpolymeric structures containing single-bonded I, Br, or Cl atoms and showing no disorder with R < 0.05 are considered.

Figure 14

XBs around hexacyclic amines and thioethers feature axial (left) and equatorial (right) directions, respectively. XBs are dotted black lines. Color code: carbon, gray; nitrogen, blue; iodine, purple; bromine, light brown; sulfur, dark yellow. Hydrogen atoms are omitted for clarity. CSD Refcodes are reported. In ULOJUA the disorder on 1,2-dibromotetrafluoroethane is omitted.

Figure 15

Angular geometries of complexes formed by FCl with simple π-electron donors (A) FCl···ethyne and (B) FCl···ethene and with aromatic π-electron donors (C) FCl···benzene and (D) FCl···furan.

Figure 16

Molecular electrostatic potential at the isodensity surface with 0.001 au for CF₄, CF₃Cl, CF₃Br, and CF₃I. Color ranges: red, greater than 27 kcal/mol; yellow, between 20 and 14 kcal/mol; green, between 12 and 6 kcal/mol; blue, negative. Adapted with permission from ref (145). Copyright 2007 Springer.

Figure 17

Molecular electrostatic potential at the isodensity surface with 0.001 au of F₂ and CF₃SO₂OCOF (the CF₃ group is on top). Color ranges: red, greater than 20 kcal/mol; yellow, between 20 and 9 kcal/mol; green, between 9 and 0 kcal/mol; blue, negative. The black hemispheres denote the positions of the most positive potentials associated with the fluorine atoms. Reprinted with permission from ref (195). Copyright 2011 Royal Society of Chemistry.

Figure 18

XB donors and XB acceptor and plot of the N···I separation in the corresponding adducts as a function of the number of fluorine atoms on the donor. N···I distances are reported in picometers. Adapted from ref (202). Copyright 2009 American Chemical Society.

Figure 19

Chemical structures of C(sp)-bonded XB donors (IEIB and BEIB), activated C(sp²)-bonded donors (1,4-DITFB and DBTFB), and nonactivated C(sp²)-bonded donors (DIB and DBB) cocrystallized using a solvent-drop grinding methodology. The six XB donor molecules are reported in order of decreasing V_S,max values (from left to right) associated with the most positive σ-hole on their halogen atoms. V_S,max values are the numbers reported near the corresponding atom and are given in kilojoules per mole. Adapted with permission from ref (209). Copyright 2013 John Wiley and Sons.

Figure 20

Ball-and-stick representation of the cocrystals of 1-(iodoethynyl)-4-iodobenzene with 4-phenylpyridine (BISBIQ) and (bromophenyl)benzimidazole (BISBEM). XBs, type I iodine···iodine contacts, and iodine···π interactions are represented as dotted black lines. Color code: carbon, gray; nitrogen, blue; iodine, purple; bromine, light brown; hydrogen, white. CSD Refcodes are reported.

Figure 21

Schematic representation of the anisotropic distribution of the electron density around covalently bound halogen atoms and the pattern of the resulting interactions.

Figure 22

Computed electrostatic potentials on 0.001 au molecular surfaces of (A) chlorobenzene, (B) pentafluorochlorobenzene, (C) bromobenzene, (D) pentafluorobromobenzene, (E) iodobenzene, and (F) pentafluoroiodobenzene. Color range (kcal/mol): red, greater than 20; yellow, between 20 and 10; green, between 10 and 0; blue, negative. Black hemispheres denote the positions of the halogen V_S,max. Adapted with permission from ref (205). Copyright 2011 Springer.

Figure 23

Computed electrostatic potential V_S(r) on the 0.001 au surface of F₃C–Br (top) and NC–Br (bottom). For each molecule bromine is at the right. Color range (kcal/mol): red, more positive than 35; yellow, 20–35; green, 0–20; blue, negative. The position of the bromine V_S.max is indicated as a black dot. In F₃C–Br, the σ-hole is an area of positive (yellow and green) V_S(r) on the outer surface of the bromine; the lateral sides of bromine are negative (blue) because of the two pairs of electrons in the 4p_x and 4p_y orbitals. In NC–Br the presence on bromine of an electron-withdrawing substituent stronger than CF₃ causes such a polarization of the charge in the doubly occupied 4p_x and 4p_y orbitals of Br that the potential V_S(r) becomes positive over the entire surface of the halogen atom. Adapted with permission from ref (254). Copyright 2010 John Wiley and Sons.

Figure 24

Calculated electrostatic potential on the 0.001 au molecular surface of a chlorine atom in the s²p_x²p_y²p_z¹ valence state configuration. Color ranges (V): red, greater than 0.43; yellow, from 0.43 to 0.22; green, from 0.22 to 0; blue, less than 0 (negative). The most positive potentials on the chlorine surface, shown in red at the left and right, have a V_S,max of 0.95 V. Computational level: M06-2X/aug-cc-pVTZ. Reprinted with permission from ref (144). Copyright 2015 Springer.

Figure 25

Computed electrostatic potential, B3PW91/6-311G(3d), of the chlorine atom in its valence state, 3s²3p_x²3p_y²3p_z¹, as a function of the radial distance from the nucleus. The upper and red curve corresponds to the z-axis, the lower and blue curve to the x- and y-axes. In this valence state, V(r) is still positive at all radial distances along the z-axis, corresponding to the half-filled p_z orbital. Along the x- and y-axes, however, V(r) is positive near the nucleus but then becomes negative, reflecting the doubly occupied p_x and p_y orbitals. Reprinted with permission from ref (26). Copyright 2010 Royal Society of Chemistry.

Figure 26

Triangular structure for the (R–X)₃ trimer.

Figure 27

Interaction energy vs bromine V_S,max for 13 Ar—Br···O=C(CH₃)₂ complexes, where Ar = substituted benzene or pyrimidine (R = 0.976). Reprinted from ref (257) Copyright 2009 American Chemical Society.

Figure 28

Top: variation of the fraction δ_i of an electronic charge transferred from B to YX on formation of the YX···B complex with the ionization energy I_B of B for the series YX = Cl₂, ClBr, and ClI. Each set of points can be fitted reasonably well by the function δ_i = A exp(−aI_B), which is represented as a solid curve on the graph. It is evident that there is a family relationship among the curves. Bottom: variation of the fraction δ_p of an electronic charge transferred from X to Y on formation of the YX···B complex plotted against the intermolecular stretching force constant k_σ for the series YX = Cl₂, Br₂, ClBr, and ClI. The solid line represents the least-squares fit of the points for each YX···B series for a given YX, and δ_p is an approximately linear function of k_σ and hence of the strength of the interaction. Moreover, for a given B δ_p increases with the polarizabilities of the interacting atoms X in YX···B.

Figure 29

(Top) V_S(r) (calculated at the B3LYP/6-311+G(dp) level on the 0.001 electron/bohr³ molecular surfaces) of the XB donors and acceptors superimposed onto X-ray structures of their complexes: (A) CBr₄/[CuBr₂]⁻; (B) CBr₄/[ZnBr₄]^2–; (C) CBr₄/[Pt₂Br₆]^2–. Blue and red colors depict positive and negative potentials, respectively. (Middle) The electrostatic potentials of bromometalate anions are negative everywhere, but noticeable variations of their values are also observed and depicted with a color gradient from the most negative (red) to the least negative (blue) values (kcal/mol): (A) [CuBr₂]⁻, from −100 (red) to −80 (blue); (B) [ZnBr₄]^2–, from −170 (red) to −150 (blue); (C) [Pt₂Br₆]^2–, from −155 (red) to −125 (blue). (Bottom) MO shapes (B3LYP/6-311+G(dp) level) of CBr₄ and halometalates, superimposed onto crystal structures of their complexes. HOMOs of bromometalates are mostly located on the bromide ligands. Adapted from ref (218). Copyright 2012 American Chemical Society.

Figure 30

Orbital interaction diagrams for (A) XB and (B) HB arising in R–X···Y^– and R–H···Y^– complexes. Only the σ interactions are shown. Adapted with permission from ref (219). Copyright 2014 John Wiley and Sons.

Figure 31

(A) V_S(r) of the CF₃I molecule and represented in blue the σ-hole. (B) Visualization of σ-hole formation using the deformation density contributions originating from NOCV. The contour of the deformation density contribution Δρ₁ describes the formation of the C–I bond in the CF₃I molecule starting from an iodine atom and the CF₃ radical (each carrying one unpaired electron with opposite spin polarization). A charge accumulation at iodine is observed due to formation of the C–I bond, which confirms significant charge anisotropy around this atom. An outflow of electron density emerges from the outer area of the iodine atom, which clearly corresponds to the formation of the σ-hole. The corresponding ETS-NOCV-based energy is shown. The numerically smallest contour values are ±0.0006 au. (C) Contour of the deformation density contribution Δρ₁ describing the formation of the XB in the CF₃I···NH₃ complex.

Figure 32

Molecular electrostatic potential at the isodensity surface of CF₃–I (A) and CI₄ (C) at the same contour value of 0.001 electron/bohr³. The red color shows the most negative potential, while the blue color represents the most positive one. The σ-holes of CF₃–I (B) and CI₄ (D) in the presence of a 1.0 point charge are also depicted. Energies are expressed in atomic units. Reprinted with permission from ref (217). Copyright 2012 Royal Society of Chemistry.

Figure 33

Molecular electrostatic potential (MEP) calculated at the MP2/aug-cc-pVDZ level on the 0.001 au isodensity surface of CH₃Cl in the presence of a charge of −0.2692 at a distance of 3.0 Å from the chlorine atom along the extension of the C–Cl bond. The MEP on the chlorine reflects the polarization caused by the electric field of the negative charge, and a region of positive electrostatic potential (σ-hole) appears on the chlorine surface. Reprinted with permission from ref (231). Copyright 2015 Wiley and Sons.

Figure 34

Top: electrostatic potentials of H₃C–Br (A), H₂FC–Br (B), HF₂C–Br (C), and F₃C–Br (D). Color code: lightest blue, <−5 kcal/mol; intermediate blue, between −5 and −2.5 kcal/mol; dark blue, between −2.5 and 0 kcal/mol; green, between 0 and 4 kcal/mol; yellow, between 4 and 8 kcal/mol; pink, between 8 and 16 kcal/mol; red, >16 kcal/mol. Bottom: potential energy curves calculated at the CCSD(T)/aug-cc-pVTZ level for the four complexes H_nF_3–nCBr···NH₃. Reprinted with permission from ref (278). Copyright 2013 Royal Society of Chemistry.

Figure 35

DFT-SAPT components, electrostatics (E(elec)), induction or polarization (E(ind)), dispersion (E(disp)), and exchange (E(exch)), and total binding energies (E(int)^T), for the H₃CBr···NH₃ (solid lines) and F₃CBr···NH₃ complexes (dashed lines) (kcal/mol). Potential energy minima are shown as vertical dashed lines. H₃CBr···NH₃ is green, and F₃CBr···NH₃ is light blue. Reprinted with permission from ref (278). Copyright 2013 Royal Society of Chemistry.

Figure 36

Variation of energy components with the tilt angle θ of FCl···B complexes away from linearity (B is the electron donor). The angle φ was held at 55° for FCl···FH, 69° for FCl···O=CH₂, 0° for FCl···OH₂, and 48° for FCl···O₂S. The components are (black solid) exchange repulsion, (red solid) electrostatics, (green dashed) dispersion, and (blue dashed–dotted) induction. The heavy black line represents the total. Reprinted from ref (279). Copyright 2013 American Chemical Society.

Figure 37

Potential energy V(φ) of the molecules ClI···OH₂ (top) and ClI···SH₂ (bottom) as a function of the angle φ made by the extension of the C₂ axis of the H₂O and H₂S molecules with the I···O and I···S internuclear axes (as defined in Table 2). Reprinted with permission from ref (188). Copyright 2015 Springer.

Figure 38

Intermolecular force constant k_σ against the nucleophilicity N_Y of Lewis bases Y for six series of halogen-bonded complexes RX···Y (top) and the two series ClI···Y and CF₃–I···Y (bottom). The slope of each line yields the electrophilicity E_RX by means of the expression k_σ = cN_YE_RX, and the value c = 0.25 N m^–1. Reprinted with permission from ref (188). Copyright 2015 Springer.

Figure 39

Fraction δ_i of an electronic charge transferred from Y to RX upon complexation, plotted versus the ionization energy I_Y of Y for a series of dihalogen molecules and fitted with negative exponential curves. Adapted with permission from ref (273). Copyright 2010 Royal Society of Chemistry.

Figure 40

Infrared absorption of the C–I fundamental stretching frequency for NC–I and its complexes with the compound reported above the respective bands. Reprinted from ref (374). Copyright 1959 American Chemical Society.

Figure 41

Infrared spectrum of the dimethylacetamide/iodine complex. As the I₂ concentration increases, the intensity of the free amide peak (1662 cm^–l) decreases, while the intensity of the complex peak (1619 cm^–l) increases. Reprinted from ref (394). Copyright 1960 American Chemical Society.

Figure 42

FTIR absorbance of C_α–F bending for heptafluoro-2-iodopropane in cyclohexane at various dilutions. Reprinted with permission from ref (408). Copyright 2013 Hindawi Publishing Corp.

Figure 43

Infrared spectra in the 1225–1050 cm^–1 region for solutions of mixtures of CF₃Cl (A), CF₃Br (B), and CF₃I (C) with dimethyl ether dissolved in liquid Ar (89 K). Tracs a in each panel represents the spectrum of the mixed solutions, while traces b and c are the spectra of the monomers CF₃X and dimethyl ether, respectively. The new bands assigned to the complex are marked with an asterisk. Reprinted with permission from ref (410). Copyright 2013 John Wiley & Sons, Inc.

Figure 44

Infrared (A, C, and E) and Raman (B, D, and F) spectra of the ν₃(CF₃X) region for solutions of mixtures of CF₃Cl (A, B), CF₃Br (C, D), and CF₃I (E, F) with dimethyl ether dissolved in liquid Ar (89 K). Trace a represents the spectrum of the mixed solution, trace b is the spectrum of the monomer CF₃X, and trace c is the spectrum of the complex, obtained by subtracting trace b from trace a. The new bands assigned to the complex are marked with an asterisk. Reprinted with permission from ref (410). Copyright 2013 John Wiley & Sons, Inc.

Figure 45

Pyridyl compounds used in the study of Schuster and Roberts.

Figure 46

Structure of [bis(pyridine)iodine]⁺ complexes used to study the symmetry of halonium XBs in solution. The bis(pyridinylethynyl)benzene was exploited to introduce a restraint to the complex geometry.

Figure 47

¹³C chemical shift of the C–I carbon of 1-iodo-1-hexyne as a function of the concentration of an n-donor compound in hexanes. The concentrations of the iodohexyne and the n-donor were kept approximately equal. Reprinted from ref (398) Copyright 2004 American Chemical Society.

Figure 48

Correlation of the log K_a for the halogen-bonded adducts 4-X-C₆F₄—I···O=PBu₃ with the (A) σ_para and (B) σ_meta substituent constants of X and with the electrostatic potential at the iodine atom, calculated with the (C) AM1 and (D) DFT (B3LYP/6-31+G**-LANLdp) computational methods. Adapted from ref (454). Copyright 2010 American Chemical Society.

Figure 49

¹³C SSNMR chemical shift as a function of the C–I distance for several diiodotetrafluorobenzene complexes with ammonium and phosphonium salts. The solid line represents the best exponential fit, while the dashed line represents a linear fit. Reproduced with permission from ref (74). Copyright 2013 Royal Society of Chemistry.

Figure 50

Representation of halogen-bonded crystal structures involving I₂ (VUKDIO), BrI (TASPEJ), Br₂ (TEYPES), ClI (GANXAV), Cl₂ (YATKIP and ULISAJ), and FCl (YATKOV). XBs are represented as solid lines, similar to covalent bonds, when their length is as short as a covalent bond, or as dotted black lines, when their length is close to the sum of the vdW radii of the involved atoms. Hydrogen atoms are omitted for clarity. Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; bromine, light brown; chlorine, light green, fluorine, yellow. CSD Refcodes are reported.

Figure 51

Representation of halogen-bonded crystal structures involving dihalogen molecules as XB donors and anionic XB acceptors. XBs are represented as solid lines, similar to covalent bonds, when their length is as short as a covalent bond, or as dotted black lines, when their length is close to the sum of the vdW and Pauling radii of the involved species. Cations are omitted for clarity. Color code: iodine, purple; bromine, light brown; chlorine, light green. CSD Refcodes are reported.

Figure 52

Library of halogen-bonded cocrystals involving haloalkanes as XB donors. Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; sulfur, dark yellow; chlorine, light green; fluorine, yellow. XBs are dotted black lines. Hydrogen atoms are omitted for clarity. CSD Refcodes are reported: CETNEW, (2R,6S)-6-phenyl-2-(trichloromethyl)-3-oxa-1-azabicyclo[4.1.0]heptane-2-carbonitrile; GIDJUY, methyl 4-bromo-4-cyano-6-oxabicyclo(3.2.1)octan-7-one-1-carboxylate; QOJROY, N-tribromoacetylhomoserine lactone; LUNZOK, 3,3′-bis(trichloromethyl)tetrahydro-5H,5′H-7a,7a′-bipyrrolo[1,2-c][1,3]oxazole-1,1′-dione; PEPCUK, 6-bromo-7-fluoro-2-methyl-2-azabicyclo[2.2.1]heptan-3-one; TUKGAI, N,N,N′,N′-tetramethylbenzene-1,4-diamine–1,4-diiodoperfluorobutane; FEGYEV, quinuclidine carbon tetrabromide; CLMPMO, 5-chloro-6-(dichloromethylene)-4-methoxy-1-methyl-4-(trichloromethyl)hexahydropyrimidin-2-one; PAWHAY, 2-bromo-2-methyl-1-[4-(methylsulfanyl)phenyl]propan-1-one; AWIFIW, 4-(trifluoromethyl)-N′-(2,2,2-trichloroethanimidoyl)benzene-1-carboximidamide; PILLIF, methyl 2-fluoro-4-iodocubane-1-carboxylate; ULOKEL, N-methylmorpholine–1,2-diiodotetrafluoroethane.

Figure 53

Examples of solvates wherein the chlorinated solvents are pinned by XBs. For the sake of clarity, only the supramolecular anion is reported. Metal atoms are labeled. Color code: carbon, gray; oxygen, red; bromine, light brown; chlorine, light green, hydrogen, white. XBs are dotted black lines. CSD Refcodes are reported: HIDMEN, trichloro(tripyrazolylmethane-N,N′,N″)rhenium(IV) perrhenate chloroform solvate; FIYLEG, [μ₂-1,1′-bis[(1,3-dimethylimidazolidin-2-ylidene)amino]ferrocene]chloropalladium hemi(tetrachloropalladium) dichloromethane solvate; VEGTIL, [N,N′-bis(2,6-diisopropylphenyl)triptycenylimidoformamidium]tetrabromoindium(II) chloroform solvate.

Figure 54

Representation of halogen-bonded crystal structures involving neutral haloarenes and haloperfluoroarenes: HIBENZ11, XB trigonal synthon present in the hexaiodobenzene structure; QIHBEO01, repeating unit in the infinite chain where 4,4′-bipyridine and 1,4-DITFB alternate; IOBNIT01, repeating unit in the 4-iodobenzonitrile infinite chain. Hydrogens are omitted for clarity. Color code: carbon, gray; nitrogen, blue; iodine, purple; fluorine, yellow. XBs are dotted black lines. CSD Refcodes are reported.

Figure 55

Representation of halogen-bonded crystal structures involving neutral and positively charged haloheteroarenes as XB donors. Hydrogen atoms are omitted for clarity, escept for acidic ones in DIQZEI and FEQBIO. Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; sulfur, dark yellow; chlorine, light green, fluorine, yellow. XBs and HBs are dotted black lines. CSD Refcodes are reported: MEFHOW, trimeric unit present in 5,5′-(1,3-phenylene)bis(3-benzyl-4-iodo-1-methyl-1H-1,2,3-triazol-3-ium) bis(trifluoromethanesulfonate); DIQZEI, repeating unit in the infinite chain formed by 4-chloropyridinium chloride; FEQBIO, dimer formed by 5-(1-benzyl-5-iodo-1H-1,2,3-triazol-4-yl)-3-methylpent-2-en-1-ol.

Figure 56

Representation of halogen-bonded crystal structures involving highly polarized halogen atoms. Hydrogen atoms are omitted for clarity. Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; bromine, light brown; sulfur, dark yellow. XBs are dotted black lines. CSD Refcodes are reported: DOXIAC, 1,4-dioxane and diiodoacetylene; AKOXON, bis(2,4,6-collidine)bromonium perchlorate; DEJFIH, dibenzoiodolyl pyrrolidinedithiocarbamate; IBIYUP, hexamethylenetetramine and N-bromosuccinimide.

Figure 57

Representation of halogen-bonded crystal structures involving radicals as XB acceptors. Hydrogen atoms are omitted for clarity. Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; bromine, light brown; sulfur, dark yellow; fluorine, yellow. In HUKTOW, Ni is green. XBs are dotted black lines. CSD Refcodes are reported: JEFFUW, (4-amino-2,2,6,6-tetramethylpiperidin-1-yl)oxy radical, 1,4-DITFB; HUKTOW, bis[3,4-bisiodo-3′,4′-(ethylenedithio)tetrathiafulvalene) bis(cis-1,2-dicyanoethylene-1,2-dithiolato-S,S′)nickel; LEHYEE, 2,6,10-tribromo-12-hydroxy-4H,8H-dibenzo[cd,mn]pyrene-4,8-dione.

Figure 58

Three main structural types of R₃PnX₂ adducts: the halogen-bonded adduct (left), the phosphonium halide (center), the pentacoordinated addition product (right).

Figure 59

Partial view of the halogen-bonded infinite chains formed by dimethyl sulfoxide with 1,3,5-trifluoro-2,4,6-tris(iodoethynyl)benzene (IFOHAO) and hexamethylphosphoric triamide with 1,3-dibromotetrafluorobenzene (PASLAY). Hydrogen atoms are omitted for clarity. Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; bromine, light brown; sulfur, dark yellow; fluorine, yellow. XBs are dotted black lines. CSD Refcodes are reported.

Figure 60

Partial view of the infine chain formed by XBs between iodine atoms and the π-electrons of the triple bonds in one of the polymorphs of haloprogin, the active pharmaceutical ingredient used in antimycotic topical drugs. Hydrogens are omitted for clarity. Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; chlorine, light green. XBs are dotted black lines. The CSD Refcode is reported.

Figure 61

Bromide anions can form from one to eight XBs: VOQMOD, 2-bromopyridinium bromide; GIXGEZ, part of the infinite chain formed by tetramethylammonium bromide and 1,4-DITFB; TPCBBR, part of the ribbon formed by tetraphenylphosphonium bromide and tetrabromomethane; VAPVUE, part of the adamantanoid network formed by tetraethylammonium bromide and tetrabromomethane; VAPWEP, supramolecular anion formed by tetramethylammonium bromide and tetrabromomethane. For the sake of clarity, cations have been omitted, except in the first adduct. Color code: carbon, gray; iodine, purple; bromine, light brown; fluorine, yellow. XBs are dotted black lines. CSD Refcodes are reported.

Figure 62

Isomorphous (6,3) networks where perchlorate (UZUQOW) and periodate (UZUQUC) anions are the nodes and 1,4-DITFB is the spacer. Cations were omitted for clarity. Color code: carbon, gray; oxygen, red; iodine, purple; chlorine, light green, fluorine, yellow. XBs are dotted black lines. CSD Refcodes are reported.

Figure 63

Crystal structures of 1,4-DITFB with various XB acceptors. N_c values and Refcodes are reported. XBs are dotted black lines. Adapted with permission from ref (674). Copyright 2013 Royal Society of Chemistry.

Figure 64

Crystal structures of selected discrete halogen-bonded dimers. Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; bromine, light brown; fluorine, yellow. XBs are shown as dotted black lines or as colored solid lines. CSD Refcodes are reported: LEZPOW, 2,6-dimethylpyridine–pentafluoroiodobenzene; NOGYUF, N,N,N-Dimethylpyridin-4-amine–1-fluoro-4-(iodoethynyl)benzene; MORIPA01, morpholine–1-iodo-2-phenylacetylene; XOHWOH, acridine–iodopentafluorobenzene; TMEAMI, trimethylamine–diiodine; PAQKAT, triphenylphosphineselenido–diiodine; CUXCON, triphenylarsine–iodine monobromine.

Figure 65

From LEJKUG to WUWMAD: representation of crystal structures of 0D dimeric adducts involving halogen atoms activated by positively charged scaffolds and halide anions. CILHIO22: crystal structure of a TTF derivative containing the triiodide anion. Hydrogen atoms are omitted for clarity. Color code: carbon, gray; nitrogen, blue; iodine, purple; bromine, light brown; chlorine, light green, sulfur, dark yellow; fluorine, yellow. XBs are dotted black lines and colored solid lines. CSD Refcodes are reported: LEJKUG, 2-[[4-(5-bromo-3-methyl-2-pyridyl)butyl]amino]-5-(6-methyl-3-pyridylmethyl)-4-pyrimidone trihydrobromide; CICRAI, (bromomethyl)trimethylammonium bromide; HOLLID, 1-(chloromethyl)pyridinium chloride; ZONXOP, 1-(bromodifluoromethyl)-4-(dimethylamino)pyridinium bromide; WUWMAD, 4-iodoanilinium chloride; WOQREB, trans-4-[2-(4-iodophenyl)ethenyl]pyridinium chloride; CILHIO02, bis[bis(ethylenedithio)tetrathiafulvalene] triiodide.

Figure 66

Trimeric discrete complexes formed by 1,4-DITFB with phenanthridine (TOKFEG), triphenylphosphine oxide (ANUQAC), and methyl(diphenyl)phosphine oxide (LICBIK). Trimeric complexes assembled by N-(4-bromo-2,3,5,6-tetrafluorophenyl)-2,3,5,6-tetrafluoro-4-iodobenzamide with t-BPE (DIMTEA) and by 3-iodoprop-2-yn-1-ylbutyl carbamate with 4,4′-bipyridine (XIDGAU). Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; bromine, light brown; chlorine, light green; phosphorus, orange; fluorine, yellow. XBs are dotted black lines. CSD Refcodes are reported.

Figure 67

Representation of the cyclic tetrameric superanions formed by CHCl₃ and the perchlorate anion of bis[μ₂-8-[(2-pyridylsulfanyl)methyl]quinoline]disilver(I) diperchlorate (INEYIJ) and CCl₄ and the perchlorate anion of (cis-2,6,9,13-tetrathiabicyclo(12.4.0)octadecane)nickel(II) diperchlorate (SUGVOF). Representation of the pentameric superanion assembled thanks to Il···Cl^– XBs in tetraphenylphosphonium chloride–tetrakis(1-iodo-2-phenylacetylene) (ZOMNAQ). Cations are omitted for clarity. Color code: carbon, gray; oxygen, red; iodine, purple; chlorine, light green. XBs are dotted black lines. CSD Refcodes are reported.

Figure 68

Top: molecular formula of TIPTEA (left) and representation of the single-crystal X-ray structure of the complex of TIPTEA with NaI (right). The I···I^– XB is shown as a black dotted line. Bottom: molecular formulas of TIBTM and of DIBU. Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; fluorine, yellow; sodium, light purple. XBs are dotted black lines. The CSD Refcodes are reported.

Figure 69

Left: molecular formula of AMII. Middle: single-crystal X-ray structure of the AMII iodide salt. Right: single-crystal X-ray structure of the AMII dihydrogen phosphate salt. Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; phosphorus, orange; hydrogen, white. XBs and HBs are dotted black lines. CSD Refcodes are reported.

Figure 70

Top: molecular formula of ITIPA, molecular formula of DITDIT hexafluorophosphate salt, and single-crystal X-ray structure of DITDIT chloride salt. Adapted with permission from ref (551). Copyright 2014 John Wiley and Sons. Bottom: molecular formulas of CAT1 (left) and CAT2 (right). Adapted with permission from refs (719) and (659). Copyright 2014 and 2012, respectively, John Wiley and Sons.

Figure 71

Left: cartoon representing the binding of the tris(iododifluoroacetate) guest to the folded structure of HTF by multiple I···N XBs, which further fastens the folded state and leads to an increase of the excimer emission of the appended pyrene units. Adapted with permission from ref (720). Copyright 2012 John Wiley and Sons. Right: molecular structure of BITN bound to the HP₂O₇^3– anion. Here, too, the recognition event leads to an increase of the excimer emission of the appended pyrene units. Adapted from ref (721). Copyright 2014 American Chemical Society.

Figure 72

Representation of single-crystal structures of halogen-bonded 1D infinite chains assembled via self-complementary modules. Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; fluorine, yellow. XBs are dotted black lines. CSD Refcodes are reported: PAPRIJ, 4-[2-[1-hexyl-5-[2-(tetrafluoro-4-iodophenyl)vinyl]-1H-pyrrol-2-yl]vinyl]pyridine; ACOKIM, 4-iodo-2,3,5,6-fluorobenzonitrile; PADHUY, 4-iodotetrafluorobenzaldehyde; JALLEO, 1-iodo-4-(phenylethynyl)tetrafluorobenzene; JEHREU, N,N-dimethyl-4-(E)-[2-(tetrafluoro-4-iodophenyl)vinyl]aniline.

Figure 73

1D infinite chains of halogen-substituted zwitterions: 4-bromo-3-(3-pyridyl)sydnone (BRPSYD10), (Z)-3-phenylsydnone-4-hydroximic acid chloride (FIHTIA), and 7-iodo-8-hydroxyquinolinium 5-sulfonate (IHQUSO01). Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; bromine, light brown; chlorine, light green; sulfur, dark yellow. XBs are dotted black lines. CSD Refcodes are reported.

Figure 74

Partial representation of the 1D chain: linear chain formed by t-BPE and 1,4-dibromotetrafluorobenzene (IKUHUR), stepped chains formed on self-assembly of 4,4′-dipyridyl and DIPFH (QANRUS) and DIPFO (LOQBAU). Hydrogen atoms are omitted for clarity. Color code: carbon, gray; nitrogen, blue; iodine, purple; bromine, light brown; fluorine, yellow. XBs are dotted black lines. CSD Refcodes are reported.

Figure 75

Representation of a part of the infinite chains between 4,4′dipyridyl and 1,3-dibromotetrafluorobenzene (IKUJIH)) and 1,2-dibromotetrafluorobenzene (IKUJON) and between 3,5-bis(pyrid-4′-yl)-1,2,4-oxadiazole and 1,6-diiodoperfluorohexane (BEWXIN). In BEWXIN the angle between the two pyridyl pendants of the XB acceptor (149.1°) is quite similar to the angle between the two formed XBs (141.5°). Hydrogen atoms are omitted for clarity. Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; bromine, light brown; fluorine, yellow. XBs are dotted black lines. CSD Refcodes are reported.

Figure 76

Representation of heteromeric 1D chains where 1,4-DITFB self-assembles with thiourea (NUSBUZ) and Michler’s ketone (FEQVON), both functioning as monotopic XB acceptors where the heteroatom is a bifurcated site, and with 1,10-phenanthroline-5,6-dione (EXIFEX), forcing the iodine atoms of 1,4-DITFB to work as a bifurcated XB donor. Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; bromine, light brown; sulfur, dark yellow; fluorine, yellow. XBs are dotted black lines. CSD Refcodes are reported.

Figure 77

Infinite chains produced on C–Br···Cl^– XB formation in bis(2-bromoimidazole)boronium chloride (IKUXER), C–Br···Br^– XB formation in (−)-sparteine hydrobromide/1,2-dibromohexafluoropropane (BOCGAB), C–I···Cl^– XB formation in bis[bis(ethylenedithio)tetrathiafulvalene] chloride/diiodoacetylene (PAVZIV), and C–I···Cl^– XB formation in tris[bis(ethylenedithio)tetraselenafulvalene] chloride/1,4-bis(iodoethynyl)benzene (AHULEU). Cations and hydrogen atoms are omitted for simplicity. “Rings and sticks” (UGULAK) and comblike (DOXTOA) architectures form when iodide anions (tridentate nodes) self-assemble with α,ω-diiodoperfluoroalkanes. Halogen-bonded ribbons form when iodide anions (tridentate nodes) self-assemble with 1,4-DITFB (GIXGOJ), or with a triiodobenzene derivative (NUZKIC). Color code: carbon, gray; nitrogen, blue; iodine, purple; chlorine, light green; boron, pink; fluorine, yellow. XBs are dotted black lines. CSD Refcodes are reported.

Figure 78

(A) Triangular motif sustained by bifurcated I···O and I···π XBs in the packing of TIPB. (B) Honeycomb-like network in TIPB. Hexagonal channels are filled by chloroform molecules (in green). (C) Two-dimensional array (sql) of tin tetrakis(iodophenyl)porphyrin with nicotinic acid (POR1) aligned parallel to the ac plane of the crystal. (D) Square-grid-type network in the crystal of tetrakis(iodophenyl)porphyrin assembled with 1-hydroxybenzotriazole (POR2). Every porphyrin unit is involved in eight XB contacts. (E) View parallel to the crystal ab plane of bis(iodoaryl)dipyridylporphyrin free base (POR3). (F) Representative section of the halogen-bonded layer in POR4, viewed within the crystal ac plane. XBs are dotted lines. Panels A and B reprinted with permission from ref (746). Copyright 2008 Royal Society of Chemistry. Panels C and D reprinted with permission from ref (748). Copyright 2013 John Wiley and Sons. Panel E reprinted from ref (749). Copyright 2015 American Chemical Society. Panel F reprinted with permission from ref (750). Copyright 2014 Royal Society of Chemistry.

Figure 79

TEHRAA: side view of the (6,3) superanion network in the halogen-bonded adduct K.2.2.2/KI/DIPFH. Cations are omitted for clarity. CIZSAG: front view of the (6,3) network of tetraethylphosphonium iodide–1,3,5-triodo-2,4,6-trifluorobenzene. Cations are shown in space-filling style. CIZSIO: side view showing the undulated (6,3) anionic net of tetra-n-butylammonium iodide–1,3,5-triodo-2,4,6-trifluorobenzene dichloromethane solvate. Cations and dichloromethane are shown in space-filling style. CIZROT, side view showing the planarity of the (6,3) anionic network of trimethylsulfonium iodide–1,3,5-triodo-2,4,6-trifluorobenzene. Cations are shown in space-filling style. Color code: carbon, gray; nitrogen, blue; iodine, purple; phosphorus, orange; sulfur, dark yellow; fluorine, yellow. XBs are dotted black lines. CSD Refcodes are reported.

Figure 80

Tilings formed by octagons and rhombs and resulting on self-assembly of iodoform with benzyltrimethylammonium iodide (HEDGOM) and carbon tetrabromide with 1-aza-8-azoniabicyclo(5.4.0)undec-7-ene bromide (VAXPAM). (4,4) networks are obtained on self-assembly of diiodoacetylene with chloride anions (ZOMWAZ), 1,4-difluoro-2,3,5,6-tetraiodobenzene with bromide anions (XERZID), and [bis[[μ₂-N,N′-bis(5-bromosalicylaldehyde)ethylenediamino]methanol]manganese(III)] perchlorate (IDEHOP). Hydrogen atoms and cations are omitted. Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; bromine, light brown; chlorine, light green; fluorine, yellow. Mn atoms in IDEHOP are shown in gray-violet. XBs are dotted black lines. CSD Refcodes are reported.

Figure 81

(A) (1) Chemical structure of DBTP. (2) Calculated molecular electrostatic potential distribution of DBTP at the isodensity surface shown in red (positive) and blue (negative). (3) Cartoon of two DBTP molecules with simplified electrostatic potential distributions around H and Br atoms (same color code as in (2)). Dotted blue lines indicate Br···Br XBs, and dotted red lines indicate Br···H HBs. (B) (1–3) STM topography images of three porous networks obtained after DBTP was deposited on Ag(111) at 80 K. (4–6) High-resolution STM images from the square-marked areas in (1), (2), and (3), respectively, with superimposed molecular models of DBTP. Adapted with permission from ref (756). Copyright 2011 Royal Society of Chemistry. (C) (1) Scheme of the self-assembly of tritopic XB acceptor TEPB and XB donor TITFB affording the TITFB/TEPB honeycomb-like network where the two modules alternate at the nodes. (2) Large-scale STM image of the TITFB/TEPB honeycomb-like structure. (3) The STM image shows the coexistence of a TEPB close-packed structure and the TITFB/TEPB honeycomb-like network. (4) High-resolution STM image of the TITFB/TEPB honeycomb-like structure. Adapted from ref (755). Copyright 2015 American Chemical Society.

Figure 82

Isomorphous adamantanoid networks formed when tetrabromomethane (the tetradentate XB donor) alternates at the network nodes with chloride (VAPVOY) or iodide (VAPWAL) anions, which function as tetradentate XB acceptors. Cations at the center of the cage are shown in space-filling style. Only one (C₂H₅)₄N⁺ is drawn for clarity. Color code: carbon, gray; iodine, purple; bromine, light brown; chlorine, light green; hydrogen, white. XBs are dotted black lines. CSD Refcodes are reported.

Figure 83

Structures of starting tectons and schematic views, obtained with TOPOS, of the corresponding interpenetrated networks: (A) DIPFH/TPP (sql, 4-fold interpenetration); (B) DIPFO/TPP (sql, 5-fold interpenetration); (C) DIPFB/TPP (dia, 8-fold interpenetration); (D) TITFPP/TPP (dia, 10-fold interpenetration).

Figure 84

Structures of starting tectons and schematic views, obtained with TOPOS, of the corresponding interpenetrated networks: (A) DIOFS/TPP adduct (sql, 3-fold interpenetration); (B) DITFB/TPC (sql, 2-fold interpenetration); (C) DAB-2-IPFB/t-BPE (sql, 5-fold interpenetration); (D) K.2.2.2/KI/DIPFH or DIPFO ((6,3) net, Borromean interpenetration).

Figure 85

Structures of starting tectons and schematic views, obtained with TOPOS, of the corresponding interpenetrated networks. (A) [Co(1IP)(1,4-BIMB)]_n (3-fold interpenetration). Adapted from ref (764). Copyright 2011 American Chemical Society. (B) HFTIPB/Ph₄PCl or Ph₄PBr (8-fold interpenetrated net of class Ia). Adapted from ref (765). Copyright 2011 American Chemical Society. (C) TITFB/Et₃MeN⁺I^– (4-fold interpenetration of class IIIa). Adapted from ref (766). Copyright 2013 American Chemical Society. (C) [Zn₂(BMIB)(TBTP)₂·2H₂O]_n (4-fold interpenetration dia of class IIIa). Adapted with permission from ref (767). Copyright 2014 Royal Society of Chemistry.

Figure 86

Top: possible structure of the molecularly imprinted polymer obtained using 2,3,5,6-tetrafluoro-4-iodostyrene as the monomer and 4-(dimethylamino)pyridine as the template. Bottom: binding affinities of different XB acceptors for the imprinted polymer. Adapted with permission from ref (768). Copyright 2005 Elsevier Ltd.

Figure 87

(A) Packing of bis(trimethylammonium)decane diiodide dihydrate (XOVBIU) viewed along the a-axis. (B) Complex bis(trimethylammonium)decane diiodide/diiodoperfluorobutane (XOVBAM) showing the molecular cavity defined by four alkyl dications, with encapsulated disordered guest molecules (space-filling style). This molecule is halogen-bonded to I^– ions at the top and the bottom. (C) Crystal packing of the same complex viewed along the c-axis. The α,ω-DIPFA molecules are disordered over two positions. In (A) only the water H atoms are reported. In (B) no hydrogen atoms are reported. Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; fluorine, yellow; hydrogen, white. XBs and HBs are dotted black lines.

Figure 88

Partial view (ball-and-stick representation) of the crystal packing of (A) the discrete I₄^2– anion hosted in a size-matched cavity formed by four HMET units, (B) the discrete I₇^3– anion surrounded by four trication units, (C) the discrete I₄^2– anion caged between two N,N′-bis(tetrafluorobenzyl)-(E)-1,2-bis(4,4′-bipyridinium)ethylene units (the cations are disordered over two positions), and (D) the complex containing the discrete pseudolinear dodecaiodide species. Polyiodide anions are represented in space-filling style. Color code: carbon, gray; nitrogen, blue; iodine, purple; fluorine, yellow; hydrogen, white.

Figure 89

Partial view (ball-and-stick representation) of the crystal packing of (A, B) the mixed trihalide adducts HMET·2XI₂^– (A, X = Br; B, X = Cl) and (C, D) the mixed tetrahalides [Br₂I₂]^2– (C) and [Cl₂I₂]^2– (D), obtained upon heating of the corresponding trihalides from (A) and (B). These mixed polyhalides are held together by XBs and are pinned by HBs in the cavities formed by four dication units. Color code: carbon, gray; nitrogen, blue; iodine, purple; bromine, light brown; chlorine, light green; fluorine, yellow; hydrogen, white. XBs and HBs are dotted black lines.

Figure 90

Different structural arrangements observed in the products of the reaction between crystalline trans-[CuX₂(3-Xpy)₂] and HCl or HBr gases. The colors of the arrows and of the chemical formulas are associated. Metal and halide ligands are shown in red, organic halogens in green, and all other atoms in blue (C, H, N). Black dotted lines represent HBs and XBs. Reprinted with permission from ref (778). Copyright 2011 Royal Society of Chemistry.

Figure 91

Top: molecular structures of the used XB donor and acceptor. Bottom: crystal packing of the halogen-bonded complex showing the ciclophane tubes. The XB is represented by dotted lines. The included chloroform molecules are omitted in the left plot and are shown in space-filling style in the right plot. Reprinted from ref (184). Copyright 2009 American Chemical Society.

Figure 92

Top: molecular structures of the used XB acceptor and donor. Bottom: crystal structures of the [NIS]₄···[HMTA] complexes obtained upon crystallization from different solvents. Crystal structures of [NIS]₄···[HMTA]@C₆H₅CH₃ and [NIS]₄···[HMTA]@CHCl₃ as well as [NIS]₄···[HMTA]@CH₃CN and [NIS]₄···[HMTA]@CH₃NO₂ are isomorphs, whereas [NIS]₄···[HMTA]@CH₂Cl₂ and [NIS]₄···[HMTA]@CCl₄ are different, but can be interconverted via guest molecule exchange. Adapted with permission from ref (781). Copyright 2012 Royal Society of Chemistry.

Figure 93

Top left: partial view (stick representation) of one layer of the ligand···HI adduct assembled by orthogonal HB and XB. I^– and H⁺ ions are shown in space-filling representation. Top right: two adjacent layers (red and green) stack along the a-axis, resulting in the partitioning of the void in the rectangular grids. Dioxane molecules have been omitted for clarity. Bottom: partial views (stick representation) of the single-crystal X-ray structures of the ligand···HI adducts containing dioxane (left) and 1,3-dibromobenzene (right). The latter system is obtained when a crystal of the former is divided into 1,3-dibromobenzene at room temperature. Reprinted with permission from ref (782). Copyright 2012 Royal Society of Chemistry.

Figure 94

Top: partial view of a layer formed on assembly of the self-complementary porphyrin. XBs are in black dotted lines. Bottom: unidirectional arrangement of two successive layers. Adapted with permission from ref (784). Copyright 2008 Royal Society of Chemistry.

Figure 95

Top: molecular structures of the XB acceptor (left) and donor (right) used for the construction of the capsule. Bottom left: space-filling representation of the molecular capsule assembled via XB. The solvent molecule are omitted to show the cavity inside the capsule. Bottom right: ball-and-stick representation of the molecular capsule where the solvent molecules are shown in space-filling style and I···N XBs are shown as dotted black lines. Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; fluorine, yellow; hydrogen, white.

Figure 96

Left: molecular structures of the XB donor, XB acceptor, and guest molecule used for the assembly of N. K. Beyeh’s capsule (top) and ball-and-stick representation of the halogen-bonded dimeric capsule with three 1,4-dioxane molecules in the cavity as space-filling CPK models (bottom). The XBs are shown in black and HBs as green and red dotted lines. Adapted with permission from ref (787). Copyright 2015 John Wiley and Sons. Middle: calculated model for the capsule developed by F. Diederich et al. with two 1,4-dioxane guests and four MeOH bridging units to stabilize intramolecular HB between imidazole walls (nearly optimized at the DFT:B3LYP/cc-pVDZ-LANL2DZ level of theory). Adapted with permission from ref (789). Copyright 2015 John Wiley and Sons. Right: chemical formula of the cavitand used by J. Rebek and co-workers and its computer-modeled dimeric capsule (top; HBs are shown as green dotted lines) and calculated model for the capsule with the encapsulated and halogen-bonded dimer (bottom). Full geometry optimization was carried out, including the capsule; the basis set for all atoms except iodine is 6-31G(d,p), and that for I is LANL2DZdp ECP. Adapted from ref (790). Copyright 2013 American Chemical Society.

Figure 97

Stick-style views of the single-crystal X-ray structure of the cucurbit[6]uril–I₂ complex. Encapsulated diiodine, in space-filling style (left), is halogen-bonded with a water molecule (middle) and is bound to the carbonyl oxygen at the upper portal (right).

Figure 98

(A) Molecular structure of the self-assembled coordination cage by Fujita. (B) Single-crystal X-ray structure of the inclusion complex between Fujita’s cage (stick representation) and 1,8-diiodoperfluorooctane (space-filling representation). Two molecules of the XB acceptor are hosted inside the cage. NO₃^– anions and H₂O molecules halogen-bonded to diiodoperfluorooctane molecules are shown as space-filling models. H atoms, NO₃^– anions, and H₂O moleculs that are not involved in XB have been omitted for clarity. Adapted with permission from ref (795). Copyright 2015 John Wiley and Sons. (C) Crystal structure of the inclusion complex between the anion-coordination-based tetragonal cage (stick representation) and CFCl₃. CFCl₃ is shown as a space-filling model. Adapted with permission from ref (796). Copyright 2015 John Wiley and Sons.

Figure 99

Schematic representation showing that on griding 1,4-diiodotetrafluorobenzene and thiomorpholine the 1:2 discrete adduct forms initially, which then evolves into 1:1 infinite chains on further grinding. Adapted with permission from ref (798). Copyright 2012 Royal Society of Chemistry.

Figure 100

Left: structural formulas of tectons assembled via LAG methodology. Middle: (succinic acid)·(caffeine)₄ host framework with guests omitted. Right: view of the hydrogen C–H···O and halogen Br···N bonds involving the bromoform included in the (succinic acid)·(caffeine)₄ host framework. Adapted with permission from ref (798). Copyright 2012 Royal Society of Chemistry.

Figure 101

(A) Molecular structures of single compounds (top) employed in LAG synthesis of a halogen-bonded MOF (bottom). (B) Partial representation of the crystal structure resulting from a combination of covalent bond formation, coordination bonds, and XBs. I···O XBs are shown as yellow solid lines, and the I···O distance is reported (N_c = 0.88). Adapted with permission from ref (801). Copyright 2014 Royal Society of Chemistry.

Figure 102

Pictures of cones of powders of pure IPBC (A, C) and its CaCl₂ cocrystal (B, D), taken after flowing the powders through a funnel from 25 mm (A, B) and 50 mm (C, D) heights. The cylindrical shape of the IPBC cones clearly indicates the high cohesion of the powders, while the flat cone shape of the CaCl₂ cocrystal indicates improved powder flow properties. Reprinted from ref (477). Copyright 2013 American Chemical Society.

Figure 103

Schematic representation of the infinite, 1D, and halogen-bonded ribbons (top), which upon light irradiation in the solid state yield quantitatively the rctt-tetrakis(4-pyridyl)cyclobutane (bottom).

Figure 104

Top: schematic representation of the solid-state photoreaction of an XB-based self-complementary tecton to yield a tetratopic self-complementary cyclobutane derivative. Bottom: views of the crystal packing of two infinite and halogen-bonded chains formed in the solid state by the starting olefin (left, XBs as dotted black lines), and of the cyclobutane derivative obtained after UV irradiation (right). Color code: carbon, gray; nitrogen, blue; iodine, purple; fluorine, yellow; hydrogen, white. XBs are dotted black lines.

Figure 105

Top: schematic representation of XB donor and acceptors used for the photochemical polymerization of diacetylene modules. Bottom: partial views (ball-and-stick representation) of the 2D supramolecular architecture given by diiodobutadiyne and bis(4-cyanobutyl)oxalamide (left) and of the related photoreacted cocrystal between poly(diiododiacetylene) and bis(4-cyanobutyl)oxalamide (right). Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; fluorine, yellow; hydrogen, white. XBs and HBs are dotted black lines.

Figure 106

(A) Chemical structures of the halogen-bonded LCs reported in ref (837) and corresponding hydrogen-bonded analogues. (B) Crystal structure of the (octyloxy)stilbazole/iodopentafluorobenzene dimer evidencing the presence of I···N XB (shown as black dotted lines) and the coplanarity of the aromatic rings. Color code: gray, carbon; yellow, fluorine; purple, iodine; sky blue, nitrogen; white, hydrogen. (C) Polarized optical micrograph of the smectic A texture of the (hexyloxy)stilbazole/iodopentafluorobenzene dimer at 69° upon cooling. Reprinted from ref (837). Copyright 2004 American Chemical Society.

Figure 107

Chemical structures of high molecular weight polymeric (A, top) and trimeric (A, bottom) LCs,^, trimeric LCs formed by diiodoperfluoroalkanes (B), and dimeric systems formed by dihalogens (C, top).^, (C) Representation of the crystal structure of two I₂···(octyloxy)stilbazole dimers interacting via type I I···I contacts. Color code: carbon, gray; nitrogen, blue; oxygen, red; iodine, purple; hydrogen, white.

Figure 108

(A) A selection of XB donors and acceptors used in ref (854). (B) Birefringent textures of complexes formed by an (S)-citronellyl-substituted stilbazole with a butoxy-substituted iodotetrafluorostilbene, obtained upon cooling from the isotropic state. (C) Molecular structures of halogen-bonded (top) and hydrogen-bonded (bottom) stilbazole–azobenzene complexes. The halogen-bonded complex is liquid-crystalline; the hydrogen-bonded complex is not.

Figure 109

(A) Chemical structures of the XB donors and acceptors used in ref (573) and the general structures of the halogen-bonded complexes. Birefringence textures of the crystal G phase of the p-BIB/p-(decyloxy)pyridine complex (at 86 °C) (B), the smectic B phase of the p-BIB/p-[[p-(tetradecyloxy)benzoyl]oxy]stilbazole complex (at 108 °C) (C), and the smectic AP phase of the m-BIB/p-tetradecyloxy)stilbazole complex (at 131 °C) (D). Reprinted from ref (573). Copyright 2013 American Chemical Society.

Figure 110

(A) Chemical structures of the PEG–iodoperfluoroalkane complexes used in ref (484). (B) Small-angle X-ray scattering patterns for iodoperfluorodecane (graph 1), PEG (graph 2), indicating poor self-assembly by segregation of the ionic end groups from the PEG core, and the supramolecular complex (graph 3), showing highly ordered self-assembly. (C) An illustration of the self-assembly mechanism of the halogen-bonded complex. (D) TEM micrographs at various locations of pure PEG showing a lack of macroscale alignment. (E) TEM micrographs of the halogen-bonded complex between PEG and 1-iodoperfluorododecane, showing exceptionally well-ordered lamellar nanostructures with overall macroscale order on the millimeter scale. The scale bars correspond to 100 nm. Reprinted with permission from ref (484). Copyright 2014 Nature Publishing Group.

Figure 111

Cartoon representing complementary halogen-bonded polymers (A) and self-assembly in solution into vesicle (B) and wormlike (C) structures, as observed by TEM micrographs. Adapted from ref (861). Copyright 2015 American Chemical Society.

Figure 112

(A) Chemical structures of the compounds used in ref (83) to obtain supramolecular low molecular weight gels. (B) X-ray crystal structure of the 1:1 adduct between 1,4-DITFB and BPUB, which confirms the presence of gel-forming urea tapes cross-linked by XBs involving the pyridyl groups. (C, D) Scanning electron micrographs of dried 1:1 cogels formed by 4,4′-DP with BIPUB, and by BPUB with BIPUB, respectively. (E) Photograph of the 1,4-bis(3-pyridylureido)butane/1,4-bis[(4-iodotetrafluorophenyl)ureido]butane cogel. Reprinted with permission from ref (83). Copyright 2013 Nature Publishing Group.

Figure 113

(A) XB (dotted black line) between the Br of IDD594 and the O(γ) of Thr113 in human aldose reductase. (B) Atomic structure of d(CCAGTACBr⁵UGG), with bromine atoms rendered as spheres and the deoxyribose backbones as solid ribbons. Panel A reprinted with permission from ref (27). Copyright 2011 Royal Society of Chemistry. Panel B reprinted from ref (878). Copyright 2003 American Chemical Society.

Figure 114

(A) Chemical formulas of the thyroid hormones T4 and T3. (B) HBs formed by T3 and (C) XBs formed by T4 with TTR. Reprinted with permission from ref (885). Copyright 2015 Springer.

Figure 115

XBs in the PDB, divided as (A) C–X···Y and (B) C–X···π contacts (X = Cl, Br, I). Reprinted from ref (871). Copyright 2013 American Chemical Society.

Figure 116

Diclofenac–cytochrome P450 complex showing that a water molecule forms at the same time an XB with one Cl atom of diclofenac (shown in pale green) and an HB with a carboxyl oxygen of the Glu297 side chain. Reprinted with permission from ref (27). Copyright 2011 Royal Society of Chemistry.

Figure 117

Number of short contacts involving halogens as a function of the angles: (A) C–X···B (θ₁) and (B) C–B···X (θ₂). π-BXB and n-BXB indicate biomolecular halogen bonds of the type C–X···π and C–X···Y, respectively. Reprinted with permission from ref (885). Copyright 2015 Springer.

Figure 118

(A) Distribution of the relative angle of approach of HBs and XBs to a common Lewis base, subdivided by the halogen involved. Representations of the orthogonality of XBs and HBs in β-sheets (B) and α-helices (C); the white sphere represents the van der Waals radius of a Br atom. Reprinted with permission from ref (250). Copyright 2009 Nature Publishing Group.

Figure 119

Competition between hydrogen-bonded (cyan strand) and halogen-bonded (magenta strand) structures in a four-stranded DNA junction. Reprinted with permission from ref (885). Copyright 2015 Springer.

Figure 120

Crystal structure of the complex between the binder PhiKan5196 and the p53 mutant Y220C. The iodine atom is shown in magenta and forms an XB with the carbonyl oxygen of Leu145. Adapted from ref (946). Copyright 2012 American Chemical Society.

Figure 121

Representation of a schematic model of the mechanism of bromination of alkenes evidencing the formation of halogen-bonded adducts of the type X···π.

Figure 122

Top: polymerization of l-lactide to poly(l-lactide) with ICl₃. Bottom: proposed mechanism for the 2-fold activation.

Figure 123

Reduction of 2-phenylquinoline in the presence of 1-iodoperfluorooctane.

Figure 124

Hydrogenation of quinoline with the Hantzsch ester in the presence of a bidentate XB donor catalyst based on a dihydroimidazoline core (right).

Figure 125

Aziridine synthesis in the presence of the fluoronium cation F⁺.

Figure 126

Solvolysis of benzhydryl bromide as a model reaction.

Figure 127

Possible modes of activation of a halogenated substrate by the bidentate XB donor catalyst (shown in red).

Figure 128

Halogenated and hydrogenated activating reagents.

Figure 129

Left: Diels–Alder benchmark reaction. Right: dicationic XB donor activating agent BAr^F = B[3,5-(CF₃)₂C₆H₃]₄^–.

Figure 130

Top: Aza-Diels–Alder reaction of an aldimine with the Danishefsky diene. Bottom: structure of the used XB donor activating agents.

Figure 131

Synthesis of 4,4′-azobis(halopyridinium)-based XB donors and reference compounds.

Figure 132

Bi- and tridentate polycationic XB donors based on the 5-iodo-1,2,3-triazolium synthon.

Figure 133

Top: structures of neutral polyfluorinated XB donors. Bottom: selected test reaction of 1-chloroisochromane (left) to the corresponding ester.

Figure 134

Figure 135

Cyclopropanation reaction with different Rh-based halogenated catalysts.

Figure 136

A selection of (A) fluorophores studied in refs (486), (1001), and (1002) and (B) halogen/hydrogen bond donors cocrystallized with 12 in ref (1002).

Figure 137

Top: crystal structures of pure 12 and related cocrystals 12:A, 12:B, 12:C, 12:D, and 12:E, which each shows a distinct packing. Bottom: photographs of samples of pure 12 and of the related cocrystals. (i, ii) Powder samples under daylight and UV illumination, respectively. (iii, iv) Single-crystal samples under UV illumination and daylight as observed through a fluorescence microscope (50×). (v) Two-photon luminescence under 800 nm laser excitation. Reprinted with permission from ref (1002). Copyright 2011 Wiley-VCH.

Figure 138

(A) Scanning electron micrograph of the 12:A nanococrystals. (B) Fluorescence spectra of the nanococrystals at different temperatures. The inset shows the fluorescenece intensity ratios at I_465nm/I_532nm and the dependence of the color coordinates on the temperature. Reprinted with permission from ref (1003). Copyright 2013 Wiley-VCH.

Figure 139

(A) Chemical structures of the hosts a and aldehydes b used in ref (1004). (B) Schematic depiction of the crystal packing of 13b, highlighting the carbonyl oxygen–bromine XB. It is believed that this contact is responsible for the phosphorescence observed from crystals of 13b (C). Reprinted with permission from ref (1004). Copyright 2011 Nature Publishing Group.

Figure 140

(A) Top: the new organic phosphor G1 appears particularly promising in enhancing phosphorescence in an amorphous PVA matrix. Bottom: the green phosphorescence of G1 embedded in PVA is explained by synergistic effects brought about by simultaneous use of halogen and hydrogen bonds. (B) The phosphorescence emission of 1 wt % G1 in PVA depends linearly on the humidity, while the fluorescence emission is insensitive to the humidity, which allows (C) fluorescent watermarks to be reversibly written onto the amorphous polymer film. Reprinted with permission from ref (1011). Copyright 2014 Wiley-VCH.

Figure 141

Top: infinite-chain structure of the carbazole/1,4-diiodotetrafluorobenzene cocrystals (left), driven by C–I···π XBs and further stabilized by π–π stacking (right). The adjacent chains are linked together by C–H···I HBs (bottom). Reprinted with permission from ref (1013). Copyright 2012 Royal Society of Chemistry. Bottom: phosphorescence excitation and emission from naphthalene/1,4-diiodotetrafluorobenzene (top) and phenanthrene/1,4-diiodotetrafluorobenzene (bottom) cocrystals. The insets display the phosphorescence color of the cocrystals under UV excitation through a mask. Reprinted with permission from ref (649). Copyright 2012 Royal Society of Chemistry.

Figure 142

Top: chemical structures of the 1,8-napthalimide (17) derivatives with 4-bromine substitution and 2-, 3-, and 4-methylpyridine substitution at the imidic N-position (18, 19, and 20, respectively) used in ref (1019). Bottom: by controlling the stoichiometry of diphenylacetylene/1,4-diiodotetrafluorobenzene cocrystals from 1:1 (top) to 1:2 ratios (bottom), the photoluminescence can be “switched” between fluorescence and phosphorescence. Reprinted from ref (1021). Copyright 2015 American Chemical Society.

Figure 143

Photoisomerization of azobenzene (A) can give rise to a cascade of molecular motions into a material system it is incorporated into. The most relevant examples in the context of halogen-bonded functional materials are (B) photoinduced phase transitions in liquid-crystalline materials, (C) photoinduced surface patterning of initially flat polymer surfaces, and (D) photoinduced bending of azobenzene-containing cross-linked liquid-crystalline polymers or molecular (co)crystals. Reprinted with permission from ref (1040). Copyright 2005 Optical Society of America.

Figure 144

(A) Chemical structures of the azobenzene compounds studied in refs (859) and (855). Comparison of (B) the diffraction kinetics and (C) the AFM surface profile of thin films of complexes between 22–24 and P4VP (10 mol % azobenzenes in a P4VP matrix). The samples were spin-coated on silicon substrates, and their thickness was ca. 90 nm. Reprinted with permission from ref (859). Copyright 2012 Wily-VCH. (D) Electrostatic potential surfaces of compounds 28 (top) and 25 (bottom), ranging from −0.03 (red) to 0.03 (blue) au. (E) Ball-and-stick representation of the crystal packing of 30·(25)₂ (top) and 30·(28)₂ (bottom). Middle: view along the crystallographic b-axis of the cocrystal 30·(25)₂, illustrating the tendency of 25 to interact via quadrupolar stacking. Reprinted with permission from ref (855). Copyright 2015 Royal Society of Chemistry.

Figure 145

(A) Chemical structure of the halogen-bonded liquid-crystalline complex employed in ref (489). (B) Polarized absorption spectra of a thin film (250 nm) of the complex shown in (A). Black curve: initial spectrum (same for both polarizations). The red and blue curves correspond to the polarized absorption spectra in the directions parallel (A_∥ < A₀) and perpendicular (A_⊥ > A₀) to the polarization plane, taken after 30 and 120 s of irradiation (488 nm, 100 mW/cm²), respectively. The absorption anisotropy is an unambiguous sign of photoinduced reorientation of the azobenzene chromophores. (C) Atomic force microscopy view of the spin-coated thin film of the complex shown in (A) after SRG inscription (5 min, 488 nm, 300 mW/cm²). The surface-modulation depth after the SRG inscription was 600 nm, 2.4 times the initial film thickness. Reprinted with permission from ref (489). Copyright 2012 Wiley-VCH.

Figure 146

Polarized optical micrographs of an azopyridine–I₂ complex (see Figure 107C) at its liquid-crystalline phase before (left) and after (right) UV irradiation. The decreased contrast indicates photoinduced phase transition due to trans–cis photoisomerization. Upon irradiation with visible light, the colored pattern can be retained due to reverse cis–trans isomerization. Reprinted with permission from ref (851). Copyright 2014 Royal Society of Chemistry.

Figure 147

Top: trans- and cis-forms of 4,4′-dibromoperfluoroazobenzene. Bottom right: in the crystal state, the photoisomerization proceeds only from the cis- to the trans-state, not vice versa. Upon cis-to-trans isomerization, thin crystals bend irreversibly away from the irradiation source. Reprinted from ref (1026). Copyright 2013 American Chemical Society.

Figure 148

(A) Compounds used in ref (1027). (B) Linear structure of supramolecular chains of (trans-31)·(trans-bpe) and the zigzag structure of (cis-32)·(cis-bpe) as determined by single-crystal X-ray diffraction analysis. (C) Photoinduced bending of halogen-bonded cocrystals, followed by in situ X-ray diffraction, reveals that the transition from the unbent cis-single crystal to the bent polycrystalline trans-state proceeds through an amorphous intermediate phase. Reprinted with permission from ref (1027). Copyright 2014 Royal Society of Chemistry.

Figure 149

(A, top) A selection of NLO-phores containing XB donor groups. (B, bottom) Upon optical poling of azobenzene chromophores 22, 23, and 24 of Figure 144A in a P4VP matrix (the molar ratio between the azobenzenes and the polymer repeat units is 1:20), XB clearly boosts the second-order nonlinear optical response of the material system. Reprinted with permission from ref (860). Copyright 2015 Royal Society of Chemistry.

Figure 150

(A) Halogen-bonded radical cation salts formed between partially oxidized halogenated TTF molecules and halide (top) or cyanometalate (bottom) anions were the first examples of halogen-bond-based molecular conductors. (B) Crystal structures of the Ag(CN)₂ (top) and Br^– (bottom) salts. Reprinted with permission from ref (600). Copyright Elsevier 1995. (C) Chemical structures of the TTF cation and various anions used in ref (1074). (D) Projection view, along the stacking axis, of the unit cell of the salt (38)₄[1,5-Napht(SO₃)₂], showing the XBs as dotted lines. Reprinted from ref (1074). Copyright 2011 American Chemical Society.

Figure 151

(A) Chemical structures of a cation radical (TSF) and the XB donor (HFTIEB) used to construct sheathed molecular nanowires. (B) and (C) display the crystal structure and the CPK model of TSF stacks isolated by a network of HFTIEB and Cl^– ions. Reprinted from ref (1080). Copyright 2008 American Chemical Society.

Figure 152

(A) Self-assembly of DITFB with (2-phenyl)-4,4,5,5-tetramethylimidazolin-1-oxyl-3-oxide (PTIO) gives rise to trimeric complexes (top right), while complexes between DITFB and ATEMPO assemble into linear chains (bottom right). Reprinted with permission from ref (610). Copyright 2006 Elsevier. (B) The assembly between TMIO and 1,2-DITFB results in a cyclic tetrameric complex. Reprinted with permission from ref (1084). Copyright 2011 Royal Society of Chemistry.

Figure 153

(A) One-dimensional halogen-bonded supramolecular chains in complexes between (3-phenyl-2,2,5,5-tetramethylimidazolin-1-yl)oxy and 1,4-diiodotetrafluorobenzene (top) and 4,4′-diiodooctafluorobiphenyl (bottom). In both cases the radicals form magnetic chains isolated by the XB donors, and within the chains, the radicals pack into dimeric units. Reprinted with permission from ref (1086). Copyright Royal Society of Chemistry 2012. (B) Halogen-bonded cocrystals 40 and 41 containing the BTEMPO radical 39 exhibit enhanced antiferromagnetic coupling as compared to the pure single crystal of 39. Reprinted from ref (1087). Copyright 2013 American Chemical Society.

Figure 154

Top: schematic representation of the XB between the passivating iodopentafluorobenzene (IPFB) unit and a generic halide anion at the perovskite surface. Bottom: performance of the perovskite solar cells with (red) and without (black) surface passivation, using spiro-OMeTAD as the hole transporter. Reprinted from ref (1094). Copyright 2014 American Chemical Society.

Figure 155

(A) Schematics of the formation of assemblies of functionalized gold nanoparticles (AuNPs) in the presence of bipyridyl cross-linkers (BPEB, TPEB, TPM) via XB. (B) Stepwise generation of assemblies consisting of functionalized gold nanoparticles and different XB-accepting cross-linkers on organic monolayers (M1 and M2). Reprinted from ref (1096). Copyright 2011 American Chemical Society.

Figure 156

Left: schematics of a diiodobenzene-bridged single-molecule junction. Right: the authors used 2D conductance histograms to determine the conductance of the molecular junction and to conclude that sufficiently strong XB is required for the junction to form. Reprinted from ref (1098). Copyright 2013 American Chemical Society.

Figure 157

Periodic table published by J. W. Retgers in 1895 in his paper in Z. Phys. Chem., a journal established in 1887 by W. Ostwald, J. H. van ’t Hoff, and S. A. Arrhenius as the first journal tailored to scientific papers on physical chemistry.

Figure 158

Molecular structures of thyroid hormones and the binding activities of the RNA aptamer complexes described in ref (1111).