The Pnictogen Bond, Together with Other Non-Covalent Interactions, in the Rational Design of One-, Two- and Three-Dimensional Organic-Inorganic Hybrid Metal Halide Perovskite Semiconducting Materials, and Beyond

Abstract

The pnictogen bond, a somewhat overlooked supramolecular chemical synthon known since the middle of the last century, is one of the promising types of non-covalent interactions yet to be fully understood by recognizing and exploiting its properties for the rational design of novel functional materials. Its bonding modes, energy profiles, vibrational structures and charge density topologies, among others, have yet to be comprehensively delineated, both theoretically and experimentally. In this overview, attention is largely centered on the nature of nitrogen-centered pnictogen bonds found in organic-inorganic hybrid metal halide perovskites and closely related structures deposited in the Cambridge Structural Database (CSD) and the Inorganic Chemistry Structural Database (ICSD). Focusing on well-characterized structures, it is shown that it is not merely charge-assisted hydrogen bonds that stabilize the inorganic frameworks, as widely assumed and well-documented, but simultaneously nitrogen-centered pnictogen bonding, and, depending on the atomic constituents of the organic cation, other non-covalent interactions such as halogen bonding and/or tetrel bonding, are also contributors to the stabilizing of a variety of materials in the solid state. We have shown that competition between pnictogen bonding and other interactions plays an important role in determining the tilting of the MX₆ (X = a halogen) octahedra of metal halide perovskites in one, two and three-dimensions. The pnictogen interactions are identified to be directional even in zero-dimensional crystals, a structural feature in many engineered ordered materials; hence an interplay between them and other non-covalent interactions drives the structure and the functional properties of perovskite materials and enabling their application in, for example, photovoltaics and optoelectronics. We have demonstrated that nitrogen in ammonium and its derivatives in many chemical systems acts as a pnictogen bond donor and contributes to conferring stability, and hence functionality, to crystalline perovskite systems. The significance of these non-covalent interactions should not be overlooked, especially when the focus is centered on the rationale design and discovery of such highly-valued materials.

Keywords: ICSD and CSD database analyses; IGM-δg analysis; MESP characterizations; inorganic-organic hybrid halide perovskites; intermolecular geometries and directionality; nitrogen as pnictogen bond donor; pnictogen bonding; sum of the van der Waals radii concept.

Scheme 1

(a) Schematic representation of five different types of Type-II (140° < θ < 180°) non-covalent interactions formed by covalently bonded hydrogen, tetrel, pnictogen, chalcogen, and halogen atoms in molecular entities, where R is the remainder part of the molecular entity and θ is the angular approach of the electrophile centered on the H/Tr/Ch/Pn/X atoms. (b) A ball-and-stick model of dodecane-1,12-diamine (H₂N-(CH₂)₁₂-NH₂), in which the ammine moiety acts both as a hydrogen bonded acceptor and a hydrogen bond donor (CSD ref: UJONUD [11]). The H···N hydrogen bonds in b) are depicted as dotted lines in green and red, with the latter are hanging contacts. Color codes: N—blue; C—gray; H—white.

Scheme 2

Some examples of ammines, diammines, and their derivatives for in crystal structures in the CSD. These include: (a) ammonium; (b) hydroxylammonium; (c) methylammonium, (d) hydrazinium; (e) diazanediium; (f) ethylenediammonium; (g) 3-chloropropan-1-aminium; (h) 3-aminopropan-1-aminium; (i) 2-methylpentane-1,5-bis(ammonium); (j) N,N’-bis(2-ammonioethyl)ethylene-1,2-diamine; (k) propane-1,3-diaminium; (l) 1,6-hexanediammonium; (m) n-butylammonium; (n) 7-aminoheptylazanium; (o) bis(hexamethylene)triammonium; (p) dodecan-1-aminium; (q) n-hexadecylammonium; (r) octadecan-1-aminium; (s) 3-(4-(3-aminopropyl)piperazin-1-yl)propan-1-aminium; (t) dodecane-1,12-diammonium.

Figure 1

(a) The ball-and-stick model of the unit-cell of crystalline diazanediium dichloride, [NH₃NH₃][Cl]₂; (b) Illustration of N···Cl and N–H···Cl pnictogen and hydrogen bonds between a single NH₃NH₃²⁺ dication and surrounding nearest-neighbor Cl⁻ ions in the [NH₃NH₃][Cl]₂ crystal. (c) The local geometry of the interaction between two anions and a cation; (d) Space-filling model showing overlapping between N and Cl atomic basins in the geometry depicted in (c); and (e) IGM-δg based isosurface volume (colored bluish-green) between N and Cl atomic basins between [NH₃NH₃]²⁺ and 2Cl⁻. (f,g) QTAIM-based molecular graphs for the [NH₃NH₃][Cl]₂ ion-pair, obtained using the extracted geometry of the same ion-pair in the crystal (CSD ref: AWEJEU [81]) and the MP2(fc)/def2-TZVPPD optimized geometry, respectively. Values (in a.u.) marked in these molecular graphs represent the charge density (ρ_b) and the Laplacian of the charge density (∇²ρ_b) at N···Cl bond critical point. Bond paths are in atom color and bond critical points between atomic basins are shown as tiny spheres in green. Bond distances and bond angles are in Å and degrees, respectively. Intermolecular contacts in (a,b,e) are colored in cyan and hanging contacts colored in red. N–H···Cl hydrogen bonds are not shown between the interacting ions in the crystal in (a).

Figure 2

MP2/Aug-cc-pVTZ level 0.001 a.u. (electrons Bohr⁻³) isoelectron density envelope mapped potential on the electrostatic surface of [NH₃NH₃]²⁺. There is no local most minima (V_S,min), but only local most maxima V_S,max (tiny red circles) identified on the surface of the two N atoms along N–N covalent bond extensions and around the central bonding region of the same bond.

Figure 3

Ball-and-stick (left) and polyhedral (right) models of the low-temperature orthorhombic phase of organic-inorganic hybrid lead halide perovskites: (a) o-CH₃ND₃PbCl₃ [86], (b) o-CH₃ND₃PbBr₃ [87] and (c) o-CD₃ND₃PbI₃ [88]. The bond distances, r(N···X) in Å, and bond angles, ∠R–N/C···X (R = C, N) in degrees, associated with the N···X and C···X (X = Cl, Br, I) pnictogen bonding and tetrel bonding interactions between the organic and inorganic frameworks are shown in each case. Dotted lines between atoms represent non-covalent interactions. Atom labeling is shown in each case, and H/D atoms are tiny spheres in white-gray. The N-H/N-D···X and C-H/N-D···X hydrogen bonds/deuterium bonds are not shown, and the CSD references are shown in capital letters. The orientation of the crystallographic axes in (a) is not the same as that in (b,c).

Figure 4

(a) QTAIM-based molecular graph and (3, –1) bond critical point charge density topologies (ρ_b) for (a) o-CH₃NH₃PbBr₃ and (b) o-CH₃NH₃PbI₃, obtained with PBE/DZP, very similar to what reported by us elsewhere [25,26]. The PBE relaxed geometry for o-CH₃NH₃PbBr₃ and the neutron diffraction geometry (T ≈ 100 K [89]) for o-CH₃NH₃PbI₃ were used. Atoms: iodine—purple, carbon—dark-grey, nitrogen—deep-blue, hydrogen—white-grey; bond paths are shown as solid and dotted lines in atom color; (3, –1) bond critical points are shown as tiny blue and red spheres between bonded atomic basins. Dotted lines (bond paths) indicate the presence of non-covalent interactions between atoms that are liked with each other. Values of ρ_b are in a.u.

Figure 5

(a,b) Two different views of the ball-and-stick model of the 2 × 2 × 2 supercell structure of the crystal of perdeuteromethylammonium iodide, [CD₃ND₃][I] (CSD ref: KUBNOK), with the unit-cell, together with the three crystallographic axes, shown for each case; (c) the nature of intermolecular bond distances and intermolecular bond angles between CD₃ND₃⁺ and I⁻; and (d) IGM-δg based 0.004 a.u. isosurface volume (colored bluish-green) between N/C and I atomic basins of interacting units CD₃ND₃⁺ and I⁻ responsible for the structure of the crystal. (e,f) QTAIM based molecular graphs for H₃C-H₃N···I and H₃N-H₃C···I, respectively, obtained using ωB97X-D/def2-TZVPPD with the geometries of the same ion-pairs as in the crystal (CSD ref. KUBNOK02). Values (in a.u.) in black and blue in (c,d) represent the charge density (ρ_b) and the Laplacian of the charge density (∇²ρ_b) at N···I (and C···I) bond critical point(s), respectively, obtained using the geometry of the adduct as in the crystal. The corresponding values calculated on the ωB97X-D/def2-TZVPPD fully relaxed geometries of H₃C-H₃N···I and H₃N-H₃C···I are shown in square brackets, respectively. Bond paths are in atom color and bond critical points between atomic basins are shown as tiny spheres in green. Bond distances and bond angles are in Å and degrees, respectively. Intermolecular contacts are colored in cyan/green and hanging contacts are colored in red. Atoms shown as balls are colored iodine—purple; nitrogen—blue; carbon—gray; hydrogen—white-gray.

Figure 6

MP2/Aug-cc-pVTZ level 0.001 a.u. isoelectron density-envelope-mapped potential on the electrostatic surface of methylammonium, CH₃NH₃⁺). There are no local most potential minima (V_S,min), but only local most maxima V_S,max (tiny red circles) identified on the surfaces of the two N atoms along the N–N bond extensions, and around the central region of the N–N covalent bond.

Figure 7

(a–c) Three different views of the ball-and-stick model of the 2 × 2 × 2 supercell structure of the crystal of ammonium cyanate, NH₄CNO (CSD ref. KEFJEN); (b–f) The local nature of intermolecular bond distances and intermolecular bond angles between NH₄⁺ and CNO⁻, showing the coordination environment around (d) N in NH₄⁺, (e) O in CNO⁻, and (f) N in CNO⁻. Bond distances and bond angles are in Å and degrees, respectively. Intermolecular contacts are colored in cyan and hanging contacts in c are colored in red. (g) MP2(FC)/def2-TZVPPD level QTAIM-based molecular graph for the ion-pair NH₄CNO, obtained on its geometry as in the crystal; it shows the bond paths as sticks in atom color (N—blue; C—grey; O—red; H—white grey), bond critical points as tiny spheres between atomic basins in green, and values (in a.u.) of charge density ρ_b and the Laplacian of the charge density ∇²ρ_b at the N···O bond critical point.

Figure 8

(a) The 0.001 a.u. isoelectron density mapped potential on the electrostatic surface of the NH₄⁺ cation, obtained using MP2/Aug-cc-pVTZ; the tiny circles in red represent the local most maxima of electrostatic potential, V_S,max. (b) The local nature of N–H···O hydrogen bonding and H–N···O pnictogen bonding interactions between the NH₄⁺ and CNO⁻ ions in NH₄CNO. (c,d) IGM-δg based isosurface volumes (colored bluish-green) between NH₄⁺ and CNO⁻ ions, with two different isovalues of IGM. (e) IGM-δg based isosurface volume (colored bluish-green) between NH₄⁺ and CNO⁻ ions as in a 2 × 2 × 2 supercell structure of the system, showing different interaction types between the interacting moieties. Bond distances and bond angles are in Å and degrees, respectively. Intermolecular contacts in (b–d) are colored in cyan/green.

Figure 9

Three views of the crystal of NH₄Cl (ICSD ref. 428519 [99]) showing (a) combined H···Cl hydrogen bonds and N···Cl pnictogen bonds, (b) N···Cl pnictogen bonds, and (c) H···Cl hydrogen bonds. Illustration of the local nature of multi-furcated charge-assisted intermolecular bonding topologies: (d) NH₄⁺ as four pnictogen bond donors; (e) NH₄⁺ as four H bond donors; and (f) Cl⁻ as four H-bond and four N-bond acceptors. Bond lengths and bond angles are in Å and degrees, respectively. The dotted lines in cyan/red represent inter-ionic interactions. (g,h) MP2(FC)/def2-TZVPPD level QTAIM-based molecular graph for the ion-pair NH₄Cl, obtained on its MP2(FC)/def2-TZVPPD gas-phase geometry and as in the crystal, respectively; both these graphs show bond paths as sticks and dotted lines in atom color (N—blue; Cl—green; H—white grey), bond critical points as tiny spheres between atomic basins in green, and values (in a.u.) of charge density ρ_b and the Laplacian of the charge density ∇²ρ_b at the N···Cl bond critical point.

Figure 10

Three views of the crystal of tetradeuterioammonium bromide IV-LT, ND₄Br (space group: P$\overline{4}$3m, ICSD ref. 26577 [103]) showing (a) combined D···Br deuterium bonds and N···Br pnictogen bonds, (b) N···Br pnictogen bonds, and (c) D···Br deuterium bonds. Illustration of the nature of the local nature of multi-furcated charge-assisted intermolecular bonding topologies: (d) ND₄⁺ as four pnictogen bond donors; (e) Br⁻ as four D-bond and four N-bond acceptors; and (f) illustration of the nature of directionality for each of the four D and four N bond donors. Bond lengths and bond angles are in Å and degrees, respectively. The dotted lines represent inter-ionic interactions. Atom type is shown in (e). (g,h) MP2(FC)/def2-TZVPPD level QTAIM-based molecular graph for the ion-pair NH₄Br, obtained on its MP2(FC)/def2-TZVPPD gas-phase geometry and as in the crystal, respectively; both these graphs show bond paths as sticks and dotted lines in atom color (N—blue; Br—dark-red; H—white grey), bond critical points as tiny spheres between atomic basins in green, and values (in a.u.) of charge density ρ_b and the Laplacian of the charge density ∇²ρ_b at the N···Br bond critical point.

Figure 11

Three views of the crystal of ND₄I (ICSD ref. 89094 [103]), showing (a) combined D···I deuterium bonds and N···I pnictogen bonds, (b) D···I deuterium bonds, and (c) N···I pnictogen bonds. Illustration of the nature of local nature of multi-furcated charge-assisted intermolecular bonding topologies: (d) N in ND₄⁺ as four pnictogen bond donors; (e) ND₄⁺ as four D bond donors; (f) I⁻ as four D-bond and four N-bond acceptors; (g,h) IGM-based isosurface plots between the interacting units as in the unit-cell of the crystal, with isovalues of 0.015 and 0.010 au, respectively. Selected bond lengths and bond angles are in Å and degrees, respectively. The dotted lines represent inter-ionic interactions. Atom type is shown in (e). (i) MP2(FC)/def2-TZVPPD level QTAIM-based molecular graph for the ion-pair ND₄I, obtained on its geometry as in the crystal; it shows the bond paths as sticks and dotted lines in atom color, bond critical points as tiny spheres between atomic basins in green, and values (in a.u.) of charge density ρ_b and the Laplacian of the charge density ∇²ρ_b at the N···I bond critical point.

Figure 12

The ball-and-stick model of the unit-cell of the crystal structure of [I₄₄Pb₁₈]⁸⁻[CH₃NH₃]₈ Atoms are shown as balls and are color coded: Iodine—purple; Carbon—gray; N—blue; H—white. The CSD ref. code is shown.

Figure 13

The spatial arrangement between the organic cations, [CH₃NH₃]⁺, and inorganic framework, [I₄₄Pb₁₈]⁸⁻, in the crystal structure of [I₄₄Pb₁₈]⁸⁻[CH₃NH₃]₈, showing a number of quasi-linear N···I Type-IIa pnictogen bonds between the interacting units (dotted lines in red/cyan): (a) Polyhedral model and (b) ball-and-stick model of the inorganic framework. Selected bond lengths and bond angles are in Å and degrees, respectively.

Figure 14

Mixed polyhedral (inorganic) and ball-and-stick (organic) models of the crystals of (a) [(CH₃(CH₂)₁₅NH₃)PbI₄] [108]; (b) [C₅H₁₂NO₂⁺]₄[Pb₂Cl₈]_n; [109]; (c) [(H₃N(CH₂)₁₂NH₃)PbI₄] [110]; and (d) [(CH₃(CH₂)₈NH₃)PbI₄] [111]. Bond lengths and bond angles associated with selected intermolecular interactions are in Å and degrees, respectively. Space groups and CSD ref codes are shown for each case.

Figure 15

Mixed polyhedral (inorganic) and ball-and-stick (organic) models of the crystals of (a) (H₃N(CH₂)₄NH₃)PbI₄] (b) (H₃N(CH₂)₈NH₃)PbI₄] (c) (H₃N(CH₂)₁₀NH₃)PbBr₄] and (d) (H₃NC₁₀H₆NH₃)PbI₄, reported by Lemmerer and Billing [110]. Bond lengths and bond angles associated with selected intermolecular interactions are in Å and degrees, respectively. Space groups are shown for each case. Intermolecular interactions are marked as dotted lines in green.

Figure 16

Polyhedral and ball-and-stick representations of (a) (C₆H₂₀N₃)₂[Cd₂Cl₁₀] (CSD ref. POHFEA [114]); (b) (OMeC₆H₄CH₂NH₃)_2n·n(CdCl₄) (CSD ref. XASKEJ [115]); (c) 2[CH₂FCH₂NH₃]·[CdCl₄] (CSD ref. QUDCIE [116]); (d) (CHCCH₂NH₃)_2n·n(CdCl₄) (CSD ref. LAPDIP [117]; and (e) (CH₃CH₂NH₂CH₂CH₂NH₃)_2n·n(CdCl₄),2nCl (CSD ref. HEZYAM [118]). Intermolecular interactions are marked as dotted lines in cyan, the hanging contacts are marked as dotted lines in red. Selected bond distances and bond angles are in Å and degrees, respectively.

Figure 17

Polyhedral and ball-and-stick models of some crystals featuring highly directional N···X (X = Br, I) pnictogen bonding interactions. (a) (I−(CH₂)₂−NH₃)₂PbI₄ [136]; (b) 2(C₉H₁₂N),0.5(C₂H₆),0.5(Pb₄I₁₄) [137]; (c) 2(C₁₂H₁₄N)(PbBr₄)_n [138]; and (d) (BA)₂CsAgBiBr₇ (BA = CH₃(CH₂)₃NH₃⁺) [139]. Intermolecular interactions are marked as dotted lines in cyan. Selected bond distances and bond angles are in Å and degrees, respectively. CSD references are shown in upper-case letters. The gray-white, purple and gray polyhedra represent the octahedral nature of Ag, Bi and Pb cations, respectively.

Figure 18

(a) Illustration of the nature of C-I···I halogen bonding, N···I pnictogen bonding, N–H···I and C–H···I hydrogen bonding interactions in the extended and unit-cell crystals of (I−(CH₂)₂−NH₃)₂PbI₄. Shown in (b,c) are an illustration of the nature of Br···I and Cl···I halogen bonding, and N–H···I and C–H···I hydrogen bonding interactions in the unit-cell crystals of (Br−(CH₂)₂−NH₃)₂PbI₄ and (Cl−(CH₂)₂−NH₃)₂PbI₄, respectively. The intramolecular N–H···X′ hydrogen bonding interaction in the cis conformation of X′−(CH₂)₂−NH₃⁺ (X′ = Br, Cl) is marked in (b,c). Labeling of selected atoms, as well as CSD reference codes in upper-case letters, is shown in all cases. Selected bond distances are in Å.

Figure 19

Polyhedral and ball-and-stick models of (a) [(CH₃)₂CHCH₂NH₃]₂PbCl₄ and (b) BA₂Ag_0.5Bi_0.5Br₄ (BA = CH₃(CH₂)₃NH₃⁺), displaying the nature of pnictogen-bonding interactions in the crystal. H-atoms of the organic cation are missing in the crystal structure shown in (b) and are not shown in (a) for clarity. The geometric aspects of the N···X (X = Cl, Br) pnictogen bonds are shown. The dark-gray and purple octahedra in (a,b) correspond to PbCl₆ and BiBr₆, respectively. Selected bond distances and bond angles are in Å and degrees, respectively. The CSD references are shown in each case. Intermolecular interactions are depicted as dotted lines in cyan and hanging contacts as dotted lines in red. The crystal structure of BA₂Ag_0.5Bi_0.5Br₄ deposited in the CSD does have a significant uncertainty in the position of Bi/Ag, which is not apparent in the polyhedral model.

Figure 20

Polyhedral and ball-and-stick models of the crystal structure of (PPA)₂(FA_0.5MA_0.5)_n−1Pb_nI_3n+1 materials in 2D/3D: (a) n = 2 and (b) n = 3. Neither of these structures, as deposited in the CSD, show the correct orientation of the organic cations within the 3D perovskite cages, as provided in the supplementary material to the study [137], and hence we replaced them here by blue ellipses. The pnictogen bonded contacts are shown as dotted lines in cyan and the hanging contacts are in red. Selected intermolecular N···I, C–H···I and N–H···I bond distances and bond angles in Å and degrees, respectively.

Figure 21

Polyhedral and ball-and-stick models of (a) (BA)₄AgBiBr₈ and (b) (BA)₂CsAgBiBr₇ (BA = CH₃(CH₂)₃NH₃⁺), displaying the nature of pnictogen- and tetrel-bonding interactions in the crystal. Shown on the right of (a,b) are the illustration of local modes of various interlayer intermolecular interactions (viz. hydrogen bonds, tetral bonds, and pnictogen bonds) formed between the inorganic and organic frameworks. Selected bond distances and bond angles are in Å and degrees, respectively. Some of the organic cations in (b) have been deleted for clarity. The CSD references are shown in each case in uppercase letters. The purple and white-gray octahedra correspond to BiBr₆ and AgBr₆ octahedra, respectively, whereas the dark-purple balls inside the cage in (b) represent the cesium cations.

Figure 22

(a,b) The polyhedral ball-and-stick models of [HOOC(CH₂)₄NH₃]₂PbBr₄ [147] showing (a) the nature of N–H···Br and C–H···Br hydrogen bonding and N···Br pnictogen bonding interactions, and (b) N···Br pnictogen bonding interactions (H atoms omitted), formed at the organic and inorganic interface. (c,d) The crystal structure of [HOOC(CH₂)₄NH₃]₂PbCl₄ (CSD refs. VUHVIG02 [109] and VUHVIG [148]) showing the nature of N–H···Cl and C–H···Cl hydrogen bonding and N···Cl pnictogen bonding interactions formed at the organic and inorganic interface. Selected bond distances and bond angles are in Å and degrees, respectively.

Figure 23

Ball-and-stick and polyhedral models of selected 1D structure. (a) bis(N¹,N¹-diethylethane-1,2-bis(aminium)) bis(μ-bromo)-octabromo-di-antimony (C₆H₁₈N₂²⁺)₂(Br₁₀Sb₂₄⁻) [154]; (b) pentakis(methylammonium) tris(μ-iodo)-hexakis(iodo)-di-lead bis(methylamine) (CH₆N⁺)₅(I₉Pb₂⁵⁻),2(CH₅N) [155]; (c) bis(3-ammoniumyl-4-amino-pyridin-1-ium) bis(μ-chloro)-octachloro-di-bismuth dehydrate (C₅H₉N₃²⁺)₂(Bi₂Cl₁₀⁴⁻)2(H₂O) [156,157]; (d) catena-[methylammonium bis(μ-iodo)-iodo-lead monohydrate (CH₆N⁺)(I₃Pb⁻)_n,(H₂O) [158]. Intermolecular contacts between bonded atomic basins are illustrated as dotted lines in cyan and hanging contacts in red. Selected bond distances and bond angles associated with the nitrogen-centered pnictogen bonds are in Å and degrees, respectively.

Figure 24

Ball-and-stick and polyhedral model of the 2 × 2 × 2 cell of the crystal of catena-(bis(3,5-dimethylanilinium) bis(μ₂-iodo)-diiodo-lead(II)) [(C₈H₁₂N⁺)_2n, (I₄Pb²⁻)] [159]. Intermolecular contacts between bonded atomic basins are illustrated as dotted lines in cyan and hanging contacts in red. Selected bond distance and bond angle associated with the nitrogen-centered pnictogen bond is in Å and degrees, respectively. The CSD reference is shown in uppercase letters.

Figure 25

Ball-and-stick and polyhedral models of some selected 0D crystal structures. (a) bis(ethylenediammonium) tetrachloro-cobalt(II) bis(chloride), [CoCl₂²⁻][C₂H₁₀N₂²⁺₂][Cl⁻]₂ [163]; (b) 1,4-phenylenediammonium tetrachloro-mercury(II) (C₆H₁₀N₂)²⁺(HgCl₄²⁻) [164]; (c) tris(4-chloroanilinium) hexachloro-bismuth monohydrate [3(C₆H₇ClN⁺)₃(BiCl₆³⁻)(H₂O) [165]; (d) bis(ethane-1,2-diaminium) bis(bromide) tetrabromo-manganese (C₂H₁₀N₂²⁺)₂,(MnBr²⁻)(Br⁻)₂ [166]. Intermolecular contacts between bonded atomic basins are illustrated as dotted lines in cyan and hanging contacts in red. Selected bond distances and bond angles associated with the nitrogen-centered pnictogen bonds are in Å and degrees, respectively.

Figure 26

Ball-and-stick and polyhedral models of selected organic-inorganic hybrid metal halide perovskite and non-perovskite 0D structures. (a) bis(1,4-phenylenediammonium) hexachloro-lead(II) (C₁₂H₁₄N₂²⁺)₂(PbCl₆⁴⁻) [167]; (b) the same compound the structure of which was reported by a different group [168]; (c) bis[(1,3-phenylene)dimethanaminium] hexabromo-tin (C₈H₁₄N₂²⁺)₂(SnBr₆⁴⁻) [169]; (d) 1,3-propanediammonium tetraiodo-cadmium(II) dihydrate (C₃H₁₂N₂²⁺)(CdI₄²⁻)·2(H₂O) [170]. Intermolecular contacts between bonded atomic basins are illustrated as dotted lines in cyan and hanging contacts in red. Selected bond distances and bond angles associated with the nitrogen-centered pnictogen bonds are in Å and degrees, respectively.

Figure 27

(a,b) Histograms illustrating the intermolecular distances r(N···X) and intermolecular bond angles ∠R–N···X (X = F, Cl, Br, I) for 81 hits (89 close contacts) found in a CSD search for the ranges 2.6–3.7 Å and 175–180°, respectively. Shown in (c,d) are the corresponding plots for 3122 geometric instances in 1690 crystals found with ranges of 2.6–4.0 Å and 140–180°, respectively. Potential false contacts in (c,d) have not been identified and omitted.

Figure 28

(a,b) Histograms illustrating the intermolecular distances r(N···I) and intermolecular bond angles ∠R–N···I for 81 hits (89 close contacts) found in a CSD search for the bond distance and bond angle ranges of 2.6–4.0 Å and 170–180°, respectively. Shown in (c,d) are the corresponding plots for 554 close instances from 309 hits for N···Br in the bond distance and bond angle ranges of 2.6–4.0 Å and 150–180°, respectively. Shown in (e,f) are the corresponding plots for 1000 close contacts from 658 hits for N···Cl in the bond distance and bond angle ranges of 2.6–4.0 Å and 150–180°, respectively. False contacts in (a,b) were removed, but not in (c–f). The bell curve in red in each case represents the normal distribution.