Tetrel Bonding in Anion Recognition: A First Principles Investigation

Abstract

Twenty-five molecule-anion complex systems [I₄Tt···X^-] (Tt = C, Si, Ge, Sn and Pb; X = F, Cl, Br, I and At) were examined using density functional theory (ωB97X-D) and ab initio (MP2 and CCSD) methods to demonstrate the ability of the tetrel atoms in molecular entities, I₄Tt, to recognize the halide anions when in close proximity. The tetrel bond strength for the [I₄C···X^-] series and [I₄Tt···X^-] (Tt = Si, Sn; X = I, At), was weak-to-moderate, whereas that in the remaining 16 complexes was dative tetrel bond type with very large interaction energies and short Tt···X close contact distances. The basis set superposition error corrected interaction energies calculated with the highest-level theory applied, [CCSD(T)/def2-TZVPPD], ranged from -3.0 to -112.2 kcal mol^-1. The significant variation in interaction energies was realized as a result of different levels of tetrel bonding environment between the interacting partners at the equilibrium geometries of the complex systems. Although the ωB97X-D computed intermolecular geometries and interaction energies of a majority of the [I₄Tt···X^-] complexes were close to those predicted by the highest level of theory, the MP2 results were shown to be misleading for some of these systems. To provide insight into the nature of the intermolecular chemical bonding environment in the 25 molecule-anion complexes investigated, we discussed the charge-density-based topological and isosurface features that emanated from the application of the quantum theory of atoms in molecules and independent gradient model approaches, respectively.

Keywords: MESP analysis; anion recognition; charge-density analysis; chemical bonding; dative bond formation; first-principles calculations; non-covalent interactions; tetrel bond; weak-to-strong interaction energy.

Figure 1

Illustration of molecule–anion interactions in the anionic part of some selected chemical systems cataloged in the CSD [9]. The crystals include: (a) bis(tetrabutylammonium) dodecachlorohexasilinane bis(iodide) dichloromethane solvate [2(C₁₆H₃₆N⁺),Cl₁₂Si₆,CH₂Cl₂,2(I⁻)] [12]; (b) bis(tetrabutylammonium) bis(bromide) dodecabromohexasilinane [2(C₁₆H₃₆N⁺),Br₁₂Si₆,2(Br⁻)] [13]; (c) bis(tetrabutylphosphanium) dodecaiodohexasilinane bis(iodide) [2(C₁₆H₃₆P⁺),I₁₂Si₆,2(I⁻)] [13]; (d) bis(tetraphenylphosphonium) 1,1,2,2,3,4,4,5,5,6-decachloro-3,6-bis(trichlorosilyl)hexasilinane bis(chloride) [2(C₂₄H₂₀P⁺),Cl₁₆Si₈,2(Cl⁻)] [14]; (e) triphenyl-N-(triphenylphosphanylidene)phosphaniminium chloride 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20-icosachloroundecacyclo [9.9.0.0^2,9.0^3,7.0^4,20.0^5,18.0^6,16.0^8,15.0^10,14.0^12,19.0^13,17]icosasilane chloroform solvate [C₃₆H₃₀NP₂⁺,Cl₂₀Si₂₀,2(CHCl₃),Cl⁻] [15]; (f) bis(triphenyl-N-(triphenylphosphanylidene)phosphaniminium) chloride 4-methylbenzene-1-sulfonate 1,3,5,8,10,13,16,19-octachloroundecacyclo [9.9.0.0^2,9.0^3,7.0^4,20.0^5,18.0^6,16.0^8,15.0^10,14.0^12,19.0^13,17]icosasilane [2(C₃₆H₃₀NP₂⁺),H₁₂Cl₈Si₂₀,C₇H₇O₃S⁻,Cl⁻] [15]. The CSD reference codes are depicted in uppercase letters. Selected bond distances and bond angles associated with the (H−)Si···Cl and/or (X−)Si···X (X = Cl Br, I) contacts are in Å and degree, respectively. Atom labeling is shown for selected atoms.

Figure 2

(Top) [ωB97X-D/def2-QZVPPD] level QTAIM-based molecular graphs of isolated TtI₄ (Tt = C, Si, Ge, Sn, and Pb), showing bond paths (solid lines in atom color) and bond critical points (tiny spheres in green) between bonded atomic basins (large spheres). The charge density(ρ_b), the Laplacian of the charge density (∇²ρ_b), the total energy density (H_b), and the delocalization index (δ) values are shown in black, blue, red, and faint-blue fonts (in a.u.), respectively. (Bottom) The 0.001 a.u. (electrons bohr⁻³) isoelectron density mapped potential on the electrostatic surfaces of the corresponding monomers, including (a) CI₄, (b) SiI₄, (c) GeI₄, (d) SnI₄, and (e) PbI₄. The strength of Tt’s and I’s σ-holes is shown in each case; filled tiny blue and red circles represent V_S,min and V_S,max, respectively; V_S,min and V_S,max values are in kcal mol⁻¹.

Figure 3

The dependence of polarizability of Tt derivative on the strength of the σ-hole on Tt in TtI₄, computed using [ωB97X-D/def2-QZVPPD]. The (polarizability, σ-hole) data for each molecule are indicated. The square of the regression coefficient R² is shown, together with the linear equation that connects polarizability with the strength of the σ-hole.

Figure 4

(a–e) [ωB97X-D/def2-QZVPPD] level QTIM-based molecular graphs of [I₄C···X⁻], showing the bond paths (solid and dotted lines in atom color) and bond critical points (tiny spheres in green) between bonded atomic basins. Large spheres represent the atomic basins. The dotted black line in (b–e) is artificially drawn to represent the presence of tetrel bond between C and X (X = Cl, Br, I, At). The charge density (ρ_b), the Laplacian of the charge density (∇²ρ_b), the total energy density (H_b), and the delocalization index (δ) values are shown in black, blue, red, and faint-blue fonts (in a.u.), respectively.

Figure 5

(a–e) [ωB97X-D/def2-QZVPPD] level QTIM-based molecular graphs of [I₄Si···X⁻] (X = F, Cl, Br, I, At), showing the bond paths (solid and dotted lines in atom color) and bond critical points (tiny spheres in green) between bonded atomic basins. Large spheres represent the atomic basins, with atoms labeled. The dotted black line in (d,e) is artificially drawn to represent the presence of tetrel bond between Si and X (X = I, At). The charge density (ρ_b), the Laplacian of the charge density (∇²ρ_b), the total energy density (H_b), and the delocalization index (δ) values are shown in black, blue, red, and faint-blue fonts (in a.u.), respectively.

Figure 6

(a–e) [ωB97X-D/def2-QZVPPD] level QTIM-based molecular graphs of [I₄Ge···X⁻] (X = F, Cl, Br, I, At), showing the bond paths (solid and dotted lines in atom color) and bond critical points (tiny spheres in green) between bonded atomic basins. Large spheres represent the atomic basins, with atoms labeled. The dotted black line in (e) is artificially drawn to represent the presence of tetrel bond between Ge and At. The charge density (ρ_b), the Laplacian of the charge density (∇²ρ_b), the total energy density (H_b), and the delocalization index (δ) values are shown in black, blue, red, and faint-blue fonts (in a.u.), respectively.

Figure 7

(a–e) [ωB97X-D/def2-QZVPPD] level QTIM-based molecular graphs of [I₄Sn···X⁻] (X = F, Cl, Br, I, At), showing the bond paths (solid and dotted lines in atom color) and bond critical points (tiny spheres in green) between bonded atomic basins. Large spheres represent the atomic basins, with atoms labeled. The charge density(ρ_b), the Laplacian of the charge density (∇²ρ_b), the total energy density (H_b), and the delocalization index (δ) values are shown in black, blue, red, and faint-blue fonts (in a.u.), respectively.

Figure 8

(a–e) [ωB97X-D/def2-QZVPPD] level QTIM-based molecular graphs of [I₄Pb···X⁻] (X = F, Cl, Br, I, At), showing the bond paths (solid and dotted lines in atom color) and bond critical points (tiny spheres in green) between bonded atomic basins. Large spheres represent the atomic basins, with atoms labeled. The charge density (ρ_b), the Laplacian of the charge density (∇²ρ_b), the total energy density (H_b), and the delocalization index (δ) values are shown in black, blue, red, and faint-blue fonts (in a.u.), respectively.

Figure 9

(a–e) [ωB97X-D/def2-QZVPPD] level IGM-δg^inter-based isosurface (bluish-green or green volumes) plots of [I₄C···X⁻] (X = F, Cl, Br, I, At), showing possible I···X halogen bonded and C···X tetrel bonded interactions between interacting molecular entities. (Top) Illustration of I···X Type-I halogen-halogen bonded interactions between the interacting units that appear with larger isovalues. (Bottom) Illustration of C···X tetrel bonded interactions between the interacting units that appear at smaller isovalues. Anion derivatives are labeled.

Figure 10

(a–e) [ωB97X-D/def2-QZVPPD] level IGM-δg^inter-based isosurface (bluish-red or green volumes) plots for [I₄Si···X⁻] (X = F, Cl, Br, I, At), showing possible I···X halogen-halogen bonded and Si···X tetrel bonded interactions between interacting molecular entities.

Figure 11

(a–e) [ωB97X-D/def2-QZVPPD] level IGM-δg^inter-based isosurface plots (bluish-red volumes) of [I₄Pb···X⁻] (X = F, Cl, Br, I, At), showing possible Pb···X tetrel bonded interactions between interacting molecular entities.

Figure 12

(a) The [ωB97X-D/def2-QZVPPD] level quadratic dependence of BSSE corrected interaction energy (E_int(BSSE)) on the distance of separation r(Tt···X) for 25 [I₄Tt···X⁻] (Tt = C, Si, Ge, Sn, Pb; X = F, Cl, Br, I, At) molecule–anion complexes. Shown in (b,c) are the corresponding dependences obtained using [MP2/def2-QZVPPD] and [CCSD(T)/def2-TZVPPD], respectively. Shown in (d–f) are the linear dependences between E_int(BSSE) and E_int obtained with [ωB97X-D/def2-QZVPPD], [MP2/def2-QZVPPD] and [CCSD(T)/def2-TZVPPD], respectively.