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.

Definition of the tetrel bond

“…On the formation of a typical tetrel bond R-Tt⋯A between two interacting entities R-Tt and A: a. a coulombic attraction occurs between the interacting regions on the TtBD Tt and TtBA A moieties; b. the sign of the binding energy (or the interaction energy, complexation energy, or stabilization energy) is likely to be negative to signify an energetically favorable interaction; [18][19][20]27 c. an energy decomposition analysis, for instance, using symmetry adapted perturbation theory 28,29 may indicate the energetic contributions to the binding energy arise from electrostatics, exchange repulsion, polarization (induction and/or charge transfer), and long-range dispersion, and are collectively responsible for the net stabilization of the TtB; d. the separation distance between the TtBD site Tt and the TtBA site A tends to be smaller than the sum of the van der Waals radii of the respective interacting atomic basins but larger than the sum of their covalent bond radii; deviation from the former condition is likely since known van der Waals radii of atoms are only accurate to within ±0.2 Å; 11,26,30,31 e. the TtB donor tends to approach the TtB acceptor along the outer extension of a σ covalent or coordinate bond, R-Tt; the angular deviation from the R-Tt bond extension is often more pronounced in TtBs than in XBs, 2 ChBs 3 and comparable to that of PnBs; 4,11 f. the angle of interaction, ∠R-Tt⋯A, tends to be linear or quasi-linear when the approach of the electrophilic site on Tt is along the R-Tt σ covalent or coordinate bond extension, but this can be potentially non-linear or bent when the TtB occurs between a π-type orbital of the bonded Tt atom and the nucleophilic region on TtBA, 32 and when secondary interactions are involved; g. when the nucleophilic region on the TtBA A, is a lone pair orbital, or a (negative) π region, the TtBD tends to approach TtBA along the axis of the lone pair, or orthogonal to the π bond plane; 32 h. the distance of the R-Tt covalent/coordinate bond opposite to the TtB (called tetrel bond donor distance) is typically longer than that in the isolated (unbound) TtBD; 33,34 i. the infrared absorption and Raman scattering observables of both R-Tt and TtBA are affected by TtB formation; the vibrational frequency of the R-Tt bond may be redshifted (or blue-shifted) 34,35 depending on the extent of the interactions involved, compared to the frequency of the same bond in the isolated molecular entity; new vibrational modes associated with the formation of the Tt⋯A intermolecular pnictogen bond should also be characteristically observed, as for HBs, XBs and CBs; j. the NMR chemical shifts of nuclei in both R-Tt and TtBA are typically affected (with the former increased or decreased…”

“…1) is also applicable to XBs, [59][60][61][62] ChBs, [63][64][65] and PnBs; 4,66,67 the nature of charge transfer may be assessable upon computing the second-order perturbation theory based stabilization energy using natural bond orbital analysis; o. the tetrel bond strength typically increases with a given TtBA A, as the electronegativity of Tt decreases in the order C > Si > Ge > Sn > Pb and the electron withdrawing ability of R increases; 13,19,39,68 there may be an exception when the chemical environment alters the nature of the reactivity between the TtB donor and acceptor moieties. 27 p. the tetrel bond strength may increase for a specific TtBA and remainder R of the R-Tt entity as the polarizability of the tetrel atom increases (Pb > Sn > Ge > Si > C). 20 This is analogous to the effect observed in the case of XB (I > Br > Cl > F), 69,70 ChB (Te > Se > S > O), 71 and PnB (Bi > Sb > As > P > N); 67 if a secondary interaction (e.g., hydrogen bond, halogen bond, chalcogen bond, tetrel bond, pnictogen bond, etc.)…”

“…20 This is analogous to the effect observed in the case of XB (I > Br > Cl > F), 69,70 ChB (Te > Se > S > O), 71 and PnB (Bi > Sb > As > P > N); 67 if a secondary interaction (e.g., hydrogen bond, halogen bond, chalcogen bond, tetrel bond, pnictogen bond, etc.) is involved either with the tetrel bond donor or its acceptor, the order of interaction strength may alter; q. the strength of a tetrel bond can be ultra-strong (≫−40.0 kcal mol −1 ), 27,34,72 very strong (−25.0 < energy ≤ −40.0 kcal mol −1 ), 27,34,72 strong (−25.0 < energy < −15.0 kcal mol −1 ), 19,27 moderately strong (−5.0 < energy < −15.0 kcal mol −1 ), 27,73 weak (−3.0 < energy < −5.0 kcal mol −1 ), 13,27,73 very weak (−1.0 < energy < −3.0 kcal mol −1 ), 19,72 or of the van der Waals type (≤−1.0 kcal mol −1 ). 74…”

“…the tetrel atom in Tt H 3 XTt (Tt = C, Si, Ge, Sn, Pb; X = halogen), TtX 4 , 27,79 TtH 3 NH 2 (ref. 41) (Tt = C, Si, Ge, Sn, Pb), 80 TtH 4 (Tt = Si, Ge, Sn, Pb), and in TtX 2 (Tt = Sn, Pb), 81 TtF 3 X (Tt = C, Si, Ge, Sn; X = Cl, Br, I) 81 and TtH 3 OH (Tt = C, Si, Ge; Sn, Pb); 82 the carbon in carboranes (CH 11 B 11 ), 83 C 2 F 4 , FCCF, 12 XCN (X = F, Cl, Br, I), 12,84 and FCCCN, 11 CO 2 , 85 and CS 2 , C(CN) 4 ; C(CN) 3 X (X = F, Cl, Br, I); 86 a positive π system (the centroids of C 5 and C 6 of aromatic compounds reinforced by more than one highly electron-withdrawing groups (e.g., C 4 F 4 N 2 , C 6 X 6 (X = F, Cl, Br), 15 C 6 F 5 Y, C 6 H 5 Y (Y = CN, NO, NO 2 ), 14 C 6 H 3 (CN) 3 , pyrene-F 10 , anthracene-F 9 , and corenene-F 12 , fullerene derivatives (C 60 , C 70 and C 80 ), single-or multiwall nanotubes, etc.…”

The pnictogen bond forming ability of bonded bismuth atoms in molecular entities in the crystalline phase: a perspective

“…While the Bi–F bond lengths in the first coordination sphere of Bi are not all equivalent, they are representatives of (dative) coordinate PnBs, and BiF 3 is a polar covalent species and a photocatalyst. 86 From knowledge of the strong electrostatic potential on the surface of Bi in BiF 3 , it seems clear that the formation of dative coordinate (pnictogen) bonds, 87 rather than ordinary PnBs, along the extension of the F–Bi is a likely consequence.…”