Dual Geometry Schemes in Tetrel Bonds: Complexes between TF4 (T = Si, Ge, Sn) and Pyridine Derivatives

Abstract

When an N-base approaches the tetrel atom of TF4 (T = Si, Ge, Sn) the latter molecule deforms from a tetrahedral structure in the monomer to a trigonal bipyramid. The base can situate itself at either an axial or equatorial position, leading to two different equilibrium geometries. The interaction energies are considerably larger for the equatorial structures, up around 50 kcal/mol, which also have a shorter R(T··N) separation. On the other hand, the energy needed to deform the tetrahedral monomer into the equatorial structure is much higher than the equivalent deformation energy in the axial dimer. When these two opposite trends are combined, it is the axial geometry which is somewhat more stable than the equatorial, yielding binding energies in the 8–34 kcal/mol range. There is a clear trend of increasing interaction energy as the tetrel atom grows larger: Si < Ge < Sn, a pattern which is accentuated for the binding energies.

On the ability of pnicogen atoms to engage in both σ and π-hole complexes. Heterodimers of ZF2C6H5 (Z = P, As, Sb, Bi) and NH3

“…This sort of deformation occurs not only in ZF 5 but also in TF 4 [112] (T = tetrel atom), which would not be considered hypervalent. These distortion energies in tetrel bonds can control the preferred equilibrium geometry [80] and tend to lessen as the size of the central tetrel atom increases [113], consonant with the findings here for pnicogen bonds. Similar distortions were observed [81] in both TR 4 (σ) and TR 2 =CH 2 (π) tetrel-bonding molecules.…”

“…Although there has been little examination of σ-hole versus π-hole bonding in pnicogen bonds, there has been some study of this question for the related tetrel bond wherein TF 4 (T = Si, Ge, Sn) molecules were paired with pyridine derivatives [80]. The approach of the Lewis base prompted large-scale geometry distortion in TF 4 , changing its shape from tetrahedral to trigonal bipyramidal.…”

“…The ability of TF 4 molecules to undergo [80] a geometrical transformation so as to form either a σ-hole or π-hole tetrel bond inspired us to wonder if something of this sort is also possible for pnicogen atoms. If such is the case, then there are a number of obvious and important questions.…”

Not Only Hydrogen Bonds: Other Noncovalent Interactions

“…It is necessary to clearly differentiate clusters (e.g., Au 2 or Ag 11 ) ( Figure 3) [58] from molecules (e.g., AuX) [59,60]. Brinck and Stenlid, based on their study of nanoclusters of Cu, Au, Pd, Pt, Rh, .…”

Versatility of the Cyano Group in Intermolecular Interactions

“…This same phenomenon occurs on a divalent chalcogen Y atom, but each of its two RY bonds leads to a separate σ-hole, and a logical extension provides three σ-holes around a Z pnicogen atom in its ZR 3 configuration. Recent works [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ] have also included tetrel atoms T (C and Si, etc.) in this category, as the tetravalent TR 4 molecule has four σ-holes, so could, at least in principle, participate in as many as four simultaneous tetrel bonds.…”