  Twenty-five molecule-anion complex systems [I4Tt...X-] (Tt = C, Si, Ge, Sn
and Pb; X = F, Cl, Br, I, At) were examined using density functional theory
(wB97XD) 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 wB97XD
computed intermolecular geometries and interaction energies of [I4Tt...X-] were
close to those predicted by the highest level of theory, the MP2 results were
shown to be misleading for some of the molecule-anion complex systems
investigated. 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 quantum theory of atoms in molecules and
independent gradient model approaches, respectively.
