Tuning σ-Holes: Charge Redistribution in the Heavy (Group 14) Analogues of Simple and Mixed Halomethanes Can Impose Strong Propensities for Halogen Bonding

Abstract

Halogen bonding between halide sites (in substituted organic molecules or inorganic halides) and Lewis bases is a rapidly progressing area of exploration. Investigations of this phenomenon have improved our understanding of weak intermolecular interactions and suggested new possibilities in supramolecular chemistry and crystal engineering. The capacity for halogen bonding is investigated at the MP2(full) level of theory for 100 compounds, including all 80 MH(4-n)X(n) systems (M = C, Si, Ge, Sn, and Pb; X = F, Cl, Br, and I). The charge redistribution in these molecules and the (in)stability of the sigma-hole at X as a function of M and n are catalogued and examined. For the mixed MH(3-m)F(m)I compounds, we identify a complicated dependence of the relative halogen bond strengths on M and m. For m = 0, for example, the H(3)C-I----NH(3) halogen bond is 6.6 times stronger than the H(3)Pb-I----NH(3) bond. When m = 3, however, the F(3)Pb-I----NH(3) bond is shorter and approximately 1.6 times stronger than the F(3)C-I----NH(3) bond. This substituent-induced reversal in the relative strengths of halogen bond energies is explained.

Tetrel bonds, penta‐ and hexa‐coordinated tin and lead centres

“…In Groups 15–17 an approximate decrease of electronegativity is observed with increasing atomic number, but not for tetrels. These anomalies connected with the shaken trend in the change of tetrel properties if the atomic number increases may be explained by the influence of the d‐orbital and f‐orbital (lanthanide) contractions on Ge and Pb elements, respectively . For the lead centre, and, in general, for period 6 elements, relativistic effects are also very important .…”

Halogen Bonding Interactions of Polychlorinated Biphenyls and the Potential for Thyroid Disruption

“…XB interactions have numerous applications to drug design and crystal engineering and are often described as an electrostatic interaction with a „σ‐hole“ along the bond axis of the halogen . However, several authors have noted that this popular model de‐emphasizes significant contributions such as covalency and dispersion to the XB interaction . Alternatively, XB can be described as the donation of electron density from the lone pair of a donor (such as S or Se) to the antibonding σ R−X * orbital (in which X=I, Br, or Cl) of the acceptor (Figure ) .…”

Theoretical investigation of the halogen bonded complexes between carbonyl bases and molecular chlorine

“…The halogen bonds are characterized by a charge transfer from the Lewis base to the RX molecule and correspond to charge transfer (CT) complexes in the old nomenclature of Mulliken . Halogen‐bonded interactions have been recently the subject of many theoretical works . The reason why halogen‐bonded complexes can be formed has been a confusing question for a long time because both the halogen atom and the electron donor are negatively charged.…”