A novel stibacarbaborane cluster with adjacent antimony atoms exhibiting unique pnictogen bond formation that dominates its crystal packing

Abstract

We have prepared nido-7,8,9,11-Sb₂C₂B₇H₉, the first cluster with simultaneous Sb–B, Sb–C and Sb–Sb atom pairs with interatomic separations with magnitudes that approach the respective sums of covalent radii. However, the length of the Sb–Sb separation in this cluster is slightly less than the sum of the covalent radii. Quantum chemical analysis has revealed that the crystal packing of nido-7,8,9,11-Sb₂C₂B₇H₉ is predominantly dictated by pnictogen (Pn) bonding, an unconventional σ-hole interaction. Indeed, the interaction energy of a very strong Sb₂⋯H–B Pn-bond in the nido-7,8,9,11-Sb₂C₂B₇H₉ dimer exceeds −6.0 kcal mol⁻¹. This is a very large value and is comparable to the strengths of known Pn-bonds in Cl₃Pn⋯π complexes (Pn = As, Sb).