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

We have prepared nido -7,8,9,11-Sb 2 C 2 B 7 H 9 , 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-Sb 2 C 2 B 7 H 9 is predominantly dictated by pnictogen (Pn) bonding, an unconventional σ-hole interaction. Indeed, the interaction energy of a very strong Sb 2 H-B Pn-bond in the nido -7,8,9,11-Sb 2 C 2 B 7 H 9 dimer exceeds −6.0 kcal mol −1 . This is a very large value and is comparable to the strengths of known Pn-bonds in Cl 3 Pn π complexes (Pn = As, Sb). The reaction of arachno -4,6-C 2 B 7 H 13 with SbCl 3 yields nido -7,8,9,11-Sb 2 C 2 B 7 H 9 , which simultaneously has Sb-Sb, Sb-B and Sb-C bonds and a unique ability to form pnictogen bonds.