Self-assembly of halogenated cobaltacarborane compounds: Boron-assisted C-H center dot center dot center dot X-B hydrogen bonds?

Full structural characterisation and complete synthetic procedures for three monohalogenated cobaltacarborane compounds closo-[3-Co(eta(5)- C5H5)-8-X-1,2-C2B9H10] (X = Cl (1), Br (2), 1 (3)) and the dibromo derivative closo-[3-Co(eta(5)-C5H5)-8,9-Br-2-1,2-C2B9H9] (4) are reported. The supramolecular structures of 1, 3, and 4 reveal the existence of intermolecular C-(HX)-X-. . .-B interactions. The role of these interactions has been investigated through a CSD search and subsequent analysis of the reported crystalline compounds. The results show that halogens become reasonably good hydrogen-bond acceptors when bonded to boron and, in this respect, are comparable in strength to metal-bound halogens.