Crystal Structure of the Potassium Salt of the 9,9',12,12'-Tetraiodo Derivative of Cobalt Bis(dicarbollide): The Role of Intermolecular Interactions Involving Iodine Substituents

The potassium salt of the 9,9',12,12'-tetraiodo derivative of cobalt bis(dicarbollide) containing substituents in the lower belt of the dicarbollide ligand was obtained by the reaction of anhydrous CoBr2 with the trimethylammonium salt of 5,6-diiodo nido-carborane (Me3NH)[5,6-I2-7,8-C2B9H10] in the presence of t-BuOK in refluxing 1,2-dimethoxyethane. The structure of [K(DME)3.25(H2O)0.75][9,9',12,12'-I4-3,3'-Co(1,2-C2B9H9)2] was determined by single-crystal X-ray diffraction. It was shown that iodine atoms at positions 9 and 12 of the dicarbollide ligand are poor electron pair acceptors, which prevents the formation of type II intermolecular halogen bonds. Unlike other known iodo derivatives of cobalt bis(dicarbollide) containing substituents in the upper belt of the dicarbollide ligands, in the 9,9',12,12'-tetraiodo derivative of cobalt bis(dicarbollide), the main structure-forming contacts are intermolecular C–H···I hydrogen bonds and weak type I halogen bonds.