The first nickelacarborane with closo-nido structure [10',11'-(Py)2-3,9'-Ni(1,2-C2B9H11)(7',8'-C2B8H8)] was isolated from the reaction of nickel(IV) bis(dicarbollide) with pyridine. The molecular structure of this complex was determined by single crystal X-ray diffraction. The nickel atom is a common vertex for the closo-NiC2B9 cluster and the nido-NC2B8 cluster where it is located together with carbon atoms in the open NiC2B2 pentagonal face. It is assumed that its formation proceeds through the nucleophile-induced removal of the B(6)H vertex followed by rearrangement of the forming 11-vertex cluster, which most likely proceeds through a sequence of closing and opening reactions.
Keywords: nickel bis(dicarbollide); nickelacarboranes; polyhedral contraction; pyridine derivative; single crystal X-ray diffraction.