Carborane superclusters formed by ion-molecule reactions in an ion trap

We report the ion-molecule reactions of o-, m- and p-carborane (C2B10H12) in an ion trap. Mass spectrometry showed that under UHV conditions carborane ions reacted sequentially with their neutral counterparts to form a series of cluster-of-clusters ions, i.e. 'supercluster' ions. This clustering reaction proceeded with elimination of hydrogen atoms from carboranes but not with any detachment of the skeletal boron and carbon atoms. The result of the H-D exchange reaction on the carborane skeletons, together with ab initio quantum chemical calculations, indicates that individual carborane skeletons were linked covalently to one another through B-B bonds. On the basis of the analysis of the number of bonds between the carborane skeletons, we offer three types of molecular structure models for carborane superclusters: one-dimensional chain-like, two-dimensional bent-plane and three-dimensional close-packed types. Comparing the calculated heats of formation for the three model structures obtained by ab initio quantum chemical calculations, it is most likely that the carboranes form the superclusters according to the two-dimensional bent-plane model.