REARRANGEMENT MECHANISMS OF B12H12(2-) AND C2B10H12

Rearrangement mechanisms for B12H122- and C2B10H12 are deduced by ab initio calculations at the minimal basis set level. In contrast to most previous discussions, but in accord with orbital symmetry considerations, all the transition states are found to have low symmetry the three carborane isomers of icosahedral B12H12- interconvert via a complex series of higher energy minima. The results illustrate how these systems adapt to the lack of low-energy orbital-symmetry-allowed pathways and show that the topology of the potential energy surface changes significantly from the borane to the carborane.