COMPUTATIONS OF BORON AND BORON-NITROGEN CAGES

The article surveys computations of several hetero-fullerenes: B36N24, B36P24, Al36N24, Al36P24, and various BmNn (m + n not equal 60). For m + n = 60 cases, the following stability order is predicted: B36N24 > B36P24 > Al36N24 > Al36P24. In addition to the pentagon-hexagon fulle rene pattern, the square-hexagon route is considered as an alternative . The new pattern always requires six squares, while the number of hex agons increases linearly with the number of atoms. The route can produ ce species of similar or even higher stability compared to the convent ional pentagon-hexagon approach. It has a unique significance for the BN clusters as it allows for a mutual compensation of the steric strai n in four-membered rings by maximizing the number of the B-N bonds (an d suppressing B-B and N-N ones). On the other hand, the square/hexagon route does not produce a particular C-60 stabilomer (as there is no c ompensation for the four-membered ring strain). Clusters purely based on boron are exemplified with B-32 (I-h), which could be considered as a topological analogy of C-60 owing to dual relationships. The specie s however is not a local energy minimum at the HF/STO-3G and HF/3-21G ab initio level. In the MNDO computations the cage relaxes into a D-2d symmetry. Atomization heat is used in evaluation of its stability. (C ) 1997 Acta Metallurgica Inc.