Structure, stability and bonding of (BC2N)(n), n=2,3: an ab initio study

The dimer and trimer of BC2N are studied at the HF and MPn levels using 3-2 1G, 6-31G* and 6-31+G* basis sets. It is found that stability is enhanced b y maintaining -BN- units together in the cyclic form. Both molecules have c yclic ground state structures with cumulenic-type equal bond lengths in the -BNBN- and polyacetylenic -CCCC- fragments. The linear-cyclic energy diffe rence increases with the size of the cluster. Electron correlation substant ially favors the cyclic structures over the linear forms. No general trend of atomic combination has been found in the linear isomers. Diffuse functio ns have negligible effects on the relative energies and geometries of the d imers. (C) 2000 Elsevier Science B.V. All rights reserved.