The smallest borazine-fused cyclacenes: Novel N-H conformations in cyclo-BN-anthracene and cyclo-BN-tetracene from Hartree-Fock and density functional calculations

The structures and properties of the smallest possible borazine-fused cyclacenes, cyclo-BN-anthracene and cyclo-BN-tetracene ([6]3BN-cyclacene and [6]4BN-cyclacene), have been determined at the RHF/6-31G∗ and B3LYP/6-31G(d) levels of theory. In addition, novel conformers of both molecules in which one or more of the N-H moieties are aligned approximately perpendicular to the belt direction have been investigated and have been found to be comparable in energy to the conformers in which all of the N-H moieties are aligned approximately parallel to the belt direction. At the density functional B3LYP/6-31G(d) level of theory, the most stable of these conformers for [6]3BN-cyclacene is not the conformer in which all of the N-H moieties are aligned approximately parallel with the belt direction, but rather the conformer in which one of the N-H moieties is aligned approximately perpendicular with the belt direction. For the [6]4BN-cyclacene, however, the conformer with all of the N-H moieties aligned parallel to the belt direction is the most stable, although other conformers are reasonably similar in energy.