An ab initio study of diarsacyclobutadienes

Møller-Plesset MP2/6-311G* and MP4SDQ/6-311G* calculations have been made for the various possible ground state conformers of the simple 1,2- and 1,3-diarsacyclobutadienes (AsCH)₂, in order to determine their geometries, the nature of the bonding, and the relative stabilities of different isomers. These calculations revealed some qualitative differences between the analogous 1,2- and 1,3-diphosphacyclobutadienes. The most stable (gas phase) isomeric form of (AsCH)₂ is predicted to be 1,2-diarsatetrahedrane. Additionally, the mono- and di-substituted compounds Bu^t(AsC)₂H, Bu^t(AsC)₂Bu^t, Ph(AsC)₂H and Ph(AsC)₂Ph have been optimized. These indicate that 1,3-diarsacyclobutadienes prefer a planar C_2h-like ring structure with localized single and double As-C bonds.