Theoretical investigations on (CO)n(CO2)m cyclic cooligomers

Ab initio calculations have been performed on the (CO)(n)(CO2)(m) cyclic copolymers. where n, m = 1,2 with m greater than or equal to n. The cyclic molecules were studied at the HF/6-311G, HF/6-311+G(df), MP2/6-311+G(df) levels and Gaussian-2 theory with reduced Moller-Plesset order. G2MP2. The structures of the three cyclic oligomers investigated, C2O3, C3O5 and C4O6 are found to have a minimum and the geometries are planar. The energy releases of the dissociation reactions indicate that these molecules are thermodynamically unstable with respect to the parent monomers CO and CO2. In addition, the heats of formation for the cyclic molecules were evaluated at the G2MP2 level using an isodesmic approach and bond separation energies. (C) 2001 Elsevier Science B.V. All rights reserved.