Charges distribution and chemical bonding in mixed-ring sandwich compounds: Ab initio calculations on some neutral and charged cyclopentadienylcycloheptatrienyl metal compounds

Abstract

Small basis set SCF-LCAO-MO calculations are described for the molecules (C 5H 5)M(C 7H 7) with M = Ti, V and Cr. Basis set effects have been investigated by means of calculations with different basis sets on the free atoms, the free rings and the moieties (C 5H 5Ti and (C 5H 5)Cr. These calculations indicate that the near minimum basis set results provide a reasonable basis for a discussion of the trends in the charge distributions of the mixed sandwich compounds. Within the framework of Mulliken's population analysis It is shown that the negative charge on the C 7H 7 ring decreases in the order Ti, V, Cr, while the negative charge on the C 5H 5 ring increases in this order. Details of the bonding are discussed. The observed trends in metal 2p and 3s, and carbon 1s ionization energies are quite well reproduced by the corresponding ground state orbital energies Independent SCF calculations on a number of electronic configurations of the positive ions show large reorganizations of the charge distributions in all cases. The corresponding relaxation energies depend strongly on the amount of metal character of the ionized ground state orbitals. The trends in the calculated ionization energies agree only partly with those derived from the measured photoelectron spectra.