Comparison between alkalimetal and group 11 transition metal halide and hydride tetramers: Molecular structure and bonding

A comparison between alkalimetal (M = Li, Na, K, and Rb) and group 11 transition metal (M = Cu, Ag, and Au) (MX)inf4/inf tetramers with X = H, F, Cl, Br, and I has been carried out by means of the Amsterdam Density Functional software using density functional theory at the BP86/QZ4P level of theory and including relativistic effects through the ZORA approximation. We have obtained that, in the case of alkalimetals, the cubic isomer of Tinfd/inf geometry is more stable than the ring structure with Dinf4h/inf symmetry, whereas in the case of group 11 transition metal tetramers, the isomer with Dinf4h/inf symmetry (or Dinf2d/inf symmetry) is more stable than the Tinfd/inf form. To better understand the results obtained we have made energy decomposition analyses of the tetramerization energies. The results show that in alkalimetal halide and hydride tetramers, the cubic geometry is the most stable because the larger Pauli repulsion energies are compensated by the attractive electrostatic and orbital interaction terms. In the case of group 11 transition metal tetramers, the Dinf4h/inf/Dinf2d/inf geometry is more stable than the Tinfd/inf one due to the reduction of electrostatic stabilization and the dominant effect of the Pauli repulsion.