Structure and bonding in an octahedral Li4C2 cluster, the dilithium bis{dihydrido(silylimino)phosphorano}methanide dimer. A combined DFT-AIM analysis

The structure and bonding in the title dimer tin Dw symmetry) and the corre sponding monomer tin CL symmetry) were studied using density functional the ory (DFT) at the B3LYP/6-311(d) level. The dimerization requires a signific ant amount of distortion of the monomer in order to align the ligand backbo ne atoms as they appear in the dimer. For the dimer, the overall agreement with crystal X-ray structural data is very good. The Li4C2 core of the dime r forms a nearly perfect octahedron, with nearly identical Li-Li (2.390 Ang strom) and Li-C (2.386 Angstrom) distances. The dimerization process was fo und to be exothermic, with the dimer product exhibiting a remarkable stabil ity of Delta B3LYP = 55.6 kcal/mol (55,7 kcal/mol with zero point energy co rrection) with respect to two monomers. Analysis of the DFT electron densit y shows that the bonding in both the monomer and the dimer species is highl y ionic. An atoms-in-molecules analysis reveals that there are no Li-Li and P-Li bond critical points; the lithium atoms appear to act predominantly a s ionic bridging agents, The remarkable stability of the dimer may be attri buted to the polarization of electronic charge upon the coalescence of two monomers, (C) 2001 Elsevier Science B.V. All rights reserved.