Electronic and geometric structure analysis of neutral and anionic alkali metal complexes of the CX series (X = O, S, Se, Te, Po): The case of M(CX) n = 1-4 (M = Li, Na) and their dimers.

Bonding mechanisms, potential energy curves, accurate structures, energetics, and electron affinities are obtained for all M(CX)1-3 species with M = Li, Na, and X = O, S, Se, Te, and Po, at the coupled-cluster level with triple-ζ quality basis sets. We discuss and rationalize the trends within different molecular groups. For example, we found larger binding energies for M = Li, for CX = CPo, and for the tri-coordinated (n = 3) complexes. All three facts are explained by the fact that the global minimum of the titled complexes originate from the first excited 2 P (2p1 for Li or 3p1 for Na) state of the metal, with each ligand forming a dative bond with the metal. All of the complexes, except Na(CO)3 , have stable anions, and their electron affinity increases as MCX < M(CX)3 < M(CX)2 . This sequence is attributed to the binding modes of these complexes. The Li(CO)3 and Li(CS)3 complexes are able to accommodate a fourth ligand, which is attached to the system electrostatically. Finally, two Li(CO)3 molecules can bind together covalently to make the ethane analog. The staggered conformer was found lower in energy and unlike ethane the CO ligands bend toward the neighboring Li(CO)3 moiety. © 2019 Wiley Periodicals, Inc.