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 (2p 1 for Li or 3p 1 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.