Electronic and geometric structure analysis of neutral and anionic metal nitric chalcogens: The case of MNX series (M=Li, Na, Be and X=O, S, Se, Te)

Coupled cluster and multireference configuration approaches are employed to study the electronic and geometric structures of mono-coordinated complexes of lithium, sodium, and beryllium with nitric oxide and its isovalent NS, NSe, and NTe species. Ground and low-lying excited states were examined for both linear-bonded and side-bonded isomers. We show that the ionic M+NX- (M=Li, Na, Be and X=O, S, Se, Te) picture is a more natural representation and can account for the symmetry of the low-lying electronic states as sigma(-), Delta, and sigma(+), the smaller excitation energies and the larger binding energies for heavier X. An additional electron binds to the positively charged Li and Na terminal creating stable anions. The electron affinity (EA) of LiNX and NaNX species is in the 0.5-0.8 eV range. Despite the negative EA of beryllium and the very small EA of NO, the BeNO molecule has an EA of similar to 1.0 eV, which is increased to similar to 1.5 eV for the heavier BeNX species. This is attributed to the fact that the additional electron goes to the beryllium end for BeNO but to a pi(MN)-pi*(NX) orbital of the rest species. Our accurate results contradict previous findings and serve as a guide for future experimental studies. (c) 2019 Wiley Periodicals, Inc.