Periodic Trends in Low-Valent Group 14 and Group 15 Compounds: Theoretical Photoelectron Spectroscopy of Tetrylenes, Tetrylones, and Singlet Pnictinidenes

Abstract

Scalar-relativistic DFT calculations have been used to calculate the lowest ionization potentials (IPs) of six series of low-valent Group 14 (tetrel) and Group 15 (pnictogen) compounds with a view to uncovering periodic trends, especially the impact of scandide contraction and the inert pair effect. The compounds studied include: (a, b) EF2 and ECl2 (where E is a tetrel), (c) N,N′-dimethylimidazol-2-ylidine and its higher tetrel analogues (tetrylenes), (d, e) a carbodiphosphorane and a carbodicarbene and their higher tetrel analogues (tetrylones), and (f) a series of singlet pnictinidenes based on a pincer ligand. For the three series of tetrylenes studied (a–c), the IPs of the tetrel-based lone pairs exhibit a distinct crest at germanium, reflecting an electronic manifestation of scandide contraction. For the two tetrylone series and the singlet pnictinidenes (d–f), the IPs of the two lone pairs exhibit divergent trends. The lower of the two IPs, corresponding to ionization of the π-type lone pair is found to decrease monotonically down the groups. The higher IP, corresponding to ionization of the σ-type lone pair, in contrast, increases down the groups, reflecting the combined influence of scandide contraction and the inert pair effect.