Electronic Structures and Stabilities of Trimethylsilyl-Masked Pnictogen and Chalcogen Complex Anions and Comparisons to Their Hydrides: A Combined Photoelectron Spectroscopy and Computational Study.

We report the first electronic structure and stability study on two series of trimethylsilyl (triMS) masked pnictogen (Pn) and chalcogen (Ch) anions Pn(triMS)2- and Ch(triMS)- (Pn = P, As, Sb, Bi; Ch = S, Se, Te) as well as AsH2- combining negative ion photoelectron spectroscopy and quantum chemical computations. The Pn and Ch series have exhibited distinct electronic structural patterns due to different numbers of lone pair electrons and triMS ligands. Based on well-defined spectra, precise adiabatic and vertical detachment energies (ADE and VDE) are determined for each of the Pn(triMS)2- and Ch(triMS)- anions, which are all noticeably larger compared to their hydride derivatives, indicating increased electronic stabilities. The magnitude of ADE increments exhibits descending trends from lighter to heavier elements along both Pn and Ch groups, i.e., 0.88, 0.77, 0.53, and 0.44 eV for Pn = P, As, Sb, and Bi and 0.46, 0.31, and 0.15 eV for Ch = S, Se, and Te, respectively. Relativistic multi-reference calculations are carried out to characterize electronic structures of Pn(triMS)2-/Ch(triMS)- anions and corresponding neutral radicals. Only those explicitly including spin-orbit coupling (SOC) effect calculations can reproduce the observed spectral profiles containing heavier Pn/Ch elements, highlighting the important roles of SOC contributions.