d¹⁰s² Post-Transition Metal Anions: Identifying and Analyzing Their Dual-Mode Lewis Basicity

Liquid-phase d¹⁰s² post-transition metal anions, such as [SnCl₃]^-, appear in a range of applications with a focus on catalysis and material preparation. However, little is known about their electronic structure and how it relates to reactivity. Using X-ray photoelectron spectroscopy and ab initio calculations, we demonstrate that liquid-phase d¹⁰s² post-transition metal anions can act as dual-mode Lewis bases, interacting through the metal center and/or the ligands, with the interaction mode depending on the identity of the Lewis acid/electron acceptor. The Lewis basicity of the metal donor atom is controlled mainly by the metal identity; the ligand can be used for fine-tuning. Changing the metal center has a strong effect on the ligand basicity. These findings provide insight into d¹⁰s² post-transition metal anion electronic structure, which will enable better molecular-level design of catalytic systems.