Comprehensive Study of Early Transition Metal–Ammonia Solvated Electron Precursors with a Methyl Ligand: The Role of Metal–Carbon Bond in Diffuse Orbitals, Excited States, and Stability

Abstract Solvated electron precursors (SEPs) are coordination complexes that accommodate one or more electrons in diffuse, hydrogenic-type orbitals at the periphery of the molecular skeleton. Prototypical metal–ammonia complexes, observed in both gas and condensed phases, serve as building units for a novel class of electrides. Anchoring SEPs to inert surfaces (surface-immobilized SEP electrides, SISEPEs) offers materials suited for redox catalysis and quantum computing hardware. The titled (NH3)5MCH3 species serve as a model for the active sites of SISEPEs. To characterize their electronic structure and stability, high-level wavefunction and density functional theory calculations are performed for M = Sc, Ti, V, and Cr. Beyond the valence 3d electrons, these complexes host one electron in hydrogenic-type diffuse peripheral orbitals, with low-lying electronic states populating the 1s, 1p, 1d, and 2s outer diffuse orbitals. Compared to the corresponding pure hexacoordinated metal–ammonia complexes, (NH3)5MCH3 disfavors migration of an ammonia ligand to the second solvation shell, and the diffuse electron density is polarized away from the methyl ligand. These findings provide a theoretical framework for designing and characterizing SISEPE materials and highlight the role of the M-C bond in modulating stability, electronic excitation patterns, and the spatial characteristics of the outer diffuse orbitals.