Molecules mimicking atoms: Monomers and dimers of alkali metal solvated electron precursors

Tetra-amino lithium and sodium complexes M(NH3)40,− (M=Li, Na) have one or two electrons that occupy diffuse orbitals distributed chiefly outside the M(NH3)4+ core. The lowest- energy 1s, 1p, and 1d orbitals follow Aufbau principles found earlier for beryllium tetra- ammonia complexes. Two ground state M(NH3)4 complexes can bind covalently by coupling their 1s1 electrons into a σ-type molecular orbital. The lowest excited states of the [M(NH3)4]2 species are obtained by promoting one or two electrons from this σ to other bonding or anti- bonding σ and π-type molecular orbitals. The electronic structure of solvated electron precursors provides insights into chemical bonding between super-atomic species that are present in concentrated alkali-metal-ammonia solutions.