Tetra-amino beryllium complexes and ions, Be(NH), have a tetrahedral Be(NH) core with one, two, or three outer electrons orbiting its periphery. Our calculations reveal a new class of molecular entities, solvated electron precursors, with Aufbau rules (1s, 1p, 1d, 2s, 1f, 2p, 2d) that differ from their familiar hydrogenic counterparts and resemble those of jellium or nuclear-shell models. The core's radial electrostatic potential suffices to reproduce the chief features of the ab initio results. Wave function and electron-propagator methods combined with diffuse basis sets are employed to calculate accurate geometries, ionization energies, electron affinities, and excitation energies.

Tetra-amino lithium and sodium complexes M(NH) (M = Li, Na) have one or two electrons that occupy diffuse orbitals distributed chiefly outside the M(NH) core. The lowest-energy 1s, 1p, and 1d orbitals follow Aufbau principles found earlier for beryllium tetra-ammonia complexes. Two ground state M(NH) complexes can bind covalently by coupling their 1s electrons into a σ-type molecular orbital. The lowest excited states of the [M(NH)] 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.

Neutral and positively charged calcium ammonia complexes are investigated by means of high-level quantum chemical calculations. We report optimal structures, binding energies, and vibrational spectra for Ca(NH 3 ) 1−8 0,+ . The bigger Ca(NH 3 ) 6−8 0,+ complexes can be classified as solvated electron precursors (SEPs) and are best described as a Ca(NH 3 ) 6−8 2+ core with two or one peripheral electrons. In their ground state, only ∼10% of the outer electron density is estimated to be within the calcium van der Waals radius. For these systems, we calculated several lowlying electronic states, where electrons populate diffuse outer orbitals. The Aufbau principle for the outer electrons is found to be identical to previously studied SEPs: 1s, 1p, 1d, 1f, 2s, and 2p. We show that going from Ca(NH 3 ) 5 , which has an incomplete first coordination shell and the two valence electrons that are mainly in the valence sphere of calcium, to Ca(NH 3 ) 6 , both the vibrational and electronic features change abruptly. Infrared, visible, and ultraviolet spectroscopy can be used to identify and characterize calcium SEPs.

Positively charged or neutral metal ammonia complexes can form molecular species called solvated electron precursors (SEPs) that accommodate peripheral electrons in approximately hydrogenic diffuse orbitals. This work expands the notion of SEPs to metal ammonia complexes wherein a second coordination shell with 12 ammonia molecules is attached to M­(NH3)4 (M = Li, Be+, B2+) SEPs via hydrogen bonding. In such complexes, denoted M­(NH3)4@12NH3, the 12 outer ammonia molecules displace the peripheral electrons even further away from the first shell of ammonia molecules. We have benchmarked several density functional methods against CCSD­(T) results and found that CAM-B3LYP provides the best M­(NH3)4@12NH3 structures. The electron attachment energies of the closed-shell cores calculated with electron-propagator methods and the corresponding Dyson orbitals reveal the Aufbau principle for the ground and excited states of M­(NH3)4@12NH3 to be 1s, 1p, 1d, 1f, 2s, 2p, 1g, 2d. These orbitals are diffuse and delocalized over the periphery of the second solvation shell.