(3hw) Aufbau Principle for Diffuse Electrons of Double–Shell Metal Ammonia Complexes

Neural or partially oxidized metal ammonia complexes can form solvated electron precursors (SEP). An SEP is a superatomic complex that shifts one or few electrons from its coordinated metal atom to the periphery of its ligands. Fascinatingly, these entities possess peripheral electrons in approximately hydrogenic type diffused orbitals. Isoelectronic M(NH₃)₄, M=Li, Be⁺, B²⁺ have an electron in a superatomic s-orbital positioned around its charged metal core. This outer electron is promoted to higher angular momentum p-, d-, f-, g-shaped orbitals. Twelve ammonia molecules bind to M(NH₃)₄ via H-bonding to form a system with a second coordination shell. We observed that the second shell of ammonia, M(NH₃)₄@12NH₃, shifted the peripheral electron further away from the first solvated shell and delocalized it over the second shell. Geometry of a such system is governed by two factors; 1) correct description of H-bonding interactions, 2) precise representation of the outer diffuse electron that is affected by the positively charged M(NH₃)₄ core. We have benchmarked several density functional methods against golden standard CCSD(T) results and found that CAM-B3LYP can accurately describe the structures of M(NH₃)₄@12NH₃. Excitation energies calculated by electron-propagator methods and corresponding molecular orbitals (see Figure 1) disclosed the Aufbau principle of M(NH₃)₄@12NH₃ to be 1s, 1p, 1d, 1f, 2s, 2p, 1g, 2d.