Aufbau Principle for Diffuse Electrons of Double-Shell Metal Ammonia Complexes: The Case of M(NH₃)₄@12NH₃, M = Li, Be⁺, B²⁺

Abstract

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.

Superatomic nature of metal encapsulated dodecahedrane: The case of M@C20H20 (M = Li, Na, Mg+)

“…In that sense these molecules are similar to the previously studied "solvated electron precursors" (SEPs), where an SEP is a complex that consists of M(L) n q+ core (M = metal, L = ligand) with one or few diffuse electrons [45][46][47][48][49][50]. Interestingly, SEPs populate atomic p-, d-, f-, and g-type orbitals in excited states.…”

Scandium in Neutral and Positively Charged Ammonia Complexes: Balancing between Sc2+ and Sc3+

“…For these systems, we focus on the effect of different methodologies on the optimal geometries and binding energies. Considering that CCSD­(T) provides the most accurate geometries, we recently found that MP2 geometries are very accurate for the Li­(NH 3 ) 4 , Be­(NH 3 ) 4 + , and B­(NH 3 ) 4 2+ complexes . We believe that despite the presence of a transition metal, MP2 is quite accurate for the Sc 3+ ammonia complexes as well, because of the quenched transition metal center (no 4s or 3d electron is present).…”

“…Metal–ammonia coordination complexes have recently been shown to exhibit unusual electronic structure motifs. − Specifically, metal complexes with saturated first coordination sphere, are best described as a positively charged M­(NH 3 ) n q + core with a number of electrons delocalized in its periphery. We have observed that both s-block and d-block metals form such species, which we named solvated electron precursors (SEPs).…”

Superatomic Nature of Metal Encapsulated Dodecahedrane: The Case of M@C20H20 (M = Li, Na, Mg+)

“…In that sense these molecules are similar to the previously studied"solvated electron precursors" (SEPs), where an SEP is a complex that consists of M(L) n q+ core (M = metal, L = ligand) with one or few diffuse electrons. [42][43][44][45][46][47] Interestingly, SEPs populate atomic p-, d-, f-, and g-type orbitals in excited states. The exact Aufbau order introduced for the M(NH 3 ) 4 (M = Li, Na) SEPs is 1s, 1p, 1d, 2s, 2p.…”