Large gallanes and the PSEPT theory: a theoretical study of Ga n H n+2 clusters (n = 7–9)

Abstract

Do alanes Al(n)H(n+2) and gallanes Ga(n)H(n+2) satisfy the polyhedral skeletal electron pair theory (PSEPT)? Taking into account previous work on this question, this paper provides a convincing answer and proposes the reformulation of the (n + 1) electron pairs rule of Wade and Mingos (W-M) for such systems. Following recent studies of tetra-, penta-, hexa-, hepta-, octa-, and nonaalanes as well as valence-isoelectronic/related gallanes, in this paper we present an analysis of the hydrides of aluminum and gallium A(n)H(n+2) (A = Al, Ga and n = 7-9). The aim is still to examine the applicability of PSEPT, especially the W-M rule, to these clusters. Exploration of the total potential energy surfaces (PESs) of hepta-, octa-, and nonagallanes shows that the absolute minima have a nido-like polyhedron arrangement. Unlike the smaller Ga(n)H(n+2) (n = 4, 5, 6), it seems that the size of the cluster largely dictates its preferred geometry. Although none of them have closed (totally triangular) cages, these clusters exhibit significant compactness, comparable to borane double anions, B(n)H(n) (2-), which are the archetypes for the PSEPT theory.

A theoretical study on the stability difference of the borane BnHn2− and carborane C2Bn−2Hn(5 ≤ n ≤ 7) clusters

“…[12] There are also some compounds that isoelectronic and isostructure with boranes, which are called borane analogs. Borane analogs began to attract the attention of chemists in recent years, such as the alanes, [9,[13][14][15][16][17][18][19][20] the gallanes, [16][17][18]21,22] the silicium clusters, [23][24][25] and the Germanium Clusters. [25][26][27][28][29][30][31][32][33][34][35] There are also many borane derivatives, such as metallaborane, macropolyhedral borane, and carborane.…”

“…There are also some compounds that isoelectronic and isostructure with boranes, which are called borane analogs. Borane analogs began to attract the attention of chemists in recent years, such as the alanes, the gallanes, the silicium clusters, and the Germanium Clusters …”

Hydrogen Adsorption on Gallium Nanoclusters

“…However, within these small systems, the lowest energy structures generally have the majority of hydrogen atoms located in atop positions. Maatallah et al 16 explored the potential energy surfaces of a range of gallanes (Ga n H n+2 , n = 7−9) to determine if these species satisfy the polyhedral skeletal electron pair theory (PSEPT). They identified many energy minima for clusters in this size range, which generally adopted nido-like polyhedral structures.…”