Theoretical study of complexes of closo-borane, alane, and gallane anions with cations of light metals inside and outside of icosahedral clusters [A12H122-] (A = B, Al, and Ga)

Oleg P. Charkin*, Nina M. Klimenko, Damian Moran, Alexander M. Mebel, Dmitry O. Charkin, Paul V.R. Schleyer

*Corresponding author for this work

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

Systematic B3LYP/6-31G* and B3LYP/6-311+G* calculations have been performed for families of closo-borane, alane, and gallane clusters consisting of A12H122- (A = B, Al, and Ga) cages with endohedral or exohedral Ln+ metal cations (Ln+ = Li+, Na+, Cu+, Be2+, Mg2+, Zn2+, Al+, Al3+, Ga+, and Ga3+). Exohedral structure 1, with tridentate cation coordination at an icosahedron face, is a global minimum for most species; bidentate coordination (structure 2) is the transition state for cation migration around the dianion exterior. Migrational barriers (hmigr), which range from 3 to 5 kcal/mol for monocations and 10-15 kcal/mol for dications, increase with increased cation charge and increased cationic radius. Ln+@B12H122- (Ln+ = Li+, Be2+,Na+, Mg2+, Al3+), Ln+@Al12H122-(Ln+ = Li+, Na+, Mg2+, Al+), and Ln+Ga12H122- (Ln+ = Li+, Na+, Mg2+, Ga3+) endohedral clusters, with their cations located at the A12H122- cage centers, are local Ih minima (3). Endohedral-exohedral isomer relative energies, Erel(3/1), which are very high for the boranes, decrease rapidly down the borane-alane-gallane group and decrease along the He-Li+-Be2+-B3+ and Ne-Na+-Mg2+-Al3+ isoelectronic series. Endohedral isomers of gallane clusters with heavy multicharged cations are predicted to be most favorable in energy. Two types of transition structures for a 3 → 1 endohedral-exohedral rearrangement exist: cation exit through an edge and Ln+ exit via a ruptured pentagonal "neck" of the cage. Li+ and Be2+ borane salts prefer the former pathway, whereas Li+, Na+, and Mg2+ alane and gallane salts favor the latter mechanism. Cation exit barriers, hrear, range from ∼15-55 kcal/mol and in an isoelectronic series decrease with increasing cation charge and increasing atomic mass. Endohedral Ln+@A12H122- clusters show significant charge transfer from the anion to the cation; the hydrogen shell [H]12 donates electrons to Ln+ via the internal [A]12 shell, which in many cases serves as an electron "conductor".

Original languageEnglish
Pages (from-to)11594-11602
Number of pages9
JournalJournal of Physical Chemistry A
Volume106
Issue number47
DOIs
Publication statusPublished - 28 Nov 2002
Externally publishedYes

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