Theoretical Study
of Stepwise Hydrogenated closo-Alane Clusters Al₁₃
(m = 112)

O. P. Charkin*, N. M. Klimenko**, and D. O. Charkin***

* Institute of Problems of Chemical Physics, Russian Academy of Sciences,
Chernogolovka, Moscow oblast, 142432 Russia

e-mail: charkin@icp.ac.ru

** Lomonosov State Academy of Fine Chemical Technology, pr. Vernadskogo 86, Moscow, 117571 Russia

e-mail: klimenko@aha.ru

*** Higher College of Materials Science, Moscow State University, Vorob’evy gory, Moscow, 119992 Russia

e-mail: charkin@inorg.chem.msu.ru

Received July 21, 2005

Abstract—The structure, energy, and vibrational characteristics of different stepwise-hydrogenated closo-
alane clusters Al₁₃ (m = 1–12) were calculated within the B3LYP approximation of the density functional
theory using 6-31G* and 6-311+G* basis sets. For each of the m values, there is a set of several low-lying,
closely spaced (within ~0.10.3 eV) isomers. In the first half of the series, inner isomers (with the centered cage
Al@Al₁₂) are preferable; and in the second half, outer isomers (with the thirteenth Al atom located on the out-
side of the empty Al₁₂ icosahedron and coordinated to its face) are more favorable. In some of the outer isomers,
the aluminum cage is severely distorted and loses its closo form. When a hydrogen atom is attached to para-
magnetic radical anions (with odd m values), the most favorable site for attack is the Al* atom located opposite
the Al^t bond and carrying most of the unpaired electron density. The resulting diamagnetic anions contain a
maximum number of linear (or quasi-linear) HAlAl_cAlH or HAl···AlH fragments in the inner and outer
isomers, respectively (the trans addition rule). The energy D_m(H) of successive addition of an H atom to the
centered icosahedron depends on m in a zigzag manner: the even bonds are always ~1 eV stronger than
the odd bonds. This trend is interpreted in the framework of the molecular model of the valence states of the
[Al₁₃] “superatom” with a variable valence increasing from 1 to 12 due to the unpairing of one to six electron
pairs of the cage when the first, third, etc. odd H atoms are attached to it.

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