Wydział Chemii

Jerzy Moc

2012

Journal of Molecular Modeling

18

3427-3438

10.1007/s00894-012-1353-z

Naukowa

Angielski

Artykuł

A comprehensive ab initio investigation using coupled cluster theory with the aug-cc-pVnZ, n = D,T basis sets is carried out to identify distinct structures of the Al₄H₁₄^— cluster anion and to evaluate its fragmentation stability. Both thermodynamic and mechanistic aspects of the fragmentation reactions are studied. The observation of this so far the most hydrogenated aluminum tetramer was reported in the recent mass spectrometry study of Li et al. (2010) J Chem Phys 132:241103–241104. The four Al₄H₁₄^— anion structures found are chain-like with the multiple-coordinate Al center and can be viewed approximately as comprising Al₂H₇^— and Al₂H₇ moieties. Locating computationally some of the Al₄H₁₄^— minima on the correlated ab initio potential energy surfaces required the triple-zeta quality basis set to describe adequately the Al multi-coordinate bonding. For the two most stable Al₄H₁₄^— isomers, the mechanism of their low-barrier interconversion is described. The dissociation of Al₄H₁₄^— into the Al₂H₇^— and Al₂H₇ units is predicted to require 20-22 (10-13) kcal mol^-1 in terms of ΔH (ΔG) estimated at T = 298.15 K and p = 1 atm. However, Al₄H₁₄^— is found to be a metastable species in the gas phase: the H₂ loss from the radical moiety of its most favorable isomer is exothermic by 18 kcal mol^-1 in terms of ΔH (298.15 K) and by 25 kcal mol^-1 in terms of ΔG(298.15 K), with the enthalpic/free energy barrier involved being less than 1 kcal mol^-1. By contrast with alane Al₄H₁₄^—, only a weakly bound complex between Ga₄H₁₂^— and H₂ has been identified for the gallium analogue using the relativistic effective core potential.

Al4H14— and Ga4H14— hydrogen-rich clusters, Coupled cluster calculations, Potential energy surfaces, Thermodynamic and kinetic stability

http://dx.doi.org/10.1007/s00894-012-1353-z

http://link.springer.com