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The ability of substituted boranes, X nBH3− n, to form stable complexes with the hydrogen molecule is analyzed by making use of computational chemistry and local reactivity parameters. In these complexes, the hydrogen molecule acts as a Lewis base while the borane moiety is the Lewis acid. Electronegative groups (X = CF3, F, OH) are selected to increase the acidity of the borane and it is found that the energetic stability of the complexes is only increased for the trifluoromethyl-substituted Lewis acids, at the MP2/6-311++g(3df, 3pd) level. It is also found that the BLYP density functional underestimates the adduct stability of these species. On the other hand, fluoroboranes and hydroxyboranes do not form donor-acceptor adducts with the hydrogen molecule; instead, we find weakly bounded van der Waals complexes. Additional features on the intrinsic reactivity of boranes are analyzed with the molecular electrostatic potential and the acceptor Fukui function. The nature of the interaction among the boranes and the hydrogen molecule is explored by using the topological analysis of the electron density through the Bader's Atoms-in-Molecules theory. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Local and global reactivity descriptors defined within { N, N S , υ( r)} and { N α, N β, υ( r)} representations provide a remedy to the problem of inadequacy of hitherto-known reactivity descriptors in { N, υ ( r)} representation in the analyses of situations where spin multiplicity changes are present. The tailor-made nature of the spin-dependent representations for specific processes is highlighted and a discussion on the convenience to use each representation is included. The connection between both representations is presented as a linear transformation. Generalized Fukui functions associated with processes where the number of electrons and/or the multiplicity change are calculated for closed-shell (NH3, H2O, HCOOH) and open-shell molecules (CH2) with BLYP/aug-cc-pVTZ level of theory, using both the finite differences and the frozen core approximations. Chemical processes involving spin transfer require the explicitly spin-dependent reactivity descriptors whose definitions and domain of applicability are analyzed. The method of calculation of these quantities, using finite differences and frozen core approximations, highlights that these two techniques provide similar trends, however for cases where orbital relaxation is important, the finite differences approximation should be used. [ABSTRACT FROM AUTHOR]