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Autori: Radu Custelcean, James, E. Jackson
Editorial: J Am Chem Soc, 122, p.5251, 2000.
The first mechanistic investigation of a topochemical dihydrogen to covalent bonding conversion is presented. Solid state decomposition of the LiBH4×TEA (TEA = triethanolamine) dihydrogen-bonded complex into a covalent material was studied using 11B solid state MAS NMR, FT-IR, XRD, and optical microscopy. The majority of this solid state reaction occurs by nucleation and two-dimensional growth of the covalent product nuclei. Variable temperature kinetics and H/D exchange experiments established that proton transfer between the OH groups of the TEA and the BH4- anions, at the reactant/product interface, is the rate limiting step, with an associated activation barrier of 21.0 ± 2.4 kcal/mol. The activation parameters DH¹ and DS¹ for the same process were calculated to be 20.1 ± 2.4 kcal/mol and -16.8 ± 6.2 e.u., respectively, comparable with the analogous values found for the aqueous hydrolysis of BH4- in neutral water, suggesting similar mechanisms for the solid and solution decompositions.
Cuvinte cheie: hydrogen bonding, self-assembly, supramolecular chemistry, topochemistry