title: H3O2 bridging ligand in a metal-organic framework. Insight into the aqua-hydroxo↔hydroxyl equilibrium: a combined experimental and theoretical study.
abstract: A metal-organic framework (MOF) bearing the aqua-hydroxo species (O2H3)(-) in the framework, as well as the processes that govern the equilibrium aqua-hydroxo (O2H3)(-)↔hydroxyl (OH) in Sc-MOFs, are studied experimentally and theoretically. Computational studies were employed to determine the relative energies for the two compounds that coexist under certain hydrothermal conditions at pH < 2.8. The thermodynamically more stable [Sc3(3,5-DSB)2(μ-O2H3)(μ-OH)2(H2O)2] (from now on, (O2H3)Sc-MOF; 3,5-DSB = 3,5-disulfobenzoic acid) was obtained as a pure and stable phase. It was impossible to isolate [Sc3(3,5-DSB)2(μ-OH)3(H2O)4] as a pure phase, as it turned out to be the precursor of (O2H3)Sc-MOF. Additionally, a third compound that appears at pH between 3.5 and 4, [Sc3(3,5-DSB)(μ-OH)6(H2O)] and a fourth, [Sc(3,5-DSB)(Phen)(H2O)](H2O), in whose formula neither OH groups nor H3O2(-) anions appear, are reported for comparative purposes. A study of the (O2H3)Sc-MOF electronic structure, and some heterogeneous catalytic tests in cyanosilylation of aldehydes reactions, are also reported.
authors.affiliation: Department of New Architectures in Materials Chemistry, Instituto de Ciencia de Materiales de Madrid, ICMM-CSIC, c/Sor Juana Inés de la Cruz, 3, 28049 Madrid, Spain.
authors.forename: Richard F
authors.initials: RF
authors.lastname: D'Vries
authors.forename: Victor A
authors.initials: VA
authors.lastname: de la Peña-O'Shea
authors.forename: Natalia
authors.initials: N
authors.lastname: Snejko
authors.forename: Marta
authors.initials: M
authors.lastname: Iglesias
authors.forename: Enrique
authors.initials: E
authors.lastname: Gutiérrez-Puebla
authors.forename: M Angeles
authors.initials: MA
authors.lastname: Monge