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 [Sc-3(3,5-DSB)(2)(mu-O2H3)(mu-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 [Sc-3(3,5-DSB)(2)(mu-OH)(3)(H2O)(4)] as a pure phase, as it turned out to be the precursor of (O(2)H3())Sc-MOF. Additionally, a third compound that appears at pH between 3.5 and 4, [Sc-3(3,5-DSB)(mu-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.