Chelation-driven fluorescence deactivation in three alkali earth metal MOFs containing 2,2′-dihydroxybiphenyl-4,4′-dicarboxylate

Three new metal-organic frameworks (MOFs) have been synthesised from alkali earth metal ions of increasing ionic radii (Mg, Ca and Sr) and 2,2'-dihydroxybiphenyl-4,4'-dicarboxylic acid (H sub(4)diol). The distinct coordination environments, framework topologies and the non-coordinated diol moieties accessed are a result of using differently sized metal ions for MOF synthesis which affects the ability of the diol moieties to chelate the metal. Detailed structural analysis of [Sr sub(3)(H sub(2)diol) sub(3)(DMF) sub(5)], [Ca sub(3.5)(Hdiol)(H sub(2)diol) sub(2)(DMF) sub(5)].1.2DMF and [Mg(H sub(2)diol)(DMF) sub(2)].DMF show distinctive variations in variable temperature expansion/contraction properties and porosity. In addition, [Sr sub(3)(H sub(2)diol) sub(3)(DMF) sub(5)] and [Ca sub(3.5)(Hdiol)(H sub(2)diol) sub(2)(DMF) sub(5)].1.2DMF display a broad fluorescence emission ( lambda sub(max) = ~435 nm) under ultraviolet light due to the presence of non-coordinated biphenyl-diol moieties within the structures, while chelation of Mg by the diol pocket in [Mg(H sub(2)diol)(DMF) sub(2)].DMF leads to quenching of the ligand fluorescence.