Structural and thermal properties of three novel alkaline earth metal coordination polymers based on 5-hydroxyisophthalate ligand

Three novel coordination polymers [Ca(5-OH-BDC)(H2O)3] · H2O (1), [Sr(5-OH-BDC)(H2O)4] · H2O (2) and [Ba(5-OH-BDC)(H2O)3] (3) were obtained by self-assembly of the corresponding alkaline earth metal chlorate with a ligand, 5-hydroxyisophthalic acid (5-OH-H2BDC), and their structures were determined by X-ray crystallography. The results revealed that complexes 1, 2 and 3 have two-dimensional network with (6, 3) topology observed in the bc plane. Moreover, the two-dimensional layers can be assembled into three-dimensional supramolecular architectures via intermolecular hydrogen bonds. The two carboxylate groups of 5-OH-BDC2− ligand adopt the same coordination mode in complex 1 as that in 2: a μ3–η2:η1 mode and a chelated mode while in complex 3 they coordinate to Ba(II) ions in a μ3–η2:η1 mode and a monodentate mode, which is not observed in previous reports. The constant-volume combustion energies, Δ cU , of these complexes were determined by a precise rotating-bomb calorimeter at 298.15 K, then their standard enthalpies of combustion, View the MathML sourceΔcHmθ, and the standard enthalpies of formation, View the MathML sourceΔfHmθ, have been calculated.