Assembly of new coordination frameworks in a pH-controlled medium:: Syntheses, structures, and properties of ∞3[Cd(Hpdc)(H2O)] and ∞3[Cd3(pdc)2(H2O)2]

Two 3D cadmium coordination networks (3)(infinity)[Cd(Hpdc)(H2O)] (1) and (3)(infinity)[Cd-3(pdc)(2)(H2O)(2)] (2) have been synthesized from hydrothermal solutions at 150 degrees C. Single-phased samples of both compounds can be isolated by adjusting the acidity level of the reactions. Both structures are constructed by a single, multifunctional ligand, 3,5-pyrazoledicarboxylic acid (H(3)pdc), in different coordination modes. Both 1 and 2 crystallize in the monoclinic crystal system, space group P2(1)/c (No. 14) with a = 6.436(1) Angstrom, b = 12.283(2) Angstrom, c = 8.934(2) Angstrom, beta = 104.23(3)degrees, Z = 4 for 1, and a = 9.744(2) Angstrom, b = 9.821(2) Angstrom, c = 7.496(1) Angstrom, Z = 2 for 2. Both compounds represent new structure types. All metal atoms are seven-fold coordinated in 1 and sis-fold coordinated in 2. A comparison is made between the title compounds and related lanthanide series on the coordination habit of the metals and the ligand, as well as the effect of pH on the final products. TGA studies indicate that loss of coordinated mater molecules in 1 and 2 occurs at around 213 and 179 degrees C, respectively, and the decomposition process completes at about 620 and 480 degrees C for 1 and 2, respectively. (C) 2000 Academic Press.