Syntheses and crystal structures of the metal complexes based on pyrazolecarboxylic acid ligands

This paper aims at introducing five new metal complexes, Co(HL1)(2)(H2O)(2) (1), {[Cu(HL1)(2)] center dot (H2O)}(n) (2), {[Zn(HL2)(H2O)(3)] center dot 2H(2)O}(n) (3), {[Co(HL2)(H2O)(3)] center dot 2H(2)O}(n) (4) and [K(H2L2)](n) (5), (in which H2L1 is 3-methyl-5-pyrazolecarboxylic acid and H3L2 is 3,5-pyrazoledicarboxylic acid, respectively), which have been synthesized under hydrothermal conditions or by using diffusion methods. Their molecular structures have been characterized by elemental analyses, IR spectroscopy and single-crystal X-ray diffraction analyses. The X-ray analyses reveal that complex 1 has a mononuclear structure, which is further assembled to a three-dimensional (3-D) framework through intermolecular hydrogen bonds; complex 2 is a 1-D coordinated polymer, which is further assembled to a 2-D layer through intermolecular hydrogen bonds and pi-pi interactions; both complexes 3 and 4 possess similar 1-D chain structures, and the adjacent chains are further linked by hydrogen bonds to form 2-D supramolecular networks; complex 5 exhibits a 3-D structure, in which, the metal-metal weak interaction, K-K, plays an important role. (C) 2008 Elsevier B.V. All rights reserved.