Influence of reaction temperature and stoichiometry on the coordination mode of a multidentate pyridylpyrazole ligand in Co(II) complexes: from a 0D mononuclear structure to 3D frameworks

One-pot solvothermal reactions of CoCl2 center dot 6H(2)O with the semi-rigid ligand 3-(pyridin-4-yl)-1H-pyrazole-5-carboxylic acid under different reaction temperatures and stoichiometry conditions gave rise to three new complexes: [Co(Hppza)(2)(H2O)(2)] (1), [Co(Hppza)(2)](n) (2) and [Co(Hppza)(H2O)Cl](n) (3), which were characterized by elemental analysis, FT-IR spectroscopy, UV-vis absorption spectroscopy, thermogravimetric analysis (TGA) and X-ray diffraction methods. A comparative study revealed the marked sensitivity of the structural chemistry of the above-mentioned ligand to the synthesis conditions. Complex 1, which exhibited a zero-dimensional (0D) structure of mononuclear cobalt(s), was formed at 120 degrees C with a metal-to-ligand molar ratio of 2:1. A further increase in the reaction temperature to 130 degrees C resulted in the two-dimensional (2D) structure of 2. Moreover, the three-dimensional (3D) structure of 3 was formed when the metal-to-ligand molar ratio was changed to 1:1 at 130 degrees C. The magnetic measurements of 3 showed weak ferromagnetic coupling with the decrease in temperature from 8 to 30 K and antiferromagnetic interaction among the Co-II ions. In addition, the luminescence and electrogenerated chemiluminescence (ECL) behavior of 1-3 were also studied.