Solid state synthesis and characterization of pyrazole and pyrazolates complexes of Cobalt (II) ions

Abstract

There were two ways used to synthesized cobalt (II) complexes of pyrazole by solid state. The first route involved direct reaction of the appropriate cobalt (II) acetate with pyrazole and pyrazolium chloride to form bispyrazole cobalt(II) salts, [(HPz)₂CoCl₂]. This was further ground in the second route with a two equivalents of a base (KOH) to make polymeric cobalt (II) pyrazolate [Co(Pz)₂]. In all the synthesis above the ratio of ligand to cobalt (II) acetate was 2:1. All the cobalt (II) complexes were found to be of different colour from the starting materials and were characterized using solubility test, which showed that the complexes have poor solubility in most of the solvents used except in dimethylsulfoxide where they were soluble and the molar conductivity measurements of the complexes have low values (ranging from 6.44-6.45Ω^-1cm²mol^-1) which showed that they are non-electrolytes. The decomposition temperature showed that all the complexes have relatively low decomposition temperatures (93^°C- 95^°C). Characterization of the complexes via infrared analysis confirmed the coordination of metal with the ligand through pyridine-nitrogen and deprotonated-nitrogen in the range of 435.93cm^-1 Co-N bonds and 406.99cm^-1Co –N (for the route A and B respectively). The magnetic susceptibility measurements were carried out at room temperature and the effective magnetic moment values for all the complexes further confirmed complexation of the metal (II) ions with the ligand and also indicates that the cobalt (II) complexes are paramagnetic. The plot of absorbance against mole fraction in each case gives a curve with maximum absorbance corresponding to the ligand mole fraction used in calculating the number of coordinated ligands and 1:2 metal-ligand ratios were obtained in all the complexes.

Keywords:  Mechanochemical, Pyrazole, Pyrazolate, Grinding, Mechanochemical Elimination.