Metal pyrazolate polymers. Part 3. Synthesis and study of Cu(I) and Cu(II) complexes of 4-Xdmpz (where X = H, Cl, Br, I, and CH3 for Cu(I) and X = H, Cl, Br, and CH3 for Cu(II); dmpz = 3,5-dimethylpyrazolate)

Abstract

The copper(I) complexes [Cu(4-Xdmpz)]3 (where X = H, Cl, Br, I and CH3; dmpz = 3,5-dimethylpyrazolate) and the copper(II) complexes [Cu(4-Xdmpz)2]x have been synthesized and characterized. Qualitative solubility, infrared spectroscopic, and differential scanning calorimetric studies are reported for all complexes. Mass spectra support trimeric formulations for the copper(I) complexes. Scanning electron micrographs and powder X-ray diffractograms have been recorded for the copper(II) compounds. Electronic and EPR spectroscopic studies as well as magnetic susceptibility studies from 2 to 300 K are also reported for the copper(II) compounds, which are proposed to have polymeric chain structures. The magnetic data reveal strong antiferromagnetic interactions in all four of the copper(II) compounds. The data have been analysed employing an isotropic Heisenberg model for antiferromagnetic coupling in extended chain polymers. Values of the exchange coupling constant, J, are determined as −58, −61, −66, and −66 cm−1 for the X = H, CH3, Cl, and Br complexes respectively. The X = Cl compound exhibits an abrupt decrease in magnetic susceptibility below 40 K and possible causes of this anomalous behaviour are discussed.