Metal pyrazolate polymers. Part 4. Synthesis, characterization, and magnetic properties of [Co(pz*)2]x complexes (where pz* = pyrazolate, 3-methylpyrazolate, and 4-substituted 3,5-dimethylpyrazolate)

Abstract

The title compounds were prepared and characterized by X-ray powder diffraction, scanning electron microscopy, vibrational and electronic spectroscopy, and magnetic susceptibility measurements. Indirect evidence supports polymeric one-dimensional chain structures involving double pyrazolate bridges linking pseudo-tetrahedrally coordinated metal centres in all six compounds. The spectroscopic studies indicate a greater degree of distortion of the CoN4 chromophore from regular stereochemistry in the 4-substituted 3,5-dimethylpyrazolate complexes. The magnetic studies reveal anisotropy in the susceptibilities and the presence of significant antiferromagnetic exchange. Magnetic modelling employing both Ising and Heisenberg models suggests the exchange behaviour is probably of the Heisenberg type with zero-field splitting effects producing Ising-like exchange at low temperatures. The derived J values (~ −2 to −6 cm−1) have been used to qualitatively rank the magnitude of exchange as follows: 4-Hpz ≈ 3-Mepz [Formula: see text] 4-Medmpz ≈ 4-Cldmpz ≈ 4-Brdmpz ≈ 4-Hdmpz.