Structural and spectral diversities in copper(II) complexes of 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine

Copper(II) complexes of a tridentate nitrogen donor ligand, 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine (L), CuLX2 (X=Cl, Br, NO3, NCS or ClO4) have been synthesized and characterized using UV-Vis and EPR spectra and electrochemistry. The EPR spectra reveal significant variations in a polycrystalline medium. Copper in all the compounds exhibits a stereochemistry close to a square based pyramid with trigonal bipyramidal distortion and the distortion is more pronounced in CuL(NO3)(2). CuLCl2 and CuLBr2 crystallize in space group C2/c and the molecules are arranged in the lattice such that they form columnar packing along the crystallographic a axis. CuL(NO3)(2) crystallizes with space group P2(1)/c and forms discrete dimeric units through inter- and intra-molecular hydrogen bonding involving the nitro group and methyl and methylene groups. The polycrystalline EPR spectrum is characteristic of a triplet state. The electrochemical properties of these compounds are also discussed.