Structural and magnetic variability of cobalt(II) complexes with bridging pyrazolate ligands bearing appended imine groups.

The synthesis of new binucleating pyrazole-derived ligands (HL2, HL3) with bulky 2,6-diisopropylphenylimine side arms and backbone phenyl groups at the pyrazole-C4 and/or at the imine-C, which are derivatives from the known ligand HL1, is reported. Crystallographic analyses of three cobalt(II) complexes coordinated by ligands [L1-3]- reveal distinct metal to ligand ratios and different structural motifs in the solid state: [L1Co2Cl3(H2O)2(EtOH)] (1), [(L2)3Co4Cl5] (2), or [(L3)2Co4Cl6(H2O)5] (3). Metal ions are five-coordinate in 1, four- and six-coordiante in 2, and six-coordinate in 3. UV-Vis spectroscopy and ESI mass spectrometry suggest that complexes 2 and 3 retain their structures also in solution, whereas 1 partially dimerizes and is in equilibrium with tetrametallic species akin to 3. Magnetic susceptibility measurements indicate weak to moderate antiferromagnetic coupling between five-coordinate or between six-coordinate cobalt(II) ions, but weak ferromagnetic coupling between four- and six-coordinate cobalt(II).