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-C-4 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: [(LCo2Cl3)-Co-1(H2O)(2)(EtOH)] (1), (L-2)(3)Co4Cl5] (2), or [(L-3)(2)Co4Cl6(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).