Magnetic behavior of dinuclear cobalt(II) complexes assumed to be caused by a paramagnetic impurity can be explained by tilts of local distortion axes

A pair of dinucleating ligands sym-hmp− [sym-hmp−: 2,6-bis[(2-hydroxyethyl)methylaminomethyl]-4-methylphenolate] incorporated two cobalt(II) ions to form a dinuclear cobalt(II) complex [Co2(sym-hmp)2](BPh4)2 (1). Magnetic susceptibility indicated the antiferromagnetic exchange interaction; however, the susceptibility increased again below 20 K. Usually, such an increase is assumed to be caused by a paramagnetic impurity. However, the tilts of local distortion axes around cobalt(II) ions were found to cause the increase despite the antiferromagnetic interaction.