Two typical cases of magnetism for dinuclear high-spin cobalt(II) complexes in trigonal-bipyramidal fields

Previously, an acyclic ligand 1,3-bis[(2-dimethylaminoethyl)iminomethyl]benzene (baib) was found to form some dinuclear metal complexes [metal=manganese(II), cobalt(II), and zinc(II)], and crystal structures of the two cobalt(II) complexes [Co2(baib)(MeCO2)3]BPh4 (1) and [Co2(baib)(PhCO2)3]BPh4 (2) were determined. Magnetic measurement was also carried out, but the magnetic analysis was not made. In this study, the cryomagnetic data for 1 were analyzed well by using isotropic Heisenberg model with the parameters g=2.30, J=−13.3 cm−1, and Nα=70×10−6 cm−1, indicating that a ground term does not possess an orbital angular momentum. On the other hand, however, the data for 2 could be interpreted using the so-called Lines’ theory with the parameters λ=−175 cm−1, κ=0.63 and J=−1.0 cm−1, indicating that a ground term possesses an orbital angular momentum. This difference was explained by the fact that the complex cation [Co2(baib)(PhCO2)3]+ in 2 was much distorted than [Co2(baib)(MeCO2)3]+ in 1, as found by the X-ray analysis.