Ferromagnetic coupling in di-µ-chloro-tetrakis(ethane-1,2-diamine)dinickel(II) dichloride, diperchlorate, and bis(tetraphenylborate)

Abstract

The temperature dependence of the magnetic susceptibilities of the three title compounds has been studied in the range 3.6–300 K. The quantitative interpretation of the magnetic data is complicated by the low-temperature monoclinic–triclinic transition as seen for [Ni₂(en)₄Cl₂]Cl₂ by heat-capacity and X-ray investigations. It is most likely that the same transition also occurs in the two other compounds. The exchange-interaction parameters J of the Hamiltonian –J₁Ŝ₁.JŜ₂ are found to be equal to 13.3, 17.8, and 19.0 cm^–1 respectively for the dichloride, diperchlorate, and bis(tetraphenylborate). These values are correlated with the sizes of the Ni–Cl–Ni bridging angles in the dimeric units and discussed in the framework of a previously described orbital model.