Magnetic Properties of Some Binuclear Complexes of Chromium and Iron

Abstract

WE have been investigating the magnetic properties of a series of polynuclear complexes of the first-row transition elements. Following the procedure of Kambe¹ and Abragam², the general interaction between the two metal ions in a binuclear complex may be formulated as , where J is the exchange interaction, s₁ and s₂ are the spins of the two metal ions, and is the Hamiltonian for the system. In the case of a binuclear chromium complex, this leads to the following expression for the atomic susceptibility per ion (χ_a): . where K = g²Nβ²/3K; x = J/KT and N(α) is the high-frequency contribution to the susceptibility. Fig. 1 shows the calculated and experimental curves, for the susceptibilities of two such two such chromium complexes, between liquid-nitrogen and room temperatures. The value of K was taken such that N (α) was about 50 × 10⁻⁶ C.G.S. units as, from, spectral measurements, the nearest quartet-level for which interaction could occur was of the order of 15,000 cm.⁻¹. The values of J, g and N(α) obtained are contained in Table 1. These values are of a similar order to those obtained by Kambe¹ in the interpretation of Welo's data on some trinuclear complexes of chromium. The increase in interaction in the mono-bridged complexes may be due to the fact that the metal–oxygen–metal angle is not restricted, as in the diol.