Different Temperature Dependence of Magnetic Susceptibility of Different Molecular Complexes of Copper (II) with 7-Hydroxy-4-methyl-5-aza-hept-4-en-2-on

Abstract

Abstract Two principally different molecular structures in the crystalline state are known from the copper (II) complex with 7-hydroxy-4-methyl-5-aza-hept-4-en-2-on. The magnetic susceptibilities of three forms of this compound [α-(CuEIA)4, β-(CuEIA)4, and β-(CuEIA)4·2 C6H6] have been measured in the temperature range 2.6-300 K. The results indicate that principally different molecular structures correspond to principally different magnetic properties. While the α-form shows antiferromagnetic spin coupling in the S′ = 0 ground state, the electrons in the β-form are coupled ferromagnetically in the S′ = 2 ground state. A fitting procedure of a theoretical equation based on the isotropic HDVV-model led to a satisfactory agreement between calculated and experimental data for α-(CuEIA)4 and β-(CuEIA)4 , while this was not possible for β-(CuEIA)4·2C6H6 . The exchange parameters obtained for α-(CuEIA)4 (g=2.13, J12= -17cm-1, J13=+3.5cm-1, and Na=60-10-8 cgs-emu) are in good agreement with the values given by Ginsberg et al. For β-(CuEIA)4 a weak antiferromagnetic intercluster interaction could be determined at low tempera­tures. The fitting procedure yielded the following values: g=2.05, J12=-6.4 cm-1, J13=+24.2 cm-1, Na=10·10-6 cgs-emu, ⊖=-0.27°.