Superexchange in linear-chain 2,5-dimethylpyrazinebis(pentane-2,4-dionato)-cobalt(II) and -nickel(II) complexes

Abstract

The complexes [M(pd)₂(2,5Me₂-pyz)](pd = MeCOCHOCMe; 2,5Me₂-pyz = 2,5-dimethylpyrazine; M = Co, Ni, or Cu) have been prepared and their powder magnetic susceptibilities measured between 1.7 and 70 K. The cobalt and nickel complexes are isomorphous, and all the three complexes probably consist of M(pd)₂ units linked axially into infinite chains by bridging 2,5Me₂-pyz molecules. The susceptibilities are analysed in terms of an exchange interaction –2JS_i·S_j between nearest neighbours within the chains, and good fits to the data are obtained with 4S²J=–1.8 ± 0.2, –1.7 ± 0.1, and 0 ± 0.1 cm^–1 for M = Co, Ni, and Cu, respectively. The significance of these values in relation to the superexchange path through 2,5Me₂-pyz is briefly discussed.