Observation of Dominant Ferromagnetic Interaction in Fumarate-Bridged 1-D Polymer of Cu(II)

The reaction of CuCl2·2H2O and Na2C4H2O4 (disodium fumarate) in dilute ammonia solution produces 1-D
polymeric chain [Cu(μ-C4H2O4)(NH3)2]n(H2O)n. The crystal structure of the compound has been solved. The
compound crystallizes in the monoclinic system, space group C2/m (No. 12), with chemical formula C4H10N2O5Cu, a = 13.955(5) Å, b = 7.330(3) Å, c = 8.927(2) Å, β = 102.39(3)°, Z = 4. The interesting feature of the
complex is that one of the carboxylic acid groups acts as a monodentate coordinating ligand whereas the remaining
carboxylate moiety acts as a monoatomic bridging bidentate ligand. This unusual coordination behavior of fumarate
anion produces a chain with alternate repetition of 4- and 14-member rings. The magnetic properties of the
compound have been studied from room temperature to 4 K, which reveal the existence of a dominant ferromagnetic
interaction with exchange coupling parameter values of JF = +12 cm-1 and JAF = −3.8 cm-1, using an alternating
ferro- and antiferromagnetic chain model for S = 1/2 local spin. The ferromagnetic interaction arises from the
alkoxo-bridged dimeric part of the chain. The fitting of the χMT vs T data continued until the maximum in the
experimental data using a single dinuclear model resulted in J = +7.8 cm-1.