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

The reaction of CuCl 2 ·2H 2 O and Na 2 C 4 H 2 O 4 (disodium fumarate) in dilute ammonia solution produces 1-D polymeric chain [Cu(μ-C 4 H 2 O 4 )(NH 3 ) 2 ] n (H 2 O) n . The crystal structure of the compound has been solved. The compound crystallizes in the monoclinic system, space group C 2/ m (No. 12), with chemical formula C 4 H 10 N 2 O 5 Cu, 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 J F = +12 cm -1 and J AF = −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 χ M T vs T data continued until the maximum in the experimental data using a single dinuclear model resulted in J = +7.8 cm -1 .