Observation of dominant ferromagnetic interaction in fumarate-bridged 1-D polymer of Cu(II)

Abstract

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.