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

The reaction of CuCl(2 .)2H(2)O and Na2C4H2O4 (disodium fumarate) in dilute ammonia solution produces 1-D polymeric chain [Cu(mu -C4H2O4)(NH3)(2)](n)( H2O)(n). The crystal structure of the compound has been solved. The compoun d crystallizes in the monoclinic system, space group C2/m (No. 12), with ch emical formula C4H10N2O5-Cu, a = 13.955(5) Angstrom, b = 7.330(3) Angstrom, c = 8.927(2) Angstrom, beta = 102.39(3)degrees, Z = 4. The interesting fea ture of the complex is that one of the carboxylic acid groups acts as a mon odentate coordinating ligand whereas the remaining carboxylate moiety acts as a monoatomic bridging bidentate ligand. This unusual coordination behavi or of fumarate anion produces a chain with alternate repetition of 4- and 1 4-member rings. The magnetic properties of the compound have been studied f rom room temperature to 4 K, which reveal the existence of a dominant ferro magnetic interaction with exchange coupling parameter values of J(F) = + 12 cm(-1) I and J(AF) = -3.8 cm(-1) , using an alternating ferro- and antifer romagnetic chain model for S = 1/2 local spin. The ferromagnetic interactio n arises from the alkoxo-bridged dimeric part of the chain. The fitting of the chi T-M vs T data continued until the maximum in the experimental data using a single dinuclear model resulted in J = +7.8 cm(-1).