EXCHANGE INTERACTIONS IN THE BIMETALLIC CHAIN COMPOUND CU(ETHYLENEDIAMINE)(2)MNCL4

The synthesis, crystal structure, and magnetic properties are reported for the new bimetallic compound Cu(en)(2)MnCl4, where en = H2NCH2CH2N H2. The compound, C4H16N4Cl4CuMn, crystallizes in the monoclinic space group P2(1)/a. Cell dimensions are as follows: a = 11.276(3) Angstrom , b = 13.904(3) Angstrom, c = 9.055(3) Angstrom, beta = 91.26(2)degree s; Z = 4; R(unweighted) = 0.029. The structure consists of chains in w hich alternating Mn(II) and Cu(II) ions are bridged by chloride ligand s. The coordination environment is tetrahedral for Mn(II) and elongagt ed octahedral for Cu(II), the apical positions being occupied by the b ridging ligands and the basal ones by the nitrogen atoms from the orga nic ligand. In the crystal, the chains lie in magnetically equivalent layers separated by about 7 Angstrom. The magnetic susceptibility of t he compound has been measured over the range 2-300 K. At room temperat ure the T-chi product (per MnCu unit) has a value of 4.80 emu . mol(-1 ). K, as expected for uncoupled S = 5/2 and S = 1/2 spins. When the te mperature is lowered, T-chi remains quite constant until 20-10 K and t hen decreases to 1.54 emu . mol(-1). K at 1.6 K. Comparison between th eory and experiment has been made with use of 1-D and 2-D models. The decrease of T-chi observed at low temperature for the compound is attr ibuted to either a dominant Mn(II)... Mn(II) antiferromagnetic interac tion within the chain or, alternatively, cooperative intrachain and in terchain Mn(II)... Cu(II) interactions of opposite-signs.