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 = H2NCH2CH2NH2. 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)degrees; Z = 4; R(unweighted) = 0.029. The structure consists of chains in which alternating Mn(II) and Cu(II) ions are bridged by chloride ligands. The coordination environment is tetrahedral for Mn(II) and elongagted octahedral for Cu(II), the apical positions being occupied by the bridging ligands and the basal ones by the nitrogen atoms from the organic ligand. In the crystal, the chains lie in magnetically equivalent layers separated by about 7 Angstrom. The magnetic susceptibility of the compound has been measured over the range 2-300 K. At room temperature 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 temperature is lowered, T-chi remains quite constant until 20-10 K and then decreases to 1.54 emu . mol(-1). K at 1.6 K. Comparison between theory 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 attributed to either a dominant Mn(II)... Mn(II) antiferromagnetic interaction within the chain or, alternatively, cooperative intrachain and interchain Mn(II)... Cu(II) interactions of opposite-signs.