INTERCHAIN INTERACTIONS AND 3-DIMENSIONAL MAGNETIC-ORDERING IN MN(II)CU(II) CHAIN COMPOUNDS - CRYSTAL-STRUCTURE AND METAMAGNETIC PROPERTIES OF MNCU(PBAOH)(H2O)(3)-CENTER-DOT-2H(2)O, WITH PBAOH=2-HYDROXO-1,3-PROPYLENEBIS(OXAMATO)

Single crystals of the novel phase MnCu(pbaOH)(H2O)(3) . 2H(2)O (A) have been obtained; pbaOH stands for 2-hydroxy-1,3-propylenebis(oxamato). A crystallizes in the monoclinic system, space group P-21/c, with a = 21.212(4), b = 5.033(1), c = 14.246(2) Angstrom, beta = 100.72(2)degrees and Z = 4. The structure consists of oxamato-bridged Mn(II)Cu(II) bimetallic chains running along the a-axis direction. The shortest metal-metal separations between adjacent chains related by, respectively, the unit cell translation along the b-axis direction and the glide translation along the c-axis direction involve metal ions of the same type, in contrast with what was found in the previously described phase MnCu(pbaOH)(H2O)(3) (B). According to our interpretation of the three-dimensional (3-D) magnetic effects in bimetallic chain compounds, the topology of the spin carriers in A should favor a 3-D antiferromagnetic ordering, while B exhibits a 3-D ferromagnetic ordering. The study of the temperature dependence of the magnetic susceptibility as well as the temperature and field dependences of the magnetization have confirmed this prediction. The antiferromagnetic ordering occurs at 2.4 K. A magnetic field of 0.9 kOe is sufficient to overcome the weak interchain interactions, so that the compound may be described as a metamagnet built from ferrimagnetic chains.