MAGNETISM OF FECU(II), COCU(II), NICU(II) BIMETALLIC CHAIN COMPOUNDS - ONE-DIMENSIONAL AND 3-DIMENSIONAL BEHAVIORS

The ACu(pbaOH)(H2O)3•nH2O chain compounds, hereafter abbreviated as ACu, have been synthesized. A is Fe (n = 3), Co, Ni, or Zn (n = 2), and pbaOH is 2-hydroxy-1,3-propylenebis(oxamato). These compounds are isomorphous with MnCu- (pbaOH)(H2O)3, of which the crystal structure was known. However, they contain two or three additional water molecules, located between the chains. The magnetic properties have been investigated in the 1.8–300 K temperature range. For A = Fe, Co, and Ni, the χMT versus T plot, χM being the molar magnetic susceptibility per ACu unit and T the temperature, shows the minimum characteristic of ferrimagnetic chains. This minimum appears at 95 K for FeCu, 53 K for CoCu, and 80 K for NiCu. At low temperature, the magnetic data are affected by three-dimensional effects. In all the cases, the interchain interactions are antiferromagnetic in nature. CoCu shows a long-range antiferromagnetic ordering at 3.4 K, and NiCu, at 2.9 K. For FeCu, the situation is more complex. The spins of the ferrimagnetic chains do not exactly cancel on the scale of the crystal lattice. There is a canting, which leads to a weak ferromagnetism and a remnant magnetization below the critical temperature Tc= 10 K. The magnetic data have been quantitatively interpreted in the temperature range where the three-dimensional effects may be ignored. For NiCu, a ring chain approach has been used, which leads to J(NiCu) = −81.4 cm−1; the interaction Hamiltonian is + 5Cu,/–1). For CoCu and FeCu involving an orbitally degenerate ion A, a model of branch chain has been developed. The interaction between local spins SA (A = Co, Fe) and SCu has been assumed to run along the chain axis while the branches have been related to the spin-orbit coupling for Co(II) or Fe(II) ions. In order to solve analytically this problem, it has been further assumed that only z components of spin and orbital momentums were coupled and that the applied field was along the quantization axis. In the frame of this model, the magnetic properties of CoCu and FeCu have been satisfactorily interpreted with J(CoCu) = −18 cm−1 and J(FeCu) = −20 cm−1. © 1990, American Chemical Society. All rights reserved.