Topological Control in Two-Dimensional Cobalt(II) Coordination Polymers by PI–PI Stacking Interactions: Synthesis, Spectroscopic Characterization, Crystal Structure, and Magnetic Properties

Mixed metal phenylphosphonates of composition MnxCo1-x(O3PC6H5)·H2O were prepared with 0x1. Atomic absorption, X-ray powder diffraction, and electron paramagnetic resonance measurements indicate that the mixed-metal solid solutions are homogeneous and isostructural with the single-metal-parent compounds over the entire concentration range, with a small, systematic evolution of the a and c in-plane unit cell parameters. The temperature dependence of the magnetic data for the pure Mn2+ (x=1) and pure Co2+ (x=0) samples was fitted by standard 2D Heisenberg and 2D Ising models, respectively, yielding nearest-neighbor exchange interaction energies of J=-2.27±0.02 K for Mn(O3PC6H5)·H2O and J=-2.43±0.05 K for Co(O3PC6H5)·H2O. The magnetic phase diagram, down to 2 K, was constructed over the entire composition range. Both dc and ac magnetic susceptibilities were used to identify the transitions to low temperature, long-range-ordered antiferromagnetic states. In the Mn2+- and Co2+-rich regions, the ordering temperature, TN, decreases relative to the pure materials, as expected for magnetic ion impurity doping. For intermediate values of x, Mn2+–Mn2+ interactions dominate, resulting in a minimum in TN near x=0.25. A weak negative magnetization was observed for x<0.25. No evidence of spin glass behavior was observed for any concentration at any temperature.