Structure and properties of poly-bis(μ-monophenylphosphinato)bis(formamide) chain polymers of cadmium(II), manganese(H) and cobalt(II). Antiferromagnetic exchange in the manganese and cobalt compounds

The compounds M(HCONH₂)₂[H(C₆H₅)PO₂]₂ where M = Co (1), Cd (2) and Mn (3) were synthesized and characterized using single crystal X-ray diffraction, differential scanning calorimetry, infrared spectroscopy and magnetic susceptibility (2 to 80 K) studies. The three compounds are isomorphous, their structures consisting of polymeric chains, propagating along the crystallographic b axis, in which two phosphinate ligands form double bridges between adjacent metal atoms. Two formamide molecules are coordinated via oxygen to each metal atom, completing an octahedral geometry. Compounds 1 and 3 are antiferromagnetic exhibiting maxima in their χ_m versus T plots at 6.3 and 5.8 K respectively. The magnetic data for the Mn(II) compound have been successfully analyzed according to the Weng and Wagner-Friedberg Heisenberg models for linear chains with exchange coupling constants of -0.47 and -0.51 cm^-1 respectively. Magnetic susceptibilities for the Co(II) compound have been compared to values calculated using five different theoretical models. Suitable fits over the range 2 to 80 K were not obtained; however, the data below 30 K agree reasonably well with both Ising and Heisenberg models employing an effective spin S′ = 1 2.