Structural and Magnetic Properties of MCl₂ (M = Fe, Mn, Co): Acetonitrile Solvates

MIICl2 (M = Mn, Fe, Co) as their acetonitrile solvates were isolated, and their structural, spectroscopic, and magnetic properties were studied. MCl2(NCMe)2 (M = Fe, Mn) form 1-D chains of octahedral MII ions with four bridging chlorides and two axial MeCN's. The presence of an axial distortion for MFe causes a significant magnetic anisotropy that increases significantly below 150 K; however, χav [=(χ∥ + 2χ⊥)/3] almost coincides with the value obtained on a polycrystalline sample. MnCl2(NCMe)2 is a paramagnet with a weak antiferromagnetic coupling. Annealing FeCl2(NCMe)2 at 55 °C forms the monosolvate of FeCl2(NCMe) composition in which two chains collapse into a double chain with formation of Fe−Cl bonding such that half of the μ-Cl's becomes μ3-Cl's. This material orders magnetically below Tc = 4.3 K. For M = Co, paramagnetic tetrahedral [CoCl3(NCMe)]- anions are isolated.