Two-Dimensional Coordination Polymers with One-Dimensional Magnetic Chains:  Hydrothermal Synthesis, Crystal Structure, and Magnetic and Thermal Properties of MCl2(4,4‘-bipyridine) (M = Fe, Co, Ni, Co/Ni)

Two-dimensional transition-metal coordination polymers MCl 2 (bpy) (M = Fe, Co, Ni; Co/Ni, bpy = 4, 4‘-bipyridine) have been synthesized in superheated water solutions. The hydrothermal routes resulted in four compounds FeCl 2 (bpy)( I ), CoCl 2 (bpy)( II ), NiCl 2 (bpy)( III ), and (Co/Ni)Cl 2 (bpy)( IV ). Compounds I − IV are isostructural and belong to orthorhombic crystal system, space group Cmmm (No. 65). Crystal data for I: a = 11.929(2) Å, b = 11.447(2) Å, c = 3.638(1) Å, V = 496.77(18) Å 3, Z = 2. Crystal data for II: a = 11.993(2) Å, b = 11.374(2) Å, c = 3.611(1) Å, V = 492.57(18) Å 3, Z = 2. The structure is a noninterpenetrating two-dimensional network containing transition-metal centers octahedrally coordinated by four bridging chlorine and two bpy ligands at trans positions. The adjacent bpy ligands within a single layer are parallel to each other at a distance of 3.6 Å. Spontaneous antiferromagnetic ordering was found in all compounds from the magnetic susceptibility χ( T ) measurements under low fields. The transition temperatures are 10.0, 5.0, 8.5, and 7.5 K, for I, II, III, and IV, respectively. The μ eff values yielded from fitting the high temperature χ( T ) indicate the high spin states of metal ions. In addition, a metamagnetic transition was observed in the field-dependent magnetization measurement for all four compounds. The magnetic properties observed in this system are attributed to the ferromagnetic intrachain M−M exchange interaction through the Cl 2 bridges along the c axis and the antiferromagnetic interchain interaction between the M ions. TGA studies indicate that all four compounds are thermally stable with an on-set temperature of weight loss greater than 400 °C.