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)

Abstract

Two-dimensional transition-metal coordination polymers [MCl2(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 [FeCl2(bpy)](I), [CoCl2(bpy)](II), [NiCl2(bpy)](III), and [(Co/Ni)Cl2(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) Å3, 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) Å3, 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 μeff 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 Cl2 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.