Magnetic Properties of Segregated Layers Containing MII33−OH)2 (M = Co or Ni) Diamond Chains Bridged by cis,cis,cis-1,2,4,5-Cyclohexanetetracarboxylate

We report the hydrothermal synthesis, X-ray crystal structures, and thermal, optical, and magnetic properties of two isostructural layered coordination polymers, [MII5(OH)2(chtc)2(H2O)10]·2H2O where M = Co (1Co) or Ni (2Ni) and chtc = cis,cis,cis-1,2,4,5-cyclohexanetetracarboxylate. The structures consist of segregated layers where each layer is formed of M3(OH)2 diamond chains, involving edge- and corner-sharing octahedra, bridged by M(chtc)2. In the space created by the chains and the bridges exists channels, which house the coordinated and noncoordinated water molecules, all hydrogen bonded to form a dodecamer, with a central cyclohexane chair shape ring. Interestingly, the water molecules of 2Ni are more difficult to remove than those of 1Co, but pyrolysis of the latter takes place at higher temperature. The magnetic properties are characterized by Néel transition to fully compensated antiferromagnets at 5.8 K (1Co) and 3.0 K (2Ni). The moments are easily reversed in an applied field of 150 Oe (1Co) and 300 Oe (2Ni) to a ferrimagnet with one uncompensated moment followed by a nonlinear increase to a saturation corresponding to a ferrimagnet with three uncompensated moments. Further, point charge calculations to estimate the weak bonding energies between the various types of interaction are reported.