Magnetic Properties of Segregated Layers Containing M<sup>II</sup><sub>3</sub>(μ<sub>3</sub>−OH)<sub>2</sub> (M = Co or Ni) Diamond Chains Bridged by <i>cis,cis,cis</i>-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, [M<sup>II</sup><sub>5</sub>(OH)<sub>2</sub>(<i>chtc</i>)<sub>2</sub>(H<sub>2</sub>O)<sub>10</sub>]·2H<sub>2</sub>O where M = Co (<b>1Co</b>) or Ni (<b>2Ni</b>) and <i>chtc</i> = <i>cis,cis,cis</i>-1,2,4,5-cyclohexanetetracarboxylate. The structures consist of segregated layers where each layer is formed of M<sub>3</sub>(OH)<sub>2</sub> diamond chains, involving edge- and corner-sharing octahedra, bridged by M(<i>chtc</i>)<sub>2</sub>. 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 <b>2Ni</b> are more difficult to remove than those of <b>1Co</b>, 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 (<b>1Co</b>) and 3.0 K (<b>2Ni</b>). The moments are easily reversed in an applied field of 150 Oe (<b>1Co</b>) and 300 Oe (<b>2Ni</b>) 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.