A novel 3D cyano-bridged mixed-valence CoII/CoIII canted antiferromagnet constructed from defective cubanes. Synthesis, X-ray structure and magnetic properties

The hydrothermal reaction of 2-pyrimidine-carboxamide, CoCl2.6H(2)O and K3[Co(CN)6] affords a novel mixed-valence Co(II)/Co(III) 3D complex K[Co3(CN)6(ox)(H(2)O)2].H2O, which contains cyano-bridged Co(7) defective cubanes connected by oxalate and cyanide bridging groups and behaves as a canted antiferromagnet with Tc = 17.5 K.     

Self-assembled cationic heterochiral honeycomb-layered metal complexes with the in situ generated pyrimidine-2-carboxylato bisdidentate ligand. Hydrothermal synthesis, crystal structures, magnetic properties, and theoretical study of [M2(micro-pymca)3]OH.H2O (M = FeII, CoII)

The hydrothermal reaction of 2-cyanopyrimidine and either CoCl2.6H2O or FeCl2.4H2O affords 2D isostructural coordination polymers [M2(micro-pymca)3]OH.H2O ((M = CoII (1) and FeII (2) pymca = pyrimidine-2-carboxylato). The bisdidentate ligand (pymca) that can be considered an intermediate between bipyrimidine and oxalato is generated in situ from the hydrolysis of 2-cyanopyrimidine. The structure of 1 and 2 consists of heterochiral (6,3) honeycomb layers, crystal water molecules, and OH- anions, the latter playing a template and balancing charge role in the structure. Both compounds exhibit antiferromagnetic interactions between metal ions through the pyrimidine-2-carboxylate bridging ligand. Compound 1 is a spin-canted antiferromagnet leading to weak ferromagnetism at Tc < 10 K with a coercitive field of 580 Oe, whereas compound 2 is an antiferromagnet with TN = 21 K. Fit of the variable-temperature magnetic susceptibility data of 2 to the empirical equation for a regular honeycomb with S = 1 derived from Monte Carlo simulations leads to the following parameters: J = -4.57(2) cm-1 and g = 2.300(4). Density functional calculations have been used to explain the magnetic coupling in 2.