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 [M-2(mu-pymca)(3

摘要

The hydrothermal reaction of 2-cyanopyrimidine and either CoCl2 center dot 6H(2)O or FeCl2 center dot 4H(2)O affords 2D isostructural coordination polymers [M-2(mu-pymca)(3)]OH center dot H2O ((M = Co-II (1) and Fe-II (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 T-c < 10 K with a coercitive field of 580 Oe, whereas compound 2 is an antiferromagnet with T-N = 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.