Cobalt(II) sheet-like systems based on diacetic ligands: from subtle structural variances to different magnetic behaviors.

The preparation, X-ray crystallography, and magnetic investigation of the compounds [Co(H(2)O)(2)(phda)](n) (1), [Co(phda)](n) (2), and [Co(chda)](n) (3) [H(2)phda = 1,4-phenylenediacetic acid and H(2)chda = 1,1-cyclohexanediacetic acid] are described herein. The cobalt atoms in this series are six- (1) and four-coordinated (2 and 3) in distorted octahedral (CoO(6)) and tetrahedral (CoO(4)) environments. The structures of 1-3 consists of rectangular-grids which are built up by sheets of cobalt atoms linked through anti-syn carboxylate bridges, giving rise to either a three-dimensional structure across the phenyl ring (1 and 2) or to regularly stacked layers with the cyclohexyl groups acting as organic separators (3). The magnetic properties of 1-3 were investigated as a function of the temperature and the magnetic field. Ferromagnetic coupling between the six-coordinate cobalt(II) ions across the anti-syn carboxylate bridge occurs in 1 (J = +1.2 cm(-1)) whereas antiferromagnetic coupling among the tetrahedral cobalt(II) centers within the sheets is observed in 2 and 3 [J = -1.63 (2) and -1.70 cm(-1) (3)] together with a spin-canted structure in 3 giving rise a long-range magnetic ordering (T(c) = 7.5 K).