Ferromagnetism of cobalt-chromium polycyanides

The magnetic properties of two cobalt(II)-chromium(III) polycyanides, (CsCoII)-Co-I[Cr-III(CN)(6)] . 0.5H(2)O and Co-1.5(II)[Cr-III(CN)(6)] . 7.5H(2)O, have been studied. These compounds exhibited a spontaneous magnetization, with critical temperatures of 46 and 30 K, respectively. Although their superexchange interactions contain an antiferromagnetic orbital contribution, their magnetic properties showed ferromagnetism. The estimation of their superexchange coupling constants (J) from the experimentally determined J values of two other hexacyanochromates, the (CsNiII)-Ni-I[(CrCN)-C-III)(6)] ferromagnet and the (CsMnII)-Mn-I[Cr-III(CN)(6)] ferrimagnet, suggests that the sum of the ferromagnetic orbital contributions is possibly greater than that of the antiferromagnetic orbital ones, resulting in the parallel spin ordering. (C) 1999 Elsevier Science B.V. All rights reserved.