Hexacyanidometalate molecular chemistry, part III: di-, tri-, tetra-, hexa- and hepta-nuclear chromium-nickel complexes: Control of spin, structural anisotropy, intra- and inter-molecular exchange couplings

Nine mu-cyanido bridged polynuclear complexes, [Cr(CN)(n)(CNNiL)(6) (n)](m+), (with n = 0-5 and L = pentadentate ligand), were synthesised: CrNi, five CrNi2, CrNi3, CrNi5 and CrNi6. The compounds have been fully characterised by IR spectroscopy, mass spectrometry and X-ray crystallography. Their magnetic properties have been studied and the spin and the anisotropy values as well as the intra- and inter-molecular exchange couplings evaluated. The spin state varies from 5/2 to 15/2 (ferromagnetic interaction) and the effective anisotropic factor varies from 0 to 0.5 cm (1). Experimentally, the exchange coupling between the mu-cyanido bridged spin carriers Cr(III) and Ni(II) varies from +4.5 to +18.3 cm (1) increasing with the C-N-Ni angle. A computational study allows to propose a magneto structural correlation and to rationalise the most relevant features of the exchange interaction between Cr(III) (t(2g)(3)) and Ni(II) (e(g)(2)) through a cyanido bridge. In order to decrease the intermolecular interactions, a dilution of the chromium(III)-nickel(II) compounds with the equivalent cobalt(III)-nickel(II) has been successfully performed by co-crystallisation.