Anion induced diversification from heptanuclear to tetranuclear clusters: Syntheses, structures and magnetic properties

Three new polynuclear complexes, [Co-7(bm)(12)]center dot(ClO4)(2)center dot 13H(2)O (1), [Co-4(bm)(4)Cl-4(C3H7OH)(4)] (2), and [Co-4(bm)(4)(mu-HCO2)(2)(mu(2)-HCO2)(2)(C3H7OH)(2)] (3) (Hbm = (1H-Benzimidazol)-methanol), have been synthesized and characterized by elemental analysis, IR, powder X-ray diffraction and X-ray single-crystal diffraction. Compound 1 features a centrosymmetric wheel-like heptanuclear Co(II) cluster. Compound 2 having a I4(1)/a space group exhibits a tetranuclear Co(II) cluster with a cubane topology in which the central Co(II) ion and oxygen atoms from bm occupy the alternate vertices of the cube. However, compound 3 has a tetranuclear Co(II) cluster with a C2/c space group different from that of compound 2. These results show that the geometries and sizes of the corresponding anions as well as their coordinating and hydrogen-bonding properties are essential in determining the final structures of the assemblies. Magnetic properties of 1-3 in the 2-300 K have also been discussed. The {Co-7} (1) and {Co-4} (2) cores display dominant ferromagnetic interactions while the {Co-4} (3) core displays dominant anti-ferromagnetic interactions.