Azide and oxo bridged ferromagnetic clusters: Three face-shared tetracubane Ni(II)/Co(II) hexamers and a wheel-shaped SMM-like Co(II) heptamer

Four azide and oxo bridged polynuclear Ni(II) and Co(II) complexes have been constructed by the simultaneous use of Hhdeo (Hhdeo = 2-hydroxy-[1,2-di(pyridin-2-yl)] ethane-1-one) and azide as ligands: [Ni6(Hhdeo)2(hdeo)4(N3)6] · (ClO4)2 · 2DMF · 2H2O (1), [Co6(Hhdeo)2(hdeo)4(N3)6] · (ClO4)2 · 2DMF · 2H2O (2), [Ni6(Hhdeo)2(hdeo)4(N3)6] · (ClO4)2 · 6H2O (3) and [Co7(hdeo)6(N3)6] · (ClO4)2 · 2H2O (4). Compounds 1–3 all crystallize in monoclinic space group P21/c, and consist of face-shared tetracubane hexanuclear cores, which are bridged by μ2, μ3-O and μ2-1,1, μ3-1,1,1-N3. Compound 4 crystallizes in triclinic space group P 1 ¯ , and is made up of wheel-like heptanuclear cores [Co7(hdeo)6(N3)6]2+ bridged by μ2-O and μ3-1,1,1-N3. For Co(II), the reaction solvents are found to play important roles in directing the final products with hexanuclear or heptanuclear topologies. Magnetic studies demonstrate overall intra-molecular ferromagnetic (F) couplings in these four compounds, which result from, according to our theoretical analysis, the competition between different kinds of exchange interactions within the metallic triangle units. No single-molecule magnet behavior was observed above 1.9 K in complex 1–3. However, compound 4 shows significant slow relaxation at static zero and 600 Oe fields below 4 K, towards single molecule magnet (SMM) behavior.