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RESEARCH PRODUCT

Syntheses, crystal structures and magnetic properties of copper(ii) dicyanamide complexes; dinuclear, chain and ladder compounds

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The preparation, crystal structures and magnetic properties of three heteroleptic copper(II) complexes with dicyanamide (dca) bridges, [Cu(bpca)(H2O)(dca)]2 (1) (bpca = bis(2-pyridylcarbonyl)amidate), [Cu(bpy)(dca)2]n (2) (bpy = 2,2′-bipyridine), [Cu2(bpm)(dca)4]n (3) (bpm = 2,2′-bipyrimidine) are reported. In addition, magnetic susceptibility measurements of the sheetlike polymer [Cu(phen)(dca)2] (4) (phen = 1,10-phenanthroline), structurally characterized previously, have been performed. In complex 1 pairs of mononuclear structural building blocks, [Cu(bpca)(dca)(H2O)], are loosely connected through a 1,3-dca bridge in which nitrile is equatorially bound and the amide is semi-coordinated in axial position to copper. The bis-monodentate 1,3-bridging mode of dca has been postulated, but not previously observed. A chain structure is present in 2, one of the dca units serving as an end-to-end out-of-plane bridging ligand, while the other dca is terminal, monodentate. The chain structure is very similar to that found in 4, but while the chains in 4 are connected, forming sheets, this is not so in 2. Compound 3 forms a ladder-like polynuclear structure in which the rungs are formed by bis-chelating bpm bridges and the uprights by end-to-end bridging dca units. The copper⋯copper separations across the dca bridges are 5.732(2) A (1), 8.1999(8) A (2) and 7.5550(2) A (3), respectively, and 5.5673(4) A across the bpm bridge (3). These values are to be compared with the intrasheet copper⋯copper separations of 7.3002(7) A (through a single end-to-end dca bridge) and 7.7079(4) A (through a double end-to-end dca bridge) in 4. Variable-temperature magnetic susceptibility measurements reveal Curie law behaviour with no detectable magnetic coupling in compounds 1 and 2, a very weak ferromagnetic interaction across the single end-to-end dca bridge in 4 (J = +0.2(1) cm−1), and a strong antiferromagnetic interaction across the bpm bridge in compound 3 (J = −211(1) cm−1).