Effect of the semirigid capping ligand on the structure formation of cyano-bridged bimetallic assemblies: Syntheses, crystal structures, and magnetic properties

The syntheses, crystal structures, and magnetic properties of three novel cyano-bridged bimetallic assemblies, [Ni(bPm)(2)](3)[Co(CN)(6)](2)center dot 3.5H(2)O (1), [Co(bPm)(2)][Fe(CN)(5)NO]center dot 2H(2)O (2), and [Co(bpm)(2)][Ni(CN)(4)] (3) (bpm = bis(1-pyrazolyl) methane), are reported. Complex 1 crystallizes in the tetragonal space group P4(3)2(1)2 with a = 12.800(5) angstrom, b = 12.800(5) angstrom, c = 42.80(3) angstrom, V = 7012(6) angstrom(3), and Z = 8. Complex 2 crystallizes in the chiral trigonal space group P3221 with a = 11.9961(19) angstrom, b = 11.9961 (19) angstrom, c = 16.062(5) angstrom, gamma = 120 degrees, V = 2001.7(8) angstrom(3), and Z = 3. Complex 1 is a trigonal bipyramidal complex in which three [Ni(bPM)(2)](2+) units are situated in the equatorial plane and are connected to the two apical [Co(CN)(6)](3-) units via three N ends of the cyanide groups. Complex 2 possesses a triangular left-handed helical chain structure composed of [Co(bpm)(2)](2+) linked by [Fe(CN)(5)NO](2-); the shortest intramolecular Co center dot center dot center dot Fe distance is 5.162 angstrom. To the best of our knowledge, this is the first observation of a heteronuclear helical chain structure based on pentacyanonitrosylferrate(II). The structure of complex 3 is roughly determined by X-ray crystallograhy analysis to be a 1 D zigzag chain. These structure variations, from a discrete cluster to a 1 D helical chain and a 1 D zigzag chain, rely on the semirigidity of the capping ligand bpm. Magnetic susceptibility measurements indicate that complex I has an intramolecular ferromagnetic interaction (J = 4.06 cm(-1)) between the nickel(II) ions; this is further confirmed by the magnetization measurements. In complexes 2 and 3, the cobalt(II) ions are located in a moderately strong field.