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]2·3.5H2O (1), [Co(bpm)2][Fe(CN)5NO]·2H2O (2), and [Co(bpm)2][Ni(CN)4] (3) (bpm = bis(1-pyrazolyl)methane), are reported. Complex 1 crystallizes in the tetragonal space group P43212 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°, 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)5NO]2-; the shortest intramolecular Co···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 1D zigzag chain. These structure variations, from a discrete cluster to a 1D helical chain and a 1D zigzag chain, rely on the semirigidity of the capping ligand bpm. Magnetic susceptibility measurements indicate that complex 1 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.