Sulfonated Schiff base dinuclear and polymeric copper(II) complexes: crystal structures, magnetic properties and catalytic application in Henry reaction

The syntheses and X-ray diffraction structures of water soluble copper(II) compounds containing the Schiff base ligand 2-(2-pyridylmethyleneamino) benzenesulfonate (L-), viz. the dinuclear bis-mu(1,1)-azido [CuL(mu(1,1)-N-3)](2) (1) and bis-mu(1,3)-thiocyanato [CuL(mu(1,3)-NCS)](2)center dot 2H(2)O (2) complexes and the mu(1,5)-dicyanamide coordination polymer [CuL(mu(1,5)-NCNCN)](n)center dot nH(2)O (3), are reported. The one dimensional chain in 3 propagated through mu(1,5)-dicyanamide bridges is stabilized by a new type of sixteen membered metalla-cycle supported by copper and H-bonds. Variable-temperature (2-300 K) magnetic studies indicate that there is a weak ferromagnetic exchange coupling in 1, while 2 and 3 have weak antiferromagnetic exchange interactions. They catalyze the diastereoselective nitroaldol (Henry) reaction of different aldehydes with nitroethane in aqueous medium. Water was the solvent used for both the syntheses and catalytic studies.