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

Abstract

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-μ_1,1-azido [CuL(μ_1,1-N₃)]₂ (1) and bis-μ_1,3-thiocyanato [CuL(μ_1,3-NCS)]₂·2H₂O (2) complexes and the μ_1,5-dicyanamide coordination polymer [CuL(μ_1,5-NCNCN)]_n·nH₂O (3), are reported. The one dimensional chain in 3 propagated through μ_1,5-dicyanamide bridges is stabilized by a new type of sixteen membered metallacycle 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.