Metal complexes as ligands — V[1]: Binuclear copper complexes derived from bidentate Schiff base complexes

Abstract

The syntheses and properties are reported for the binuclear copper(II) complexes obtained when cupric chloride is reacted with bis(NR-salicylaldimino)copper(II) complexes, where R is a normal, secondary or tertiary alkyl, or a phenyl group. The binuclear complexes exhibit the pair-wise antiferromagnetism that typifies so many dimeric copper(II) complexes, but the singlet-triplet separation is unusually high (of the order of 300 cm −1, or higher), and the magnetic properties do not differ greatly from compound to compound. This is in stark contrast to the known behaviour of copper halide adducts of tetradentate salicylaldimine copper(II) complexes, which have smaller singlet-triplet separations but exhibit much larger variations from compound to compound. These properties are explained in terms of a trans structure. ▪ for the binuclear compounds derived from the bidentate salicylaldimines, as opposed to the cis structure for the analogous tetradentate salicylaldimine derivatives. The trans structure allows the two copper atoms to adopt a configuration near to planar, with only a small amount of steric distortion towards tetrahedral, as the R-group on the salicylaldimine nitrogen becomes more bulky. The ligand field absorption spectra are also in keeping with the trans structure: the differences from compound to compound are consistent with a quite small trend from planar towards tetrahedral configuration as the R-group becomes more bulky; and the environment seems alike about each copper atom: band positions indicate that the copper in the binuclear complexes is closer to a planar configuration than in the parent bis(NR-salicylaldimino)copper(II) complexes.