Some water-soluble Schiff-base complexes of nickel(II): the role of water

Abstract

Disodium [NN′-propane-1,3-diylbis(salicylideneimine-5′-sulphonato)(4–)]nickelate(II), Na₂[Ni(salpds)], and disodium bis[salicylaldoxime-5-sulphonato(2–)]nickelate(II) have been prepared. Electronic spectra and magnetic susceptibility measurements show that in aqueous solution there is an equilibrium between the square-planar forms and six-co-ordinate species produced by co-ordination of two water molecules. Thermodynamic parameters are reported for the Na₂[Ni(salpds)] system. The room-temperature i.r. spectrum of solid (diamagnetic) Na₂[Ni(salpds)]·2H₂O gives two well resolved bands in the O–H stretching region One of these is extremely sharp (bandwidth 16 cm^–1) and occurs at an unusually high frequency (3 630 cm^–1). The i.r. spectra of samples having various extents of deuteriation show that the two water molecules are crystallographically equivalent, with C₁ site symmetry. In each H₂O, one hydrogen atom is almost non-hydrogen-bonded while the other is involved in a hydrogen bond of moderate strength.