pH-metric and spectroscopic properties of new 4-hydroxysalicylidene-2-aminopyrimidine Schiff-base transition metal complexes

The new complexes, cis-[WO2(Hsap)2], [Ru(PPh3)2(Hsap)2], [Pd(Hsap)Cl(H2O)], [Pd(PPh3)2(Hsap)]Cl, [Ag(Hsap)(H2O)2], [Ni(Hsap)(AcO)(H2O)2], [Ni(Hsap)2] and [Cu(Hsap)Cl(H2O)] are reported, where H2sap is 4-hydroxysalicylidene-2-amino pyrimidine Schiff-base. The complexes were characterized by elemental analyses, spectroscopic (IR, NMR, UV–vis, ESR and mass) and physical techniques (conductivity, magnetic and thermal measurements). The Schiff-base H2sap behaves as a bidentate chelate with the deprotonated 2-hydroxy and azomethine nitrogen centers with the pendant pyrimidine cyclic nitrogen functionality playing no role in coordination. The dissociation constants of H2sap and the stability constants of the metal complexes have been determined pH-metrically at various temperatures, and the thermodynamic activation parameters (ΔS*, ΔG*, ΔH*) calculated.