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

doi:10.1016/j.molstruc.2010.03.037

Journal of Molecular Structure

Volume 973, Issues 1–3, 2 June 2010, Pages 69-75

https://doi.org/10.1016/j.molstruc.2010.03.037 Get rights and content

Abstract

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.

Introduction

Schiff-bases are important class of chelating agents in coordination chemistry as they easily form stable complexes with most transition metal ions [1]. The bioinorganic chemistry field has increased the interest in Schiff-bases complexes, as they serve as models for important biological species [2]. Such complexes are also of interest due to their catalytic activity [3], [4], [5], removal of toxic metal ions [6], corrosion inhibitors [7], ability to reversibly bind oxygen [8] and their photo-chromic properties [9].

The interaction of Schiff-bases derived from salicylaldehyde moiety and primary amines, especially amino acids with variety of transition metals have been reported [4], [10], [11], [12], [13]. Moreover, pyrimidine rings are present in nucleic acids, several vitamins, coenzymes and antibiotics [14] and act as valuable substrates in the synthesis of antitumor agents [15]. We have previously reported the chemotherapeutic potential of Pd(II) and Ag(I) complexes with 4,6-diamino-5-hydroxy-2-mercaptopyrimidine. These complexes were found to display significant anticancer activity against Ehrlich ascites tumor cell (EAC) in albino mice [15]. As a continuation of our interest in anticancer activity of complexes containing pyrimidine rings, here we describe the preparation and characterization of new 4-hydroxysalicylidene-2-aminopyrimidine Schiff-base (H₂sap) transition elements complexes. Also, we report the dissociation constants of H₂sap, the stability constants of the metal complexes and the thermodynamic activation parameters (ΔS^*, ΔG^*, ΔH^*) which are calculated pH-metrically at various temperatures, as these studies can give some knowledge in their examination as anticancer agents.

Section snippets

Experimental

All reagents were purchased from Aldrich and all manipulations were performed under aerobic conditions using materials and solvents as received. [Pd(PPh₃)₂Cl₂] was prepared from K₂[PdCl₄] and PPh₃ in aqueous-ethanol solution [16] and [Ru(PPh₃)₃Cl₂] was synthesised as previously reported [17]. DMF and DMSO used in conductivity and electronic spectral measurements were dried over molecular sieves. DMSO-d₆ (NMR) was referenced using TMS.

Results and discussion

The experimental section lists some new complexes of 4-hydroxysalicylidene-2-aminopyrimidine Schiff-base (H₂sap). The elemental analyses (Table 1) of the complexes are in agreement with the assigned formulae. The molar conductivities (Λ_M) in DMSO at room temperature, suggest that all complexes are non-electrolytes except [Pd(Hsap)(PPh₃)₂]Cl which behaves as 1:1 electrolyte, supporting its ionic formulation [20]. [WO₂(Hsap)₂] and [Pd(Hsap)Cl(H₂O)] complexes were prepared from the reaction of H₂

Acknowledgement

We wish to thank Prof. W.P. Griffith (Chemistry Department, Imperial College of London) for the language corrections.

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

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Acknowledgement

Polyhedron

J. Mol. Cat. A

Electrochim. Acta

J. Inorg. Nucl. Chem.

Spectochim. Acta

Inorg. Chim. Acta

Polyhedron

Polyhedron

Polyhedron

Spectrochim. Acta

Spectrochim. Acta

Thermochim. Acta

Transition Metal Chem.

J. Ind. Eng. Chem.

J. Ind. Eng. Chem.

J. Chem. Soc. Pak.

Chem. Rev.

Photochromism

J. Inorg. Biochem.

Bull. Korean Chem. Soc.

J. Korean Chem. Soc.

Transition Metal Chem.

Appl. Organomet. Chem.