Thermal, spectroscopic, X-ray and theoretical studies of metal complexes (sodium, manganese, copper, nickel, cobalt and zinc) with pyrimidine-5-carboxylic and pyrimidine-2-carboxylic acids

G Świderski,R Świsłocka,W Lewandowski,S Wojtulewski,M Samsonowicz,R Łyszczek

doi:10.1007/s10973-019-08594-x

Abstract

The new 3d metal complexes of pyrimidine-2-carboxylic (2PCA) and pyrimidine-5-carboxylic (5PCA) acids were synthesized and characterized using thermal analysis (TG–DSC, TG–FTIR), X-ray, spectroscopic (IR, Raman) methods and theoretical (DFT) studies. In the complexes of pyrimidine-2-carboxylic acid of the general formula M(2PCA)2·xH2O (where 2PCA-pyrimidine-2-carboxylate; M = Mn(II), Co(II), Ni(II), Cu(II) and Zn; x = 0 for Mn and Cu; x = 2 for Co, Ni and Zn) coordination of metal ions occurs through nitrogen atom from pyrimidine ring and carboxylate oxygen atom. The complexes of pyrimidine-5-carboxylic acid of the general formula M(5PCA)2·xH2O (where 5PCA—pyrimidine-5-carboxylate; M = Mn(II), Co(II), Ni(II), Cu(II) and Zn; x = 6 for Cu and 4 for remaining complexes) were obtained as monomeric isostructural compounds. Coordination of metal centers occurs through two nitrogen atom from different pyrimidine-5-carboxylate ligand and four oxygen atoms from water molecules. The IR and Raman spectra of free acids as well as obtained metal(II) complexes were described in detail. Aromaticity (HOMA, EN, GEO and I6) of complexes was determined and discussed. The investigated compounds decompose in air in two main stages connected with dehydration and decomposition/burning of anhydrous compounds to the suitable metal oxides. Thermal decomposition in nitrogen leads to the evolution of water, carbon oxides, ammonia and pyrimidine molecules.

Highlights

Complexes of transition metals (Co, Mn, Ni, Zn, Cu) play an important role in the life processes of living organisms
In the complexes of pyrimidine-2-carboxylic acid of the general formula M(2PCA)2ÁxH2O (where 2PCA-pyrimidine-2-carboxylate; M = Mn(II), Co(II), Ni(II), Cu(II) and Zn; x = 0 for Mn and Cu; x = 2 for Co, Ni and Zn) coordination of metal ions occurs through nitrogen atom from pyrimidine ring and carboxylate oxygen atom
The bonds of the coordination sphere M–N1, M– O1 and M–Ow are nearly equal in length (2.066(1)– 2.123(2) A ), and the overall coordination sphere around cobalt and zinc cations can be described as an octahedral

Summary

Introduction

Complexes of transition metals (Co, Mn, Ni, Zn, Cu) play an important role in the life processes of living organisms. They are, among others, components of enzymes, proteins and vitamins; they participate in oxidation–reduction. Studies have shown that transition metals influence the stability of the electron system of complexes the aromatic acids [11,12,13,14]. This impact depends on the properties of metal, and on the way the ligand–metal coordination. The pyrimidine-5-carboxylic acid may form complexes by attaching a metal via a ring nitrogen atom without the participation of a carboxylic group [19]

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