Spectrochimica Acta Part A 63 (2006) 740–748 Electronic structure of orotic acid III geometric feature and thermal properties of some transition metal orotic acid complexes Rifaat Hilal a , Z.M. Zaky b , Shabaan A.K. Elroby b,∗ a Chemistry Department, Faculty of Science, Cairo University, Egypt b Chemistry Department, Faculty of Science, Cairo University, Beni-seuf Branch, Egypt Received 25 September 2004; received in revised form 19 March 2005; accepted 15 June 2005 Abstract The complexes of orotic acid with Co(II), Ni(II), Fe(III), Cu(II), and Cd(II) were prepared and their stoichiometry were determined by elemental analysis. Co(II) and Ni(II) give complexes with orotic acid of 1:1 ratio whereas that of the remaining transition metals give complexes of 1:2 ratio. The stereochemistry of the studied metal complexes has been established by analyses of their electronic spectra and magnetic susceptibilities. The mode of bonding in the studied series of metal complexes was established via, analysis of their infrared spectra. The present analysis leads to the conclusion that all metal ions studied coordinate to orotic acid via N 1 and the adjacent carboxylate group. Thermal decomposition studies of orotic acid complexes have been carried out as to understand the status of water molecules present in these complexes as well as to know their general decomposition pattern. Theoretical investigation of the electronic structure of the studied metal complexes has been carried out. MO computations at the HF-level were performed. Charge density distribution, extent of distortion from regular geometry, dipole moment, and orientation were computed and discussed. © 2005 Elsevier B.V. All rights reserved. Keywords: Orotic acid; Metal complexes; MO computations; IR; Thermal analysis; Reflectance spectra 1. Introduction Pyrimidine derivatives constitute a very important class of compounds because they are components of the biologi- cally important nucleic acids and have been shown to exert a pronounced physiological effect [1–6]. Orotic acid (Vitamin B 13 ) and its salts play an important role in biological sys- tems as precursors of pyrimidine nucleotide and are found in cells and body fluids of many living organisms, these com- ∗ Corresponding author. E-mail addresses: rhhilal@hotmail.com (R. Hilal), Sha kamel@yahoo.com (S.A.K. Elroby). pounds are applied in medicine as biostimulators of the ionic exchange processes in organisms. There is also a great interest for orotic acid in relation to food protection and nourishment research [7–9]. The IR and Raman spectra of polycrystalline anhydrous orotic acid and its N 1 ,N 3 , and O 14 trideuterated isotopomers are recorded in the 4000–40 cm -1 spectral interval as part of a series of vibrational analysis of nucleosides, nucleotides, and related compounds. The frequencies of the fundamen- tal transitions and the potential energy distributions of the 39 normal modes of orotic acid and its isotopomers were calculated by an ab initio density functional theory at the Becke3P86/6-311G ** level of theory [10]. The coordination chemistry of orotic acid (2,6-dioxo- 1,2,3,6-tetrahydropyrimidine-4-carboxylic acid, Vitamin B 13 ,H 3 L) has been studied in detail in recent years, research in this area ranging from bioinorganic to pharmaceutical and materials chemistry. Attachment of a ribose phosphate group to orotate, assisted by metal ions and followed by decarboxylation, finally results in the formation of uridylate 1386-1425/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2005.06.031