Inorganica Chimica Acta, 136 (1987) 87-92 87 Studies on Pyrimidine Derivative Complexes: Spectroscopy, Thermal Behaviour and Crystal Structure of Cc-Dichloro-+wlphur-chloro(4,6-diamino-l , 2-dihydro- 2-thiopyrimidine-N3,S 2)cadmium( II) Monohydrate M. A. ROMERO-MOLINA*, M. D. GUTIERREZ-VALERO, R. LOPEZ-GARZON, J. M. SALAS-PEREGRIN Departamento de Quimica Inorginica, Universidad de Granada, 18071 Granada, Spain M. I. ARRIORTUA Departamento de Cristalografia y Mineralogia, Universidad de1 Pais Vasco, 48080 Bilbao. Spain and F. J. ZURIGA Departamento de Fisica, Universidad de1 Pais Vasco, 48080 Bilbao, Spain (Received October 17, 1986) Abstract The crystal structure of Cd(DATP)C12*Hz0 has been determined by X-ray diffraction methods. It crystallizes in the tetragonal space group Z4& with a = 24.296(7), c = 7.108(9) A, V= 4196(4) A3, and Z = 16. The structure has been solved by Patter- son and Fourier syntheses and refined by full-matrix least-squares procedure to R = 0.049 for 1688 ob- served reflections. The crystal does not contain individual Cd(DATP)C12*Hz0 neutral molecules. Cadmium atoms show a coordination number of six. On the basis of the molecular structure of the Cd(DATP)C12*Hz0 complex the most significant IR bands have been assigned in the 4000-600 cm-’ range. Likewise, the v(Cd-N), v(Cd-S) and v(Cd-X) bands were assigned by comparing the IR spectra of the Cd(DATP)C12.Hz0 and Cd(DATP)*Brz complexes in the 600-l 80 cm-’ range. Finally, by using an IR technique for the identifi- cation of intermediates, a thermal decomposition mechanism for the Cd(DATP)C12*Hz0 complex has been proposed. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Introduction Cadmium, as well as other metals of the first transition series, has been found to be an environ- mental pollutant and to inhibit RNA polymerase activity in vivo [I], and it is one of the most potent agents in diminishing the fidelity of DNA [2] and RNA [3] syntheses in vifro. Soft metal ions will bind tightly to a range of biological sites, particularly those with sulphur ligands. They will often displace native metal ions and inhibit metalloenzymes [4]. *Author to whom correspondence should be addressed. 0020-1693/87/$3.50 Several general reviews of the biochemical toxicity of these cations are available [S-7]. The toxicity is reflected in behavioural disturbances, anaemia, alterations in membrane permeability, and inhibition of oxidative phosphorylation and protein synthesis. There is also much evidence of the carcinogenic effects of a wide range of metals, including Cd, and their compounds, all of which are associated with cancer in humans [8]. Cadmium is also notori- ous for its toxic effect on bone, as in ‘itai-itai byo’ disease [9, lo]. In spite of this, only relatively few data have been recorded about reactions of cadmium with nucleic acid constituents [ 11-l 31. The present paper reports the spectroscopic characterization, thermal behaviour and crystal structure of the octahedral complex formed between Cd and 4,6-diamino-1,2-dihydro-2-thiopyrimidine in aqueous medium. Experimental Preparation of the Complexes Cd(DA lF’)Cl, l Hz 0 This complex was prepared by dissolving Cd&* 2Hz0 and DATP (3:l molar ratio) in a minimum amount of hot water, and slowly evaporating at room temperature. Pale yellow prismatic crystals precipitated over several days and were found suitable for X-ray work. Anal. Calc. for C4H&dC12N40S: C, 14.02; H, 2.34; N, 16.36; Cd, 32.83. Found: C, 14.34; H, 2.29; N, 16.27; Cd, 33.85%. Cd(DA TP), Brz This complex was obtained by the same method as the above complex, using as solvent a Cd&/ DATP/KBr aqueous solution in which CdClz and KBr were in a 1: 10 molar ratio. 0 Elsevier Sequoia/F’rinted in Switzerland