Acta Chim. Slov. 2001, 48, 257-264. 257 STUDIES ON 7V-[2-THIENYLMETHYLIDENE]-2-AMINOTHIAZOLE COMPLEXES OF Fe(II), Co(II), Ni(II), Cu(II), Zn(II) AND Cd(II) Cezar Spinu", Angela Krizab, Lacramioara Spinuc a University of Craiova, Faculty of Chemistry, Department of Inorganic Chemistry University of Bucharest, Faculty of Chemistry, Department of Inorganic Chemistry 'National College ,,Fratii Buzesti ' ' Craiova Received 20-10-2000 Abstract Metal complexes ML2C12, where M is Fe", Co", Ni11, Cu", Znn and Cdn and L is Schiff base formed by condensation of 2-thiophenecarboxaldehyde and 2-aminothiazole, N-[2-thienylmethylidene]-2-aminothiazole (TNATZ), have been prepared and characterized by elemental analysis, magnetic and spectroscopic measurements. IR and NMR spectra show that the nitrogen of the azomethine group and sulphur of the thiophene ring take part in coordination. Magnetic, Mössbauer, ESR and electronic spectral studies show a distorted octahedral structure for the Fe(II) complex, a square-planar geometry for NifTNATZ^C^ and Cu(TNATZ)2Cl2 complexes and a tetrahedral geometry for Co(II), Zn(II) and Cd(Il) complexes. Conductance measurements suggest the 1:2 electrolytic nature of the complexes, with the exception the of the FefTNATZ^Cl? compound. Key words: Schiff base, N-[2-thienylmethylidene]-2-aminothiazole Introduction Investigation on metal complexes of thiazole derivatives, particularly the 2-substituted ones have received considerable attention, " owing to their importance in biological and industrial processes.4 In continuation of our work on a metal complexes of Schiff bases ' we report here the results of our studies on the complexes of Schiff base derived from 2-thiophenecarboxaldehyde (2-TFCA) and 2-aminothiazole (2-ATZ), N-[thienylmethyli-dene]-2-aminothiazole (TNATZ), with Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II). Tentative structures have been proposed on the basis of analytical, spectral, magnetic and conductance data. Results and discussion C. Spinu, A. Kriza, L. Spinu: Studies on N-[2-thienylmethylidene]-2-aminothiazole complexes... 258 Acta Chim. Slov. 2001, 48, 257-264. The complexes of Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) with N-[2-thienylmethylidene]-2-aminothiazole (TNATZ) (Fig. 1) appear as powders with medium melting points. They are not soluble in methanole, ethanol, ethylether and chloroform but soluble in DMF. IN- CH: N- Figure 1. The structure of N-[2-thienylmethylidene]-2-aminothiazole Based on the elemental analysis, the formula ML2CI2 (Table 1) has been suggested for all compounds. Table 1. Analytical and physical data of the complexes* Compounds Melting point °C Colour Pdf (MB) (Q-1 ci^mol"1) Fe(TNATZ)2Cl2 160 red 5.14 10.2 Co(TNATZ)2Cl2 170 blue 4.41 125.8 Ni(TNATZ)2Cl2 150 brownish diam. 118.4 Cu(TNATZ)2Cl2 130 brown 1.78 143.7 Zn(TNATZ)2Cl2 210 yellowish - 115.4 Cd(TNATZ)2Cl2 145 white - 120.6 *All the complexes give satisfactory metal, C, H, S, N and CI analyses; ** in DMF solution IR and NMR spectra. Some important IR bands of TNATZ and its complexes along with their assignments are presented in Table 2. Table 2. Characteristic infrared absorption frequencies (in cm1) of ligands and complexes Compound ^C=N azomcthinc VC=N thioplicnc Vc-s-r Vo-S Vm-N TNATZ 1656 1503 890 708 - Fe(TNATZ)2Cl2 1630 1504 892 860 710 638 430 Co(TNATZ)2Cl2 1626 1505 894 854 711 626 425 Ni(TNATZ)2Cl2 1620 1502 890 878 708 620 422 Cu(TNATZ)2Cl2 1616 1503 895 879 703 667 428 Zn(TNATZ)2Cl2 1618 1505 885 855 705 625 408 Cd(TNATZ)2Cl2 1615 1501 889 868 704 635 410 C. Spinu, A. Kriza, L. Spinu: Studies on N-[2-thienylmethylidene]-2-aminothiazole complexes... Acta Chim. Slov. 2001, 48, 257-264. 259 The IR spectrum of the ligand shows a band at 1656 cm" which is assigned to the Vc=n of the azomethyne group and an intense band at 1503 cm" corresponding to the C=N stretching of the thiazole ring. The comparison of the positions of these bands with those observed in the IR spectra of the complexes indicates that the band at 1656 cm" shifts towards lower frequencies, while that at 1503 cm" does not show a marked shift. This behaviour suggests that TNATZ is coordinated to the central metal ion through the azomethine nitrogen. The proof of the coordination to the N atom is provided by the occurrence of the bands in the 408-430 cm" region in the IR spectra of the compounds. The band observed in the free ligand spectrum at 890 cm" can be ascribed to vc-s-c stretching vibration . In the IR spectra of the complexes, two distinct bands appear in this region: the first one at 854-879 cm" (shifted to lower frequency side) and the second one at 885-895 cm" (which remains almost unchanged on complexation). These observations suggest that one of the two sulphur atoms takes part in coordination. The important canonical form of the TNATZ places a positive charge on the thiazole sulphur rendering it as a poor donor and we can suggest bonding of the ligand through the thiophene sulphur atom. The band observed at 708 cm" in the ligand spectrum assigned to the Vc-s stretching vibration is similarly shifted. This also confirms that the thiophene ring sulphur is a donor atom. In the H-NMR spectrum of the ligand, the thiophene ring proton 5-H appears at 8 7.2 ppm and the azomethine proton ( -CH=N- ) at 8.7 ppm. These signals register downfield shifts (0.4-0.6 ppm) in the Ni(II), Zn(II) and Cd(II) complexes. These observations support the bonding of TNATZ through nitrogen and sulphur atoms. The C-NMR spectra provide further support for the mode of coordination of TNATZ. In the complexes spectra, the signals due to azomethine carbon, 2-C and 5-C (thiophene ring) show a distinct downfield shift by nearly 5-6.2 ppm clearly demonstrating the coordination of the ligand via the nitrogen and sulphur atoms. Electronic and ESR spectra. Within the UV spectrum of the ligand, the existence of two absorption bands assigned to the transition n-^n* and n^-ii* at 40 310 and 36 180 cm" , respectively, has been observed. These transitions are to be found also in the C. Spinu, A. Kriza, L. Spinu: Studies onN-[2-thienylmethylidene]-2-aminothiazole complexes... 260 Acta Chim. Slov. 2001, 48, 257-264. spectra of the complexes, but they are shifted to lower frequencies (Av=1500-2000 cm" ), confirming the coordination of the ligand to the metal ions. The information, referring to the geometry of these compounds, is obtained from the electronic spectra (Table 3) and from values of the magnetic moments. Table 3. Electronic spectra of the complexes Compound Absorption maxima (cm"') [Fe(TNATZ)2Cl2] 12 600 10 200 [Co(TNATZ)2]Cl2 15 000 8 330 [Ni(TNATZ)2]Cl2 20 276 15 973 [Cu(TNATZ)2]Cl2 19 157 15 280 [Zn(TNATZ)2]Cl2 25 260 (C.T.) [Cd(TNATZ)2]Cl2 24 320 (C.T.) The electronic spectrum of the iron(II) complex consists of a pair of low intensity bands at 12600 and 10200 cm" arising from T2g —» Eg transitions, similar to those found for distorted octahedral complexes. The doublet is attributed to Jahn-Teller distortion in the excited state. The room temperature magnetic moment (5.14 BM) corresponds with the octahedral symmetry. Also, in the Mössbauer spectrum, the value of isomer shift (0.874 mm-s" ) indicates a high spin variety for iron(II) complex. Further, the somewhat lower value of the isomer shift than expected for perfect octahedral structure suggests a distortion from octahedral geometry. The solid state electronic spectral bands of the Co(II) complex around 8330 (V2) and 15000 cm"1 (v3), the value of Dq (487 cm"1), B (725 cm"1), ß (0.75) and v2/ v,(1.71) calculated using Underhill and Billing equation as well as the magnetic moment value 4.41 B.M., all reveal the tetrahedral coordination of ligands around the Co(II) ion. The diamagnetism of the Ni(II) complex indicates an essentially square-planar environment about Ni(II), which is in agreement with the reflectance spectrum of the Ni(TNATZ)2Ci2 compound. The bands at 20276 and 15973 cm" can be assigned to the transitions 'Aig^'Big and ' A|g—»'A2g, respectively. The electronic spectrum of Cu(II) complex shows absorption bands at 19157 I 9 9 9 9 and 15280 cm" assignable to Big^- Eg and Big—» Aig transition, supporting square- C. Spinu, A. Kriza, L. Spinu: Studies onN-[2-thienylmethylidene]-2-aminothiazole complexes... Acta Chim. Slov. 2001, 48, 257-264. 261 planar configuration. The ESR spectrum for this compound, measured in polycrystalline sample at room temperature, gives gn and g± values about 2.15 and 2.07, respectively. The value gn > g± is well consistent with a primarily dx2 - y2 ground state having an elongated square-planar structure . The parameter G, determined as: G =( gii-2)/(g±-2) is found to be much less than 4 suggesting a considerable interaction in the solid state. From stoichiometry and other physicochemical evidences, four-coordinated tetrahedral geometry is suggested for Zn(II) and Cd(II) complexes. The molar conductance of the complexes in DMF (10" M) are in the range 1 9 1 115.4-143.7 Q" cm mol" indicating their 1:2 electrolytic nature, with the exception of the Fe(TNATZ)2Cl2 compound (AM = 10.2 Q'Wmol"1). Conclusions In this paper we report about preparation, isolation and characterisation of a new bidentate Schiff base ligand derived from 2-thiophenecarboxaldehyde and 2-amino thiazole, and its complexes with FeIT, Co11, NiTI, CuTT Zn11 and Cd11. The products were characterised by elemental analysis, magnetic and spectroscopic measurements. Correlating the experimental data, one can estimate the stereochemistry of the prepared complexes: distorted octahedral for the [Fe(TNATZ)2Cl2], square-planar for the [M(TNATZ)2]C12 (M=Nin and CuTT) and tetrahedral for the [M(TNAP)2]C12 (M=CoTI, ZnTI and Cd11) compounds. The proposed structural formulas of these compounds are presented in Figure 2. C. Spinu, A. Kriza, L. Spinu: Studies onN-[2-thienylmethylidene]-2-aminothiazole complexes... 262 Acta Chim. Slov. 2001, 48, 257-264. Figure 2. The proposed formulae of the complexes: a.[M(TNATZ)2]Cl2 (M = Ni", Cu"); b.[M(TNATZ)2]Cl2 (M = Co" Znn, Cd11); c.[M(TNATZ)2Cl2] (M= Fen) Experimental Reagents: FeCl2-6H20 (Merck, 99.9%), CoCl2-6H20 (Merck, 99.99%), NiCl2-6H20 (Merck, 99.99%), CuCl2-2H20 (Merck, 99.99%), thiophenecarboxaldehyde (Merck, 98%), 2-aminothiazole (Merck, 98%). Synthesis of bidentate Schiff bases. An ethanolic solution of 2-TFCA (0.002 mol, 25 ml) was added to an ethanolic solution of 2-ATZ (0.002 mol, 25 ml) and refiuxed for 3h on a water-bath. After the concentration of the solution, the precipitate C. Spinu, A. Kriza, L. Spinu: Studies on N-[2-thienylmethylidene]-2-aminothiazole complexes... Acta Chim. Slov. 2001, 48, 257-264. 263 was filtered, washed with ethanol and dried over CaCl2 in vacuum. Anal. Calculated for C8H6N2S2 : C, 49.46; H, 3.11; N, 14.43; S, 33.01. Found: C, 49.45; N, 14.46; S, 33.02. 'H NMR: o, 8.7; ô2 7.2; 13C NMR: ô, 150.7; ô2 133.3; ô3 111.7. Synthesis of the ML2C12 complexes. A mixture of 2-TFCA (0.004 mol, 50 ml), 2-ATZ (0.004 mol, 50 ml) in ethanol was added to an ethanolic solution of metal chlorides (0.002 mol, 50ml), at pH=8.5-9. The mixture of reactants was refluxed on a water-bath for 10-12 h. The excess of solvent was then distilled. The compounds separated were filtered, washed with ethanol and dried over CaCl2 in vacuum. Anal. Calculated for Co(TNATZ)2Cl2: Co, 11.38; C, 37.08; N, 10.81; S, 24.74; CI, 13.68. Found: Co, 11.42; C, 37.05; N, 10.78; S, 24.75; CI, 13.67. Calculated for Ni(TNATZ)2Cl2: Ni, 11.34; C, 37.09; N, 10.82; S, 24.75; Cl, 13.68. Found: Ni, 11.31; C, 37.05; N, 10.86; S, 24.76; Cl, 13.68. Calculated for Cu(TNATZ)2Cl2: Cu, 12.16; C, 36.75; N, 10.72; S, 24.52; Cl, 13.57. Found: Cu, 12.11; C, 36.72; N, 10.75; S, 24.52; Cl, 16.11. Calculated for Zn(TNATZ)2Cl2: Zn, 12.47; C, 36.62, N, 10.68; S, 24.44; Cl, 13.59. Found: Zn, 12.44; C, 36.58, N, 10.66; S, 24.45; Cl, 13.56. 'H NMR: ô, 9.2; ô2 7.5; 13C NMR: 0,155.6; ô2 134.7; ô3 114.3. Calculated for Cd(TNATZ)2Cl2: Cd, 19.67; C, 33.60, N, 9.80; S, 22.43; Cl, 12.41. Found: Cd, 19.71; C, 33.56, N, 9.40; S, 22.43; Cl, 12.38. 'H NMR: ô, 9.0; ô2 7.6; 13C NMR: ô, 156.4; ô2 135.2; ô3 115.6. Calculated for Fe(TNATZ)2Cl2: Fe, 10.84; C, 37.29, N, 10.86; S, 24.89; Cl, 13.76. Found: Fe, 10.64; C, 36.98, N, 11.03; S, 24.92; Cl, 13.11. 'hNMR: ô, 9.3; ô2 7.6; l3C NMR: 0,154.8; ô2 137.2; ô3 116.1. Instruments. The ligand and the complexes were analysed for M, S and Cl by conventional methods, ' while C, H and N by microanalytical methods. The IR spectra were obtained in KBr discs using a BIO-RAD FTS 135 spectrophotometer. The UV-VIS spectra were recorded on an UNICAM UV-VIS UV-4 spectrophotometer in DMF solution. The reflectance spectra were recorded on a VSU-2P spectrometer at room temperature. . The Mössbauer spectrum of iron compond was measured at 293 K on an en i ECIL MBS 35 spectrometer using Co in Pd matrix as source. The H-NMR spectra (in CDCI3) were recorded on a Varian T60, and the C-NMR spectra were obtained using a Bruker WH 270 spectrometer. The ESR spectrum of a polycrystalline sample was C. Spinu, A. Kriza, L. Spinu: Studies onN-[2-thienylmethylidene]-2-aminothiazole complexes... 264 Acta Chim. Slov. 2001, 48, 257-264. recorded on an ART 5 spectrometer at room temperature. The magnetic moments have been determined by the Faraday method. A digital conductivity meter K 612 was used to measure the molar conductivities in DMF solution. References 1. J. A. Weaver, P. Hambrigh, Inorg. Chem. 1970, 9, 268. 2. E. J. Duff, M. N. Hughes, K. J. Rutt, Inorg. Chim. Acta, 1972, 6, 408. 3. W. E. Estes, D. P. Gavel, W. E. Hatfield, Inorg. Chem. 1978,17, 1415. 4. M. M. Campbell, Comprehensive Organic Chemistry, vol. 4, Pergamon Press, Oxford, 1979. 5. A. Kriza, C. Spinu,./ Indian Chem. Soc. 2000, 76, 84. 6. C. Spinu, A. Kriza, Acta Chim. Slov. 2000, 47, 179. 7. S. C. Mohapatra, D. V. R. Rao,./. Indian Chem. Soc. 1980, 57, 262. 8. S. Burman, D. N. Sathyanarayana,./. Inorg. Nucl.Chem. 1981, 43, 1940. 9. A. B. P. Lever, Inorganic Electronic Spectroscopy, Elsevier, New York, 1984. 10. T. G. Gibb, N. N. Greenwood, Mössbauer Spectroscopy., Chapman & Hall, London, 1971. 11. D. E. Billing, A. E. Underhill, Nature (London) 1966, 843. 12. B. T. Hathaway, Struct. Bonding 1973,14, 60. 13. A. I. Vogel, A Text Book of Quantitative Inorganic Analysis 3r ed., ELBS, London., 1961. 14. A. Steyemark, R. Calancertle,./. Assoc. Anal. Chem. 1972, 55, 680. Povzetek Pripravili in karakterizirali smo komplekse s sestavo ML2CI2, kjer je M Fe11, Co11, Nin, Cu11, ZnIT ali Cd11 in L je Schiffova baza, ki jo dobimo s kondenzacijo 2-tiofenkarboksaldehida z 2-aminotiazolom oziroma A/-[2-tienilmetiliden]-2-aminotiazolom (TNATZ). Z merjenjem IR, NMR, magnetnih, Mössbauerjevih in EPR spektrov smo sklepali na geometrijo pripravljenih kompleksov. C. Spinu, A. Kriza, L. Spinu: Studies on N-[2-thienylmethylidene]-2-aminothiazole complexes...