Acta Chim. Slov. 2000, 47, 179-185. 179 Co(II), Ni(II) and Cu(II) COMPLEXES OF BIDENTATE SCHIFF BASES Cezar Spinu*, Angela Kriza** *University of Craiova, Faculty of Chemistry, Department of Inorganic Chemistry ** University of Bucharest, Faculty of Chemistry, Department of Inorganic Chemistry Received 2.2.2000 Abstract Cobalt (II), nickel (II) and copper (II) complexes of type ML2Cl2, where M is CoII, NiII and CuII, and L is Schiff base formed by condensation of 2-thiophenecarboxaldehyde and propylamine, N-[2-thienylmethylidene]-1-propanamine (TNAP), or ethylamine, N-[2-thienylmethylidene]ethanamine (TNAE), have been prepared and characterised by elemental analysis, magnetic and spectroscopic measurements. Elemental analysis suggests the stoichiometry to be 1:2 (metal:ligand). Magnetic susceptibility data coupled with electronic and ESR spectra suggest a distorted octahedral structure for the Cu(II) and Ni(TNAE)2Cl2 complexes, a tetrahedral geometry for Ni(TNAP)2Cl2 and a D4h symmetry for the Co(II) complexes. Infrared and NMR spectra of the complexes agree with the coordination to the central metal atom through nitrogen and sulfur atoms. Conductance measurements suggest the non-electrolytic nature of the complexes and the 1:2 electrolytic nature of the Ni(TNAP)2Cl2. Keywords: Schiff base, N-[2-thienylmethylidene]ethanamine, N-[2-thienylmethylidene]-1-propan-amine Introduction Metal complexes of Schiff base are studied extensively due to synthetic flexibility of these compounds and their selectivity as well as sensitivity towards the central metal atom. Complexes with Schiff bases derived from 2-thiophenecarboxaldehyde were prepared and used for extracting some metal ions. In most complexes presented in previous works1-3, the ligand co-ordination to the metal ions achieves both nitrogen and sulphur atoms. In the present study, a series of new Schiff bases have been synthesised using 2-thiophenecarboxaldehyde (2-TFCA) and propylamine (PA) or ethylamine (EA). These bidentate ligands form 1:2 complexes with Co(II), Ni(II) and Cu(II) ions. Results and discussion The complex combinations of Co(II), Ni(II) and Cu(II) with N-[2-thienylmethylidene]-1-propanamine (TNAP) and N-[2-thienylmethylidene]ethanamine (TNAE) (fig. 1) appears as powders with high melting points. They are not soluble in ethanol, ethyl ether and chloroform but soluble in acetone and more soluble in DMF. C. Spinu, A. Kriza: Co(II), Ni(II) and Cu(II) Complexes of Bidentate Schiff Bases. 180 Acta Chim. Slov. 2000, 47, 179-185. \ / S CH N CH2 CH2 CH3 a. s CH N CH2 CH3 b. Figure 1. The structure of: a. N-[2-thienylmethylidene]-1-propanamine ( C8H11NS ) (TNAP) b. N-[2-thienylmethylidene]ethanamine ( C7H9NS ) (TNAE) Elemental analysis data suggest that the complexes have 1:2 (metal-ligand) stoichiometry. Based on the elementary chemical analysis has been suggested, for all compounds, the formula ML2Cl2 (table 1). Table 1. Analytical and physical data of the complexes* Compounds Melting point oC Colour meff (MB) LM** (W-1cm2mol-1) Co(TNAP)2Cl2 220 purple 4.59 12.1 Ni(TNAP)2Cl2 150 blue 3.52 130.2 Cu(TNAP)2Cl2 128 green 1.92 10.4 Co(TNAE)2Cl2 250 pink 4.75 22.5 Ni(TNAE)2Cl2 215 yellow 3.02 7.8 Cu(TNAE)2Cl2 180 greenish 1.93 8.9 *All the complexes give satisfactory metal, C, H, S, N and Cl analyses; ** in DMF solution In order to get data conceiving the ligand way of co-ordination to the metal ions, the IR spectra on the 400-4000 cm-1 range (table 2) have been carried out. Table 2. Characteristic infrared absorption frequencies in (cm-1) of ligands and complexes Compound n C=N nCSC nChtiophen nC-Ctiophen nCSsym. nCsasym. nM-N TNAP 1670 850 3070 1520 690 640 - Co(TNAP)2Cl2 1632 822 3068 1511 - 620 418 Ni(TNAP)2Cl2 1615 830 3071 1518 - 617 420 Cu(TNAP)2Cl2 1620 825 3063 1520 - 625 415 TNAE 1656 845 3060 1523 680 650 - Co(TNAE)2Cl2 1611 815 3063 1522 - 615 422 Ni(TNAE)2Cl2 1618 820 3065 1520 - 608 425 Cu(TNAE)2Cl2 1625 825 3058 1515 - 610 428 I.R. and NMR spectra. The IR spectra of the ligands exhibits a band at 1656-1670 cm-1 assignable to nC=N of the azomethyne group. This band shift to lower region by about 38- C. Spinu, A. Kriza: Co(II), Ni(II) and Cu(II) Complexes of Bidentate Schiff Bases. Acta Chim. Slov. 2000, 47, 179-185. 181 60 cm-1 in case of the all complexes, suggesting co-ordination through N atom of the azomethyne group. The medium intensity band at ~850 cm-1 observed in free ligand ascribed to nCSC (ring) stretching vibration4 is shifted to lower values with 28-30 cm-1 for all compounds, suggesting the involvement of sulphur atom in the bonding with the metal's ions. The band assigned to the asymmetric nC-S is shifted to lower frequency after complexation and the symmetric nC-S is completely disappears in all the complexes. This also confirms that the sulphur atom is taking part in the complex formation2,5. The proof of coordination to the N atom is provided by the occurrence of the bands from 415-428 cm-1 in the I.R. spectra of the compounds. In the 1H-NMR spectra of the ligands the formation of Schiff bases is supported by the presence of a singlet at d 9.54 and 9.72 ppm respectively, corresponding to the azomethyne proton ( -CH=N- ) and a peak at d 159.7 and 162.3 ppm respectively, in the 13C-NMR spectra. Electronic and ESR spectra. Within the UV spectrum of the ligand has been observed the existence of two absorption bands assigned to the transition n®p* and p®p* at 42 522 and 35 100 cm-1 respectively. These transitions are to be found also in the spectra of the complexes, but they are shifted to lower frequencies (Dn=1100-3000 cm-1), 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-1) [Co(TNAP)2Cl2] 19 870 19 020 15 600 9 500 7 300 [Co(TNAE)2Cl2] 20 030 19 130 16 200 10 100 8 070 [Ni(TNAP)2]Cl2 17 300 9 650 [Ni(TNAE)2Cl2] 25 800 14 100 8 560 7 200 [Cu(TNAP)2Cl2] 11 760 [Cu(TNAE)2Cl2] 16 670 C. Spinu, A. Kriza: Co(II), Ni(II) and Cu(II) Complexes of Bidentate Schiff Bases. 182 Acta Chim. Slov. 2000, 47, 179-185. The reflectance spectra of the Co(II) complexes are similar. In the spectra appear bands at 19870, 19020, 15600, 9500 and 7300 cm-1 and 20030, 19130, 16200, 10100 and 8070 cm-1 respectively. By analogy with the band assignments of Ferguson6, the bands at 19870, 19020 cm-1, in the spectrum of Co(TNAP)2Cl2, and 20030, 19130 cm-1, in the spectrum of Co(TNAE)2Cl2, arise from the 4T1g(F)^4T1g(P) transition which is split in complexes of D4h symmetry. That at 15600 cm-1 and 16200 cm-1 respectively, arise from 4T1g(F)^4A2g transition, and those at 9500, 7300 cm-1 and 10100, 8070 cm-1 respectively, from the 4T1g(F)^4T2g(F) transitions. This geometry is confirmed by the values of the effective magnetic moment too (4.59 and 4.75 BM respectively). Within the spectrum of Ni(TNAP)2Cl2 compound, the presence of the absorption bands at 17 300 and 9650 cm-1 ascribed to the transitions 3T1(F) -^3T1(P) and 3T1(F) -^3A2, can be notice. These transition are characteristic to the tetrahedral environment around the Ni2+ ion. The value of the magnetic moment, 3.52 BM, confirmed that structure. Using the method of Ballhausen7 we calculate values Dq = 450 cm-1 and B = 772. The electronic spectrum of the Ni(TNAE)2Cl2 could be assigned assuming that the stereochemistry pseudo-octahedral. The energies represent the next electronic transitions from the 3A2g(F) ground state to 3T2g(F) (v1), 3T1g(F) (v2) and 3T1g(P) (V3) excited states for nickel (II). The low energy band of this complex is broad and split in two components (at 8560 and 7200 cm-1) indicating tetragonal distortion. The magnetic moment (3.02 MB) lie in the region expected for octahedral complexes. The Cu(II) complexes exhibit only one broad asymmetric band at 11760 - 16670 cm-1. The calculated values of Dq (1400 cm-1), LFSE (24.7 - 25 kcal/mol) and the effective magnetic moments (1.92 and 1.93 BM) suggest a distorted octahedral geometry8. The ESR spectra for copper compounds, measured in polycrystalline sample at room temperature, give the following values: gII = 2.0577, g± = 2.1419 for the Cu(TNAP)2Cl2 and gII = 2.0827, g± = 2.1514 for the Cu(TNAE)2Cl2. The trend, gII < g± showed that the electron is delocalised in dz2 orbital of the ground state of CuII and the spectra are characteristic of axial (compressed octahedral) symmetry. The parameter G, determined as G =( gII-2)/( g±-2) is found to be much less than 4 suggesting considerable interaction in the solid state9. C. Spinu, A. Kriza: Co(II), Ni(II) and Cu(II) Complexes of Bidentate Schiff Bases. Acta Chim. Slov. 2000, 47, 179-185. 183 The molar conductance of the complexes in DMF (10-3 M) are in the range 7.8-22.5 W-1cm2mol-1 indicating their nonelectrolytic nature, excepting the Ni(TNAP)2Cl2 compound which is an 1:2 electrolyt (L = 130.2 W-1cm2mol-1). Conclusions In this paper we report the isolation and characterisation of two new bidentate Schiff base ligands derived from 2-thiophenecarboxaldehyde and propylamine or ethylamine and their complexes with CoII, NiII and CuII. The products were characterized by elemental analysis, magnetic and spectroscopic measurements. Correlating the experimental data one can estimate that the stereochemistry of the prepared complexes belong to the octahedral symmetry group, with the formula [ML2Cl2] (M = CoII, NiII and CuII; L = TNAP and TNAE), excepting the [Ni(TNAP)2]Cl2 compound which has a tetrahedral geometry. The proposed structural formulas of these compounds are presented in the figure 2. \ CH2 H2C H3C \ CH2 H2C \ HC Ni. \ H CH H2C \ CH3 2 + a. b. Figure 2. The structural formulas of the complexes: a.[ML2Cl2] (M = CoII, NiII, CuII; L = TNAP and TNAE); R=CH3, H b. [Ni(TNAP)2]Cl2 Experimental N S 2 R C. Spinu, A. Kriza: Co(II), Ni(II) and Cu(II) Complexes of Bidentate Schiff Bases. 184 Acta Chim. Slov. 2000, 47, 179-185. Reagents: CoCl2·6H2O (Merck, 99.99%), NiCl2·6H2O (Merck, 99.99%), CuCl2·2H2O (Merck, 99.99%), thiophenecarboxaldehyde (Merck, 98%), propylamine (Merck, 98%), ethylamine (Merck, 98%). Synthesis of bidentate Schiff bases. The Schiff bases were prepared thus: an ethanolic solution of 2-TFCA (0.002 mol, 25 ml) was added with an ethanolic solution of PA or EA (0.002 mol, 25 ml) and refluxed for 12h on a water-bath. After the concentration of the solution, the precipitate was separated, filtered, washed with ethanol and dried over CaCl2 in vacuum. Anal. Calculated for C8H11NS: C, 62.74; H, 7.19; N, 9.15; S, 20.19. Found: C, 62.76; H, 7.22; N, 9.13; S, 20.14. 1H NMR: d1 9.54; d2 7.25; d3 6.9; d4 6.92. 13C NMR: d1 159.7; d2 133.28; d3 112.08. Calculated for C7H9NS: C, 60.43; H, 6.47; N, 10.07; S, 23.02. Found: C, 60.39; H, 6.50; N, 10.11; S, 22.98. 1H NMR: d1 9.72; d2 7.22; d3 6.85; d4 6.88. 13C NMR: d1 162.3; d2 133.41; d3 112.23. Synthesis of the ML2Cl2 complexes. A mixture of 2-TFCA (0.004 mol, 50 ml), and PA or EA (0.004 mol, 50 ml) in ethanol was added to an ethanolic solution of metal chlorides (0.002 mol, 50ml). The mixture of reaction was refluxed on a water-bath for 16-18h. 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(TNAP)2Cl2: Co, 13.52; C, 44.05; H, 5.05; N, 6.42; S, 14.68; Cl, 16.27. Found: Co, 13.55; C, 44.01; H, 5.09; N, 6.47; S, 14.66; Cl, 16.25. Calculated for Ni(TNAP)2Cl2: Ni, 13.47; C, 44.08; H, 5.05; N, 6.43; S, 14.69; Cl, 16.27. Found: Ni, 13.50; C, 44.06; H, 5.08; N, 6.47; S, 14.67; Cl, 16.24. Calculated for Cu(TNAP)2Cl2: Cu, 14.43; C, 43.60; H, 5.00; N, 6.36; S, 14.53; Cl, 16.10. Found: Cu, 14.40; C, 43.57; H, 5.05; N, 6.40; S, 14.50; Cl, 16.11. Calculated for Co(TNAE)2Cl2: Co, 14.45; C, 41.19, N, 6.86; S, 15.69; Cl, 17.38. Found: Co, 14.40; C, 41.22, N, 6.83; S, 15.68; Cl, 17.43. Calculated for Ni(TNAE)2Cl2: Ni, 14.40; C, 41.22, N, 6.87; S, 15.70; Cl, 17.39. Found: Ni, 14.43; C, 41.19, N, 6.88; S, 15.65; Cl, 17.43. Calculated for Cu(TNAE)2Cl2: Cu, 15.41; C, 40.73, N, 6.72; S, 15.52; Cl, 17.19. Found: Cu, 15.40; C, 40.70, N, 6.78; S, 15.70; Cl, 14.41. Instruments. The ligand and complexes were analysed for M, S and Cl by a conventional methods10,11 , while C, H and N by microanalytical methods. The IR spectra were obtained in KBr disc using a BIO-RAD FTS 135 spectrophotometer. The UV-VIS C. Spinu, A. Kriza: Co(II), Ni(II) and Cu(II) Complexes of Bidentate Schiff Bases. Acta Chim. Slov. 2000, 47, 179-185. 185 spectra were recorded on a UNICAM UV-VIS UV-4 spectrophotometer in DMF solution. The reflectance spectra were recorded on a VSU-2P spectrometer at room temperature. The 1H-NMR spectra (in CDCl3) were recorded on a Varian T60 and the 13C-NMR spectra were obtained using a Bruker WH 270 spectrophotometer. The ESR spectra of the were recorded on a ART 5 spectrophotometer, in a polycrystalline sample 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. Shigeki A.; Tyo S. Anal. Chim. Acta 1993, 274(1), 141. 2. Suresh CG.; Deshapande A.; Tavale S.S. J. Crystallogr. Spectrosc. Res. 1991, 21(4), 485. 3. Kriza A.; Spinu C. J. Indian Chem. Soc. 2000, 76, 84. 4. Mohapatra S.C.; Rao D.V.R. J. Indian Chem. Soc. 1980, 57, 262. 5. Srivastava S.K.; Gupta K.A. Acta Chim. Hung. 1985, 118(3), 255. 6. Ferguson J. J. Chem. Phys. 1960, 32, 533. 7. Ballhausen CJ. Advan. Chem. Phys., 1963, 5, 33. 8. Rana V.B.; Singh P.; Singh D.P., Teotia M.P. Polyhedron 1982, 1, 337. 9. Hathaway B.T. Struct. Bonding 1973, 14, 60. 10. Vogel A.I. A Text Book of Quantitative Inorganic Analysis 3rd ed., ELBS, London., 1961. 11. Steyemark A.; Calancertle R. J. Assoc. Anal. Chem. 1972, 55, 680. Povzetek Kobaltovi(II), nikljevi(II) in bakrovi(II) kompleksi ML2Cl2 in ML’2Cl2, kjer je M oznaka za CoII, NiII in CuII , L in L’ pa oznaka za Shciffove baze dobljene s kondenzacijo 2-tiofenkarboksaldehida in propilamina oziroma etilamina., so bili pripravljeni in karakterizirani z elementno analizo, magnetnimi in spektroskopskimi meritvami. Mag netna susceptibilnost, elektronski in ESR spektri kažejo na popačeno oktaedrično geometrijo pri CuII in NiII L’2Cl2 kompleksih, na tetraedrično geometrijo pri Ni IIL2Cl2 in na D4h simetrijo pri Co(II) kompleksih. Infrardeči in NMR spektri so v skladu s koordinacijo dušikovih in žveplovih donorskih atomov na centralni kovinski atom. Na osnovi meritev prevodnosti predpostavljamo, da je NiIIL2Cl2 1:2 elektrolit, ostali kompleksi pa niso elektroliti. C. Spinu, A. Kriza: Co(II), Ni(II) and Cu(II) Complexes of Bidentate Schiff Bases.