untitled European Journal of Chemistry 4 (3) (2013) 255‐259 European Journal of Chemistry ISSN 2153‐2249 (Print) / ISSN 2153‐2257 (Online)  2013 EURJCHEM DOI:10.5155/eurjchem.4.3.255‐259.833 European Journal of Chemistry Journal homepage: www.eurjchem.com New lanthanide complexes of 1,1`‐bis[(2‐thienylmethylidene)hydrazono‐1‐ ethyl]‐ferrocene and 1,1`‐bis(2,3‐dihydro‐2‐methylbenzo[d]thiazol‐2‐yl) ferrocene: Synthesis, characterization and antimicrobial properties Wael Hussein Hegazy Department of Chemistry, Faculty of Science, Suez University, Suez, 43533, Egypt *Corresponding author at: Department of Chemistry, Faculty of Science, Suez University, Suez, 43533, Egypt. Tel.: +20.100.7777180; fax: +20.2.33033059. E‐mail address: whchemistry@hotmail.com (W.H. Hegazy). ARTICLE INFORMATION ABSTRACT Received: 18 May 2013 Received in revised form: 11 June 2013 Accepted: 14 June 2013 Online: 30 September 2013 KEYWORDS In this paper; synthesis, characterization and biocidal properties of new prepared Sc(III), Y(III), La(III) and Ce(III) complexes with the two ferrocenyl ligands of 1,1`‐bis[(2‐ thienylmethylidene)hydrazono‐1‐ethyl]ferrocene and 1,1`‐bis(2,3‐dihydro‐2‐methylbenzo[d] thiazol‐2‐yl)ferrocene are reported. These organometallic compounds are potential ligands for lanthanide metal ions. The composition of these complexes is discussed on the basis of elemental analysis, IR, NMR, magnetic moments, electronic absorption spectra and conductivity measurements. In vitro antimicrobial activity of the prepared complexes was screened. All complexes showed remarkable antibiotic activity. Scandium complexes are very effective towards Salmonella spp. Sc‐L2 complex found to have inhibition activity against B. subtilis more than the standard drugs. Antibiotics Complexes Lanthanoids Ferrocenyl ligands Bioinorganic chemistry Organometallic compounds 1. Introduction In the past few years, the versatile chemistry of ferrocene has attracted the attention of many researchers [1‐13]. It has been used as a precursor for the preparation of coordination and biologically active compounds. Ferrocene is nontoxic and has a unique structure as well as an excellent redox property, allowing wide applications in medicinal chemistry. These interesting applications of ferrocenyl compounds resulted in several reports of hetero‐bimetallic complexes [14‐17], since some ferrocenyl complexes showed enhanced biological activity compared to parent ligand. The aim of this work is to prepare a series of lanthanide complexes with two ferrocenyl ligands and to characterize the structure of these complexes. The antibacterial activities of the prepared complexes were assessed against Gram‐positive bacteria B. subtilis and S. aureus and Gram‐negative bacteria E. coli, S. typhi and Salmonella spp. 2. Experimental All chemicals and solvents (AR) were obtained from Merck except absolute ethanol was (Sigma‐Aldrich). Sc(NO3)3·xH2O 99%, Y(NO3)3·6H2O 99%, Ce(NO3)3·6H2O 99%, and La(NO3)3·6H2O 97% were purchased from BDH (England). 1,1`‐ Diacetyl‐ferrocene was prepared according to Rosenblum and Woodward method [18]. 1,1`‐Bis[(2‐thienylmethylidene) hydrazono‐1‐ethyl]‐ferrocene (L1) and 1,1`‐bis(2,3‐dihydro‐2‐ methylbenzo[d]thiazol‐2‐yl)ferrocene (L2) were synthesized and characterized as described in the literature [15,19]. Yields refer to analytically pure compounds and were not optimized. 1H and 13C NMR was recorded on Perkin Elmer 283B and 300 MHz Varian XL‐300 instruments. IR spectra were recorded on a Perkin Elmer (Spectrum 1000) Fourier‐transform infrared (FT‐ IR) spectrometer, using KBr pellets. Elemental analyses were determined at the College of Science, King Saud University, and the results are in agreement with calculated values. Electronic absorptions were recorded on a Shimadzu UV‐1800 automatic spectrophotometer. Molar Conductance Am, (Ω‐1 cm2 mol‐1), at 25 °C of freshly prepared (0.001 mol.dm‐3) metal chelates in DMF was determined using a YSI‐32 model conductometer. The magnetic susceptibilities were measured using a Sherwood Scientific Ltd. Magnetic susceptibility balance (England). 2.1. Preparation of the complexes A solution of 3 mmol of ligand was refluxed with 4 mmol of Sc(III), Y(III), La(III) or Ce(III) nitrates in 50 cm3 dry absolute ethanol with L1 and in methanol with L2 for about 5 h, cooled to room temperature, filtered, washed and dried. The separated complexes recrystallized from dry ethanol, and dried. The physical properties of the prepared complexes are stable under ordinary conditions (Figure 1 and 2). 1,1`‐Bis[(2‐thienylmethylidene)hydrazono‐1‐ethyl]‐ferrocene (L1): C24H22FeN4S2. Yield: 67%. M.p.: 89 °C. FT‐IR (KBr, ν, cm‐1): 1659 (s ‐C=N), 1520 (s ‐C=C thiophene), 1043 (m N‐N), 854 (m C‐S‐C ring). 1H NMR (300 MHz, CDCl3, δ, ppm): 2.21 (s, 6H, 2CH3), 4.21 (m 4H, C5H4), 4.43 (m, 4H, C5H4), 6.71‐7.55 (m, 6H thiophene ring), 8.36 (s, 2H, H‐C=N). 13C NMR (75 MHz, DMSO‐ d6, δ, ppm): 22.9, 68.8, 69.6, 73.1, 146.6, 121.3, 124.8, 139.8, 144.5. UV/Vis (CHCl3, λmax, nm): 456. Anal. calcd. for C24H22FeN4S2: C, 59.26; H, 4.56; N, 11.52. Found: C, 59.29; H, 4.49; N, 11.51 %. 1,1`‐Bis[(2‐thienylmethylidene)hydrazono‐1‐ethyl]ferrocene scandium nitrate (Sc‐L1): C24H22FeScN7O9S2. Yield: 63%. M.p.: >360 °C. FT‐IR (KBr, ν, cm‐1): 1642 (s ‐C=N), 1630, 1310 (m ‐ NO3), 1511 (s ‐C=C thiophene), 1026 (m N‐N), 821 (m C‐S‐C 256 Hegazy / European Journal of Chemistry 4 (3) (2013) 255‐259 ring), 422 (w Sc‐N), 369 (w Sc‐S). 1H NMR (300 MHz, CDCl3, δ, ppm): 2.32 (s, 6H, 2CH3), 4.42 (m 4H, C5H4), 4.61 (m, 4H, C5H4), 6.82‐7.81 (m, 6H thiophene ring), 8.49 (s, 2H, H‐C=N). 13C NMR (75 MHz, DMSO‐d6, δ, ppm): 23.3, 69.1, 70.4, 73.6, 146.9, 122.1, 124.9, 140.3, 144.8. UV/Vis (CHCl3, λmax, nm): 239, 456. Anal. calcd. for C24H22FeScN7O9S2: C, 40.18; H, 3.09; N, 13.67. Found: C, 40.31; H, 3.21; N, 13.71 %. AM (Ω‐1 cm2 mol‐1): 84.32. µeff = diamagnetic. 1,1`‐Bis[(2‐thienylmethylidene)hydrazono‐1‐ethyl]ferrocene yttrium nitrate (Y‐L1): C24H22FeYN7O9S2. Yield: 54%. M.p.: >360 °C. IR (KBr, ν, cm‐1): 1638 (s ‐C=N), 1561, 1342 (m ‐NO3), 1494 (s ‐C=C thiophene), 1032 (m N‐N), 834 (m C‐S‐C ring), 415 (w Y‐N), 374 (w Y‐S). 1H NMR (300 MHz, CDCl3, δ, ppm): 2.31 (s, 6H, 2CH3), 4.44 (m 4H, C5H4), 4.58 (m, 4H, C5H4), 6.84‐7.80 (m, 6H thiophene ring), 8.53 (s, 2H, H–C=N). 13C NMR (75 MHz, DMSO‐d6, δ, ppm): 23.4, 68.9, 70.6, 74.5, 147.3, 123.1, 125.5, 141.2, 145.3. UV/Vis (CHCl3, λmax, nm): 247, 456. Anal. calcd. for C24H22FeYN7O9S2: C, 37.86; H, 2.91; N, 12.88. Found: C, 37.21; H, 3.05; N, 12.91 %. AM (Ω‐1 cm2 mol‐1): 2.41. µeff = diamagnetic. 1,1`‐Bis[(2‐thienylmethylidene)hydrazono‐1‐ethyl]ferrocene lanthanum nitrate (La‐L1): C24H22FeLaN7O9S2. Yield: 59%. M.p.: >360 °C. IR (KBr, ν, cm‐1): 1643 (s ‐C=N), 1587, 1296 (m ‐NO3), 1502 (s ‐C=C thiophene), 1041 (m N‐N), 831 (m C‐S‐C ring), 426 (w La‐N), 377 (w La‐S). 1H NMR (300 MHz, CDCl3, δ, ppm): 2.29 (s, 6H, 2CH3), 4.51 (m 4H, C5H4), 4.54 (m, 4H, C5H4), 6.79‐ 7.72 (m, 6H thiophene ring), 8.57 (s, 2H, H–C=N). 13C NMR (75 MHz, DMSO‐d6, δ, ppm): 23.3, 69.3, 71.2, 73.8, 147.1, 122.4, 125.2, 140.6, 145.2. UV/Vis (CHCl3, λmax, nm): 221, 456. Anal. calcd. for C24H22FeLaN7O9S2: C, 35.53; H, 2.73; N, 12.08. Found: C, 34.98; H, 2.75; N, 12.52 %. AM (Ω‐1 cm2 mol‐1): 3.57. µeff = diamagnetic. 1,1`‐Bis[(2‐thienylmethylidene)hydrazono‐1‐ethyl]ferrocene cerium nitrate (Ce‐L1): C24H22FeCeN7O9S2. Yield: 58%. M.p.: >360 °C. IR (KBr, ν, cm‐1): 1650 (s ‐C=N), 1576, 1322 (m ‐NO3), 1496 (s ‐C=C thiophene), 1033 (m N‐N), 835 (m C‐S‐C ring), 432 (w Ce‐N), 364 (w Ce‐S). 1H NMR (300 MHz, CDCl3, δ, ppm): 2.31 (s, 6H, 2CH3), 4.46 (m 4H, C5H4), 4.56 (m, 4H, C5H4), 6.83‐ 7.84 (m, 6H thiophene ring), 8.54 (s, 2H, H–C=N). 13C NMR (75 MHz, DMSO‐d6, δ, ppm): 23.0, 69.2, 71.3, 74.2, 147.3, 122.6, 125.3, 140.4, 145. UV/Vis (CHCl3, λmax, nm): 358, 371, 456. Anal. calcd. for C24H22FeCeN7O9S2: C, 35.47; H, 2.73; N, 12.11. Found: C, 35.57; H, 2.81; N, 12.11 %. AM (Ω‐1 cm2 mol‐1): 2.13. µeff = 2.51 µB. N N S N N S Fe Sc O N O O O N O O NO3 Figure 1. Suggested structure of L1 complexes, M= Y, La or Ce. HN S Fe HN S Sc O N O O O N O O O N O O Figure 2. Suggested structure of L2 complexes, M: La or Ce. 1,1`‐Bis(2,3‐dihydro‐2‐methylbenzo[d]‐thiazol‐2‐yl)‐ ferrocene (L2): C26H24FeN2S2. Yield: 84%. M.p.: 63‐65 °C. IR (KBr, ν, cm‐1): 3,294 (N‐H), 1,455 (C=C, Fc moiety), 1,112 (C–C, Fc moiety), 1,028 (δ C‐H, Fc moiety), 844 (C‐S‐C), 806 (π C‐H, Fc moiety), 487 (δ Fe‐ring). 1H NMR (300 MHz, CDCl3, δ, ppm): 2.11 (s, 6H, 2CH3 in Fc), 4.80 (m, 4H, C5H4), 5.00 (m, 4H, C5H4), 5.63 (s, 2H, NH), 6.62‐7.32 (m, 8H, Ph). 13C NMR (75 MHz, DMSO‐d6, δ, ppm): 24.8, 68.4, 69.6, 72.7, 78.9, 118.8, 127.5, 138.3, 146.5. UV/Vis (CHCl3, λmax, nm): 454. Anal. calcd. for C26H24FeScN5O9S2: C, 64.46; H, 4.99; N, 5.78. Found: C, 64.52; H, 4.82; N, 5.67%. 1,1`‐Bis(2,3‐dihydro‐2‐methylbenzo[d]‐thiazol‐2‐yl)‐ ferrocene scandium nitrate (Sc‐L2): C26H24FeScN5O9S2. Yield: 67%. M.p.: >360 °C. IR (KBr, ν, cm‐1): 3287 (N‐H), 1588, 1289 (m ‐NO3), 1456 (C=C, Fc moiety), 1121 (C‐C, Fc moiety), 1027 (δ C‐H, Fc moiety), 822(C‐S‐C), 804 (π C‐H, Fc moiety), 480 (δ Fe‐ring), 384 (w Sc‐S). 1H NMR (300 MHz, CDCl3, δ, ppm): 2.32 (s, 6H, 2CH3 in Fc), 4.85 (m, 4H, C5H4), 5.08 (m, 4H, C5H4), 5.82 (s, 2H, NH), 6.82‐7.61(m, 8H, Ph). 13C NMR (75 MHz, DMSO‐d6, δ, ppm): 25.2, 68.9, 70.6, 73.2, 79.4, 120.3, 128.6, 140.3, 148.5. UV/Vis (CHCl3, λmax, nm): 248, 454. Anal. calcd. for C26H24FeScN5O9S2: C, 43.65; H, 3.59; N, 9.88. Found: C, 43.38; H, 3.59; N, 9.88 %. AM (Ω‐1 cm2 mol‐1): 3.68. µeff = diamagnetic. 1,1`‐Bis(2,3‐dihydro‐2‐methylbenzo[d]‐thiazol‐2‐yl)‐ ferrocene yttrium nitrate (Y‐L2): C27H28FeYN5O10S2. Yield: 52%. M.p.: >360 °C. IR (KBr, ν, cm‐1): 3585 (OH methanol), 3282 (N‐ H), 1611, 1324 (m‐NO3), 1457 (C=C, Fc moiety), 1116 (C‐C, Fc moiety), 1027 (δ C‐H, Fc moiety), 833 (C‐S‐C), 808 (π C‐H, Fc moiety), 478 (δ Fe‐ring) 391 (w Y‐S). 1H NMR (300 MHz, CDCl3, δ, ppm): 2.34 (s, 6H, 2CH3 in Fc), 3.38 (s, 3H, methanol CH3), Hegazy / European Journal of Chemistry 4 (3) (2013) 255‐259 257 1.12 (s, 1H methanol OH), 4.91 (m, 4H, C5H4), 5.11(m, 4H, C5H4), 5.84 (s, 2H, NH), 6.84‐7.62 (m, 8H, Ph). 13C NMR (75 MHz, DMSO‐d6, δ, ppm): 25.1, 47.2, 68.6, 70.2, 72.9, 79.3, 123.1, 127.9, 140.6, 147.3. UV/Vis (CHCl3, λmax, nm): 262, 454. Anal. calcd. for C27H28FeYN5O10S2: C, 41.92; H, 3.65; N, 9.05. Found: C, 42.16; H, 3.51; N, 9.17 %. AM (Ω‐1 cm2 mol‐1): 3.09. µeff = diamagnetic. 1,1`‐Bis(2,3‐dihydro‐2‐methylbenzo[d]‐thiazol‐2‐yl)‐ ferrocene lanthanum nitrate (La‐L2): C28H32FeLaN5O11S2. Yield: 61%. M.p.: >360 °C. IR (KBr, ν, cm‐1): 3592 (OH methanol), 3301 (N‐H), 1628, 1275 (m‐NO3), 1460 (C=C, Fc moiety), 1119 (C‐C, Fc moiety), 1029 (δ C‐H, Fc moiety), 834 (C‐S‐C), 805 (π C‐ H, Fc moiety), 476 (δ Fe‐ring) 389 (w La‐S). 1H NMR (300 MHz, CDCl3, δ, ppm): 2.29 (s, 6H, 2CH3 in Fc), 3.40 (s, 3H, methanol CH3), 1.15 (s, 1H, methanol OH), 4.87 (m, 4H, C5H4), 5.06 (m, 4H, C5H4), 5.79 (s, 2H, NH), 6.86‐7.64 (m, 8H, Ph). 13C NMR (75 MHz, DMSO‐d6, δ, ppm): 24.9, 47.1, 68.7, 70.4, 73.2, 79.6, 119.5, 128.1, 139.7, 147.9. UV/Vis (CHCl3, λmax, nm): 232, 454. Anal. calcd. for C28H32FeLaN5O11S2: C, 38.49; H, 3.69; N, 8.02. Found: C, 38.53; H, 3.70; N, 7.99 %. AM (Ω‐1 cm2 mol‐1): 2.73. µeff = Diamagnetic. 1,1`‐Bis(2,3‐dihydro‐2‐methylbenzo[d]‐thiazol‐2‐yl)‐ ferrocene cerium nitrate (Ce‐L2): C28H32FeCeN5O11S2. Yield: 56%. M.p.: >360 °C. IR (KBr, ν, cm‐1): 3479 (OH methanol), 3285 (N‐H), 1572, 1309 (m‐NO3), 1454 (C=C, Fc moiety), 1114 (C‐C, Fc moiety), 1023 (δ C‐H, Fc moiety), 829 (C‐S‐C), 806 (π C‐ H, Fc moiety), 484 (δ Fe‐ring) 388 (w Ce‐S). 1H NMR (300 MHz, CDCl3, δ, ppm): 2.32 (s, 6H, 2CH3 in Fc), 3.38 (s, 3H, methanol CH3), 1.07 (s, 1H, methanol OH), 4.83 (m, 4H, C5H4), 5.04 (m, 4H, C5H4), 5.90 (s, 2H, NH), 6.87‐7.62 (m, 8H, Ph). 13C NMR (75 MHz, DMSO‐d6, δ, ppm): 25.1, 47.1, 69.3, 70.5, 73.1, 79.5, 120.7, 128, 140.2, 148.4. UV/Vis (CHCl3, λmax, nm): 375, 387, 454. Anal. calcd. for C28H32FeCeN5O11S2: C, 38.44; H, 3.69; N, 8.01. Found: C, 38.21; H, 3.43; N, 7.54%. AM (Ω‐1 cm2 mol‐1): 2.54. µeff = 2.46 µB. 2.2. Antimicrobial activity 2.2.1. Preparation of the discs The complex (30 μg) in DMF (0.01 cm3) was mounted on a paper disc (prepared from blotting paper (5 mm diameter)) with the help of micropipette. The discs were left at room temperature till dryness and then applied on the microorganism‐grown agar plates. 2.2.2. Preparation of agar plates Minimal agar was used for the growth of specific microbial species. The preparation of agar plates for B. subtilis, S. aureus, E. coli, S. typhi and Salmonella spp. utilized nutrient agar (2.30 g; obtained from Panreac Quimica SA, Spain). 2.2.3. Application of the discs Sterilized forceps were used for the application of the paper disc on previously inoculated agar plates. When the discs were applied, they were incubated at 37 °C for 24 h. The zone of inhibition around the disc was then measured in millimeters [20]. 3. Results and discussion 3.1. Synthesis and characterization of the ligands 1,1`‐Diacetylferrocene dihydrazone was prepared by dissolving 1,1`‐diacetyl‐ferrocene in small amount of dry ethanol and in presence of excess of hydrazine hydrate while stirring under nitrogen atmosphere. The ligand L1, 1,1`‐bis[(2‐ thienylmethylidene)hydrazono‐1‐ethyl]ferrocene was prepa‐ red by addition of 2‐thiophenealdehyde to 1,1`‐diacetyl‐ ferrocene dihydrazone in ∼2:1 molar ratio in ethanol with reflux for 2h [15]. Characterization of the ligand L1 was confirmed from the elemental analysis, IR, 1H NMR and 13C NMR spectra. It was found that the band at 1659 cm‐1 due to ‐ C=N became stronger and broader than that of the dihydrazone. This may be due to the formation of another two ‐ C=N bonds in the ligand. It was also noted that new bands appeared in the 1H NMR spectrum at 6.71‐7.55 ppm, which were assigned to the thiophene ring protons. The proton in the H–C=N group appeared at 8.36 ppm in the 1H NMR spectrum. 13C NMR spectrum (in ppm) is at 22.9, 68.8, 69.6, 73.1 (ferrocenyl), 146.6 (C=N), 121.3, 124.8, 139.8, 144.5 ppm (thiophene). In the UV‐Vis spectra, a broad band centered at 456 nm was noted for the ligand. This band was attributed to charge transfer 1A1g → 1E1g in the ferrocenyl group (transition of the 3d electrons on iron to either the nonbonding or the antibonding orbitals of the cyclopentadienyl ring) [21]. The ligand is red in color, soluble in MeOH, C2H5OH, dimethylformamide, CH2Cl2 and CHCl3 and it was purified by crystallization from CHCl3. The ligand L2, 1,1`‐bis(2,3‐dihydro‐2‐methylbenzo[d] thiazol‐2‐yl)ferrocene was prepared from the reaction of 1,1`‐ diacetylferrocene with 2‐aminothiophenol using 1:2 molar ratio [19]. The ligand L2 was characterized from the elemental analysis, IR, 1H NMR and 13C NMR spectra. In the IR spectra, no bands were found due to the ferrocenyl ‐C=N or ‐SH groups. A new broad band centered at 3294 cm‐1 was found in the spectra of ligand, this band was assigned to the N–H bond. Another medium band appeared at 844 cm‐1 which was assigned to the C‐S‐C (ring) stretching vibration. The characteristic peaks of the ferrocenyl moiety occurred at about 1112, 1028, 806, and 487 cm‐1. These bands were attributed to ν(C–C), δ(C–H), π(C– H), and δ (Fe‐ring), respectively. In the 1H NMR spectra of ligand L2, the signal of the two methyl groups occurred at 2.11 ppm and the spectra showed a peak at 5.63 ppm, which was assigned to the N–H group. The protons of the ferrocenyl moiety appeared as two multiplets at 4.80 and 5.00 ppm. These signals were assigned to the α‐ and β‐protons of the substituted cyclopentadienyl rings. The signals of the phenyl protons occurred at (6.62‐7.32) ppm. The spectra showed that no signal at 3.5 ppm was found due to the proton of SH groups. 13C NMR spectrum (in ppm) is at 24.8 (2 CH3), 68.4 (tert. carbon), 69.6, 72.7, 78.9 (ferrocenyl), 118.8, 127.5, 138.3, 146.5 (aromatic). In the UV–Vis spectra, a weak broad band centered at 454 nm were noted for the ligand. This band was attributed to charge transfer 1A1g → 1E1g in the ferrocenyl group. The ligand is deep orange in color, soluble in CH3OH, C2H5OH, dimethylformamide and dimethylsulphoxide and it was purified by crystallization from ethanol. 3.2. Synthesis and characterization of the complexes Reactions of Sc(NO3)3.xH2O, Y(NO3)3.6H2O, La(NO3)3.6H2O and Ce(NO3)3.6H2O with L1, were performed in dry absolute ethanol while with L2 were performed in methanol. The complexes show 1:1, metal:ligand ratio as indicated by their analyses. The IR spectra of the complexes of L1 exhibit strong bands at (1638‐1643) cm‐1 assigned to ‐C=N and are shifted to lower frequencies than that of the free ligand 1659 cm‐1. This shift indicates that the azomethine nitrogens are involving in coordination. It was also found that the medium band due to N‐ N in the free ligand at 1043 cm‐1 was shifted to lower frequency by 10‐17 cm‐1 in the complexes. This shift indicates the bonding in the complexes were through the nitrogen atom. The medium intensity band at 854 cm‐1 observed in the free ligand assigned to C‐S‐C (ring) stretching vibration [22] was shifted to lower frequencies by (18‐33) cm‐1 for all complexes that indicates the participation of the sulfur atom in the bonding with the metal ions. 258 Hegazy / European Journal of Chemistry 4 (3) (2013) 255‐259 Table 1. Antimicrobial activity data for the complexes *. Compound Diameter of the inhibition zone B. subtilis S. aureus E. coli S. typhi Salmonella spp. L1 11.5 10.4 12.4 10.3 7.4 Sc‐L1 16.4 15.3 15.3 14.8 18.6 Y‐L1 15.7 16.2 14.6 13.1 14.8 La‐L1 17.1 16.1 16.1 14.8 15.4 Ce‐L1 16.0 15.8 15.8 13.9 13.7 L2 10.2 11.7 9.5 7.6 6.8 Sc‐L2 19.4 17.2 15.7 15.6 19.3 Y‐L2 18.2 18.7 14.5 14.5 15.2 La‐L2 18.1 17.1 14.8 14.4 14.1 Ce‐L2 18.0 15.9 14.6 13.5 13.3 Ampicillin 18.2 16.7 14.0 15.4 14.5 Tetracycline 16.5 15.1 17.4 17.6 19.2 Chloramphenicol 18.8 19.8 18.3 16.5 20.1 * Inhibition zone diameter mm (% inhibition): 6‐10 (27‐45%); 10‐14 (45‐64%); 14‐18 (64‐82%); 18‐22 (82–100%). Percent inhibition values are relative to inhibition zone (22 mm) of the most active compound with 100% inhibition. Two new sets of bands are observed at 1561, 1587, 1576 cm‐1 and 1342, 1296, 1322 cm‐1 for the Y‐L1, La‐L1 and Ce‐L1, respectively. These bands are assigned to symmetric and asymmetric stretching modes of NO3 as ligands under C2V symmetry. The separation of the two sets is large (219, 291, 254 cm‐1) confirming the bidentate character of the nitrate as a ligand. In the low IR wavenumbers region, two new weak bands at 415‐432 and 364‐377 cm‐1, were also observed in the complexes and not found in the free ligand and they are attributed to M‐N and M‐S bonds in the complexes. The 1H NMR spectra of the ligand and complexes were recorded at room temperature in CDCl3; they showed two multiplets for the α‐ and β‐protons for the substituted cyclopentadienyl rings appearing at (4.43 and 4.21 ppm) for the ligand and 4.61‐4.54 and 4.51‐4.42 ppm for the complexes. The signal appearing at 8.36 ppm (H‐C=N) in the ligand was shifted down field to (8.57‐8.49) ppm for the complexes confirming the coordination through the azomethine nitrogen's and sulfur atoms [20,23]. The 13C NMR spectra of the complexes showed the same signals of the ligand slightly shifted downfield which may be due to coordination. On the other hand, comparing the IR frequencies (given in the experimental section) of L2 with its complexes, we cannot observe remarkable shifts except for the C‐S‐C stretching frequency where there is shifting to lower frequencies by 10‐22 cm‐1. This shift indicates the bonding in the complexes were through the sulfur atoms. Two new sets of bands are observed at 1588, 1611, 1628, 1572 cm‐1 and 1289, 1324, 1275, 1309 cm‐ 1 for the Sc‐L2, Y‐L2, La‐L2 and Ce‐L2, respectively. These bands are assigned to ν4 and ν1 modes of NO3 as ligands under C2V symmetry, which suggest that the nitrate anions in the complexes are covalently bonded and are present inside the coordination sphere [24]. As noted above, the separation of the two sets are large (299, 287, 253, 263 cm‐1) confirming the bidentate character of the nitrate as a ligand [25]. One new week band attributed to M‐S vibrations also created in the complexes spectra at 384‐391 cm‐1. New bands are observed at 3585, 3582, 3479 cm‐1 for Y‐L2, La‐L2 and Ce‐L2, respectively, representing the OH stretching vibrations of the methanol ligand. The 1H and 13C NMR spectra of complexes (Sc‐L2, Y‐L2, La‐ L2 and Ce‐L2) were recorded at room temperature using deuterated dimethyl sulfoxide (DMSO‐d6) as solvent. The spectra of the complexes showed slight downfield shift compared with the spectra of L2, which may be due to coordination of sulfur atoms to the metal ion. New chemical shifts are observed in NMR spectra at 3.38, 1.12 pm; 3.40, 1.15 ppm and 3.38, 1.07 ppm and at 47.2 pm; 47.1 ppm; and 46.8 ppm in Y‐L2, La‐L2 and Ce‐L2, respectively. These 1H and 13C NMR shifts are characteristic for methanol inside the coordination sphere. Magnetic moment data show that Sc(III), Y(III) and La(III) complexes are diamagnetic, while Ce(III) complexes have magnetic moments 2.51 and 2.46 BM for Ce‐L1 and Ce‐L2, respectively which agree well with the expected values of Ce(III) complexes due to the presence of 4f electrons whose effectively shielded by 5s25p66s2 electrons. The molar conductivity of the complexes (0.001 mol dm‐3 in DMF) were measured at 25 °C using YSI‐32 model conductometer. The results for all complexes except Sc‐L1 were in the range 2.13‐3.57 Ω‐1 cm2 mol‐1, which means that these complexes are neutral, whilst the molar conductance of complex Sc‐L1 was 84.3 Ω‐1 cm2 mol‐1 suggesting the presence of nitrate anion. The electronic spectra of ligands and their corresponding lanthanide (III) complexes are recorded in in the region 200‐ 900 nm. The ligands L1 and L2 Show weak bands at 456 and 454 nm, respectively. The broad bands observed at (239 for Sc‐ L1 and 248 nm for Sc‐L2), (247 nm for Y‐L1, 262 nm for Y‐L2) and (221 nm for La‐L1, and 232 nm for La‐L2) complexes are attributed to ligand to metal charge transfer (LMCT). Although the f‐f transition is forbidden by the Laporte rule, the electronic spectra of Ce‐L1 and Ce‐L2 show high intensity bands in the near UV region at (358, 371 nm for Ce‐L1) and (375, 387 nm for Ce‐L2) which are due to 4f→5d transition [18,26]. On the basis of the physical and spectral data of the complexes, one can assume that L1 bonded to the metal(III) ions through one of the azomethine nitrogen atoms and the thiophene sulfur atom and they complete their coordination number 8, 10, 10 and 10 (Sc‐L1, Y‐L1, La‐L1 and Ce‐L1, respectively) by nitrate anions as represented in Figure 1, while L2 bonded to the metal(III) ions as represented in Figure 2 with coordination numbers 8, 9, 10 and 10 for Sc‐L2, Y‐L2, La‐ L2 and Ce‐L2, respectively. In the last three complexes methanol molecule appears as a monodentate ligand, which is elucidated by elemental analysis, IR and NMR. Many disappointing unsuccessful trials are made to prepare single crystal for X‐ray analysis. 3.3. Antimicrobial activity In vitro antibacterial screening activity of the prepared ligands and their lanthanide complexes with trivalent Sc, Y, La and Ce were carried out successfully with B. subtilis, S. aureus, E. coli, S. typhi and Salmonella spp., (obtained from microbial genetics department, National Research Center, Giza, EGYPT), using paper disc method on appropriate nutrient medium. The results included in Table 1 revealed that the complexes are more effective than their parent ligands. Complexes of L2 show great efficiency towards B. subtilis and S. aureus to the extent that Sc‐L2 has inhibition activity against B. subtilis more than the standard drugs. Scandium complexes are very effective towards Salmonella spp. All complexes showed remarkable Hegazy / European Journal of Chemistry 4 (3) (2013) 255‐259 259 antibiotic activity compared with the standard drugs (Ampicillin, tetracycline and chloramphenicol). 4. Conclusion The present work reported the preparation and characterization of new organometallic lanthanide complexes using physical and spectral techniques. The new complexes are screened in vitro as antibiotics for some Gram‐positive and Gram‐negative bacteria. The results reveal that the complexes possess significant antibacterial activity compared with standard antibiotics, ampicillin, tetracycline and chloram‐ phenicol. Scandium complexes are very effective towards Salmonella spp. Sc‐L2 complex found to have inhibition activity against B. subtilis more than the given standard drugs. 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