Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Indian Journal of Chemistry Vol 49, December 2010, pp.1601-1606 Notes Synthesis and characterization of a new nickel(II) mixed ligand complex with 2-(2'-pyridyl) benzothiazole good biological agent and exhibits excellent hydrogen bonding, making them suitable candidates in medicine and biochemistry. R N Patel*, Anurag Singh, K K Shukla, Dinesh K Patel & V P Sondhiya Experimental Nickel(II) nitrate hexahydrate was purchased from S D Fine-Chemicals, India. All other chemicals used were of synthetic grade and used without further purification. Elemental analyses of the complexes were performed on an Elementar Vario EL III Carlo Erba 1108 analyzer. FAB mass spectra were recorded on a Jeol SX 102/DA 6000 mass spectrometer using xenon (6 kV, 10 mA) as the FAB gas. The accelerating voltage was 10 kV and the spectra were recorded at room temperature. UV-vis spectra were recorded at 25 °C on a Shimadzu UV-visible recording spectrophotometer UV-160 in quartz cells. IR spectra were recorded in KBr medium on a Perkin-Elmer spectrophotometer. Magnetic susceptibility measurements were made on a Gouy balance using mercury(II) tetrathiocynatocobaltate(II) as calibrating agent (χg = 16.44 × 10-6 cgs units). Cyclic voltammetry was carried out on a BAS-100 Epsilon electrochemical analyzer having an electrochemical cell with a three-electrode system. Ag/AgCl was used as the reference electrode, glassy carbon as the working electrode and platinum wire as the auxiliary electrode. NaClO4 (0.1 M) was used as supporting electrolyte and DMSO as solvent. All measurements were carried out at 298 K under a nitrogen atmosphere. The in vitro SOD activity was measured using alkaline DMSO as a source of superoxide radical (O2-) and nitro blue tetrazolium chloride (NBT) as O2- scavenger7. Molar conductivities of the freshly prepared DMSO solutions (2×10-3 M) were measured on a Systronics conductivity TDS meter 308. Crystals suitable for single crystal X-ray analysis for the complex [Ni(L1)](L2)(H2O])(ClO4) were grown by slow evaporation of the reaction mixtures at room temperature. These were mounted on a glass fiber and used for data collection. Crystal data were collected on Enraf-Nonius MACH3 diffractometer using graphite monochromatized Mo-Kα radiation (λ = 0.71073Å). The crystal orientation, cell refinement and intensity measurements were made using the program CAD-4PC performing ψ-scan measure- Department of Chemistry, APS University, Rewa 486 003, (MP), India Email: [email protected] Received 16 August 2010; revised and accepted 18 November 2010 A new complex, [Ni(L1)(L2)(H2O)]ClO4, (L1 = 2-(2′-pyridyl)benzothiazole), L2 = N-[(1)-pyridin-2-ylmethylidene] benzohydrazone), has been synthesized and characterized by various physico-chemical techniques. The nickel atom is coordinated in a distorted octahedral geometry. The metal center is coordinated through azomethine nitrogen, pyridine nitrogens, carbonyl oxygen and one nitrogen atom of L1. Additionally, the pyridyl planes in complex are engaged in intra- and intermolecular hydrogen bonding interactions. Keywords: Coordination chemistry, Nickel, SOD activity, Schiff bases IPC Code: Int. Cl.9 C07F15/04 Nickel(II) complexes containing sulfur have received considerable attention due to the identification of a sulfur-rich coordination environment in biologically active nickel centres, such as the active sites of certain ureases, methyl-S-coenzyme-M-methyl reductase and hydrogenases1. A number of metal complexes with similar type of Schiff base of 2-aminothiophenol have been reported from our laboratory2. The synthesis of low molecular weight nickel(II) complexes mimicking superoxide dismutase (SOD) activity is a challenge for bioinorganic chemists and recently some complexes with high catalytic activity have been reported3. Nickel-containing superoxide dismutase (NiSOD) has been isolated from several Streptomyces species4. The enzymatic activity of NiSOD5 is as high as that of Cu-ZnSOD at about 109 M-1s-1 per metal center. Although numerous organic, inorganic or coordination compounds with antiproliferative activity have been reported6, most of them are excluded from further clinical studies due to their toxicity and numerous undesirable side effects. In the present investigation, the Ni(II) complex of 2-(2′-pyridyl)benzothiazole is a fairly 1602 INDIAN J CHEM, SEC A, DECEMBER 2010 ments. The structures were solved by direct method using the program SHELXS-978 and refined by full-matrix least-squares techniques against F2 using SHELXL-979. All non-hydrogen atoms were refined anisotropically. All the hydrogen atoms were geometrically fixed and allowed to refine using a riding model. For synthesis of the complex, equimolar (1:1) methanolic solutions (10 mL each) of metal salt (NiNO3.6H2O 1.0 mmol, 0.291 g) and L1 (1 mmol, 0.212 g) were mixed and stirring was continued for 30 min at room temperature. To this reaction mixture, ligand L2 (1.0 mmol, 0.225 g) was added after 1 hr and further stirred for 45 min. Finally, to this solution one equivalent of sodium perchlorate was added slowly drop by drop and stirred further for 30 min. The resultant clear solution was left for slow evaporation. After 3-4 days, brownish yellow crystals which were suitable for X-ray crystallography were collected and washed with MeOH and diethyl ether. These were dried in air at room temperature and stored in CaCl2 desiccator, (yield 65%). The empirical formula given for the compound C25H18ClN5NiO6S was confirmed by elemental analysis: Found(calcd): C, 49.01(49.12); H, 2.71(2.94); N, 11.23(11.46)%. Results and discussion By the condensation reaction of 2-pyridinecarboxaldehyde with 2-mercaptoarylamine, a sulfur containing Schiff base ligand, 2-(2′-pyridyl)benzothiazole, is formed. Sulphur containing heteroaromatic Schiff bases easily cyclize under alkaline condition. The Schiff base of such type can undergo elimination reaction through the detachment of atom. Miernicka et al.10 have also reported that the confirmation of detachment of a molecule can be achieved by thermogravimetric analysis. Detachment of hydrogen atom suggests the cyclization of S containing ligand to the 2-(2′-pyridyl)benzothiazole.We successfully performed the cyclization of S containing ligand to its 2-(2′-pyridyl)benzothiazole. The sequential route for the synthesis of complex is given in Scheme 1. X-ray diffraction quality single crystal of the complex [Ni(L1)(L2)(H2O)]ClO4 was obtained by vapor diffusion of methanolic solution of the complex. The ORTEP diagram of complex is shown in Fig. 1 and the related crystal structure refinement data is given in Table 1. Selected bond lengths and angles within the complex are listed in Table 2. Single crystal analysis of complex reveal that the reddish brown complex crystallizes in the monoclinic crystal system with space group P21/c having four molecule in the unit cell. The X-ray data of the complex show that water molecule is present in the coordination sphere. It reveals that the nickel(II) center has a N4O2 coordination moiety and has distorted octahedral geometry. The two ligands are coordinated in the meridonial fashion11. L2 undergoes deprotonation in the presence of metal ion and consequently, the complex of the deprotonated and cyclized ligand is formed in neutral media. Thus, L2 coordinates to the nickel atom as a uninegatively charged chelating agent in its deprotonated hydrazone form via the ketonic oxygen atom, azomethine nitrogen atom and the pyridine nitrogen atom. NH N O N + Methanol, at rt Ni(NO3)2.6H2O + NaClO4 N N O H2O Ni N + N N N S N S Scheme 1 ClO 4 NOTES 1603 Table 1—Crystal data and structural refinement for complex [Ni(L1)(L2)(H2O)]ClO4 Fig. 1—ORTEP diagram of complex [Ni(L1)(L2)(H2O)]ClO4. There is extensive delocalization of the negative charge12, which is generated upon deprotonation of the ligand, in the C-N-N-C chain as indicated by the intermediate C(18)-N(4) = 1.271(4) Å, N(4)-N(5) = 1.317(5) Å and N(5)-C(19)= 1.347(19) Å bond distances. The two Ni-N distances (~2.074Å) are close to the sum of the non-polar covalent radii (2.15 Å) (ref. 13), indicating strong nickel-nitrogen interaction. However, the Ni-N(4)(azo) bond distance (1.991(2) Å) in the present complex is shorter than the Ni-N(2)(azo) distance (2.116(2) Å). The stronger coordination of the nickel atom to the azomethine nitrogen of L2 as compared with the azomethine nitrogen atom of L1 is consistent with the higher basicity of the azomethine nitrogen atom and also a consequence of the atom being shared by the adjacent 5-membered chelate rings. The Ni-N distance in the complex lies within a close range (2.074 Å) and is consistent with the corresponding values of Ni(II)-N system14 but is considerably shorter than the van der waals radii (4.0 Å) (ref. 15). In the octahedral geometry, N3O atoms are involved in the plane whereas a pair of NO atoms is in the apical position. The values obtained in this study are comparable with those obtained previously16. However, the mutual disposition of the ligands deviates noticeable from perpendicularity which is indicated by decreased values of the trans angle, N(4)-Ni-N(1) 173.89°(10), N(3)-Ni-O(1) 155.26°(9) and N(2)-Ni-O(2) 167.69°(9). Individual bond distances and angles within the coordination polyhedron compare well with those found in other octahedral complexes of nickel(II) involving N donor atoms17. The ranges of the cisoid and the transoid angles reflect the degree of distortion from the ideal octahedron geometry. The distortion of the geometry Empirical formula Formula weight Temperature (T) (K) Wavelength (Mo-Kα)(Å) Crystal system Space group Unit cell dimensions a (Å) b (Å) c (Å) α (°) β (°) γ (°) Volume (Å 3) Z Calc. density (mg m-3) Abs. coeff. (mm-1) F(000) Crystal size (mm) θ Range for data collection Limiting indices Reflections collected / Unique reflections Completeness to theta Abs. correction equiv. Max. and min. transmission Refinement method F2 Data / restraints / parameters Goodness-of-fit on F2 Final R indices [I > 2σ (I)] R indices (all data) Largest diff. peak and hole (e.A-3) C25H18ClN5NiO6S 610.66 120(2) 0.71073 Monoclinic P21/c 12.3537(11) 13.5555(9) 15.459(3) 90 100.266(11) 90 2547.3(5) 4 1.592 1.001 1248 0.33 × 0.28 × 0.22 3.07 to 24.99 -14≤ h ≤ 14, -16 ≤ k ≤ 16, -18 ≤ l ≤ 18 19667 4482 [R(int) = 0.0529] 24.99 99.8 % Semi-empirical from 0.8099 and 0.7336 Full-matrix least squares on 4482 / 0 / 352 0.916 R1 = 0.0347, wR2 = 0.0725 R1 = 0.0626, wR2 = 0.0758 0.583 and -0.367 Table 2—Bond lengths and angles of complex Ni(L1)(L2)(H2O)]ClO4 Bond lengths (Å) Ni(1)-N(4) 1.991(2) Ni(1)-N(1) 2.085(2) Ni(1)-O(2) 2.091(2) Ni(1)-N(3) 2.104(2) Ni(1)-O(1) 2.081(2) Ni(1)-N(2) 2.116(2) Bond angles(°) N(4)-Ni(1)-O(2) 92.94(8) O(1)-Ni(1)-N(2) 89.63(9) N(4)-Ni(1)-O(1) 76.63(9) N(1)-Ni(1)-N(2) 79.27(10) O(2)-Ni(1)-O(1) 88.61(8) N(3)-Ni(1)-N(2) 95.05(9) N(4)-Ni(1)-N(1) 173.89(10) O(2)-Ni(1)-N(3) 91.63(9) O(2)-Ni(1)-N(1) 89.78(9) O(1)-Ni(1)-N(3) 155.26(9) O(1)-Ni(1)-N(1) 108.93(9) N(1)-Ni(1)-N(3) 95.81(9) N(4)-Ni(1)-N(3) 78.65(10) N(4)-Ni(1)-N(2) 98.50(10) Symmetry transformations used to generate equivalent atoms. is also evidenced from the rms deviations and dihedral angles of the planes. The dihedral angle formed by the two least square planes is equal to 88.49° (0.07), which confirms the non-coplanarity of the two rings. The deviation from octahedral geometry is due to the restricted bite size of the ligand. The C-S bond distance (1.746 Å) being similar 1604 INDIAN J CHEM, SEC A, DECEMBER 2010 to that in the free ligand, is indicative of non-coordination of S atom in the complex. Similarly, the N(4)-N(5) bond distance (1.377(3) Å) is closer to the single bond length (1.45 Å) rather than a double bond length(1.25 Å) (ref. 18). The packing of the molecule in a unit cell is shown in Fig. 2. The unit cell is viewed down the ‘c’-axis and four molecules of the complex are arranged in the unit cell. It is evident from the figure that the complex exhibit a 2D supramolecular architecture arising from two types of hydrogen bonding interactions (Table 3). The solvent water molecule (O2W), amine nitrogens (N(4), N(5) and N(1), enolic sulfur and carbonyl oxygen (O1) atom play a vital role in the formation of the 2D sheet through intra-molecular hydrogen bonding interactions. Four neighboring mononuclear units are held together through inter-molecular interactions generated by anionic oxygen atoms. These two types Fig. 2—Unit cell packing diagram of complex Ni(L1)(L2)(H2O)]ClO4. of hydrogen bonding are interwoven and facilitate the formation of a 2D supramolecular sheet in the c-axis (Fig. 2). The C-N (2.845 Å) and C-O (2.793 Å) distances between hydrogen bonded groups are indicative of the presence of moderate directional hydrogen bonding, which may be used in crystal engineering19. The paramagnetic nickel(II) complexes are characterized by two main absorptions bands at about 300 and 400 nm. These bands are present in [Ni(L1)(L2)(H2O)](ClO4) complex. The complex shows three strong absorption and one weak absorption [3A2g→3T2g, (11499 cm-1 (0.2)υ1), 3 A2g→3T1g (F) (14286 cm-1 (0.8)υ2), 3A2g→3T1g (P) (26316 cm-1 (3.0) υ3)], characteristic of regular octahedral nickel(II) complex16. The medium intensity band around 1610 cm-1 due to ν(C=N)16 of L2 shifts to 1590-1600 cm-1 in the complex, indicating the azomethine coordination to the metal through nitrogen. The coordination of the azomethine nitrogen is further evidenced by the presence of a new band in the range 450-490 cm-1, assignable to ν(Ni-N) for this complex20. Two bands are clearly observed at 3420 cm-1 s (ν(OH)assym) and 3330 cm-1 mw (ν(OH)sym) for the coordinated water molecule21. The presence of bands at ~ 1100 cm-1 and ~ 625 cm-1 indicates that the Td symmetry of ClO4- is maintained in the complex. This therefore, suggests the presence of ClO4- outside the coordination sphere in the complex22. The molar conductivity of the complex was measured in DMSO solution (3 × 10-3M). The molar Table 3—Hydrogen bonding interactions (Å and °) for complex [Ni(L1)(L2)(H2O)]ClO4 D---H....A Intra-molecular C1 -H1 ...O2 (0) C4 -H4 ...S1 (0) C11 -H11 ...N4 (0) C11 -H11 ...N5 (0) C13 -H13 ...N1 (0) C21 -H21 ...N5 (0) C25 -H25 ...O1 (0) C4 -H4 ...O1 (3) Inter-molecular C10 -H10 ...O444 (0) C1 -H1 ...O111 (1) C25 -H25 ...O222 (1) C14 -H14 ...O333 (2) C13 -H13 ...O444 (2) C8 -H8 ...O111 (4) C15 -H15 ...O333 (6) D - H (Å) H...A (Å) D...A (Å) ∠ D - H...A (°) 0.950(.003) 0.950(.003) 0.950(.003) 0.950(.003) 0.950(.003) 0.950(.003) 0.950(.003) 0.950(.003) 2.532(.002) 2.802(.101) 2.627(.002) 2.592(.002) 2.848(.002) 2.543(.003) 2.493(.002) 2.543(.002) 3.086(.004) 3.179(.004) 3.361(.004) 3.476(.004) 3.353(.004) 2.845(.004) 2.793(.004) 3.279(.003) 117.30( 0.20) 104.68( 0.21) 134.36( 0.21) 155.09( 0.21) 114.34( 0.20) 98.59 ( 0.22) 98.29 ( 0.20) 134.36( 0.20) 0.950(.004) 0.950(.003) 0.950(.003) 0.950(.004) 0.950(.003) 0.950(.003) 0.950(.003) 2.782(.002) 2.793(.002) 2.690(.003) 2.838(.003) 2.523(.003) 2.711(.002) 2.597(.003) 3.395(.004) 3.372(.004) 3.367(.004) 3.392(.004) 3.309(.004) 3.385(.004) 3.314(.004) 123.03( 0.21) 120.19( 0.20) 128.76( 0.20) 118.21( 0.21) 140.14( 0.20) 128.47( 0.21) 132.56( 0.21) 0 = x,y,z; 1 = x,+y-1,+z; 2 = x,-y+1/2,+z-1/2; 3 = -x+1,-y,-z+1; 4 = -x+1,-y+1,-z+1; 6 = -x,+y-1/2,- z+1/2; NOTES Fig. 3—Cyclic voltammogram of the ligands, L1 (1) and L2 (2), and, the Ni(II) complex (3) in DMSO. [Conc.: 0.003 mol-1 dm-3; supporting electrolyte: 0.1M NaClO4; scan rate: 200 mV/s]. conductivity value (121 ohm-1cm2mol-1) indicates the presence of 1:1 electrolyte23, suggesting the presence of deprotonated coordination of L2 in solution. The room temperature effective magnetic moment (µeff) of the complex is 2.89 BM. The L1 and L2 along with a water molecule may provide a octahedral geometry around nickel(II). The observed magnetic moment values favor an octahedral geometry. The cyclic voltammogram of complex was recorded in DMSO, with sodium perchlorate as supporting electrolyte. The cyclic voltammogram for nickel(II) complex exhibits metal centered electrochemical process (Fig. 3). The complex shows two reduction peaks corresponding to Ni(II)-Ni(I) and Ni(I)-Ni(0). Although the voltammogram shows two reduction peaks and two oxidation peaks, the oxidation peak of the second redox couple is ill-defined. This may be due to the width of the peak24. The first redox couple is obtained at Epc = -0.431 V and Epa = -0.30 V which may be due to ligand based reduction, whereas the second redox couple is obtained at Epc = -0.768 V and Epa = -0.27 V. Both originate from an irreversible process with a peak-to-peak separation, ∆Ep = -495 V and Ipa/Ipc ratio is less than unity (Ipa/Ipc = 0.45) confirming the irreversible process. The superoxide dismutase activity (SOD) for the present complex was measured. Superoxide was 1605 enzymatically supplied from alkaline DMSO and the SOD activity was evaluated by the NBT assay1 following the reduction of NBT to MF+ kinetically at 560 nm. The observed IC50 value of the present complex was compared with the earlier reported values (43-58 µmol dm-3) for nickel(II) complexes17. The catalytic activity of NiSOD5, however, is on the same high level as that of Cu-ZnSOD at about 109 M-1 s-1 per metal center. The IC50 data of the SOD activity assay of the present complex is 65 µmol dm-3 while the kinetic catalytic constant, kMccF is1.462 ×104 M-1 s-1. In the above study, the synthesis and characterization of [Ni(L1)(L2)(H2O)]ClO4 and L1 is described. L1 undergoes cyclization in basic medium whereas L2 deprotonates in presence of metal and coordinates with the nickel atom as uninegative charged NNO tridentate chelating agent. Both ligand and water molecules bind to the nickel(II) ion and show a distorted octahedral geometry around the nickel center. The various bonding parameters indicate that substantial delocalization occurs within the chelate rings of L2 mediated via in-plane-π-bonding along with σ-donation, thus resulting in an increased structural stability. Metal centered process that is strongly influenced by the nature of binding does not seems to dominate the redox behavior of the complex. It is due to the non coordination behavior of S atom. In general, the oxidation process which occurs at lower potential due to sulfur atom does not favor the coordination through sulfur atom. Supplementary data CCDC 766598 and 766597 contain the supplementary crystallographic data for the ligand L1 and its complex [Ni(L1)(L2)(H2O)]ClO4. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: (+44) 1223-336-033; Email: deposit@ ccdc.cam.ac.uk. Acknowledgement Our grateful thanks are due to the National Diffraction Facility, X-ray Division and RSIC (SAIF), IIT Bombay, Mumbai, for single crystal data collection. The Head RSIC (SAIF), Central Drug Research Institute, Lucknow, is also thankfully acknowledged for providing analytical and spectral facilities. Financial assistance from UGC 1606 INDIAN J CHEM, SEC A, DECEMBER 2010 [Scheme no.36-28/2008 (SR)] and DRDO [Scheme no. ERIP/Er 0603574/m/01/1118], Delhi is also thankfully acknowledged. References 1 2 3 4 5 6 7 8 9 10 Naik A D, Annigeri S M, Gangadharmath U B, Revankar V K & Mahale V B, J Mol Struct, 616 (2002) 119. Patel R N, Gundla V L N & Patel D K, Indian J Chem, 47A (2008) 353. Patel R N, Kesharwani M K, Singh A, Patel D K & Choudhary M, Trans Met Chem, 33 (2008) 733. Stroupe M E, DiDonato M & Tainer J A, Handbook of Metalloproteins, Vol 2, edited by A Messerschmidt, (Wiley, UK) 2001, p. 941. Youn H D, Kim E J, Roe J H, Hah Y C & Kang S O, J Biochem, 318 (1996) 889. Ziegler C J, Silverman A P & Lippard S J, J Bioinorg Chem, 5 (2000) 774. Patel R N, Shukla K K, Singh A, Patel D K, NiclosGutierrez J & Choquesillo-lazarte D, J Coord Chem, 63(20) (2010) 3648. Sheldrick G M, Acta Crystallo, A46 (1990) 467. Sheldrick G M, SHELXL-97. Program for the Refinement of Crystal Structures, (University of Goettingen, Germany) 1997. Miernicka M, Szulawska A, Czyz M, Lorenz I-P, Mayer P, Karwowski B & Budzisz E, J Inorg Biochem, 102 (2008) 157. 11 Garcia I, Bermejo E, El Sawaf A K, Castineiras A & West D X, Polyhedron, 21 (2002) 729. 12 Akbar Ali M, Mirza A H, Ravoof T B S A & Bernhardt P V, Polyhedron, 23 (2004) 2031. 13 Sanderson R T, Inorganic Chemistry (Reinhold, New York) 1967, p. 174. 14 Niu D Z, Sun B W, Lu Z S, Wang Z M & Yan C H, Acta Crystallogr, E57 (2001) M590. 15 Bondi A, J Phys Chem, 68 (1964) 441. 16 Patel R N, Shukla K K, Singh A, Choudhary M, Patel D K, Niclós-Gutiérrez J & Choqusillo-Lazarte D, Trans Met Chem, 23 (2009) 239. 17 Patel R N, Gundla V L N & Patel D K, Polyhedron, 26 (2007) 757. 18 Huheely J E, Keiter E A & Keiter R L, Inorganic Chemistry, Principles of Structure and Reactivity, 4Th Edn, (Harper Collins College, New York) 1993. 19 Rahaman S H, Bose D, Chowdhary H, Mostaffa G, Fun H-K & Ghosh B K, Polyhedron, 24 (2005) 1837. 20 Hathaway B J & Underhill A E, J Chem Soc, (1961) 3091. 21 Vallarino L M, Goedken V L & Quagliano J V, Inorg Chem, 12 (1973) 102. 22 Ali M A, Hossain S M G, Majumdar S M M H, Nazimuddin M & Tarafder M T H, Polyhedron, 6 (1997) 1653. 23 Geary W J, Coord Chem Rev, 78 (1971) 81. 24 Tabbi G, Dressen W L, Reedijk J, Bonomo R P, Veldman N & Spek A L, Inorg Chem, 36 (1997) 1168.