Synthesis, characterization and properties of some ternary ... - NOPR

Indian Journal of Chemistry Vol. 47A, March 2008, pp. 353-360

Synthesis, characterization and properties of some ternary copper(II) complexes containing NOS donor Schiff base and NN donor bidentate ligands R N Patel*, V L N Gundla & D K Patel Department of Chemistry, A.P.S. University, Rewa 486 003, M.P., India Email: [email protected] Received 3 December 2007; revised 6 February 2008 Six ternary copper(II) complexes, viz., [Cu(SAT)(H2O)] (1), [Cu(SAT)(phen)].0.5 H2O (2), [Cu(SAT)(bipy)] (3), [Cu(SAA)(dmp)] (4), [Cu(SAT)(en)] (5) and [Cu(SAT)(temed)] (6), where SAT = Salicylideneaminothiophenol, phen = 1,10-phenanthroline, bipy = 2,2′-bipyridyl, dmp = 2,9-dimethyl 1,10-phenanthroline, en = ethylenediamine, temed = N,N,N′,N′-tetramethylethylinediamine have been synthesized and characterized by various physico-chemical techniques. The metal ligand bonding parameters evaluated from the EPR spectra of the complexes indicate strong in-plane σ and in-plane π bonding. The magnetic and spectroscopic data indicate a square planar geometry for complex 1 and a square pyramidal geometry for remaining complexes. The crystal structure of complex 2 has been determined by X-ray diffraction technique. The superoxide dismutase activity of the complexes has also been measured and discussed. IPC Code: Int. Cl.8 CO7F1/08; CO7C251/02

Transition metal complexes of Schiff bases have been the most widely studied coordination compounds in the past few years due to their unusual magnetic properties, novel structural features and relevance to biological systems1-4. Schiff base ligands particularly molecules possessing nitrogen, oxygen and sulphur donor sites are important in the development of coordination chemistry as well as in the biomimetic chemistry of a number of metal ions, particularly the transition metals5. The ability of nitrogen and/or sulphur based donors to stabilize reduced and oxidized forms of copper(II) has sparked interest in their bioinorganic systems6. Copper is a bioelement and an active site in several metalloenzymes and proteins7−10. The most important contribution to copper chemistry must be the role that biological copper11,12 has played in stimulating research in the inorganic chemistry of copper, not only in the chemistry of copper proteins, for which Cu(I), Cu(II) and Cu(III) species are relevant, but also in systems where more than one type of copper is considered to be present. Another interesting aspect of copper(II) coordination complexes is their biological activity, which is of interest in pharmacology. Copper(II) complexes containing various Schiff bases and their derivatives are of great interest since they exhibit numerous biological acivities such as anticancer13, antitumor14, antibacterial15, antifilarial16 and antiviral17, etc. On the basis of these findings, we

reported recently the synthesis, structure and properties of ternary copper(II) complexes of ONO donor Schiff base, imidazole, 2,2′-bipyridyl, and 1,10-phenanthroline18. We report herein the synthesis, characterization and properties of some copper(II) complexes containing NOS donor Schiff base and NN donor bidentate ligands. The superoxide dismutase activity of the complexes and the crystal structure of [Cu(SAT)(phen)].0.5 H2O (2) have also been described. Materials and Methods Cupric acetate, 1,10-phenanthroline, 2,2′-bipyridyl, 2,9-dimethyl 1,10-phenanthroline, ethylenediamine, N,N,N′,N′-tetramethylethylinesdiamine, CH3OH, CH3CN, CH2Cl2, C4H10O (S.D. Fine Chem.), NaClO4 (Sigma Aldrich) were used as purchased. The Schiff base (SAT) was synthesized by reacting salicylaldehyde and 2-aminothiophenol in an equimolar ration at room temperature in methanol. Elemental analysis was performed on Elementar vario ELIII Carlo Erba 1108 analyser. FAB Mass spectra were recorded on Jeol SX-102/DA 6000 mass spectrometer using Xenon (6 Kv, 10 mA) as the FAB gas. The magnetic susceptibility data were recorded on Gouy balance at room temperature using mercury(II) tetrathiocyanato cobaltate(II) (χg = 16.44 × 10−6 cgs unit) as the calibrant. The EPR spectra were recorded at room temperature (298 K)

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INDIAN J CHEM, SEC A, MARCH 2008

and also at liquid nitrogen temperature (77 K) on Varian E-line Century Series EPR spectrometer operating at 9.4 GHz with TCNE as a calibrant. Electronic spectra were recorded on Schimadzu UVVis 160 spectrophotometer in quartz cells. The IR spectra (400-4000 cm−1) of the complexes were recorded on Varian-3100 FT IR Excaliber Series spectrophotometer with samples prepared as KBr pellets. A BAS-100 Epsilon Electrochemical Analyzer was used for cyclic voltammetric experiments in a DMSO solution of the complex containing NaClO4 as the supporting electrolyte. The three electrode measurement was carried out at 298 K under a nitrogen atmosphere with a platinum working electrode, a platinum wire auxiliary electrode and a silver/silver chloride reference electrode (Ag/AgCl). The SOD activities were evaluated using alkaline DMSO as a source of superoxide radicals (O2−) and nitrobluetetrazolium chloride (NBT) as a scavenger19,20. CAUTION! Perchlorate salts in the presence of organic ligands are potentially explosive. Only a small amount of the materials should be prepared and handled with care.

filtration and washed with a little amount of methanol and then with diethyl ether successively. The solid was dried in air at room temperature and stored in a CaCl2 desiccator. Yield, ~50%. Anal. Calc. for C25H19N3O2SCu (2): C, 66.24; H, 3.88; N, 8.58. Found: C, 63.54; H, 3.72; N, 8.54%. FAB Mass (m/z) Calc.: 471. Found: 471. Complexes 3, 4, 5 and 6 were prepared as described above by employing bipy (1.0 mmol, 156 mg), dmp (1.0 mmol, 208 mg), en (1.0 mmol, 0.06 mL) and temed (1.0 mmol, 0.15 mL) respectively in place of phen. Anal. Calc. for C23H17N3OSCu (3): C, 61.74; H, 3.80; N, 9.39. Found: C, 61.59; H, 3.92; N, 8.95%. FAB Mass (m/z) Calc.: 447. Found: 446. Anal. Calc. for C27H21N3OSCu (4): C, 64.91; H, 4.20; N, 8.41. Found: C, 64.84; H, 4.31; N, 8.20%. FAB Mass (m/z) Calc.: 499.12. Found: 499. Anal. Calc. for C15H17N3OSCu (5): C, 51.30; H, 4.84; N, 11.97. Found: C, 51.42; H, 4.97; N, 11.75%. FAB Mass (m/z) Calc.: 350.85. Found: 351. Anal. Calc. for C19H25N3OSCu (6): C, 56.01; H, 6.14; N, 10.31. Found: C, 55.87; H, 6.23; N, 10.08%. FAB Mass (m/z) Calc.: 407.06. Found: 407. Crystal structure determination

Synthesis of [Cu(SAT)(H2O)] (1)

To a methanolic solution (10 mL) of cupric acetate (1.0 mmol, 199 mg) a methanolic solution (10 mL) of the Schiff base (1.0 mmol, 229 mg) was added with stirring. After stirring the above reaction mixture for 1 h at 25°C, the dark green precipitate thus formed was collected by filtration and washed with a little amount of methanol and then with diethyl ether successively. The solid was dried in air at room temperature and stored in a CaCl2 desiccator. Yield, ~60%. Anal. Calc. for C13H11NO2SCu (1): C, 50.51; H, 3.56; N, 4.53. Found: C, 50.25; H, 3.72; N, 4.55%. FAB Mass (m/z) Calc.: 308.85. Found: 308. Synthesis of [Cu(SAT)(phen)].0.5 H2O (2), [Cu(SAT)(bipy)] (3), [Cu(SAT)(dmp)] (4), [Cu(SAT)(en)] (5) and [Cu(SAT)(temed)] (6)

All of these mixed ligand complexes were prepared by a general procedure. To a methanolic solution of cupric acetate (1.0 mmol, 199 mg) a methanolic solution (10 mL) of the Schiff base (1.0 mmol, 229 mg) was added and the reaction mixture was stirred for 30 min at 25°C. To the above reaction mixture, a methanolic solution (10 mL) of phen (1.0 mmol, 198 mg) was added and the stirring was continued for another 30 min. After completion of the reaction, the wine red precipitate thus formed was collected by

Crystals suitable for single crystal X-ray analysis for the complex [Cu(SAT)(phen)]. 0.5 H2O (2) were grown by slow evaporation of the solution CH2Cl2: CH3OH (2:1, v/v) of the complexes 2 at room temperature. Crystal data were collected on an Oxford Xcalibur-S CCD diffractometer using graphite monochromatized Mo Kα radiation (λ = 0.71073 Å). The crystal orientation, cell refinement and intensity measurements were made using the program CAD-4PC performing psi-scan measurements. The structure was solved by the direct methods using the program SHELXS-9721 and refined by fullmatrix least-squares techniques against F2 using SHELXL-9722. All the hydrogen atoms were refined anisotropically. All the hydrogen atoms were geometrically fixed and allowed to refine using a riding model. Results and Discussion Reaction of equimolar ratios of cupric acetate, Schiff base ligand and the corresponding NN donor bidentate ligands yielded mixed ligand copper(II) complexes in good yield. Complexes 2 and 4 are wine red in color and are highly soluble in CH2Cl2 whereas the remaining complexes are dark green in colour and are soluble in DMSO.

PATEL et al.: SYNTHESIS OF SOME TERNARY COPPER(II) SCHIFF BASE COMPLEXES

Table 1 — Crystal data and structure refinement for [Cu(SAT)(phen)].0.5 H2O (2) Empirical formula

C25H17CuN3O1.5S

Formula weight Temperature (K) Wavelength (Å) Crystal system Space group Unit cell dimensions a (Å) b (Å) c (Å) α (°) β (°) γ (°) Volume (Å3) Z, Calculated density (mg/m3) Absorption coefficient (mm−1) F(000) Crystal size (mm) θ Range for data collection Limiting indices

479.02 120(2) 0.71073 Monoclinic P21/a

11.5157(7) 12.5041(7) 15.2949(11) 90 108.29(7) 90 2091.1(2) 4, 1.522 1.170 980 0.36 × 0.28 × 0.21 3.12° - 25.00° -13 ≤ h ≤ 13, -14 ≤ k ≤ 14, -18 ≤ l ≤ 18 Reflections collected / unique 19365 / 3671 [Rint = 0.1005] 99.7 % Completeness to θ = 25.00° Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.7912 and 0.6780 Refinement method Full-matrix least-squares on F2 Data / restraints/parameters 3671 / 0 / 289 Goodness-of-fit on F2 1.300 R1 = 0.1188, w R2 = 0.2317 Final R indices [I > 2σ (I)] R indices (all data) R1 = 0.1335, w R2 = 0.2377 Largest diff. peak and hole (e Å−3) 1.154 and -1.572

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Table 2 — Selected bond lengths (Å) and angles (º) for [Cu(SAT)(phen)].0.5 H2O (2) Bond lengths Cu(1)-O(1) Cu(1)-N(3) Cu(1)-N(1) Cu(1)-S(1) Cu(1)-N(2) S(1)-C(13) Bond angles O(1)-Cu(1)-N(3) O(1)-Cu(1)-N(1) N(3)-Cu(1)-N(1) O(1)-Cu(1)-S(1) N(3)-Cu(1)-S(1) N(1)-Cu(1)-S(1)

1.936(8) 1.988(9) 2.037(9) 2.268(3) 2.272(8) 1.732(11)

N(3)-C(19) N(3)-C(18) O(1)-C(25) C(13)-C(18) C(19)-C(20) C(20)-C(25)

1.283(13) 1.423(12) 1.337(16) 1.414(12) 1.429(15) 1.398(19)

94.0(4) 87.2(4) 178.1(3) 163.9(3) 87.8(2) 90.7(2)

O(1)-Cu(1)-N(2) N(3)-Cu(1)-N(2) N(1)-Cu(1)-N(2) S(1)-Cu(1)-N(2) C(1)-N(1)-C(5)

91.4(3) 103.9(3) 77.5(3) 103.7(2) 117.8(9)

Magnetic susceptibility measurements

The magnetic susceptibility measurements of the complexes in the solid state show that the present complexes are paramagnetic at room temperature. The observed magnetic moments of these complexes are quite close to the values expected for copper(II) complexes. The observed magnetic moment values of the complexes are 1.78 for 1, 1.81 for 2, 1.85 for 3, 1.81 for 4, 1.83 for 5 and 1.88 B.M. for 6. Magnetic moment values (µeff) lie within the range normally found for other magnetically dilute copper(II) complexes23,24. X-ray crystallographic study

Wine red colored plate shaped crystals of [Cu(SAT)(phen)].0.5 H2O (2) suitable for analysis were grown from a solution of the complex 2 dissolved in a mixture of dichloromethane and methanol (2:1, v/v). The structure refinement parameters are given in Table 1 and the selected bond

Fig. 1 — The ORTEP diagram of the complex [Cu(SAT)(phen)].0.5 H2O (2).

angles and distances are given in Table 2. The ORTEP view of the complex is shown in Fig. 1. NOS-donor Schiff base and a NN-donor polypyridine ligand bind to the copper(II) ion to form two five membered chelate rings [1. Cu(1)-N(3)-C(18)-C(13)S(1); 2. Cu(1)-N(1)-C(5)-C(9)-N(2)] and a six membered chelate ring [Cu(1)-N(3)-C(19)-C(20)C(25)-O(1)]. Due to Jahn-Teller effect and also due to non-equivalent nature of the donor atoms, there are considerable variations in bond lengths. So the plane defined by the azomethine nitrogen, an enolate oxygen and a thiolate sulphur is chosen as the basal plane of the copper(II) distorted square pyramidal geometry. The remaining two nitrogens of polypyridine ligand occupy the axial and equatorial positions. This complex crystallizes in the monoclinic


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Table 3 — EPR spectral parameters of the copper(II) complexes

Polycrystalline state (298 K) g|| g⊥ giso or gav DMSO or CH2Cl2 (77 K) g|| g⊥ A|| (G) G α2 β2 γ2 K|| K⊥

1

2

3

4

5

6

2.245 2.077

2.166 2.060

-

2.169 2.050

-

2.161

2.113

2.096

2.162 (g3) 2.050 (g1) 2.063 (g2) 2.092

2.109

2.098

2.238 2.06 180 3.24 0.801 0.968 0.983 0.776 0.788

2.233 2.062 175 2.81 0.782 0.977 0.994 0.765 0.778

2.238 2.062 172 0.779 0.988 0.994 0.770 0.775

2.234 2.061 174 2.94 0.780 0.978 0.985 0.763 0.768

2.236 2.063 175 3.49 0.785 0.967 0.986 0.760 0.775

2.238 2.064 176 0.791 0.969 0.992 0.766 0.784

system and the structure was solved in P21/a space group. The distortion (τ = 0.24) from square pyramidal (4+1) geometry was ascertained by the τ value (the structure index is defined as τ = (θ1–θ2)/60, where θ1 and θ2 are the largest coordination angles). The largest distortions from the square pyramidal geometry are indicated by N(3)-Cu(1)-N(1) = 178.1(3), O(1)-Cu(1)-S(1) = 163.9(3) angles. Similar type of copper(II) complexes containing nitrogen, oxygen and sulphur donor atoms having distorted square pyramidal geometry have also been reported by some other workers25−27. EPR spectral study

The EPR spectra of the complexes in the polycrystalline state at 298 K and in solution at 77 K were recorded in the X-band, using 100 kHz field modulation and the g factors were quoted relative to the standard marker TCNE (g = 2.00277). The EPR parameters of the complexes are presented in Table 3. Some representative EPR spectra are shown in Figs 2 and 3. The EPR spectra of the complexes 3 and 6 in the polycrystalline state at 298 K show only one broad signal at g = 2.096 and 2.098, respectively. Such isotropic spectra consist a broad signal and hence only one g value arises from extensive exchange coupling through misalignment of the local molecular axes between different molecules in the unit cell and enhanced spin lattice relaxation. This type of spectra unfortunately gives no information on the electronic ground state of the copper(II) ion present in the complexes. The EPR spectrum of the complex 4 give

Fig. 2 — EPR spectrum of the complex [Cu(SAT)(en)] (5) in powder at 298 K.

three g values, viz., g1, g2 and g3 which indicate rhombic distortions in their geometry. The EPR spectra of the complexes 1, 2 and 5 show typical axial features with well-resolved g|| and g⊥ values. The geometric parameter G, which is a measure of the exchange interaction between the copper centers in the polycrystalline compounds is calculated using the equation: G = (g|| − 2.0023)/(g⊥ − 2.0023) for axial spectra and for rhombic spectra, G = (g3 − 2.0023)/ (g⊥ −2.0023) where g⊥ = (g1 + g2)/2. The G values calculated for the present copper(II) complexes are in


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α2=(A||/0.036)+(g||−2.0023)+3/7(g⊥−2.0023)+0.04 The orbital reduction factors K|| and K⊥ were estimated from the expressions32: K||2 = (g|| − 2.0023) Ed-d/8 λ0 K⊥2 = (g⊥ − 2.0023) Ed-d/2 λ0

Fig. 3 — EPR spectrum of the complex [Cu(SAT)(phen)] 0.5 H2O (2) at 77 K in CH2Cl2.

the range of 2.8 to 3.4. In all the complexes, g|| > g⊥ > 2.0023 and the G values less than 4.0 is consistent with a dx2-y2 ground state28,29. The EPR spectra of the complexes 2 and 4 in glassy state at 77 K were recorded in CH2Cl2 and the remaining complexes in DMSO. The EPR spectra of the complexes 2 and 4 show axial features with three of the four copper hyperfine lines are moderately resolved while perpendicular features overlap the fourth one and the seven superhyperfine lines are observed on the high field copper hyperfine splitting component. The seven super hyperfine lines arise from the coupling of the electron spin with the nuclear spin of the three nitrogen atoms. The EPR spectral studies of the complexes are in agreement with the X-ray diffraction studies of the complex 2. Similar type of spectral features has also been reported by some other groups30. The EPR spectra of the remaining complexes in DMSO solution at 77 K show clearly four well-resolved hyperfine lines. All these spectral features are showing axial features (g|| > g⊥ > 2.0023) indicating a dx2−y2 ground state and suggest a square planar or square based pyramidal geometry in the copper(II) complexes. The EPR parameters and d-d transition energies were used to evaluate the bonding parameters α2, β2 and γ2 which may be regarded as measures of the covalency of the in-plane σ bonding and the in-plane and out-of-plane π bonding respectively. The in-plane σ bonding parameter α2 was calculated by using the expression31:

where K|| = α2β2, K⊥ = α2γ2 and λ0 represents the one electron spin-orbit coupling constant for the free ion, equal to –828 cm−1. Significant information about the nature of bonding in the copper(II) complexes can be derived from the magnitude of K|| and K⊥. In case of pure σ bonding K|| ≈ K⊥ ≈ 0.77, whereas K|| < K⊥ implies considerable in-plane π bonding, while for out-of-plane π bonding, K|| > K⊥. In all the present copper(II) complexes, it is observed that K|| < K⊥, which indicates the presence of significant in-plane π bonding. The evaluated values of α2, β2 and γ2 of the complexes are consistent with both strong in-plane σ and in-plane π bonding. Electronic spectral study

The electronic spectra of the complexes 2 and 4 were recorded in CH2Cl2 while the other complexes were recorded in DMSO solution at 25°C. Complex 1 exhibits a broad band at 590 nm, similar to those reported for a copper(II) ion in square planar environments33,34. The ligand to metal charge transfer band appeared at 415 nm with a shoulder at 450 nm. The d-d transition for complexes 2-6 is observed as a broad band at 595-610 nm. The ligand to metal charge transfer band for these complexes appeared at 415-417 nm with a shoulder at 461 - 470 nm. Similar type of observations for d-d band and MLCT band were reported for a copper(II) distorted square pyramidal geometry35. Infrared spectral study

The ν(C=N) band of the ligand at 1646 cm−1 is found to be shifted to lower energies (1602-1607 cm−1) in the spectra of the complexes indicating the coordination via the azomethine nitrogen. This is confirmed by the bands in the range 431-471 cm−1 which have been assigned to the ν(Cu-N) band36. The two bands appearing at the frequency 1339 and 877 cm−1, in the spectra of ligand have been shifted to lower frequencies in the ranges 1323-1331 and 800-856 cm−1 respectively, indicating coordination of the thiolato sulphur37. In the IR spectra of the complexes 1 and 2, the peaks observed at 3425 and


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Table 4 — Cyclic voltammetric measurements of the copper(II) complexes Scan rate (mV/sec)

Epc (mV)

[Cu(SAT)(H2O)] (1) 100 -535 200 -558 [Cu(SAT)(phen)].0.5 H2O (2) 100 -500 200 -530 [Cu(SAT)(bipy)] (3) 100 -550 200 -576 300 -593 [Cu(SAT)(dmp)] (4) 100 -528 200 -548 [Cu(SAT)(temed)] (6) 100 -570 200 -595 Scan rate (mV/sec)

Epc1

[Cu(SAT)(en)] (5) 100 240 200 224 300 230

Ipc (μA)

Epa (mV)

Ipa (μA)

ΔEp

Eo'

Ipa/Ipc

1.563 2.213

-325 -303

0.821 1.214

210 255

-430 -430

0.53 0.54

1.692 2.413

-307 -274

0.912 1.321

193 256

-403 -402

0.55 0.55

1.443 2.141 2.472

-313 -290 -270

0.725 1.125 1.236

237 286 323

-431 -433 -431

0.50 0.53 0.50

1.325 1.864

-335 -313

0.753 1.034

193 235

-431 -430

0.57 0.56

1.413 2.017

-355 -331

0.794 1.132

215 264

-462 -463

0.56 0.56

Ipc1

Epc2

Ipc2

Epa

Ipa

ΔEp

Eo'

Ipa/Ipc

0.543 0.726 0.889

-596 -620 -644

1.120 1.584 1.945

-373 -350 -328

0.560 0.793 0.971

223 270 316

-484 -485 -486

0.50 0.50 0.50

3435 cm−1 support the presence of ν(H2O) in the complexes. Vibrations at 433-471 cm−1 (weak) (and expected below 400 cm−1; out of our measuring limit) can be attributed to M-O, M-N and M-S vibrations38,39. Cyclic voltammetric measurements

The redox properties of 1 mM solution of the complexes 1-6 has been investigated in DMSO containing 0.1 M NaClO4 as supporting electrolyte at a platinum working electrode. The cyclic voltammetric results for the complexes are given in Table 4. A representative voltammogram is shown in Fig. 4. For the complexes 1, 2, 3, 4 and 6, a negative scan initiated at 1000 mV in the potential range 1000 to −1000 mV yielded irreversible couple corresponding to Cu(II)/(I) redox process40. In all cases peak potential difference increases as scan rate is increased (Table 4). Constancy of Eo' shows that in all cases both peaks are complementary to each other. The peak current ratio Ipa/Ipc is less than unity showing that the electron transfer reaction is followed by a chemical reaction (EC mechanism)41−43.

Fig. 4 — Cyclic voltammogram of the complex [Cu(SAT)(phen)] 0.5 H2O (2) in 0.1 M NaClO4 [Scan Rate: 100 (m V/sec)]

For complex 5, a negative scan initiated at 1000 mV in the potential range 1000 to -1000 mV at different scan rates yielded an irreversible couple corresponding to Cu(II)/Cu(I) redox process at Eo' = −484 mV with ΔEp = 223 mV at 100 mV/s. The peak potential difference of the couple increases as scan rate is increased. Along with this couple, a cathodic peak at Epc1 = 240 mV at 100 mV/sec scan rate was also observed. A perusal of Table 4 shows


that the magnitude of cathodic peak current Ipc1 and Ipc2 differ significantly. Ipc2 being larger than that of Ipc1 indicates that two complex species presumably exist in equilibrium in solution. Superoxide dismutase activity

The superoxide dismutase activity (SOD) of the present complexes was assayed by the use of alkaline dimethyl sulfoxide as a superoxide anion generating system in association with nitrobluetetrazolium chloride as a scavenger of superoxide radical19. Alkaline DMSO as a O2– generating system has the advantage that there is a marked decrease in the spontaneous dismutation rate of O2– due to the use of a relatively high pH combined with low temperature and that a large amount of O2– is generated in solution as compared to SOD concentration. The complexes in the present study exhibit catalytic activity towards the dismutation of superoxide anions. The IC50 values of the present complexes (60 μmol dm−3 for 1, 58 μmol dm−3 for 3, 52 μmol dm−3 for 5 and 62 μmol dm−3 for 6) are higher than the native enzyme (IC50 = 0.04 μmol dm−3) on a molar base. This reduced activity may be due to the strong ligand field created by the Schiff base (SAT), which opposes the interaction of the complexed copper with superoxide radical. Supplementary material

Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC No. 661714 for the complex [Cu(SAT)(phen)].).0.5 H2O (2). Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK, fax: +44 1223 336 033, e-mail: [email protected] or http://www.ccdc.cam.ac.uk. Acknowledgement One of the authors (VLNG) thanks the CSIR, New Delhi, India, for awarding SRF. Our grateful thanks are due to National Diffraction Facility, X-ray Division and RSIC (SAIF), IIT Bombay for single crystal data collection and EPR measurements respectively. The Head RSIC, Central Drug Research Institute, Lucknow is also thanked for providing analytical and spectral facilities. References 1 Johnson D K, Murphy T B, Rose N J & Goodwin W H, Inorg Chim Acta, 67 (1982) 159.

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