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Synthesis and characterization of a series of copper(II) complexes with azo-linked salicylaldimine Schiff base ligands.
www.elsevier.nl/locate/poly Polyhedron 19 (2000) 607–613
Synthesis and characterization of a series of copper(II) complexes with azo-linked salicylaldimine Schiff base ligands. Crystal structure of Cu5PHAZOSALTNPCHCl3 A.A. Khandar *, K. Nejati Department of Inorganic Chemistry, Faculty of Chemistry, Tabriz University, Tabriz, Iran Received 5 August 1999; accepted 6 December 1999
Abstract Complexes of copper (II) with Schiff bases obtained by condensation of 5-phenylazo salicylaldehyde with di-or tri-amines have been synthesized and characterized by their infrared spectra and elemental analysis. The copper(II) chelates investigated are [bis(5-phenylazo salicylaldehyde)ethylene diiminato]copper(II) (Cu5PHAZOSALEN) (I), [bis(5-phenylazo salicylaldehyde)O-phenylene diiminato]copper(II) (Cu5PHAZOSALOPHEN) (II), [bis(5-phenylazo salicylaldehyde)trimethylen diiminato]copper(II) (Cu5PHAZOSALTN) (III) and [bis(5-phenylazo salicylaldehyde)diethylene triiminato]copper(II) (Cu5PHAZOSALDETA) (IV). The single-crystal X-ray diffraction is reported for Cu5PHAZOSALTNPCHCl3. The copper atom lies in a near square-planar coordination with Cu–N bond lengths of ˚ and Cu–O lengths of 1.903(5) and 1.931(6) A. ˚ Cyclic voltammetry indicates that copper complexes III and IV 1.962(7) and 1.949(7) A have a quasi-reversible redox behaviour and complexes I and II undergo irreversible and reversible reduction (at a scan rate 0.05 V sy1), respectively, under the experimental conditions. q2000 Elsevier Science Ltd All rights reserved. Keywords: Schiff bases; Copper complexes; X-ray structure; 5-Phenylazosalicylaldehyde; Cyclic voltammetry
1. Introduction
2. Experimental
Schiff base complexes containing different central metal atoms such as Cu, Ni, Co and Pd have been studied in great detail for their various crystallographic features, enzymatic reactions, steric effects [1–4], structure–redox relationships [5], mesogenic characteristics [6–9], catalysis, magnetic properties [10,11] and their important role in the understanding of the coordination chemistry of transition metal ions [12]. CuN2O2 coordination is very common in copper chemistry and the redox behaviour of a wide series of mononuclear copper(II) Schiff base complexes was reviewed some years ago in relation to their structural changes [5]. We report here the synthesis, characterization and cyclic voltammetry of copper(II) complexes of a series of Schiff base ligands derived from condensation of 5-phenylazo salicylaldehyde with dior tri-amines (Scheme 1). We also report the crystal structure of [bis(5-phenylazo salicylaldehyde)trimethylen diiminato]copper(II) (Cu5PHAZOSALTN) (III) as determined by single-crystal X-ray diffraction.
2.1. Reagents
* Corresponding author. Tel.: q98-41-348917; fax: q98-41-340191; e-mail: [email protected]
All reagents and solvents were used as supplied by Merck. 2.2. Physical measurements Elemental (C, H and N) analyses were made on a PerkinElmer Model 240B automatic analyser. Electron impact (70 eV) mass spectra were recorded on a Finnigan-mat GC-MSDS spectrometer Model 8430. Infrared (IR) spectra were recorded on an IR-408 Shimadzu 568. The redox properties of the complexes were studied by cyclic voltammetry. The voltammetric experiments were carried out in deaerated (with purged nitrogen) dimethylformamide (DMF) solutions of the complexes containing 0.1 M tetrabutylammonium perchlorate (TBAP) as supporting electrolyte. Spectroscopic grade DMF was distilled and dried on 0.4-nm molecular sieves. TBAP was dried in an oven and used without further purification. Cyclic voltammograms were performed using an AMEL Instruments Model 2053 as potentiostat connected with a
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the program SHELXTL Plus, version 5, and refined by the full-matrix least-squares method. In subsequent refinements, the function Sw(NFoNyNFcN)2 was minimized, where Fo and Fc are the observed and calculated structure factor amplitudes. The agreement indices RsSNNFoNyNFcNN/SNFoN and Rws[Sw(NFoNyNFcN)2/SwNFoN)2]1/2 were used to evaluate the results. Atomic scattering factors are from the international tables for X-ray crystallography. Hydrogen atoms were introduced at theoretical positions with a C–H distance ˚ for the aromatic H atoms and 0.99 A ˚ for methylene of 0.95 A groups. 2.3. Materials [1] 2.3.1. 5-Phenylazo salicylaldehyde 5-Phenylazo salicylaldehyde was obtained as described elsewhere [13].
Scheme 1.
function generator (AMEL Model 568).When an iR drop (ohmic drop) was compensated a multipurpose instrument from EG&G was used, comprising potentiostat/galvanostat Model 273 coupled with an IBM personal computer connected to an Epson Model FX-850 printer. In all electrochemical experiments, an aqueous saturated calomel electrode (SCE) was used as reference electrode and all potential cited are given versus SCE. A platinum wire was used as counter electrode and a glassy carbon disc with a diameter of 3 mm was used as working electrode. The ferricinium/ferrocene (Fcq/Fc) couple was used as an internal standard; the ferrocene solution concentration was 1 mM. All experiments were carried out at room temperature. NMR spectra were measured in CDCl3 on a Brucker ACE-300 NMR spectrometer, 300.133 MHz. All chemical shifts are reported in d units downfield from Me4Si. 2.2.1. X-ray crystallography Crystallographic data for complex III are given in Table 1 as a typical example. Single crystals of complex were acquired by slow evaporation from a chloroform–ethanol (5:1) solution at room temperature and mounted in sealed glass capillaries. Diffraction data were collected on a Siemens P3/PC diffractometer (four-circle geometry) at 293 K. Intensity data were obtained using Mo Ka radiation (0.7107 ˚ monochromatized from graphite; the v–2u scan mode A) was used to a maximum 2u value of 47.97. The data were reduced and the structure was solved by direct methods using
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2.3.2. Ligands All ligands were prepared in a similar manner. First, 0.013 mole of related amine and 0.026 mole of 5-phenylazo salicylaldehyde were condensed by refluxing in 80 ml of absolute ethanol for 1 h. The solution was left at room temperature. Bis(5-phenylazo salicylaldehyde)ethylene diimine (5PHAZOSALEN) and bis(5-phenylazo salicylaldehyde)trimethylen diimine (5PHAZOSALTN) were obtained as yellow microcrystals, and bis(5-phenylazo salicylaldehyde)O-phenylene diimine (5PHAZOSALOPHEN) and Table 1 Crystallographic data for Cu5PHAZOSALTNPCHCl3 (III) Empirical formula Formula weight Temperature (K) Space group Unit cell dimensions ˚ a (A) ˚ b (A) ˚ c (A) a (8) b (8) g (8) ˚ 3) Volume (A Z Density (calc.) (Mg my3) Absorption coefficient (mmy1) F(000) Crystal size (mm) u Range for data collection (8) Limiting indices Reflections collected Independent reflections Reflections observed Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I)2s(I)] Rw Largest difference peak and hole ˚ y3) (e A
C29H24CuN6O2PCHCl3 671.45 293(2) P1¯ (No. 2) 9.646(4) 10.961(5) 15.791(6) 82.12 84.68(3) 64.54(3) 1492.0(11) 2 1.495 1.040 686 0.1=0.4=3 2.07 to 23.96 0FhF10, y11FkF11, y17FlF17 4079 3760 (Rints0.0436) 1980 3745/0/388 1.099 0.0758 0.1653 0.484 and y0.454
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Mass (m/e) (fragment, intensity %)
Formula Yield (%) M.p. (8C) IR (cmy1) n(O–H) n(N–H) n(C–H) (aromatic) n(C–H) (aliphatic) n(C_O) n(C_N) 1 H NMR (d) 3050 2900–2950
3050
226 (M, 25) 121 (MyC6H5N2, 25) calc.: 226.2
227 (Mq1, 12)
1640 13.8 (br s, 2H, OH) 8.5 (s, 2H, CH_N,s) 7.96–7.99 (2H, aromatic) 7.85–7.92 (6H, aromatic) 7.44–7.53 (6H, aromatic) 7.057.08 (d, 2H, aromatic, Js9 Hz) 4.04 (s, 4H, CH2, s)
3450
3250
1666
C28H24N6O2 93.5 229
5PHAZOSALEN
C13H10N2O2 65 128
5-Phenylazo salicylaldehyde
Compound
Table 2 Physical and characterization data for ligands
524 (M, 18) 314 (My2* C6H5N2, 78.6) calc.: 524.6
525 (Mq1, 7)
1610 13.6 (br s, 2H, OH) 8.78 (s, 2H, CH_N,s) 8.03–8.06 (4H, aromatic) 7.87–7.90 (4H, aromatic) 7.15–7.53 (10H, aromatic) 6.86–6.90 (2H, aromatic)
3050
3450
C32H24N6O2 84.5 208.6
5PHAZOSALOPHEN
1635 14 (br s, 2H, OH) 8.48 (s, 2H, CH_N, s) 7.97–8.01 (2H, aromatic) 7.85–7.91 (6H, aromatic) 7.40–7.51 (6H, aromatic) 7.07 (d, 2H, aromatic, Js8.8 Hz) 3.78 (t, 4H, CH2, s, Js6.6 Hz) 2.18 (p, 2H, CH2, Js6.6 Hz)
3050 2900–2950
3450
C29H26N6O2 86 144.3
5PHAZOSALTN
1635 14.01 (br s, 2H, OH) 8.43 (br s, 2H, CH_N, s) 7.92–7.95 (2H, aromatic) 7.83–7.86 (6H, aromatic) 7.42–7.50 (6H, aromatic) 7.00 (d, 2H, aromatic, Js8.9 Hz) 3.74 (br s, 4H, _N–CH2–, s) 3.03 (br s, 4H, _N–C–CH2–) 1.25 (br s, 1H, NH)
3450 3250 3050 2900–2950
C30H29N7O2 92 126
5PHAZOSALDETA
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bis(5-phenylazo salicylaldehyde)diethylene triimine (5PHAZOSALTEDA) were obtained as red microcrystals; the microcrystals were filtered off, washed with 10 ml of absolute ethanol and then recrystallized from ethanol– chloroform (1:3, v/v). 2.3.3. Complexes All complexes were prepared in a similar manner. A solution of 0.004 mole of Cu(CH3COO)2P4H2O in 10 ml of ethanol was added to an ethanol–chloroform (1:1, v/v) solution containing 0.004 mole of ligand and refluxed for 1 h. The obtained brown solution was left at room temperature and brown microcrystals were collected by filtration, washed with 15 ml of ethanol and then recrystallized from ethanol– chloroform (2:1, v/v).
3. Results and discussion 3.1. Syntheses The 5-phenylazo salicylaldehyde (pre-ligand), Schiff base ligands and related copper complexes were obtained in good yield and purity. The pre-ligand and Schiff base ligands were characterized by 1H NMR and IR and mass spectroscopy. Copper complexes were characterized by elemental analysis and IR spectroscopy. All physical and characterization data for the ligands and complexes are given in Tables 2 and 3, respectively. In the mass spectra of 5-phenylazo salicylaldehyde and the related Schiff base (5PHAZOSALOPHEN), [Mq1], M and [MyC6H5N2] for aldehyde and [My2*C6H5N2] for Schiff base were observed. For the IR spectra of the four title complexes, n(C_N) shifted to a lower wavenumber by 10–30 cmy1 upon coordination. On the other hand, the disappearance of the OH band of free ligands in copper(II) complexes indicates that the OH group has been deprotonated and bonded to the metal ions as –Oy. On the basis of these results it can be deduced that in complexes I, II and III the Schiff bases are coordinated to copper atom as tetradentate ONNO ligands. The IR spectra of complex IV shows no shift for N–H bond in comparison
to the IR spectra of the ligand. Therefore complex IV is also four-coordinate via ONNO of the ligand atoms. 3.2. Crystal structure of [bis(5-phenylazo salicylaldehyde)trimethylen diiminato]copper(II) (Cu5PHAZOSALTN) (III) The crystal structure and unit cell diagram of complex III are illustrated in Figs. 1 and 2, respectively. The selected bond distances and angles are given in Table 4. The coordination geometry around copper can be described as a near square-planar. The Cu–O(1) and Cu– ˚ are similar O(19) distances of 1.903(5) and 1.931(6) A ˚ in to the corresponding value [Cu–O(2), 1.915(7) A] N,N9-trimethylene bis(salicylaldehyde imine)copper(II), Cu(sal2tn), as reported by Xiong et al. [12], and the differences are not significant, but the differences between Cu– ˚ in O(1) and Cu–O(19) with Cu–O(1) [1.840(9)A] Cu(sal2tn) are probably just significant. The Cu–N(1) and Cu–N(19) distances are 1.949(7) and ˚ The corresponding values of complex 1.962(7) A. ˚ Cu(sal2tn) are 1.954(7) and 1.995(8) A. The bond angles O(19)–Cu–O(1), N(19)–Cu–N(1), N(1)–Cu–O(19) and N(19)–Cu–O(1) are 79.8(2), 95.7(3), 171.9(3) and 171.8(3)8, respectively. The two former bond angles are similar to the values in Cu(sal2tn) [79.8(4) and 95.5(4)8], but on the basis of the two latter bond angles [(171.9(3) and 171.8(3)8] we can conclude that the coordination geometry around copper in the title complex is near to square-planar in comparison to Cu(sal2tn), which has corresponding values of 159.7(4) and 158.2(4)8, respectively. The central carbon atom in the trimethylene diamine chelate ring (labelled C(1) and C(19); see Fig. 1) is disordered over two positions, one of which is above and another below the coordination plane. The disorder is quite common and is observed, for example, in some of the transition metal complexes with Schiff base ligands [14]. Complex III has been prepared and recrystallized in ethanol solution. The elemental analysis confirms the formulation of the complex. Recrystallization of complex III for preparing a single crystal was carried out in ethanol–chloroform. The crystal structure shows the presence of a CHCl3
Table 3 Physical and characterization data for complexes Compound
Formula Yield (%) IR (cmy1) n(C_N) n(N–H) Anal.: found (calc.) (%) C H N
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I
II
III
IV
C28H22CuN6O2 94
C32H22CuN6O2 92
C29H24CuN6O2 94
C30H27CuN7O2 92
1630
1600
1605
1625 3250
62.3 (62.50) 4.0 (4.09) 15.5 (15.62)
65.4 (65.58) 3.7 (3.75) 14.1 (14.34)
62.8 (63.09) 4.3 (4.35) 15.1 (15.23)
61.8 (62.01) 4.6 (4.65) 16.7 (16.88)
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Fig. 1. Structure of Cu5PHAZOSALTNPCHCl3 (III).
Fig. 2. Stereoview of the unit cell of the Cu5PHAZOSALTNPCHCl3 (III). Table 4 ˚ and angles (8) for Cu5PHAZOSALTNPCHCl3 Selected bond lengths (A) (III) Cu(1)–O(1) Cu(1)–N(19) N(1)–C(2) C(2)–C(1) C(29)–C(1)
1.903(5) 1.949(7) 1.482(10) 1.44(2) 1.46(3)
Cu(1)–O(19) Cu(1)–N(1) N(19)–C(29) C(2)–C(19) C(29)–C(19)
1.931(6) 1.962(7) 1.459(10) 1.36(3) 1.36(3)
O(1)–Cu(1)–O(19) O(19)–Cu(1)–N(19) O(19)–Cu(1)–N(1) C(5)–O(1)–Cu(1) C(2)–N(1)–Cu(1) C(39)–N(19)–Cu(1)
79.8(2) 92.4(3) 171.9(3) 130.5(5) 123.3(6) 123.4(6)
O(1)–Cu(1)–N(19) O(1)–Cu(1)–N(1) N(19)–Cu(1)–N(1) C(3)–N(1)–Cu(1) C(59)–O(19)–Cu(1) C(29)–N(19)–Cu(1)
171.8(3) 92.1(3) 95.7(3) 124.8(6) 130.6(5) 124.4(6)
molecule in the crystal structure, with the empirical formula C29H24CuN6O2PCHCl3 (formula weight 671.45). 3.3. Cyclic voltammetry The cyclic voltammograms recorded (without iR compensation) for complexes I–IV are shown in Fig. 3 and the
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corresponding characteristic data are given in Table 5. Note that the free ligands are electroinactive in the working potential region. On the basis of the cyclic voltammograms in Fig. 3, complex I undergoes an irreversible reduction process under the experimental condition (Fig. 3a). The peak separations DE (sEpayEpc) for complexes II, III and IV were 82, 103 and 227 mV, respectively, at a scan rate of 0.05 V sy1, and decreased to 62, 78 and 204 mV when the iR drop was compensated by the cyclic voltammetry set-up; thus the redox process for complex II is reversible and quasi-reversible for complexes III and IV [15]. Note that when a similar iR compensation is applied to the cell, the ferrocene behaved ideally and the peak separation for the ferricinium/ferrocene couple was at 60 mV, which can be used as a criterion for electrochemical reversibility in the present experimental conditions. As seen in Table 5, the peak:current ratio decreases with increasing scan rate, indicating a weak adsorption of the reactants on the electrode [16]. For N2O2 Schiff base complexes of copper the redox potential is correlated with the degree of
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Fig. 3. Cyclic voltammograms (recorded without iR compensation) for (a) Cu5PHAZOSALEN (I), (b) Cu5PHAZOSALOPHEN (II), (c) Cu5PHAZOSALTN (III), (d) Cu5PHAZOSALDETA (IV) in DMF (0.002 M) with 0.1 M TBAP as supporting electrolyte at a scan rate 0.1 V sy1.
Table 5 Cyclic voltammetry data (without iR compensation) for complexes I–IV Scan rate (V sy1)
Ec (V)
Cu5PHAZOSALEN (I) 0.05 0.1 0.2 0.3 0.4 0.5
y0.991 y1.005 y1.009 y1.015 y1.021 y1.031
Cu5PHAZOSALOPHEN (II) 0.05 0.1 0.2 0.3 0.4 0.5
y0.970 y0.974 y0.981 y0.993 y1.005 y1.025
y0.888 y0.871 y0.865 y0.856 y0.848 y0.840
0.082 0.103 0.116 0.137 0.157 0.185
Cu5PHAZOSALTN (III) 0.05 0.1 0.2 0.3 0.4 0.5
y0.851 y0.863 y0.873 y0.881 y0.890 y0.900
y0.748 y0.733 y0.725 y0.718 y0.710 y0.701
Cu5PHAZOSALDETA (IV) 0.05 0.1 0.2 0.3 0.4 0.5
y0.785 y0.798 y0.820 y0.825 y0.852 y0.860
y0.558 y0.553 y0.549 y0.541 y0.531 y0.511
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Ea (V)
DE
Ic (mA)
Ia (mA)
Ia/Ic
25.4 30.8 42.5 51.9 60.1 66.2
19.3 23.1 30.8 36.9 41.6 44.7
0.77 0.75 0.72 0.71 0.69 0.67
0.103 0.130 0.148 0.163 0.180 0.199
28.6 38.6 50.5 59.8 67.8 77.1
22.6 29.3 37.9 43.9 47.9 51.9
0.79 0.76 0.75 0.73 0.71 0.67
0.227 0.245 0.271 0.284 0.321 0.349
23.9 33.2 43.9 51.9 58.5 67.8
21.3 28.6 37.2 43.9 47.9 53.2
0.89 0.86 0.85 0.85 0.82 0.78
30 42 57 69 78 84
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tetrahedral distortion of the copper coordination environment [17,18]. The more tetrahedral geometries correspond to less negative redox potential for Cu(II)/Cu(I) couples, whereas more planar geometries give rise to more negative potentials. Complexes I and II can be assumed to be planar complexes [5]. The angles N(19)–Cu–O(1) 171.88 and N(1)–Cu– O(19) 171.9 in complex III indicate that the copper coordination environment is near square-planar; therefore the redox potential of this complex is less negative than the planar analogue. On the basis of the redox potential, we conclude that complex IV has a structure deviating from square-planar with N2O2 and not N3O2 coordination [5,19].
Supplementary data Supplementary crystallographic data are available from the CCDC, 12, Union Road, Cambridge CB2 1EZ, UK (fax. q44-1223-336033; e-mail: [email protected]) on request, quoting the deposition number CCDC 120858.
Acknowledgements We thank Professor A.I. Yanovsky, Russian Academy of Science, Moscow, for X-ray structure determination, Professor M.H. Pournaghi Azar for useful discussions on cyclic voltammetry investigations and Dr Pakdel, Laval University, Quebec, Canada, for 1H NMR spectra.
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References [1] S.C. Bhatia, J.M. Bindlish, A.R. Saini, P.C. Jain, J. Chem. Soc., Dalton Trans. (1981) 1773. [2] J.M. Bindlish, S.C. Bhatia, P.C. Jain, Indian J. Chem. 13 (1975) 81. [3] R.P. Kashyap, J.M. Bindlish, P.C. Jain, Indian J. Chem. 11 (1973) 388. [4] J.M. Bindlish, S.C. Bhatia, P. Gautam, P.C. Jain, Indian J. Chem., Sect. A 16 (1978) 279. [5] I. Bernal, in: I. Bernal (Ed.), Stereochemical Control, Bonding and Steric Rearrangements, Elsevier, Amsterdam, 1990, Chapter 3. [6] A.M. Giroud, P.M. Maitlis, Angew. Chem., Int. Ed. Engl. 30 (1991) 375. [7] P. Espinet, M.A. Esteruelas, L.A. Oro, J.L. Serrano, E. Sola, Coord. Chem. Rev. 117 (1992) 215. [8] S.A. Hudson, P.M. Maitlis, Chem. Rev. 93 (1993) 861. [9] J.L. Serrano, J.L. Serrano, Metallomesogens, Syntheses, Properties and Applications, VCH, Weinheim, 1996. [10] K.K. Chaturvedl, J. Inorg. Nucl. Chem. 39 (1977) 901. [11] R.D. Archer, B. Wang, Inorg. Chem. 29 (1990) 39. [12] R.-G. Xiong, B.-L. Song, J.-Z. Zuo, X.-Z. You, Polyhedron 15 (1996) 903. [13] A.A. Khandar, Z. Rezvani, Polyhedron 18 (1998) 129. [14] C.A. Root, J.D. Hoeschele, C.R. Cornman, J.W. Kampt, V.L. Pecoraro, Inorg. Chem. 32 (1993) 3855. [15] A.J. Bard, L.R. Faulkner, Electrochemical Methods, Fundamentals and Applications, Wiley, New York, 1980, p. 230. [16] A.J. Bard, L.R. Faulkner, Electrochemical Methods, Fundamentals and Applications, Wiley, New York, 1980, p. 530. [17] G.S. Patterson, R.H. Holm, Bioinorg. Chem. 7 (1975) 257 and references cited therein. [18] C. Fraser, B. Bosnich, Inorg. Chem. 33 (1994) 338. [19] E.D. Mckenzie, S.J. Selvey, Inorg. Chim. Acta 18 (1976) L1.
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Synthesis and characterization of a series of copper(II) complexes with azo-linked salicylaldimine Schiff base ligands. Crystal structure of Cu5PHAZOSALTNPCHCl3 A.A. Khandar *, K. Nejati Department of Inorganic Chemistry, Faculty of Chemistry, Tabriz University, Tabriz, Iran Received 5 August 1999; accepted 6 December 1999
Abstract Complexes of copper (II) with Schiff bases obtained by condensation of 5-phenylazo salicylaldehyde with di-or tri-amines have been synthesized and characterized by their infrared spectra and elemental analysis. The copper(II) chelates investigated are [bis(5-phenylazo salicylaldehyde)ethylene diiminato]copper(II) (Cu5PHAZOSALEN) (I), [bis(5-phenylazo salicylaldehyde)O-phenylene diiminato]copper(II) (Cu5PHAZOSALOPHEN) (II), [bis(5-phenylazo salicylaldehyde)trimethylen diiminato]copper(II) (Cu5PHAZOSALTN) (III) and [bis(5-phenylazo salicylaldehyde)diethylene triiminato]copper(II) (Cu5PHAZOSALDETA) (IV). The single-crystal X-ray diffraction is reported for Cu5PHAZOSALTNPCHCl3. The copper atom lies in a near square-planar coordination with Cu–N bond lengths of ˚ and Cu–O lengths of 1.903(5) and 1.931(6) A. ˚ Cyclic voltammetry indicates that copper complexes III and IV 1.962(7) and 1.949(7) A have a quasi-reversible redox behaviour and complexes I and II undergo irreversible and reversible reduction (at a scan rate 0.05 V sy1), respectively, under the experimental conditions. q2000 Elsevier Science Ltd All rights reserved. Keywords: Schiff bases; Copper complexes; X-ray structure; 5-Phenylazosalicylaldehyde; Cyclic voltammetry
1. Introduction
2. Experimental
Schiff base complexes containing different central metal atoms such as Cu, Ni, Co and Pd have been studied in great detail for their various crystallographic features, enzymatic reactions, steric effects [1–4], structure–redox relationships [5], mesogenic characteristics [6–9], catalysis, magnetic properties [10,11] and their important role in the understanding of the coordination chemistry of transition metal ions [12]. CuN2O2 coordination is very common in copper chemistry and the redox behaviour of a wide series of mononuclear copper(II) Schiff base complexes was reviewed some years ago in relation to their structural changes [5]. We report here the synthesis, characterization and cyclic voltammetry of copper(II) complexes of a series of Schiff base ligands derived from condensation of 5-phenylazo salicylaldehyde with dior tri-amines (Scheme 1). We also report the crystal structure of [bis(5-phenylazo salicylaldehyde)trimethylen diiminato]copper(II) (Cu5PHAZOSALTN) (III) as determined by single-crystal X-ray diffraction.
2.1. Reagents
* Corresponding author. Tel.: q98-41-348917; fax: q98-41-340191; e-mail: [email protected]
All reagents and solvents were used as supplied by Merck. 2.2. Physical measurements Elemental (C, H and N) analyses were made on a PerkinElmer Model 240B automatic analyser. Electron impact (70 eV) mass spectra were recorded on a Finnigan-mat GC-MSDS spectrometer Model 8430. Infrared (IR) spectra were recorded on an IR-408 Shimadzu 568. The redox properties of the complexes were studied by cyclic voltammetry. The voltammetric experiments were carried out in deaerated (with purged nitrogen) dimethylformamide (DMF) solutions of the complexes containing 0.1 M tetrabutylammonium perchlorate (TBAP) as supporting electrolyte. Spectroscopic grade DMF was distilled and dried on 0.4-nm molecular sieves. TBAP was dried in an oven and used without further purification. Cyclic voltammograms were performed using an AMEL Instruments Model 2053 as potentiostat connected with a
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the program SHELXTL Plus, version 5, and refined by the full-matrix least-squares method. In subsequent refinements, the function Sw(NFoNyNFcN)2 was minimized, where Fo and Fc are the observed and calculated structure factor amplitudes. The agreement indices RsSNNFoNyNFcNN/SNFoN and Rws[Sw(NFoNyNFcN)2/SwNFoN)2]1/2 were used to evaluate the results. Atomic scattering factors are from the international tables for X-ray crystallography. Hydrogen atoms were introduced at theoretical positions with a C–H distance ˚ for the aromatic H atoms and 0.99 A ˚ for methylene of 0.95 A groups. 2.3. Materials [1] 2.3.1. 5-Phenylazo salicylaldehyde 5-Phenylazo salicylaldehyde was obtained as described elsewhere [13].
Scheme 1.
function generator (AMEL Model 568).When an iR drop (ohmic drop) was compensated a multipurpose instrument from EG&G was used, comprising potentiostat/galvanostat Model 273 coupled with an IBM personal computer connected to an Epson Model FX-850 printer. In all electrochemical experiments, an aqueous saturated calomel electrode (SCE) was used as reference electrode and all potential cited are given versus SCE. A platinum wire was used as counter electrode and a glassy carbon disc with a diameter of 3 mm was used as working electrode. The ferricinium/ferrocene (Fcq/Fc) couple was used as an internal standard; the ferrocene solution concentration was 1 mM. All experiments were carried out at room temperature. NMR spectra were measured in CDCl3 on a Brucker ACE-300 NMR spectrometer, 300.133 MHz. All chemical shifts are reported in d units downfield from Me4Si. 2.2.1. X-ray crystallography Crystallographic data for complex III are given in Table 1 as a typical example. Single crystals of complex were acquired by slow evaporation from a chloroform–ethanol (5:1) solution at room temperature and mounted in sealed glass capillaries. Diffraction data were collected on a Siemens P3/PC diffractometer (four-circle geometry) at 293 K. Intensity data were obtained using Mo Ka radiation (0.7107 ˚ monochromatized from graphite; the v–2u scan mode A) was used to a maximum 2u value of 47.97. The data were reduced and the structure was solved by direct methods using
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2.3.2. Ligands All ligands were prepared in a similar manner. First, 0.013 mole of related amine and 0.026 mole of 5-phenylazo salicylaldehyde were condensed by refluxing in 80 ml of absolute ethanol for 1 h. The solution was left at room temperature. Bis(5-phenylazo salicylaldehyde)ethylene diimine (5PHAZOSALEN) and bis(5-phenylazo salicylaldehyde)trimethylen diimine (5PHAZOSALTN) were obtained as yellow microcrystals, and bis(5-phenylazo salicylaldehyde)O-phenylene diimine (5PHAZOSALOPHEN) and Table 1 Crystallographic data for Cu5PHAZOSALTNPCHCl3 (III) Empirical formula Formula weight Temperature (K) Space group Unit cell dimensions ˚ a (A) ˚ b (A) ˚ c (A) a (8) b (8) g (8) ˚ 3) Volume (A Z Density (calc.) (Mg my3) Absorption coefficient (mmy1) F(000) Crystal size (mm) u Range for data collection (8) Limiting indices Reflections collected Independent reflections Reflections observed Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I)2s(I)] Rw Largest difference peak and hole ˚ y3) (e A
C29H24CuN6O2PCHCl3 671.45 293(2) P1¯ (No. 2) 9.646(4) 10.961(5) 15.791(6) 82.12 84.68(3) 64.54(3) 1492.0(11) 2 1.495 1.040 686 0.1=0.4=3 2.07 to 23.96 0FhF10, y11FkF11, y17FlF17 4079 3760 (Rints0.0436) 1980 3745/0/388 1.099 0.0758 0.1653 0.484 and y0.454
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Mass (m/e) (fragment, intensity %)
Formula Yield (%) M.p. (8C) IR (cmy1) n(O–H) n(N–H) n(C–H) (aromatic) n(C–H) (aliphatic) n(C_O) n(C_N) 1 H NMR (d) 3050 2900–2950
3050
226 (M, 25) 121 (MyC6H5N2, 25) calc.: 226.2
227 (Mq1, 12)
1640 13.8 (br s, 2H, OH) 8.5 (s, 2H, CH_N,s) 7.96–7.99 (2H, aromatic) 7.85–7.92 (6H, aromatic) 7.44–7.53 (6H, aromatic) 7.057.08 (d, 2H, aromatic, Js9 Hz) 4.04 (s, 4H, CH2, s)
3450
3250
1666
C28H24N6O2 93.5 229
5PHAZOSALEN
C13H10N2O2 65 128
5-Phenylazo salicylaldehyde
Compound
Table 2 Physical and characterization data for ligands
524 (M, 18) 314 (My2* C6H5N2, 78.6) calc.: 524.6
525 (Mq1, 7)
1610 13.6 (br s, 2H, OH) 8.78 (s, 2H, CH_N,s) 8.03–8.06 (4H, aromatic) 7.87–7.90 (4H, aromatic) 7.15–7.53 (10H, aromatic) 6.86–6.90 (2H, aromatic)
3050
3450
C32H24N6O2 84.5 208.6
5PHAZOSALOPHEN
1635 14 (br s, 2H, OH) 8.48 (s, 2H, CH_N, s) 7.97–8.01 (2H, aromatic) 7.85–7.91 (6H, aromatic) 7.40–7.51 (6H, aromatic) 7.07 (d, 2H, aromatic, Js8.8 Hz) 3.78 (t, 4H, CH2, s, Js6.6 Hz) 2.18 (p, 2H, CH2, Js6.6 Hz)
3050 2900–2950
3450
C29H26N6O2 86 144.3
5PHAZOSALTN
1635 14.01 (br s, 2H, OH) 8.43 (br s, 2H, CH_N, s) 7.92–7.95 (2H, aromatic) 7.83–7.86 (6H, aromatic) 7.42–7.50 (6H, aromatic) 7.00 (d, 2H, aromatic, Js8.9 Hz) 3.74 (br s, 4H, _N–CH2–, s) 3.03 (br s, 4H, _N–C–CH2–) 1.25 (br s, 1H, NH)
3450 3250 3050 2900–2950
C30H29N7O2 92 126
5PHAZOSALDETA
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bis(5-phenylazo salicylaldehyde)diethylene triimine (5PHAZOSALTEDA) were obtained as red microcrystals; the microcrystals were filtered off, washed with 10 ml of absolute ethanol and then recrystallized from ethanol– chloroform (1:3, v/v). 2.3.3. Complexes All complexes were prepared in a similar manner. A solution of 0.004 mole of Cu(CH3COO)2P4H2O in 10 ml of ethanol was added to an ethanol–chloroform (1:1, v/v) solution containing 0.004 mole of ligand and refluxed for 1 h. The obtained brown solution was left at room temperature and brown microcrystals were collected by filtration, washed with 15 ml of ethanol and then recrystallized from ethanol– chloroform (2:1, v/v).
3. Results and discussion 3.1. Syntheses The 5-phenylazo salicylaldehyde (pre-ligand), Schiff base ligands and related copper complexes were obtained in good yield and purity. The pre-ligand and Schiff base ligands were characterized by 1H NMR and IR and mass spectroscopy. Copper complexes were characterized by elemental analysis and IR spectroscopy. All physical and characterization data for the ligands and complexes are given in Tables 2 and 3, respectively. In the mass spectra of 5-phenylazo salicylaldehyde and the related Schiff base (5PHAZOSALOPHEN), [Mq1], M and [MyC6H5N2] for aldehyde and [My2*C6H5N2] for Schiff base were observed. For the IR spectra of the four title complexes, n(C_N) shifted to a lower wavenumber by 10–30 cmy1 upon coordination. On the other hand, the disappearance of the OH band of free ligands in copper(II) complexes indicates that the OH group has been deprotonated and bonded to the metal ions as –Oy. On the basis of these results it can be deduced that in complexes I, II and III the Schiff bases are coordinated to copper atom as tetradentate ONNO ligands. The IR spectra of complex IV shows no shift for N–H bond in comparison
to the IR spectra of the ligand. Therefore complex IV is also four-coordinate via ONNO of the ligand atoms. 3.2. Crystal structure of [bis(5-phenylazo salicylaldehyde)trimethylen diiminato]copper(II) (Cu5PHAZOSALTN) (III) The crystal structure and unit cell diagram of complex III are illustrated in Figs. 1 and 2, respectively. The selected bond distances and angles are given in Table 4. The coordination geometry around copper can be described as a near square-planar. The Cu–O(1) and Cu– ˚ are similar O(19) distances of 1.903(5) and 1.931(6) A ˚ in to the corresponding value [Cu–O(2), 1.915(7) A] N,N9-trimethylene bis(salicylaldehyde imine)copper(II), Cu(sal2tn), as reported by Xiong et al. [12], and the differences are not significant, but the differences between Cu– ˚ in O(1) and Cu–O(19) with Cu–O(1) [1.840(9)A] Cu(sal2tn) are probably just significant. The Cu–N(1) and Cu–N(19) distances are 1.949(7) and ˚ The corresponding values of complex 1.962(7) A. ˚ Cu(sal2tn) are 1.954(7) and 1.995(8) A. The bond angles O(19)–Cu–O(1), N(19)–Cu–N(1), N(1)–Cu–O(19) and N(19)–Cu–O(1) are 79.8(2), 95.7(3), 171.9(3) and 171.8(3)8, respectively. The two former bond angles are similar to the values in Cu(sal2tn) [79.8(4) and 95.5(4)8], but on the basis of the two latter bond angles [(171.9(3) and 171.8(3)8] we can conclude that the coordination geometry around copper in the title complex is near to square-planar in comparison to Cu(sal2tn), which has corresponding values of 159.7(4) and 158.2(4)8, respectively. The central carbon atom in the trimethylene diamine chelate ring (labelled C(1) and C(19); see Fig. 1) is disordered over two positions, one of which is above and another below the coordination plane. The disorder is quite common and is observed, for example, in some of the transition metal complexes with Schiff base ligands [14]. Complex III has been prepared and recrystallized in ethanol solution. The elemental analysis confirms the formulation of the complex. Recrystallization of complex III for preparing a single crystal was carried out in ethanol–chloroform. The crystal structure shows the presence of a CHCl3
Table 3 Physical and characterization data for complexes Compound
Formula Yield (%) IR (cmy1) n(C_N) n(N–H) Anal.: found (calc.) (%) C H N
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I
II
III
IV
C28H22CuN6O2 94
C32H22CuN6O2 92
C29H24CuN6O2 94
C30H27CuN7O2 92
1630
1600
1605
1625 3250
62.3 (62.50) 4.0 (4.09) 15.5 (15.62)
65.4 (65.58) 3.7 (3.75) 14.1 (14.34)
62.8 (63.09) 4.3 (4.35) 15.1 (15.23)
61.8 (62.01) 4.6 (4.65) 16.7 (16.88)
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Fig. 1. Structure of Cu5PHAZOSALTNPCHCl3 (III).
Fig. 2. Stereoview of the unit cell of the Cu5PHAZOSALTNPCHCl3 (III). Table 4 ˚ and angles (8) for Cu5PHAZOSALTNPCHCl3 Selected bond lengths (A) (III) Cu(1)–O(1) Cu(1)–N(19) N(1)–C(2) C(2)–C(1) C(29)–C(1)
1.903(5) 1.949(7) 1.482(10) 1.44(2) 1.46(3)
Cu(1)–O(19) Cu(1)–N(1) N(19)–C(29) C(2)–C(19) C(29)–C(19)
1.931(6) 1.962(7) 1.459(10) 1.36(3) 1.36(3)
O(1)–Cu(1)–O(19) O(19)–Cu(1)–N(19) O(19)–Cu(1)–N(1) C(5)–O(1)–Cu(1) C(2)–N(1)–Cu(1) C(39)–N(19)–Cu(1)
79.8(2) 92.4(3) 171.9(3) 130.5(5) 123.3(6) 123.4(6)
O(1)–Cu(1)–N(19) O(1)–Cu(1)–N(1) N(19)–Cu(1)–N(1) C(3)–N(1)–Cu(1) C(59)–O(19)–Cu(1) C(29)–N(19)–Cu(1)
171.8(3) 92.1(3) 95.7(3) 124.8(6) 130.6(5) 124.4(6)
molecule in the crystal structure, with the empirical formula C29H24CuN6O2PCHCl3 (formula weight 671.45). 3.3. Cyclic voltammetry The cyclic voltammograms recorded (without iR compensation) for complexes I–IV are shown in Fig. 3 and the
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corresponding characteristic data are given in Table 5. Note that the free ligands are electroinactive in the working potential region. On the basis of the cyclic voltammograms in Fig. 3, complex I undergoes an irreversible reduction process under the experimental condition (Fig. 3a). The peak separations DE (sEpayEpc) for complexes II, III and IV were 82, 103 and 227 mV, respectively, at a scan rate of 0.05 V sy1, and decreased to 62, 78 and 204 mV when the iR drop was compensated by the cyclic voltammetry set-up; thus the redox process for complex II is reversible and quasi-reversible for complexes III and IV [15]. Note that when a similar iR compensation is applied to the cell, the ferrocene behaved ideally and the peak separation for the ferricinium/ferrocene couple was at 60 mV, which can be used as a criterion for electrochemical reversibility in the present experimental conditions. As seen in Table 5, the peak:current ratio decreases with increasing scan rate, indicating a weak adsorption of the reactants on the electrode [16]. For N2O2 Schiff base complexes of copper the redox potential is correlated with the degree of
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Fig. 3. Cyclic voltammograms (recorded without iR compensation) for (a) Cu5PHAZOSALEN (I), (b) Cu5PHAZOSALOPHEN (II), (c) Cu5PHAZOSALTN (III), (d) Cu5PHAZOSALDETA (IV) in DMF (0.002 M) with 0.1 M TBAP as supporting electrolyte at a scan rate 0.1 V sy1.
Table 5 Cyclic voltammetry data (without iR compensation) for complexes I–IV Scan rate (V sy1)
Ec (V)
Cu5PHAZOSALEN (I) 0.05 0.1 0.2 0.3 0.4 0.5
y0.991 y1.005 y1.009 y1.015 y1.021 y1.031
Cu5PHAZOSALOPHEN (II) 0.05 0.1 0.2 0.3 0.4 0.5
y0.970 y0.974 y0.981 y0.993 y1.005 y1.025
y0.888 y0.871 y0.865 y0.856 y0.848 y0.840
0.082 0.103 0.116 0.137 0.157 0.185
Cu5PHAZOSALTN (III) 0.05 0.1 0.2 0.3 0.4 0.5
y0.851 y0.863 y0.873 y0.881 y0.890 y0.900
y0.748 y0.733 y0.725 y0.718 y0.710 y0.701
Cu5PHAZOSALDETA (IV) 0.05 0.1 0.2 0.3 0.4 0.5
y0.785 y0.798 y0.820 y0.825 y0.852 y0.860
y0.558 y0.553 y0.549 y0.541 y0.531 y0.511
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Ea (V)
DE
Ic (mA)
Ia (mA)
Ia/Ic
25.4 30.8 42.5 51.9 60.1 66.2
19.3 23.1 30.8 36.9 41.6 44.7
0.77 0.75 0.72 0.71 0.69 0.67
0.103 0.130 0.148 0.163 0.180 0.199
28.6 38.6 50.5 59.8 67.8 77.1
22.6 29.3 37.9 43.9 47.9 51.9
0.79 0.76 0.75 0.73 0.71 0.67
0.227 0.245 0.271 0.284 0.321 0.349
23.9 33.2 43.9 51.9 58.5 67.8
21.3 28.6 37.2 43.9 47.9 53.2
0.89 0.86 0.85 0.85 0.82 0.78
30 42 57 69 78 84
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tetrahedral distortion of the copper coordination environment [17,18]. The more tetrahedral geometries correspond to less negative redox potential for Cu(II)/Cu(I) couples, whereas more planar geometries give rise to more negative potentials. Complexes I and II can be assumed to be planar complexes [5]. The angles N(19)–Cu–O(1) 171.88 and N(1)–Cu– O(19) 171.9 in complex III indicate that the copper coordination environment is near square-planar; therefore the redox potential of this complex is less negative than the planar analogue. On the basis of the redox potential, we conclude that complex IV has a structure deviating from square-planar with N2O2 and not N3O2 coordination [5,19].
Supplementary data Supplementary crystallographic data are available from the CCDC, 12, Union Road, Cambridge CB2 1EZ, UK (fax. q44-1223-336033; e-mail: [email protected]) on request, quoting the deposition number CCDC 120858.
Acknowledgements We thank Professor A.I. Yanovsky, Russian Academy of Science, Moscow, for X-ray structure determination, Professor M.H. Pournaghi Azar for useful discussions on cyclic voltammetry investigations and Dr Pakdel, Laval University, Quebec, Canada, for 1H NMR spectra.
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References [1] S.C. Bhatia, J.M. Bindlish, A.R. Saini, P.C. Jain, J. Chem. Soc., Dalton Trans. (1981) 1773. [2] J.M. Bindlish, S.C. Bhatia, P.C. Jain, Indian J. Chem. 13 (1975) 81. [3] R.P. Kashyap, J.M. Bindlish, P.C. Jain, Indian J. Chem. 11 (1973) 388. [4] J.M. Bindlish, S.C. Bhatia, P. Gautam, P.C. Jain, Indian J. Chem., Sect. A 16 (1978) 279. [5] I. Bernal, in: I. Bernal (Ed.), Stereochemical Control, Bonding and Steric Rearrangements, Elsevier, Amsterdam, 1990, Chapter 3. [6] A.M. Giroud, P.M. Maitlis, Angew. Chem., Int. Ed. Engl. 30 (1991) 375. [7] P. Espinet, M.A. Esteruelas, L.A. Oro, J.L. Serrano, E. Sola, Coord. Chem. Rev. 117 (1992) 215. [8] S.A. Hudson, P.M. Maitlis, Chem. Rev. 93 (1993) 861. [9] J.L. Serrano, J.L. Serrano, Metallomesogens, Syntheses, Properties and Applications, VCH, Weinheim, 1996. [10] K.K. Chaturvedl, J. Inorg. Nucl. Chem. 39 (1977) 901. [11] R.D. Archer, B. Wang, Inorg. Chem. 29 (1990) 39. [12] R.-G. Xiong, B.-L. Song, J.-Z. Zuo, X.-Z. You, Polyhedron 15 (1996) 903. [13] A.A. Khandar, Z. Rezvani, Polyhedron 18 (1998) 129. [14] C.A. Root, J.D. Hoeschele, C.R. Cornman, J.W. Kampt, V.L. Pecoraro, Inorg. Chem. 32 (1993) 3855. [15] A.J. Bard, L.R. Faulkner, Electrochemical Methods, Fundamentals and Applications, Wiley, New York, 1980, p. 230. [16] A.J. Bard, L.R. Faulkner, Electrochemical Methods, Fundamentals and Applications, Wiley, New York, 1980, p. 530. [17] G.S. Patterson, R.H. Holm, Bioinorg. Chem. 7 (1975) 257 and references cited therein. [18] C. Fraser, B. Bosnich, Inorg. Chem. 33 (1994) 338. [19] E.D. Mckenzie, S.J. Selvey, Inorg. Chim. Acta 18 (1976) L1.
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