Gilles Bouet

Mustayeen Khan

Ouassini Benali-Baitich

Sabrina Belaid

Safia Djebbar

Comptes Rendus Chimie

C. R. Chimie 10 (2007) 568e572http://france.elsevier.com/direct/CRAS2C/Account / RevueComplex formation between manganese(II), cobalt(II),nickel(II), copper(II) and a series of new ligandsderived from N,N0-O-phenylenebis(salicylideneimine)Sabrina Belaid a, Safia Djebbar a, Ouassini Benali-Baitich a,*,Mustayeen Khan b, Gilles Bouet ba Laboratoire d’hydrométallurgie et chimie inorganique moléculaire, USTHB, BP 32 El Alia, 16111 Bab-Ezzouar, Alger, Algeriab Laboratoire SONAS, Chimie de coordination, faculté de pharmacie, 16, bd Daviers, 49045 Angers cedex 01, FranceReceived 22 May 2006; accepted after revision 15 September 2006Available online 20 December 2006AbstractA series of new ligands derived from N,N0-O-phenylenebis(salicylideneimine) have been synthesized and characterized byspectrometric methods. Their protonation constants and the stability constants of their complexes with Mn2þ, Co2þ, Ni2þet Cu2þ have been determined by potentiometric methods in a watereethanol (90:10 v/v) mixture at a 0.2 mol l1 ionic strength(NaCl) and at 25.0 0.1 C. The Sirko program was used to determine the protonation constants as well as the binding constantsof both species [M(HL)]þ and [ML]. The stability order obtained is in agreement with IrvingeWilliams series. To cite this article:S. Belaid et al., C. R. Chimie 10 (2007). 2006 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.RésuméUne série de nouveaux ligands dérivés de la N,N0-O-phenylenebis(salicylidèneimine)a été synthétisée et caractérisée par lesméthodes spectrométriques conventionnelles. L’étude de la complexation des ions métalliques Mn2þ, Co2þ, Ni2þ et Cu2þ, parces ligands, a été effectuée par pH-métrie en milieu eaueéthanol 90 :10 (vol./vol.) à 25 C 0.1 et à force ionique constante0,2 M en milieu NaCl. Les constantes de protonation des ligands et les constantes de stabilités des deux espèces [M(HL)]þ et[ML] ont été déterminées à l’aide du programme Sirko. L’ordre de stabilité obtenu pour les complexes est en accord avec la séried’Irving et Williams. Pour citer cet article : S. Belaid et al., C. R. Chimie 10 (2007). 2006 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.Keywords: Schiff base; Reduction; Potentiometry; Stability constantsMots-clés : Base de Schiff ; Réduction ; Potentiométrie ; Constantes de stabilités* Corresponding author.E-mail address: benali-baitich@netcourrier.com (O. Benali-Baitich).1631-0748/$ - see front matter  2006 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.doi:10.1016/j.crci.2006.09.012569S. Belaid et al. / C. R. Chimie 10 (2007) 568e5721. IntroductionSchiff bases constitute an interesting class ofchelating agents. Due to their preparative accessibility,diversity and structure variability, they are capable ofcoordinating metal ions, giving complexes whichexhibit wide applications in biological systems and in-dustrial uses [1e3].Schiff bases derived from ortho-phenylenediamineare of particular interest because of the proximity ofthe nitrogen atoms, which permits their simultaneouscoordination to the same metal cation, leading mainlyto stable monomer species [4e6].However, these Schiff bases can be reduced to thecorresponding amine derivatives, which have a higherstability because they are more flexible and not con-strained to remaining planar [7e9], and they do not suf-fer the hydrolytic processes encountered with Schiffbase analogues [10].Our interest in the chemistry of reduced Schiff baseshas also stemmed from previous results about antitumoractivities of complexes of Cu(II) with a reduced Schiffbase [11e13].In the present work, we report the determination bypotentiometric method of the protonation constants ofa series of reduced Schiff bases (Fig. 1) derived from or-tho-phenylenediamine, and stability constants of theircomplexes with Mn(II), Co(II), Ni(II) and Cu(II) ions.The aim of this study is the determination of both theeffect of the R group and the reduction of the C]N bondson the stability of the complexes, by comparison of theresults with those reported for Schiff base analogues.2. Experimental2.1. Reagentsortho-Phenylenediamine, 3,4-diaminotoluene, 4-chloro-1,2-phenylenediamine and salicylaldehyde wereNHHNCH2 CH2OHOHRFig. 1. Formula of ligands: H2L1: R¼H; H2L2: R¼CH3; H2L3:R¼Cl.purchased from Fluka and used without furtherpurification.Hexahydrated metal chlorides were obtained fromMerck, exact concentrations of metal solutions weredetermined by titration with EDTA.Carbonate-free sodium hydroxide used for thepotentiometric titrations was prepared and standardizedagainst a standard hydrochloric acid solution.2.2. Potentiometric measurementsThe potentiometric titrations were carried out inwatereethanol (90:10 v/v) solution at a 0.2 mol l1 ionicstrength (NaCl) in a thermostated vessel at 25.0 0.1 Cunder nitrogen atmosphere. The solutions were titratedwith carbonate-free NaOH (0.1 mol l1), the pH valueswere measured with a Hanna instruments HI 8417 pHmeter.The pH meter readings in watereethanol (90:10 v/v)mixture pH(r) differs by an amount from the correctedreading in aqueous medium pH*, according to theequation: pH*¼ pH(r) d [14]. The value of d forwatereethanol (90:10 v/v) mixture was reported to be0.02. Accordingly, the presence of 10% of ethanol inthe solvent has a minor influence on the protonationor the complexes’ stability constants obtained.The measurements were carried out for the ligandalone at the concentration CL¼ 5 103 mol l1, andfor the ligand in the presence of metal cation (ligand/metal ratio 1:1), at the concentration CM¼ CL¼5 104 mol l1.The Sirko program [15] was used to calculate bothprotonation and stability constants of the ligands andtheir complexes. Computer-refined values of theconstants, corresponding to the minimum standarddeviation were retained, and used for the calculationof species distribution.2.3. Synthesis of ligandsThe ligands were synthesized by reduction of Schiffbase analogues by NaBH4 [16]. The Schiff bases havebeen prepared by refluxing in ethanol 2 mmol of salicy-laldehyde and 1 mmol of ortho-phenylenediamine forH2L1, 3,4-diaminotoluene for H2L2, 4-chloro-1,2-peny-lenediamine for H2L3. The resulting Schiff bases wererecrystallized in ethanol, and then characterized byelemental analysis, NMR and IR.In order to reduce the imine bonds, 1 mmol of Schiffbase was dissolved in absolute ethanol, and 3 mmol ofNaBH4 was added in small portions over 1 h. Theresulting mixture was stirred for 2 h, during which570 S. Belaid et al. / C. R. Chimie 10 (2007) 568e572time it changed color. Then, the solution was dilutedand acidified with hydrochloric acid in order to destroythe excess of NaBH4.The new ligand was extracted with CH2Cl2, thesolvent was removed under vacuum and the resultingresidue was washed with diethyl ether and stirred inhexane until it was transformed into a solid powder.The elemental microanalyses were carried out at theCentral Service of Analysis, CNRS Vernaison (France).The IR Spectra were recorded on a PerkinElmer spec-trum one Fourier transform infrared spectrometer. 1HNMR was recorded on a Jeol Gsx 270 MSB (270MHz) spectrometer.3. Results and discussion3.1. Characterization of ligandsAnalytical data: found (calc.) for H2L1: C, 75.32(75.00); H, 6.49 (6.25); N, 8.28 (8.75). For H2L2: C,75.56 (75.44); H, 6.35 (6.58); N, 8.42 (8.38). ForH2L3: C, 67.56 (67.70); H, 5.49 (5.35); N, 7.45(7.89); Cl, 10.25 (10.01).The analysis of IR spectra of the ligands shows theabsence of any strong absorption at 1615 cm1 attribut-able to the imine bond, indicating the reduction ofC]N bond to the CeNH one. This is confirmed bythe presence of new absorption bands at 3390 cm1 as-signed to n (NeH) of the amino groups [17].The IR spectra of the ligands exhibit broad mediumintensity band in the 3200e3270 cm1 range, which isassigned to the OeH vibrations.The aromatic rings give an intense band due to CeHdeformation at 700 cm1.The 1H NMR spectra of the ligands (Table 1) have noazomethine hydrogen peaks at 8.2e8.5 ppm, but showTable 11H NMR spectral chemical shifts (d in ppm)Ligand Aromatic protons CH2eN CH3 eOHH2L1 6.25e6.46 (m) 4.30 (s) 11.256.72e7.02 (m)6.89e7.08 (m)H2L2 6.05e6.18 (m) 4.30 (s) 2.42 (s) 11.086.42e7.05 (m)6.45e7.02 (m)H2L3 6.20e6.48 (m) 4.30 (s) 11.106.58e7.12 (m)6.45e7.06 (m)Measured as saturated solution in CDCl3, using TMS as the reference,s¼ singlet, m¼multiplet.new peaks at 4.2 ppm attributable to the methylenegroups. The amine hydrogen peak was not observed.Nevertheless, these observations support the infrareddata, and confirm the reduction of imine bonds to amineones.3.2. Potentiometric measurementsThe constant bpqr calculated by the Sirko programare defined by the equilibrium:pM2þ þ qHþ þ rL2 % ½MpHqLrð2pþq2rÞbpqrThe successive constants log K for the ligandscalculated from the overall constants log bpqr are listedin Table 2.The ligands are tetradentate with two adjacent weakamine donors and two strongly basic phenolate groups.Four constants were obtained for each ligand; the basic-ity sequence obtained is H2L2>H2L1>H2L3.The higher basic character of H2L2 is attributable tothe electron-donor effect of the methyl group; and thelower basic character of H2L3 is due to the electron-withdrawing effect of the chloride atom.Comparison of these results with those reported forSchiff base analogues [4e6] indicates that the proton-ation constants of these ligands are higher, especiallyTable 2Protonation constants of the ligands (log K)Equilibrium Log KH2L1 H2L2 H2L3L2/HL 11.30 (0.04) 12.32 (0.03) 10.88 (0.08)HL/H2L 10.29 (0.04) 10.76 (0.02) 9.86 (0.06)H2L/H3Lþ 5.12 (0.01) 6.02 (0.04) 4.30 (0.07)H2L/H3Lþ 5.82 (0.01) 6.75 (0.04) 4.96 (0.07)Watereethanol (90:10 v/v), I¼ 0.2 M NaCl.2 4 6 8 10020406080100pH% [H2L]H4L2+H3L+L2-HL-H2LFig. 2. Species distribution diagram of H2L1.571S. Belaid et al. / C. R. Chimie 10 (2007) 568e572Table 3Stability constants (log K) for the complexesSpecies Mn Co Ni Cu[M(HL1)]þ 7.94 (0.01) 10.32 (0.10) 10.58 (0.08) 10.95 (0.05)[ML1] 14.23 (0.04) 16.41 (0.06) 16.85 (0.04) 17.31 (0.01)[M(HL2)]þ 8.02 (0.05) 10.87 (0.04) 11.05 (0.10) 11.45 (0.06)[ML2] 14.81 (0.06) 17.2 (0.02) 17.32 (0.08) 17.81 (0.04)[M(HL3)]þ 6.13 (0.01) 9.81 (0.07) 9.74 (0.09) 10.21 (0.07)[ML3] 12.48 (0.07) 15.31 (0.05) 15.22 (0.03) 16.1 (0.08)Watereethanol (90:10 v/v), I¼ 0.2 M NaCl.those assigned to the nitrogen atoms of the aminogroups. This arises because the nitrogen atoms of theSchiff base are not able to disperse charge to the solventby hydrogen bonding [18].The species distribution diagram as function of pH(Fig. 2) shows that the deprotonation of H4L2þ occurat pH¼ 4 and leads to the successive formation ofH3Lþ, H2L, HL and L2, the deprotonation of bothphenolic groups is completed at pH> 10.Similar diagrams were obtained for H2L2 and H2L3.The stability constants (log K) obtained for the com-plexes are listed in Table 3. For all the systems studied,only monomer species were formed, the model that bestfits the experimental data is the one with formation oftwo species [MHL]þ and [ML].The [MHL]þ species may be assumed to be pro-tonated at the phenol oxygen of salicylaldehyde moi-ety. The complex [ML] results from the coordinationof the metal to the ligand fully deprotonated. It ismore stable than the complex [MHL]þ, indicatingthat in the ML complex, the ligand is coordinatedto the metal by both amino groups and phenolateoxygen atoms.2 4 6 8 10020406080100NiL[NiHL]+Ni+2% Ni+2 pHFig. 3. Species distribution diagram of NieH2L3.The systems H2L2eM(II) (M(II)¼Ni, Cu, Co andMn) give complexes that are more stable than thosefor the systems H2L1eM(II) due to the electron-donoreffect of the methyl group, which is favorable tocoordination.For the systems H2L3eM(II), the opposite effect ap-plies and the stability of their complexes are less thanthose for H2L1eM(II) systems, as a consequence ofthe electron-withdrawing effect of the chloride atom.Thus, for any metal the stability sequence isH2L2>H2L1>H2L3 in agreement with the basic char-acter order of these ligands.For the systems ML (H2L¼H2L1, H2L2, H2L3), thestability sequence observed is Cu>Ni> Co>Mn, inagreement with IrvingeWilliams series.The complexes of Ni(II) and Co(II) with these li-gands are more stable than those reported with Schiffbase analogues [4e6]. In fact, the complexes of reducedSchiff bases are expected to be more flexible as they arenot constrained to be planar.The species distribution diagram for NieH2L3andCueH2L2 systems are reported in Figs. 3 and 4. Similardiagrams were obtained for the other systems.Cu2+[Cu(HL)]+CuL0204060801002 4 6 8 10pH% CuFig. 4. Species distribution NieH2L3 diagram of CueH2L2.572 S. Belaid et al. / C. R. Chimie 10 (2007) 568e572References[1] J.A. McCleverty, T.J. Meyer, Comprehensive CoordinationChemistry II, From Biology to Nanotechnology, vol. 1,Elsevier, 2004, p. 411.[2] D. Xu, B. Chen, K. Chen, K. Miki, N. Kasai, Bull. Chem. Soc.Jpn. 62 (1989) 275.[3] P.H. Hang, J.G. Keck, E.T. Lien, J. Med. Chem. 33(1990) 608.[4] R. Hernandez-Molina, A. Mederos, P. Gili, S. Dominguez,P. Nunez, Polyhedron 16 (1997) 4191.[5] R. Hernandez-Molina, A. Mederos, P. Gili, S. Dominguez,P. Nunez, G. Germain, T. Debaerdemaeker, Inorg. Chim. Acta256 (1997) 319.[6] A. Mederos, A. Medina, P. Gili, F.G. Manrique, P. 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Soc., Dalton Trans. (1993) 265.[17] G. Socrates, Infrared Characteristic Group Frequencies, Wileyand Sons, 1980.[18] A.E. Martell, R.D. Hancock, Metal Complexes in AqueousSolutions, Plenum Press, New York, 1996, p. 54.

Complex formation between manganese(II), cobalt(II), nickel(II), copper(II) and a series of new ligands derived from N,N′-O-phenylenebis(salicylideneimine)

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Complex formation between manganese(II), cobalt(II), nickel(II), copper(II) and a series of new ligands derived from <i>N</i>,<i>N</i>′-<i>O</i>-phenylenebis(salicylideneimine)

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