O M N O N OEt EtO O O M X (H2O) n O (H2O) n Mn, Cu, Zn, Cd, Hg Co Ni 133 Cl Cl OH M n X 16 J. CHEM. RESEARCH (S), 1998 J. Chem. Research (S), 1998, 16–17 J. Chem. Research (M), 1998, 0201–0213 Dinuclear Complexes of Diethyl 2-(2-Carboxyphenylhydrazono)-3-oxopentanedioate with some Transition Metal Ions Yousry M. Issa,* Nour T. Abdel-Ghani and Maha F. Abo El-Ghar Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt Manganese(II), cobalt(II), copper(II), zinc(II), cadmium(II) and mercury(II) complexes of diethyl 2-(2-carboxyphenylhydrazono)- 3-oxopentanedioate have been prepared and characterized by IR, 1H NMR and UV spectroscopy, magnetic moment measurements and thermogravimetric analysis.Coordination compounds with several dinucleating ligands have been studied as models for naturally occurring systems1 and in the domain of metallo-enzymes and homogeneous catalysis. The synthesis of dinuclear complexes involves choice of a suitable ligand which can coordinate through more than one chelation centre.5 Diethyl 3-oxopentanedioate can be regarded as a precursor for 2-arylhydrazone derivatives having two separate centres of chelation. This article deals with the synthesis and structural characterization of diethyl 2-(2-carboxyphenylhydrazono)-3-oxopentanedioate (H3L) complexes with some divalent metal ions, MnII, CoII, NiII, CuII, ZnII, CdII and HgII.The ligand acts as a b-oxo ester and an a-oxo 2-carboxyphenylhydrazone: it may chelate to two metal ions via the enolic OH and CO (unconjugated ester) on one side, and the NH, CO (conjugated ester) and OH (carboxylic) on the other side.Diethyl 2-(2-carboxyphenylhydrazono)-3-oxopentanedioate was prepared according to the method described in the literature.14 The complexes were prepared by mixing 1 mol equiv. of the ligand with 2 mol equiv. of the metal chloride in ethanol and boiling for 10 min. NaOH (3 mol equiv.) was then added gradually with continuous stirring while boiling.The mixture was diluted with distilled water and the product was collected by filtration and washed several times with ethanol till the filtrate was colourless. The complexes, M2LCl.nH2O [M=MnII, CoII, CuII, ZnII, CdII, HgII; n=2–6] and Ni2L.OH.6H2O, were isolated in 60–65% yield. The structure of the dinuclear complexes may be proposed as: The IR spectra of the MII–H3L complexes showed masking of the vNH of the hydrazo group and vOH of the carboxylic group attached to the aromatic moiety by a very broad band centred at ca. 3400 cmµ1 which can be assigned to vOH of the water molecules coordinated to the metal ion. New bands at 1275–1264 cmµ1 corresponding to a dOH(H2O) deformation and at 690 cmµ1 assigned to a H2O rocking vibration17 were observed. vC——O appeared as a medium-intensity band at 1732–1676 cmµ1 which could be taken as evidence for the participation of C�O groups in chelation. The CH bending vibration band of the ·CH2·CO· moiety at 1420 cmµ1 disappeared on chelation, indicating its involvement in the coordination through the enolic form of the ligand.The appearance of a new band at 1610, 1611 and 1613 cmµ1 for the CoII, ZnII and CdII complexes, respectively, emphasized the presence of C�C as a result of enolization. New bands observed at 468–428 and 406–416 cmµ1 were assigned to vM·N 19 and vM·O 20 respectively. The 1H NMR spectrum of the ligand showed two adjacent triplets at d 1.20 and 1.30, and two quartets at d 4.10 and 4.35 corresponding to the six protons (two CH3) and four protons (two CH2) of the two ethyl groups, respectively.A singlet was observed at d 3.95 corresponding to the active methylene group.21 The aromatic protons were shown as multiplet signals at d 7.25, 7.75, 7.90 and 8.05. The NH and CO2H protons showed signals at d 13.89 and d 3.40, respectively, which disappeared on deuteration. [Cd2LCl.2H2O] and [Hg2LCl.2H2O] showed disappearance of the NH proton, indicating the involvement of the NH in chelation.Disappearance of the active methylene protons as well as the appearance of a new singlet at d 7.0 corresponding to the methine proton (�CH) indicated enolization of the oxo group as a result of chelation. The participation of the CO2H proton in chelation cannot be accounted for from the 1H NMR spectra because of the water peak that appeared as a strong sharp singlet at the same position (d 3.5).Thermogravimetric analysis curves showed no mass loss below 150 °C, indicating absence of water of hydration in the complexes. Removal of coordinated water molecules started at about 200 °C. This was supported by the appearance of an endothermic peak in the DTA curves over the same temperature range. The decomposition of the MnII, CoII, CuII and ZnII complexes proceeded as a one-step combustion, associated by an exothermic peak in the DTA curve, at 330–490 °C, leading to a final product as MnO2, Co2O3, CuO or ZnO associated with their corresponding metal chlorides. The final residue of the NiII complex amounted to 28%, indicating the formation of NiO.The data were in conformity with the metal content obtained from EDTA titration. The electronic absorption band of [Mn2LCl.2H2O] at 27 144 cmµ1 suggested a tetrahedral structure and the value of the magnetic moment meff (5.21 mB per metal ion) was as expected for a high-spin 3d5 system.22 Bands at 17 500 and 26 247 cmµ1 for [Co2LCl.6H2O] and [Ni2L.OH.6H2O] assigned to 4T1g(F)h4T1g(P) and 3A2g(F)h3T1g(P) transitions, respectively, reflected the octahedral geometry around the CoII and NiII metal ions, while the values of meff (3.97 mB and 3.00 mB per metal ion, respectively) were typical of those reported for high-spin CoII ions23 and were in the same range as reported for octahedral geometry around NiII ions.24 The magnetic moment of [Cu2LCl.2H2O] was 1.64 mB per metal ion, a lower value than that normally reported for an unpaired electron in the CuII metal ion and which may be attributed to a spin-exchange interaction between the two CuII ions.25 The electronic spectrum showed a band at 24 746 *To receive any correspondence.J.CHEM. RESEARCH (S), 1998 17 cmµ1 assigned to a ligand–metal charge transfer, probably a p–p* transition.26 ZnII, CdII and HgII ions were diamagnetic in their complexes. Techniques used: IR, 1H NMR, UV, magnetic moment measurements, TG References: 26 Tables: 4 (formula, elemental analyses, magnetic moment, UV, IR, 1H-NMR and TG) Received, 27th May 1997; Accepted, 19th September 1997 Paper E/7/03623J References cited in this synopsis 1 K.Takahashi, Y. Nishida, Y. Maeda and S. Kida, J. Chem. Soc., Dalton Trans., 1985, 2375. 5 M. Tanaka, M. Kitaoka, H. Okawa and S. Kida, Bull. Chem. Soc. Jpn., 1976, 49, 2469. 14 (a) C. B�ulow and W. Hopfner, Ber. Dtsch. Chem. Ges., 1901, 34, 71; (b) C. B�ulow and H. Goller, Ber. Dtsch. Chem. Ges., 1911, 44, 2835. 17 R. C. Mishra, B. K. Mahapatra and D. Panda, J. Indian Chem. Soc., 1983, 58, 80. 19 E. P. Powell and N. Sheppard, Spectrochim Acta, 1961, 17, 68. 20 C. Djordjevic, Spectrochim. Acta, 1961, 17, 448. 21 B. P. Dailey and J. W. Shoolery, J. Am. Chem. Soc., 1955, 77, 3977. 22 D. H. L. Goodgame and F. A. Cotton, J. Chem. Soc., 1961, 3735. 23 A. T. Casey and S. Mitra, in Theory and Application of Molecular Paramagnetism, ed. E. A. Boudreaux and I. N. Mulay, Wiley, New York, 1976. 24 G. M. Abou El-Reash, Synth. React. Inorg. Met.-Org. Chem., 1993, 23, 825. 25 H. C. Rai and B. N. Sharma, Asian J. Chem., 1995, 7, 775. 26 A. K. Gregson, R. L. Martin and S. Mitra, Proc. R. Soc. London, Ser. A, 1971,