The ligational behavior of an isatinic quinolyl hydrazone towards copper(II)- ions
© Seleem et al 2011
Received: 5 February 2011
Accepted: 19 April 2011
Published: 19 April 2011
The importance of the isatinic quinolyl hydrazones arises from incorporating the quinoline ring with the indole ring. Quinoline ring has therapeutic and biological activities whereas, the indole ring occurs in Jasmine flowers and Orange blossoms. As a ligand, the isatin moiety is potentially ambidentate and can coordinate the metal ions either through its lactam or lactim forms. In a previous study, the ligational behavior of a phenolic quinolyl hydrazone towards copper(II)- ions has been studied. As continuation of our interest, the present study is planned to check the ligational behavior of an isatinic quinolyl hydrazone.
New homo- and heteroleptic copper(II)- complexes were obtained from the reaction of an isatinic quinolyl hydrazone (HL) with several copper(II)- salts viz. Clˉ, Brˉ, NO3ˉ, ClO4-, SO42- and AcO-. The obtained complexes have Oh, Td and D4h- symmetry and fulfill the strong coordinating ability of Clˉ, Brˉ, NO3ˉ and SO42- anions. Depending on the type of the anion, the ligand coordinates the copper(II)- ions either through its lactam (NO3ˉ and ClO4-) or lactim (the others) forms.
The effect of anion for the same metal ion is obvious from either the geometry of the isolated complexes (Oh, Td and D4h) or the various modes of bonding. Also, the obtained complexes fulfill the strong coordinating ability of Clˉ, Brˉ, NO3ˉ and SO42- anions in consistency with the donor ability of the anions. In case of copper(II)- acetate, a unique homoleptic complex (5) was obtained in which the AcO- anion acts as a base enough to quantitatively deprotonate the hydrazone. The isatinic hydrazone uses its lactim form in most complexes.
Results and discussion
Characterization of the hydrazone
Analytical and physical data of the copper(II)- isatinic complexes.
Reactants (HL + metal salt)
Elemental Analysis; % Found/(Calcd.)
HL (C19H16N4O; 316.36)
[Cu (L) (HL) (H2O)2] ClO4.3H2O (884.79)
[Cu (HL)2 (NO3)2].1¼ H2O (842.81)
[Cu (L) (H2O) Cl].1/2 H2O.1/8 MeOH (445.38)
[Cu (L) (H2O)3 Br].3/8 H2O (519.60)
Granulated greenish brown
[Cu (L)2].1/8 H2O.1/8 MeOH (700.51)
Bright greenish brown
[Cu2 (L)2 (H2O)4 SO4].2 H2O.MeOH (994)
Magnetic, conductivity, electronic and IR spectral data of the copper(II)- isatinic complexes.
IR spectral bands; cm-1
ν (C = O)
ν (C = N)
1387 and 1297; ν (NO)
1135; ν3 (SO)
Characterization of the isatinic complexes
IR spectra of the complexes
The mode of bonding was studied by comparing the IR spectral bands of the metal complexes with those of the free ligand (Table 2). Inspection of the data revealed the following: (i) All complexes showed a broad band in the range 3463-3203 cm-1 due to ν(OH) of the associated water or methanol molecules. (ii) The band at 1605 cm-1 assignable to ν(C=N) in the free ligand was shifted to higher values indicating the participation of C=N of the hydrazone moiety in the chelation with π- electron delocalization. (iii) In most complexes, the band located at 1706 cm-1 due to ν(C=O) of the free ligand disappeared indicating the participation of the lactim- form in the chelation. In contrast, the lactam- form participates in the chelation in case of the nitrato (2) and perchlorato (1) complexes as indicated by the shift of the above band to lower wave numbers; 1692 and 1653 cm-1, respectively. However, the greater lower value 1653 cm-1 for the perchlorate complex (1) may suggest mixed modes of bonding (lactim + lactam) ; Scheme 3. (iv) In complex 1, the strong broad band centered at 1100 cm-1 (antisymmetric stretch) and the sharp band at 621 cm-1 (antisymmetric bend) suggest uncoordinated ClO4ˉ anion . (v) For the binuclear sulfato complex (6), the chelating bidentate nature of the SO42ˉ group is indicated by the appearance of ν3(S-O) strong band at 1135 cm-1 characteristic for the high symmetry Td (tetrahedral) point group. The nitrato complex (2) showed two bands at 1387 and 1297 cm-1 confirming the monodentate nature of the coordinated NO3ˉ group; C2v symmetry. (vi) Finally, the detection of the non ligand bands; ν(M-O) and ν(M-N) in the finger print region is more difficult and tentative.
Conductivity and magnetic properties
The recorded conductance for 10-3 molar DMF solutions of the complexes (Table 2) indicates that all complexes are non-conducting due to their neutrality (Λ = 17.0-1.9 Ω-1 cm2 mol-1). The only exception is [Cu(L)(HL)(H2O)2]ClO4.3H2O (1) which showed molar conductance of 95 Ω-1 cm2 mol-1, indicating its 1:1 electrolytic nature which is consistent with the IR spectra; ν3(Cl-O) at 1100 cm-1. In contrast, the halo-complexes (3 and 4) showed molar conductance of 37 and 40 Ω-1 cm2 mol-1, respectively indicating their partial electrolytic nature which is due to the replacement of the coordinated Clˉ and Brˉ ions by DMF solvent molecules . On the other side, the effective magnetic moments (μeff) of the copper(II)- complexes (1-5) lie in the range 1.93-1.77 B.M. (Table 2) which is consistent with one unpaired electron and falls within the range reported for mononuclear copper(II)- complexes. However, the binuclear copper(II)- complex (6) exhibits lower μeff value at 1.4 B.M. indicating some metal---metal interaction.
Mass and electronic spectra
Electron spin resonance spectroscopy
In summary, the Td- complex (5) with the lactim mode showed either higher values of G, α2, and f or lower values of β2 and AΠ as compared to the Oh complex (1) with the mixed mode (lactam + lactim) which is consistent with the greater discrepancy of the observed spectra.
Thermal (TG-DSC) analysis
The thermal degradation behavior of the investigated complexes was followed by the thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques. The decomposition occurs in one or more steps according to the nature of each complex. Attempts to generalize the thermal degradation patterns were unsuccessful indicating that there is no simple relation or general trend for explaining these thermal degradations. However, the decomposition ends with the formation of Cu2O in most cases. Inspection of the TG thermograms revealed the following: (i) The perchlorato complex (1) decomposes in one strong endothermic step (ΔH = 391 J/g at 272°C) to form Cu2O as the end product, a phenomenon encountered with ClO4‾ anions . (ii) For the nitrato- (2) and sulfato (6)- complexes, the decomposition is not completed up to 800°C, indicating that the metal-ligand bonds are strong. This is consistent with the data extracted from IR. (iii) In contrast, for the other complexes(1, 4 & 5), the decomposition process is ended with Cu2O.
Kinetic and thermodynamic parameters
Thermodynamic and kinetic parametersa of the copper(II)- isatinic complexes.
A × 10-9sec-1
1.709 × 107
The biological activity* of HL and its copper(II)- complexes.
Gram - positive bacteria
Gram - negative bacteria
The chemicals used in this investigation were of the highest purity available (Merck, BDH, Aldrich and Fluka). They included copper(II)- nitrate, perchlorate, sulfate, chloride, bromide and acetate as well as o-toluidine, ethyl acetoacetate, phosphorus oxychloride, hydrazine hydrate and isatin. Organic solvents were reagent grade chemicals and were used without further purification.
Microanalyses were carried out on a Perkin-Elmer 2400 CHN elemental analyzer. Thermal analyses (TG-DSC) were carried out on a Shimadzu-50 thermal analyzer. Electronic spectra were recorded on a Jasco V-550 UV/VIS spectrophotometer. IR spectra were recorded on a Bruker Vector 22 spectrometer using KBr pellets. ESR spectra were recorded on a Bruker Elexsys, E 500 operated at X-band frequency. Mass spectra were recorded either at 70 eV on a gas chromatographic GCMSQP 1000-EX Shimadzu mass spectrometer or Direct Inlet unit (DI-50) of Shimadzu GC/MS - QP5050A. 1H NMR spectra were recorded as DMSO-d6 solutions on a Varian Mercury VX-300 NMR spectrometer using TMS as a reference. Molar conductivity was measured as DMF solutions on the Corning conductivity meter NY 14831 model 441. Magnetic susceptibility of the complexes was measured at room temperature using a Johnson Matthey, MKI magnetic susceptibility balance. Melting points were determined using a Stuart melting point apparatus.
An ethanolic mixture of 2-hydrazinyl-4,8-dimethyl quinoline (0.01 mol) and isatin (0.012 mol) was refluxed for 1/2 h. The formed red compound was filtered off, washed with ethanol and crystallized from DMF. The results of elemental analysis, % yield and m.p°C are shown in Table 1.
Preparation of the metal complexes
Methanolic solutions of the metal salt and the ligand were mixed in the mole ratio 1:1 and/or 1:2; M:L and refluxed for 6-10 hours depending on the nature of the isolated complexes. The resulting precipitates were filtered off, washed with methanol then ether and finally air-dried. The results of elemental analysis, % yield and m.p°C are shown in Table 1.
Antimicrobial and antifungal activities
The standardized disc-agar diffusion method was followed to determine the activity of the synthesized compounds against the sensitive organisms Staphylococcus aureus (ATCC 25923) and Streptococcus pyogenes (ATCC 19615) as Gram-positive bacteria, Pseudomonas fluorescens (S 97) and Pseudomonas Phaseolicola (GSPB 2828) as Gram-negative bacteria and the Fungi Fusarium oxysporum and Aspergillus fumigatus. The antibiotic chloramphencol and Cephalothin were used as standard references in case of Gram-negative and Gram-positive bacteria, respectively, whereas Cycloheximide was used as a standard antifungal reference. The tested compounds were dissolved in DMF which have no inhibition activity to get concentration of 2 mg/mL. The test was performed on medium potato dextrose agar (PDA) which contain infusion of 200 g potatoes, 6 g dextrose and 15 g agar. Uniform size filter paper disks (3 disks per compound) were impregnated by equal volume (10 μL) from the specific concentration of dissolved tested compounds and carefully placed on inoculated agar surface. After incubation for 36 h at 37°C in case of bacteria and for three days at 25°C in case of fungi, inhibition of the organisms which evidenced by clear zone surround each disk was measured and used to calculate mean of inhibition zones.
The present study is planned to check the effect of the counteranions on the isolated complexes as well as the ligational behavior of the isatinic hydrazone ligand. The effect of anion for the same metal ion is obvious from either the geometry of the isolated complexes (Oh, Td and D4h) or the various modes of bonding. Also, the obtained complexes fulfill the strong coordinating ability of Clˉ, Brˉ, NO3ˉ and SO42- anions as compared to the ClO4ˉ anion in consistency with the donor ability of the anions . In case of copper(II)- acetate, a unique homoleptic complex (5) was obtained in which the AcO- anion acts as a base enough to quantitatively deprotonate the hydrazone. The isatinic hydrazone uses its lactim form in most complexes.
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