Transition metal complexes of an isatinic quinolyl hydrazone
© Seleem et al 2011
Received: 27 March 2011
Accepted: 27 June 2011
Published: 27 June 2011
The importance of the isatinic quinolyl hydrazones arises from incorporating the quinoline ring with the indole ring in the same compound. Quinoline ring has therapeutic and biological activities. On the other hand, isatin (1H-indole-2,3-dione) and its derivatives exhibit a wide range of biological activities. Also, the indole ring occurs in Jasmine flowers and Orange blossoms. Recently, the physiological and biological activities of quinolyl hydrazones arise from their tendency to form metal chelates with transition metal ions. In this context, we have reported to isolate, characterize and study the biological activity of some transition metal complexes of an isatinic quinolyl hydrazone; 3-[2-(4-methyl quinolin-2-yl)hydrazono] indolin-2-one.
Mono- and binuclear as well as dimeric chelates were obtained from the reaction of a new isatinic quinolyl hydrazone with Fe(III), Co(II), Ni(II), Cu(II), VO(II) and Pd(II) ions. The ligand showed a variety of modes of bonding viz. (NNO)2-, (NO)- and (NO) per each metal ion supporting its ambidentate and flexidentate characters. The mode of bonding and basicity of the ligand depend mainly on the type of the metal cation and its counter anion. All the obtained Pd(II)- complexes have the preferable square planar geometry (D4h- symmetry) and depend mainly on the mole ratio (M:L).
The effect of the type of the metal ion for the same anion (Cl-) is obvious from either structural diversity of the isolated complexes (Oh, Td and D4h) or the various modes of bonding. The isatinic hydrazone uses its lactim form in all complexes (Cl-) except complex 5 (SO42-) in which it uses its lactam form. The obtained Pd(II)- complexes (dimeric, mono- and binuclear) are affected by the mole ratio (M:L) and have the square planar (D4h) geometry. Also, the antimicrobial activity is highly influenced by the nature of the metal ion and the order for S. aureus bacteria is as follows: Nickel(II) > Vanadyl(II) > Cobalt(II) > Copper(II) ≈ Palladium(II) >> Iron(III).
Results and discussion
Characterization of the hydrazone
Effect of solvent on the spectra of the hydrazone
Electronic spectral data*of the isatinic hydrazone in various solvents
Characterization of the isatinic complexes
Analytical and physical data of the isatinic complexes
Elemental Analysis; %Found/(Calcd.)
Metal salt + H2L
[Fe(HL)2Cl(H2O)].1⊠ H2O (741.15)
[Pd2 (HL)Cl3(EtOH)] (666.5)
IR spectra of the complexes
Most complexes showed a broad band in the range 3463-3203 cm-1 due to ν(OH) of the associated water or ethanol molecules. The band at 1633 cm-1 assignable to ν(C = N) in the free ligand was shifted to higher or lower values indicating its participation in the chelation with π- electron delocalization. In all complexes, the band located at 1684 cm-1 due to ν(C = O) of the free ligand disappeared indicating the participation of the lactim form in the chelation. An exception is complex 5 in which this band is shifted to lower wave number; 1670 cm-1. The variable intensity bands of the quinoline ring of the free hydrazone at 1554,1482 and 1455 cm-1 are greatly altered as a result of the complexation.
The free sulfate ion belongs to the high symmetry Td point group. Of the four fundamentals, only υ3 and υ4 are IR active; bands at ~ 1105 and ~ 615 cm-1, assignable to υ3 stretching [υ(SO)] and υ4 bending [δ(OSO)] modes, respectively [15, 16]. The υ1 stretching [υ(SO)] and υ2 bending [δ(OSO)] fundamentals are not IR-active. However, the coordination of SO42- to metal ions in a bidentate fashion decreases the symmetry of the group and the υ3 and υ4 modes may be split [15–17]. For the sulfato complex (5) in this study, the chelating bidentate nature of the SO42- group is indicated by the strong band at 1100 cm-1; ν3(S-O) as well as a medium band at 657 cm-1; ν4[δ(OSO)] characteristic for the tetrahedral (Td) point group. These spectral features suggest a low symmetry for the sulfato ligand in the complex.
Magnetic, conductivity and electronic spectral data of the isatinic complexes
Mass, ESR and electronic spectra
Antimicrobial activity * of the H2L and its complexes
Mean of zone diameter (mm)
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), cobalt(II), nickel(II), palladium(II) and iron(III) chlorides, as well as vanadyl sulfate monohydrate. Also, they included aniline, 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. Analyses of metal ions followed dissolution of the solid complex in hot concentrated nitric acid, HNO3, then diluting with doubly distilled water and filtration. The resultant solution was neutralized with ammonia and the metal ions were then titrated against EDTA. 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-methyl quinoline (0.01mol) and isatin (0.012 mol) was refluxed for 15 min. The formed scarlet red compound was filtered off, washed with ethanol and crystallized from DMF; Yield: 77% and m.p 302°C.
Preparation of the metal complexes
Ethanolic solutions of the metal salt and the ligand were mixed in the mole ratio 1:1 (M:L) and refluxed for 2-4 hours depending on the nature of the isolated complexes (1-6). Also, the mole ratio 1:2 and 2:1 (M:L) was tried in case of PdCl2 (complexes 7 and 8). The resulting precipitates were filtered off, washed with ethanol then ether and finally air- dried. The results of elemental analysis and % yield are shown in Table 2. All the isolated complexes are stable at room temperature, non- hygroscopic and insoluble in water and alcohols and soluble in DMSO and DMF. The melting points of the complexes were above 300°C. The molar conductance of milli-molar DMF solutions indicates a non-electrolytic nature for all complexes (Table 3).
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 (ATCC19615) as Gram- positive bacteria, Pseudomonas fluorescens (S 97) and Pseudomonas phaseolicola (GSPB 2828) as Gram- negative bacteria. The antibiotics chloramphencol and Cephalothin were used as standard reference in case of Gram- negative and Gram- positive bacteria, respectively. The tested compounds were dissolved in dimethyl formamide (DMF) which have no inhibition activity to get concentrations of 2 mg / mL and 1 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 27 °C, inhibition of the organisms which evidenced by clear zone surround each disk was measured and used to calculate mean of inhibition zones.
Conclusion and comments
The effect of the type of the metal ion for the same anion (Cl-) is obvious from either the geometry of the isolated complexes (Oh, Td and D4h) or the various modes of bonding. The isatinic hydrazone uses its lactim form in all complexes (Cl-) except complex 5 with doubly charged SO42- anion in which it uses its lactam form. For the tetra-coordinated (tetrahedral or square planar) Co(II) and Ni(II)-complexes, their geometries are well defined by the magnetic measurements. Tetrahedral Co(II)- complexes have three unpaired electrons and square planar only one. Similarly, tetrahedral Ni(II)- complexes have two unpaired electrons and square planar are diamagnetic. Therefore, the obtained μeff values of 1.46 and 2.96 B.M. (Table 3) for Co(II) and Ni(II)-complexes (2,3) support the dimeric square planar of the former and a tetrahedral environment of the later. In case of Palladium(II)-complexes (6-8), the isatinic hydrazone produces ligand field strong enough to cause spin pairing. On the other hand, the antimicrobial activity is highly influenced by the nature of the metal ion and the order for S. aureus bacteria is as follows: Nickel(II) > Vanadyl(II) > Cobalt(II) > Copper(II) ≈ Palladium(II) >> Iron(III). Based on the above characterization, the proposed structures of the isatinic- complexes are shown in Schemes 3 and 4.
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