The ligational behavior of a phenolic quinolyl hydrazone towards copper(II)- ions
© Seleem et al 2011
Received: 14 November 2010
Accepted: 11 January 2011
Published: 11 January 2011
The heterocyclic hydrazones constitute an important class of biologically active drug molecules. The hydrazones have also been used as herbicides, insecticides, nematocides, redenticides, and plant growth regulators as well as plasticizers and stabilizers for polymers. The importance of the phenolic quinolyl hydrazones arises from incorporating the quinoline ring with the phenolic compound; 2,4-dihydroxy benzaldehyde. Quinoline ring has therapeutic and biological activities whereas, phenols have antiseptic and disinfectants activities and are used in the preparation of dyes, bakelite and drugs. The present study is planned to check the effect of the counter anions on the type and geometry of the isolated copper(II)- complexes as well as the ligational behavior of the phenolic hydrazone; 4-[(2-(4,8-dimethylquinolin-2-yl)hydrazono)methyl] benzene-1,3-diol; (H2L).
A phenolic quinolyl hydrazone (H2L) was allowed to react with various copper(II)- salts (Cl‾, Br‾, NO3‾, ClO4‾, AcO‾, SO42-). The reactions afforded dimeric complexes (ClO4‾, AcO‾ ), a binuclear complex (NO3‾ ) and mononuclear complexes (the others; Cl‾, Br‾, SO42-). The isolated copper(II)- complexes have octahedral, square pyramid and square planar geometries. Also, they reflect the strong coordinating ability of NO3‾, Cl‾, Br‾, AcO‾ and SO42- anions. Depending on the type of the anion, the ligand showed three different modes of bonding viz. (NN)0 for the mononuclear complexes (3, 4, 6), (NO)- with O- bridging for the dimeric complexes (1, 5) and a mixed mode [(NN)0 + (NO)- with O- bridging] for the binuclear nitrato- complex (2).
The ligational behavior of the phenolic hydrazone (H2L) is highly affected by the type of the anion. The isolated copper(II)- complexes reflect the strong coordinating power of the SO42-, AcO‾, Br‾, Cl‾ and NO3‾ anions. Also, they reflect the structural diversity (octahedral, square pyramid and square planar) depending on the type of the counter anion.
The heterocyclic hydrazones constitute an important class of biologically active drug molecules which have attracted attention of medicinal chemists due to their wide ranging pharmacological properties including iron scavenging and antitubercular activities [1–6]. The hydrazones have also been used as herbicides, insecticides, nematocides, redenticides, and plant growth regulators  as well as plasticizers and stabilizers for polymers [7, 8]. Furthermore, some hydrazones are used as quantitative analytical reagents, especially in colorimetric and fluorimetric determination of metal ions [4–6]. The importance of the phenolic quinolyl hydrazones arises from incorporating the quinoline ring with the phenolic compound; 2,4-dihydroxybenzaldehyde. Quinoline ring has therapeutic and biological activities whereas, phenols have antiseptic and disinfectants activities and are used in the preparation of dyes, bakelite and drugs. The metal complexes of hydrazones have potential applications as catalysts , luminescent probes  and molecular sensors . The present study is planned to check the effect of the counter anions on the type and geometry of the isolated copper(II)- complexes as well as the ligational behavior of the phenolic hydrazone; 4-[(2-(4,8-dimethylquinolin-2-yl)hydra-zono)methyl]benzene-1,3-diol; (H2L). This work is an extension to our previous studies on the chelating ability of quinolyl hydrazones [12–14].
Results and discussion
Characterization of the hydrazone
Analytical and physical data of the copper(II)- phenolic complexes.
Elemental analysis; % Found/(Calcd.)
[Cu(HL)(H2O)2]2 (ClO4)2. 1/2H2O.¼MeOH
[Cu (H2L) (H2O)2 Cl2]. 11/8 H2O
[Cu (H2L) (H2O) Br2].1/2 H2O
[Cu (HL) (OAc)]2.MeOH
Magnetic, conductivity, electronic and IR spectral data for the copper(II)- phenolic complexes.
IR spectral bands; cm-1
ν (C = N)
266, 320, 371
285, 348, 461
ν (ClO); 1094
276, 346, 435, 460, 485
ν (NO); 1394
279, 348, 375, 438
279, 352, 381, 488
269, 346, 429, 458
ν (C = O); 1635
268, 287, 371, 436, 460, 485
ν3 (SO); 1109
Characterization of the complexes
IR spectra of the complexes
Comparison of the IR bands of the free phenolic hydrazone (H2L) and its complexes revealed the following: (i) All complexes showed broad bands in the region 3423-3385 cm-1 due to OH stretches of either the phenolic or the associated water/methanol molecules. (ii) The strong band at 1603 cm-1 assignable to ν(C = N) stretch in the free ligand undergoes a shift to higher wave numbers (1641-1612 cm-1) upon complexation, supporting the coordination of the hydrazone linkage to all metal ions. This can be explained on the basis of the diminished repulsion between the lone pairs of electrons of the two adjacent N atoms upon complexation and hence, π- electron delocalization . (iii) The perchlorato and sulfato complexes (1 & 6) showed the ν(S-O) or ν(Cl-O) stretches around 1100 cm-1 . Also, the nitrato complex (2) showed the ν(N-O) stretch at 1394 cm-1. (iv) In the acetato complex (5), the new band at 1635 cm-1; ν(C = O), confirm the monodentate nature of the acetate ion.
Conductivity and magnetic properties
The molar conductance values (Table 2) of the current chelates in DMF (1.0 mmol/L) revealed a non- electrolytic nature of all complexes except the perchlorato- complex (1) which showed molar conductance of 175 and Ohm-1 cm2 mol-1 suggesting its 1:2 electrolytic nature. The complex (1) has 3 mol ions/mol ( +2, -1), one of which is bi- positive. In case of complexes 2-4, the relatively high values of the molar conductance may be due to their partial dissociation in DMF solutions. However, they did not reach the previously reported values for 1:1 electrolytes in DMF solutions (~70 - 110 Ohm-1 cm2 mol-1) . On the other hand, the copper(II)- complexes (1-6); d9-system exhibit μeff values in the range 1.33-2.01 B.M. (Table 2) indicating the presence of one unpaired electron. The subnormal μeff values for complexes (1, 2 & 5) indicate MII--- MII interactions in the solid state supporting either dimeric or binuclear nature of the complexes.
Electronic, ESR and mass spectra
Thermal behavior of the copper(II)- phenolic complexes.
% Wt. loss
* Decomp. in one step;
ΔΗ = 830.21 J/g
* ¾ MeOH + ¼ H2O
* 2 MeOH + H2O + 2HNO3
* 31/8 H2O with decomp.
[Cu (H2Lc) (H2O)2 Cl2]. 11/8 H2O
(Cu2O + CuO);
* Two overlapped steps;
* 11/2 H2O + 2HBr
(Cu2O + Cu);
* 2 AcOH
* MeOH with decomp.
(Cu2O + Cu);
* 2¼ H2O
(Cu2O + CuO);
* 2 H2O with decomp.
Kinetic and thermodynamic parameters
Thermodynamic and kinetic parametersa of copper(II)- phenolic complexes.
A × 10-9sec-1
Microanalyses were carried out on a Perkin- Elmer 2400 CHN elemental analyzer. Analyses of the metal ions followed decomposition of their complexes with concentrated nitric acid. The resultant solution was diluted with doubly distilled water and filtered. The solution was then neutralized with aqueous ammonia solution and the metal ions titrated with EDTA. Thermal analyses (TG-DSC) were carried out on a Shimadzu- 50 thermal analyzer in nitrogen atmosphere and a heating rate of 20°C/min using the TA-50 WS1 program. 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. 1H NMR spectra were recorded as DMSO- d6 solutions on a Varian Mercury VX- 300 NMR spectrometer using TMS as an internal standard. 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.
Preparation of the phenolic hydrazone
An ethanolic mixture of 2-hydrazinyl-4,8-dimethyl quinoline (0.01 mol) and 2,4-dihydroxybenzaldehyde (0.012 mol) was refluxed for 1/2 h. The formed yellow compound was filtered off, washed with ethanol and crystallized from ethanol. The results of elemental analysis, % yield and m.p°C are shown in Table 1.
Synthesis of the complexes
A general method has been used for the preparation of all complexes. A methanolic solution of the metal salt was added gradually to a methanolic solution of the phenolic hydrazone (H2L) in the mole ratio 1 : 1; metal ion : ligand. Then, the reaction mixture was refluxed for 2-6 h where the solid complexes were precipitated, filtered off, washed with methanol and finally diethyl ether and then dried in vacuo. In general, the obtained complexes (Table 1) are colored and quite stable in atmospheric conditions. Also, most of the complexes have high melting points (>300) indicating their strong bonds. The complexes are insoluble in water and most common solvents; but they are soluble in DMF and DMSO solvents.
Conclusion and comments
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