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SALICYLALDEHYDE SALICYLOYLHYDRAZONE- A SHORT REVIEW.

Byline: Muhammad Vaqas, Shehnila Chaudhary, Muhammad Adnan Iqbal and Muhammad Haroon

ABSTRACT:

Salicylaldehyde Salicyloylhydrazone belongs to the family known as Schiff bases and impart as bidentate ligand with transition metals to synthesize organometallic compounds. Its metal complexes are useful against bacteria and fungi cause diseases like infection, illness, hearing problem or hearing loss and cancer.

Key words: Salicylaldehyde Salicyloylhydrazone, Schiff Bases, 2-hydroxy-N'-[(E)-(2-hydroxyphenyl)methylidene]benzohydrazide, Organometallic.

1. INTRODUCTION

Schiff bases represent one of the most widely used families of organic compounds and their chemistry is essential material in many organic chemistry textbooks [1-3]. In general, this class of compounds can be easily prepared by the condensation reaction of primary amines with carbonyl compounds. The first report of this kind of reaction has been published by Hugo Schiff in the 1860s [4-6]. Thereafter Schiff bases have been intensively used as synthetic intermediates and as ligands for coordinating transition and inner transition metal ions, and recently also for coordinating anions [7-9]. During the past two decades they have become some of the most typical ligands in the field of coordination chemistry [10-16].

These ligands may act as bidentate through N,O-, tridentate N,O,O-, N,O,N-, N,O,S-, tetradentate N,N,O,O-, and hexadentate N,N,O,O,S,S-donor ligands [17-23], which can be designed to yield mononuclear or binuclear complexes or one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) metal-organic frameworks [24-31]. The synthesis and structural research of Schiff bases derived from the above mentioned aldehydes and amines bearing various alkyl and aryl N-substituents, as well as their metal complexes have been of interest of researchers for over two decades [32-43]. Schiff base ligands may contain a variety of substituents with different electron-donating or electron-withdrawing groups, and therefore may have interesting chemical properties. They have attracted particular interest due to their biological activities [44,45] for example acting as radiopharmaceuticals for cancer targeting [46,47]. They have also been used as model systems for biological macromolecules [48,49].

Other applications extent its use in catalysis [50,51], dying processes [52,53] and analytical applications [54] . In this review we attempted to summarize the salicylaldehyde salicyloylhydrazone-metal complexes that have been published to the date.

For the review, we have endeavored to include Group III-A, Alkaline earth metal, 3d Transition metals and Group III-B metal complexes with salicylaldehyde salicyloylhydrazone, we have also mentioned that what type of characterization was done.

2. HISTORY OF SALICYLALDEHYDE SALICYLOYLHYDRAZONE

The kinetics of the polarographic reduction of 1 in universal buffer containing 40% EtOH was reported by Temerk and coworkers [55]. They demonstrated the mechanism involves in formation of RMe and salicylic acid hydrazide at pH (less than) 5.8 in a single wave 4 electron reduction. They also discussed the substituent effect on rate of electron transfer in the reduction of compound 1 [55].

A mass spectrum of salicylaldehyde salicyloylhydrazide (at an ionizing energy of 70 eV) was first recorded by Bhasin and coworkers in 1973. They reported the relative intensities of the fragments from the compound and further discussed those in relation to fragmentation modes [56].

Another group worked on the rate of hydrolysis of 2 in 40% (vol./vol.) EtOH-Buffer mixture by differential pulse polarogram. They reported that hydrolysis was catalyzed by H+ and rate follows strictly first-order kinetics. The rate constant decreased with increasing pH up to around pH 3.9, beyond which no measurable reaction was observed and at that point the protonation of imine begins to be significantly incomplete. The attack of H2O on the protonated substrate was the rate-determining step while the effects of pH, molecular structure and temperature on the reaction rate as well as the activation energy were reported. Thermodynamic parameters ( (delta) G, (delta) H and (delta) S) for the hydrolysis were also discussed [57].

Polarographic reduction was investigated by Issa and coworkers. They reported that the reduction involved a 4- electron process in acidic buffers and a 2-electron process in alkaline buffers. They further reported that Hammett plot of half-wave potential had a negative slope while also detected the Kinetic parameters of the electrode process [58].

Solid state photochronic properties were examined in detail by Rawat and coworkers. They prepared the title compound 3 and 4. They reported that 3 was photochromic in sunlight (5 min) and was thermally reversed in the dark (1 wk at 25oC) while 4 was not photochromic [59].

3. COMPLEXES

3.1. Group III-A Metal Complexes

3.1.1. Aluminum

The first Al-SASH complex reported late by 20th century, Jian and coworkers synthesized a fluorescent reagent and established ionization constant spectrophotometrically. The fluorescent reaction of above mentioned reagent was further studied with Aluminium. By this chelation reaction, they developed a spectrofluorometric method for the detection of Aluminium in a water-EtOH (3+2vol./vol.) medium at pH 3.4. They further reported that under such conditions, the Al- SASH complex showed excitation and emission maxima at 375nm and 450nm, respectively while the linear range of the method was 0.0-140 ppb and the detection limit was 1.2 ppb of Aluminium when a standard addition method was used in the assay. The reported molar ratio of Aluminium to the reagent was 1:3 and interferences of other ions were also studied [60].

3.1.2. Gallium

Tang and coworkers studied the fluorogenic reaction of salicylaldehyde salicyloylhydrazone with Gallium (Ga). They described the molar ratio of Ga to the reagent was 1:3 and the reaction was carried out in an aq. medium of 2:3 EtOH:H2O at pH 3.2 with excitation and emission at 370nm and 455nm respectively. They also reported the linear range of detection 0-0.14mg/L and the detection limit 1.4ug/L [61].

3.1.3. Indium

In the early years of 21th century Han and coworkers studied the fluorescent reaction of salicylaldehyde salicyloylhydrazone (SASH) with Indium(III). Based on this chelation reaction, they succeeded to develop a sensitive spectrofluorometric method for detection of Indium inwater-EtOH (vol. ratio 3:7) medium at pH 4.0. They also reported that under such conditions In-SASH complex displays an excitation and emission maxima at 396nm and 461nm respectively. The linear range of the method was 4.7-1000ng/mL and the detection limit was 0.94ng/mL. The molar ratio of Indium to the reagent was 1:1 while they also studied the interferences of other ions. The method was successfully applied for the detection of Indium in chemical reagents of Lead, Tin, Zinc, Zinc chloride and geol by standard addition method [62].

3.2. Alkaline Earth Metal

3.2.1. Beryllium

The fluorescent reaction of SASH with Beryllium was studied by Bing and coworkers. They developed a spectrofluorometric method for detection of Beryllium, in acetic acid-NaOAc buffer solution at pH 5.2. They reported that under such conditions the complex has excitation and emission maxima at 370nm and 450nm respectively while linear range was 0-180 ppb and the detection limit was 3.2 ppb. The molar ratio of Beryllium to the reagent was 1:1 while the interferences of other ions were also studied. The method is successfully applying to the detection of Beryllium in mineral H2O and reagents [63].

3.3. 3d. Transition metal complexes

3.3.1. Zinc

Hu and coworkers obtained crystals of one-dimensional binuclear zinc complex in DMF and 2-MPy and was characterized by IR, UV, elemental analysis and X-ray diffraction analysis. They reported the crystal data and theoretical investigation of title complex as a structure unit was carried out at B3LYP/6-31G and HF/6-21G levels with Gaussian 03W program and also discussed the atomic charges, natural bond orbital analysis and bond energies [64].

Another author grew the crystals of zinc complex with salicylaldehyde salicylhydrazone in DMF and Py. Coordinated forms were confirmed by IR, UV, elemental analysis, MS and 1H NMR. Bond parameters and crystal structure were analyzed [65].

Crystals of tri-nuclear zinc complex with salicylaldehyde salicyloylhydrazone in DMF was grew by Ding and coworkers. The complex was characterized by IR, elemental analysis and x-ray diffraction analysis. They reported that the crystals are monoclinic. They further studied the fluorescence activities in DMF of the complex and Schiff base ligand [66].

3.3.2. Nickel

Sharma and coworkers synthesized nickel complex and characterized using elemental analysis, molar conductance, molecular weight detection, magnetic measurements, LR and electronic spectra. They analyzed in vitro screening of ligand and metal complex against two bacteria S. aureus, E. coli and two fungi A. niger and A. flavus [67].

Salam and coworkers prepared H2L ligand and its nickel complex using NiCl2 (H2L = salicylaldehyde salicyloylhydrazones) and analyzed the complex by elemental analysis, IR, electronic spectra, conductance and magnetic measurement [68].

3.3.3. Copper

Two Copper complexes were reported by Temerk and coworkers. Both the complexes were characterized by IR and electronic spectra, molar conductance measurements and thermal decomposition temperature. They further described that the ligand was bidentate [69].

3.3.4. Chromium, Iron, Cobalt and Manganese

The SASH and metal complexes of Chromium, Iron, cobalt and Manganese were reported by Narang and coworkers. They prepared [ML2X]2 complexes (M = Cr, Fe, Co and Mn; X = OAc, Cl) and characterized by UV-visible, IR spectra and magnetic susceptibility. The central metal in each complex has octahedral coordination with an enolized carbonyl O atom acting as a bridging group between two metal ions [70].

3.4. Group III-B Metal Complexes

3.4.1. Scandium

The fluorescent reaction with Scandium was first studied in 1998. Based on this chelation reaction, they developed a highly sensitive spectrofluorometric method for detection of Scandium in EtOH-H2O (1+1 vol./vol.) medium at pH 5.0. They reported that under such conditions, the Sc-SASH complex had excitation and emission maxima at 388nm and 465nm, respectively. The linear range of the method was 0.40-100ppb while the detection limit was 0.12ppb of Scandium, when a standard addition method was used in the assay. The molar ratio of Scandium to the reagent was 1:1 [71].

3.4.2. Lanthanum, Neodymium, Gadolinium, Terbium, Dysprosium, Yttrium

These complexes were firstly reported by Navaneetham and coworkers. They synthesized the Schiff base by condensation of salicylaldehyde and salicyloyl hydrazide. The complexes were prepared by novel method consisting of refluxing the mixtures of Schiff base ligand and lanthanide trichloroacetate in acetone. Solid complexes of formulae Ln(SHSASB)3*2H2O were isolated. They further reported that 1H NMR and IR spectra for complexes revealed bidentate binding of Schiff base ligand to the lanthanide ion [72].

Another research group reported two types of complexes. The complexes were characterized and those also showed high decomposition points while dehydration study indicated water molecules both in the lattice and coordination sphere of the Complex-metal ions. They further reported that IR and 1H NMR spectral data suggest trinegative tetradentate and dinegative tridentate coordination of salicylaldehyde salicyloylhydrazone in the complexes while the chloro and nitrato groups coordinate to the metal ion as monodentate and bidentatechelating species respectively. Solid state electronic conduction data at various frequencies show semi- conducting nature of the complexes and also optical band gap studies showed [Gd(ssh)(H2O)3].H2O to be a direct band gap semiconducting material with a band gap of 2.64eV [73].

3.4.3. Cerium, Praseodymium, Promethium, Samarium, Europium, Holmium, Erbium, Thulium, Ytterbium

These complexes were firstly reported by Navaneetham and coworkers. They synthesized the Schiff base by condensation of salicylaldehyde and salicyloyl hydrazide while actinide complexes were prepared by novel method consisting of refluxing the mixtures of Schiff base ligand and lanthanide trichloroacetate in acetone. They further reported that electronic spectra along with the conductance data for the complexes indicated a coordination number of six for the lanthanide ions in the complexes [72].

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1Department of Chemistry, Minhaj University Lahore, Main Campus, Township Lahore, Pakistan.

2The School of Chemical Sciences, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia

3Department of Chemistry, Quaid-i-Azam University, Islamabad, Pakistan

E-mail: muhammad_vaqas@yahoo.com
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