1. Schiff base is a compound with a functional group that contains a carbon-nitrogen double bond with the nitrogen atom connected to an aryl or alkyl group. General formula:
2. Schiff base is usually formed by condensation reaction of a carbonyl with primary amine.
3. There are three main approaches to prepare Schiff base ligand systems: Direct Synthesis Template Effect Conventional Method
4. UV-Visible IR Spectroscopy 1H and 13C NMR EPR Mass Spectrometry TGA/DTA Elemental Analysis The Schiff base ligands and their complexes are characterized on the basis of following:
5. It is mainly applied for the detection of functional groups (chromophore),the extent of conjugation , detection of polynuclear Compounds etc. The radiation in the wavelength range 200-400nm corresponds to Ultra-violet region while radiation in the wavelength range 400-800nm corresponds to visible region. The absorption of radiation in the UV-visible region causes the excitation of electron in a conjugation or an non conjugation system. Thus UV-visible spectrum is quite useful for detection of conjugation, carbonyl group etc.
6. APPLICATIONS Identification of an unknown compound Examination of polynuclear hydrocarbons Elucidation of the structure of vitamins A and K Detection of two isomeric forms Determination of configurations of geometrical isomers Identification of a compound in different solvents Determination of strength of hydrogen bonding Distinguishes between equatorials and axial conformations LIMITATION : UV-visible spectrum does not provide any information about the remaining part of the molecule.
7. The formation of Schiff base complexes and bonding modes are inferred from position of characteristic bands in IR spectra and resonance signals in 1H and 13 C-NMR spectra. A strong intensity band(sharp) 1618-1622cm-1 v(C=N) A medium intensity band 440-460 cm-1 v(MN) A weak absorption band 2906-2942cm-1 v(CH3) A broad absorption band 3330cm-1 v(OH)
8. Nuclear magnetic resonance (NMR), induces changes in the magnetic properties of certain atomic nuclei, notably that of hydrogen(hydrogen atoms in different environments can be detected, counted and analysed for structure determination). In the Nuclear magnetic resonance (NMR), radiations of longest wavelength range,i.e., Radiowaves are useful which lie in the frequency range about 60- 300MHz.
9. Electron paramagnetic resonance(EPR) spectroscopy investigate those systems which are organic or inorganic free radicals and ions of transition metals which contain unpaired d or f electrons. Mass spectrometry is the most accurate method for determining molecular mass of the compound and its elemental composition and deduction of molecular structure from fragments. Mass spectrum of a substance is potted between m/z values of ions versus relative abundance
10. The thermal stabilities of Schiff metal complexes are investigate using (TGA/DTA) under N2 atmosphere at a heating rate of 20 C min-1 in the temperature range 25-800 C The thermal analysis results are in agreement with the elemental analysis findings. Elemental analysis confirms the stoichiometry of ligands and their complexes.
11. Schiff base nitrogen donar ligands and their complexes show biologically activities i.e. toxicity against bacterial growth, anticancerous, antimalarial antimicrobial, antitubercoluosis and antifungal activities. Due to their resemblance with natural proteins like hemerythrin enzymes they are also used as biomimic model compounds.
12. They are potential inorganic and organic cation receptors , electron transfer agents , homogenous catalysts and DNA , RNA interacting agents. They also employed in hydrometallurgy, material science as luminescence materials and as non linear optical materials.
13. Schiff base ligands are formed by the condensation reaction between aldehydes/ketones and aliphatic amines. Their complexes are prepared by the interaction of ligands with metal salts. The stoichiometry and the nature of bonding was ascertained on the basis of elemental analysis and conductivity data. The formation of the proposed compounds is inferred by the appearance of imine bands in the IR and corresponding proton resonance signals in the 1H spectra. Schiff base ligands and their complexes have numerous applications in the field of pharmacy.
14. H.Khanmohammadi et al./ Spectrochimica Acta Part A 77 (2010) 342-347 H. Keypour et al./ Polyhedron 51 (2013) 117-122 M.Tyagi et al./ Spectrochimica Acta Part A : Molecular and biomolecular specroscopy 118 (2014) 1056-1061 T.A.Khan et al./ Spectroahimica Acta Part A 73 (2009) 622-629