The Schiff base ligand, 2-[(E)-[{3--[(2-hydroxybenzylidene)amino]phenyl}imino)methyl]phenol was synthesized by condensing 1,3-diaminobenzene and 2-hydroxybenzaldehyde in absolute ethanol. Its Cr(III) and Cr(VI) complexes were equally synthesized. The ligand was characterized via UV, IR and NMR spectroscopy, whereas the complexes were characterized based on UV and IR spectroscopy and conductivity values. Stoichiometric studies indicated 1:1 metal to ligand ratio for both complexes. Cr(III) complex absorbed at 1042.56 cm-1 υ(C-O), 532.37 cm-1 υ(Cr-N) and 607.60 cm-1 υ(Cr-O) while the Cr(VI) complex absorbed at 1182 cm-1 υ(C-O), 749.37 cm-1 υ(Cr-O) and 457 cm-1 for υ(Cr-N).   Based on UV, IR and NMR studies, the ligand coordinated to the metals using the nitrogen and oxygen atoms. Spectrophotometric determination of the metals using the ligand was done at 368 nm for Cr(III)  and 465 nm  for Cr(VI).Optimum conditions for complexation and stability were studied and it was shown that optimum pH for Cr(III) and Cr(VI) were 13.0 and 2.0 respectively. Very few ions such as Co2+, Cu2+, Mn2+, Mg2+, Fe3+ and Zn2+ interfered with the determination. Beer’s law was obeyed between 0.02 to 0.14ppm for both metals. The method was successfully applied in the analysis of steel.

Title page - - - - - - - - - -   i

Approval     -    - - - - - - - - - ii

Declaration - - - - - - - - - - iii

Dedication - - - - - - - - - - iv       Acknowledgements - - - - - - - - - v

Abstract - - - - - - - - - - vi

Table of contents - - - - - - - - - vii

List of Tables - - - - - - - - - - xi

List of Figures - - - - - - - - - - xii

List of Schemes - - - - - - - - -          xiii

CHAPTER ONE

10   INTRODUCTION - - - - - - - - 1

11   Spectrophotometry - - - - - - - - 1

111 Beer- lambert’s law - - - - - - - - 2

12 Schiff Base Ligands - - - - - - - - 4

121   Preparation of Schiff bases - - - - - - - 4

122   Uses of Schiff Bases - - - - - - - - 6

123   Biological Importance of Schiff Bases - - - - - 7

124    Schiff Base Metal Complexes - - - - - - - 8

13     Chromium - - - - - - - - - 9

131   Determination of Chromium - - - - - - - 9

132   Uses - - - - - - - - - - 10

14 Statement of the Problem - - - - - - - 11

15 Aims and Objectives - - - - - - - 12

CHAPTER TWO

20 LITERATURE REVIEW - - - - - - - - 14

21   Catalytic Spectrophotometric Determination of Chromium - - - 14

22  Spectrophotometric Determination Of Trace Level Chromium Using Bis 

       (Salicylaldehyde) OrthophenyleneDiamine In Non-ionic Micellar Media - 14   

23  Spectrophotometric Determination of Chromium(III) and chromium(VI)

       in sea water- - - - - - - - - - 15

24   Determination of Hexavalent Chromium in drinking water by ion chromatography

       with post-column derivatization and UV-visible spectroscopic detection - 15                                   

25   Determination of Cr(VI) in environmental sample evaluating Cr(VI)

         impact in a contaminated area - - - - - - - 16                                                                                                    26   Indirect Extraction - Spectrophotometric Determination of chromium - - 17

27   Sensitivity Determination of Hexavalent chromium in drinking water - - 18

28  Determination of Dissolved Hexavalent Chromium in Drinking Water, Ground Water 

       and Industrial Waste Water Effluents by Ion Chromatography- - - - 18

CHAPTER THREE

30   Experimental - - - - - - - - - 19

31   Apparatus - - - - - - - - - 19

32   Preparation of Stock Solution - - - - - - - 19

33    Preparation of Buffer Solutions - - - - - - - 20

34   Synthesis of the Ligand (HBAPP) - - - - - - 20

35  Synthesis of Chromium (III) and Chromium (VI)  Complexes of HBAPP -    21

351 Determination of the Stoichiometry of the Complexes by Slope-Ratio Method  22

36  General Procedure for the Complexation Studies - - - - 23

361 Effect of Time on the Formation of the Complexes - - - - 23

362 Effect of Temperature on the Formation of the Complexes - - - 23

363 Effect of Concentration of Reagent on the Formation of the Complexes - 23

36 4 Effect of pH on the Formation of the Complexes - - - - 23

365 Effect of Interfering Ions on the Formation of the Complexes - - - 23

366 Calibration Curve-Beer’s Law - - - - - - - 24

37  Determination of Chromium in Alloy - - - - - - 24

371  Determination of Chromium in Alloy with Flame Atomic Absorption 

       Spectrophotometry - - - - - - - - 24

372 Determination of Chromium in Alloys with UV Spectrophotometry - - 24

CHAPTER FOUR

40     Results And Discussion - - - - - - - 26

41 Physical Characterization and Molar Conductivity Data of the Ligands and Its 

           Cr(III) and Cr(VI) Complexes - - - - - - - 26

42     Spectroscopic Characterization Of The Ligand And Its Cr(III) And Cr(VI) 

          Complexes - - - - - - - - - 26

421 Electronic Spectral Data of the Ligand and Its Complexes - - 26

422   Infrared Spectra - - - - - - - - 27

423  1H and 13C NMR Spectra of the Ligand - - - - - 28

424   13C NMR - - - - - - - - - 29

425   APT (Attached Proton Test) - - - - - - - 29

43     Stiochiomery of the Complexes - - - - - - 30

431 Metal-Ligand Mole Ratio of Cr(III) Complex - - - - 30

432 Metal-Ligand Mole Ratio of Cr(VI) Complex - - - - 31

433   Molecular Formulae and Structures of the Ligand and Its Complexes - 33

 44      Complexation Studies - - - - - - - - 35

441   Effect of Time on the formation of the Complexes - - - - 35

442  Effect of the concentration of the reagent on the formation of the complexes - 36

443  Effect of temperature on the formation of the complexes - - - 38

444  Effect of pH on the absorbance of the complexes - - - - 41

445  Effect of interfering ions on the formation of Cr(III) and Cr(VI) complexes - 42

45     Calibration curve for determination of Cr(III) and Cr(VI) complexes - 44

451  Cr(III) complex - - - - - - - - - 44

452  Cr(VI) complex - - - - - - - - - 45

46    Application using steel solution - - - - - - - 46

461 Determination of Cr(III) in the steel solution - - - - - 47

462 Determination of Cr(VI) in steel solution - - - - - 47

47 Conclusion - - - - - - - - - 47

48 Recommendation - - - - - - - - - 48

References - - - - - - - - - - 49

Appendix A - - - - - - - - - - 55

Appendix B - - - - - - - - - - 58

LIST OF TABLES

31: Preparation of Buffer Solution - - - - - - - 21

41: Physical Data of the Ligands and Its Complexes - - - - 26

42: Electronic Spectra - - - - - - - - 27

43: Infrared Spectral Data of the Ligand and Its Complexes - - - 28

44: 1HNMR Spectral of the Ligand in CDCl3 relative to TMS (ppm) - - 28

45: 13CNMR Spectral Data of the Ligand - - - - - - 29

46 Effect of some interfering ions on Cr(III) Complex - - - - 43

47  Effect of some interfering ions on Cr(VI) complex - - - - 44

48 Determination of Cr(III) in the steel solution-   - - - - - - 47

49 Determination of Cr(VI) in the steel solution-   - - - - - 47

410 Result of slope-Ratio plot for Cr(III) complex-fixed ligand(10X 10-3  M) 55

411 Result of Slope- Ratio plot for Cr(III) complex- fixed metal (10 X10-3 M) 55

412 Result of Slope-Ratio plot for Cr(VI) complex; fixed ligand (10 X 10-3 M) 55

413 Result of Slope- Ratio plot for Cr (VI) complex; fixed metal (10 X-3M) 56

414Variation of Absorbance With Time for the Formation of the Complexes 56

415Variation of Absorbance with Reagent Concentration for the Formation of 

      Complexes - - - - - - - - - 56

416Variation of Absorbance with Temperature for the Formation of the 

       Complexes - - - - - - - - - 57

417 Variation of Absorbance with pH for the Formation of the Complexes - 57

418   Results of Calibration Curve-Beer’s Law for Cr(III) and Cr (VI) Complexes 57

LIST OF FIGURES

45: Effect of Time on the formation of Cr(III)complex - - - - 35

46: Effect of Time on the formation of Cr(VI)complex - - - - 36

47: Effect of concentration on the formation of Cr(III) complex - - 37

48: Effect of concentration on the formation of Cr(VI) complex - - 38

49: Effect of Temperature on the formation of Cr(III)complex - - - 39

410: Effect of Temperature on the formation of Cr(VI)complex - - - 40

411: Effect of pH on the formation of Cr(III)Complex - - - - 41

412: Effect of pH on the formation of Cr(VI) Complex - - - - 42

413 Calibration curve of Cr(III) complex - - - - - - 45

414 Calibration Curve of Cr(VI) Complex - - - - - - 46

 

 

LIST OF SCHEMES

1  Formation of Schiff  base - - - - - - - - 22

 2  The ligand - - - - - - - - - - 33

 3 Chromium(III) complex - - - - - - - - 34

 4  Chromium(VI) complex - - - - - - - - 34

CHAPTER ONE

INTRODUCTION

11  SPECTROPHOTOMETRY

Spectrophotometry is the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength1 It is more specific than the general term electromagnetic spectroscopy in that spectrophotometry deals with visible light, near-ultraviolet, and near-infrared, but does not cover time-resolved spectroscopic techniques Spectrophotometry is a very fast and convenient method of qualitative analysis, due to the fact that absorption occurs in less than one second and can be measured very rapidly Molecular absorption is valuable for identifying functional groups in a molecule and for the quantitative determination of compounds containing absorbing groups2,3 A spectrophotometer is commonly used for the measurement of transmittance or reflectance of solutions, transparent or opaque solids, such as polished glass or gases However, they can also be designed to measure the diffusivity of any of the listed light ranges that usually cover around 200 – 250 nm using different controls and calibrations1

The most common spectrophotometers are used in the UV and visible regions of the spectrum and some of these instruments also operate into the near-infrared region as well Visible region (400 – 700 nm) spectrophotometry is used extensively in colorimetry science Ink manufacturers, printing companies, textile, vendors and many more, need the data provided through colorimetry They take readings in the region of every 5 – 20 nanometers along the visible region and produce a spectral reflectance curve or a data stream for alternative presentations

Spectrophotometeric method is undoubtedly the most accurate method for determining, among other things, the concentration of substances in solution, but the instruments are of necessity more expensive A spectrophotometer may be regarded as a refined filter photoelectric photometer which permits the use of continuously variable and more nearly monochromatic bands of light The essential parts of a spectrophotometer are (1) a source of radiant energy (2) a monochromator ie a device for isolating monochromatic light or, more accurately, narrow bands of radiant energy from the light source (3) glass or silica cells for the solvent and for the solution under test and (4) a device to receive or measure the beams of radiant energy passing through the solvent4  

Infrared (IR)5 light is electromagnetic radiation with longer wavelengths than those of visible light, extending from the nominal red edge of the visible spectrum at 700 nm to 1mm Infrared spectroscopy is very useful for obtaining qualitative information about molecules For absorption in infrared region to occur, there must be a change in the dipole moment (polarity) of the molecule Absorbing groups in the infrared region absorb within a certain wavelength region, and the exact wavelength will be influenced by neighbouring groups Their absorption peaks are much sharper than the ultraviolet or visible regions and easier to identify The most important use of infrared spectroscopy is in identification and structure analysis; it is useful for qualitative analysis of complex mixtures of similar compounds because some absorption peaks for each compound will occur at a definite and selective wavelength, with intensities proportional to the concentration of absorbing species

Nuclear magnetic resonance spectroscopy5 is a research technique that exploits the magnetic properties of certain atomic nuclei It measures the absorption of electromagnetic radiation in the radiofrequency region of roughly 4 MHz to 750 MHz, nuclei of atoms rather than outer electrons are involved in the absorption process It determines the physical and chemical properties of atoms or the molecules in which they are contained It relies on the phenomenon of NMR and can provide detailed information about the structure, dynamics, reaction state and chemical environment of molecules NMR is used to investigate the environment of molecules NMR is used to investigate the properties of organic molecules, although it is applicable to any kind of sample that contains nuclei possessing spin

Beer- Lambert’s Law

In optics, the Beer-Lambert law, also known as Beer’s law or the Lambert- Beer’s law (named after August Beer, Johann Heinrich Lambert and Pierre Bouguer) relates the absorption of light to the properties of the material through which the light is travelling6

The law states that there is a logarithmic dependence between the transmission (transmissivity), T, of light through a substance and the product of the absorption coefficient of the substance, the light travels through the material (the path length), l The absorption coefficient can, in turn, be written as a product of either a molar absorptivity (extinction coefficient) of the absorber, £ and the molar concentration, c of absorbing species in the material, or an absorption cross section,  and the (number) density N’ of absorbers6

For liquids: T=I/I_o =10^(-εlc)

Whereas in biology and physics, they are normally written

 T=I/I_o =e^(-αl)=e^(-αln)

Where IO and I are the intensities (power per unit area) of the incident light and the transmitted light respectively α is cross section of light absorption by a single particle and n is the density of absorbing  particles  The transmission (transmissivity) is expressed in terms of an absorbance which for liquids, is defined as6 

 A=-log_10⁡(I/I_o )

Whereas, for gases, it is usually defined as 

  A^1=-ln⁡(I/I_o )

This implies that absorbance becomes linear with the concentration according to6

A=εlc=αl 

Historically, the Lambert law states that absorption is proportional to the light path length, whereas the Beer law states that absorption is proportional to the concentration of absorbing species in the material6

The modern derivation of the Beer-Lambert law combines the two laws and correlates the absorbance to both, the concentration as well as the thickness (path length) of the sample6

T=I_l/I_o =e^(-αln)=e^(-αl)

This implies that

   A=-ln⁡〖(I_l/I_o )=αl=αln�“

And  A=-log_10⁡(I_l/I_o )=αl/2303=αl=εlc

The linearity of the Beer-Lambert law is limited by chemical and instrumental factors

12 Schiff Base Ligands

Schiff base (imine or azo