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KINETIC STUDIES OF ADDUCT FORMATION OF COBALT (II) TETRAAZA SCHIFF BASE COMPLEXES WITH DIFFERENT ANIONS

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M.Sc. THESIS IN

NORGANIC CHEMISTRY

KINETIC STUDIES OF ADDUCT FORMATION OF COBALT (II) TETRAAZA SCHIFF BASE COMPLEXES WITH DIFFERENT ANIONS

ABSTRACT

In this thesis some tetraaza Schiff base complexes were prepared by condensation reaction via template method between two diamine (1,2-ethylenediamine, and 1,3-propylenediamine) and two ketone (2-amino-benzophenone, and 2-amino-5-chlorobenzophenone) and Co(OAc)₂ in DMF solvent. The synthesized complexes were characterized by IR, UV-vis and C.H.N. analyses. Kinetic studies were performed spectrophotometrically for the reaction between different anions as donor and some Schiff base complexes as acceptor. The low ΔH^# values and the large negative were DS^# values, an excellent linearity of k_obsvs. the molar concentration of the donor, the high span of k₂ values, were compatible with (A) mechanism. By comparing the rate constants (k₂) and the activation parameters, it was obvious that two parameters were effective in the rate of reactions.

Electronegativity: more electronegative group acts as weak donor:

I^–>Br^–>Cl^–

Steric : more steric reduced the rate of the reaction:

[Co(campen]>[Co(capten]

Key words: Kinetic, cobalt (II), tetraaza, Schiff base, anion

دسته: زبان خارجه, زبان خارجه برچسب: anion, cobalt (II), Key words: Kinetic, Schiff base, tetraaza

توضیحات

Table of contents

Content Page

CHAPTER ONE: INTRODUCTION AND LITERATURE REVIEW

1.1. Schiff bases. 2

1.1.1. Introduction and literature review.. 2

1.1.2. The nomenclature of Schiff bases. 10

1.1.3. Metal Schiff Base complexes. 12

1.1.4. Structural aspects of metallo-salen complexes. 12

1.1.5. Stereochemistry. 13

1.2. Chemistry of cobalt 15

1.3. The kinetics and mechanism of reactions of coordination compounds 17

1.4. The objective of this project 22

CHAPTER TWO: EXPERIMENTAL

2.1. Materials. 24

2.2. Instruments. 24

2.3. Synthesis and characterization of compounds. 25

2.3.1. Synthesis of cobalt(II) tetraaza complexes. 25

2.3.2. Synthesis of the kinetic product 26

2.4. Kinetic studies. 27

CHAPTER THREE: RESULTS AND DISCUSSION

3.1. Characterization of the complexes. 30

3.1.1.FT- IR spectra. 30

3.1.2. Elemental analyses (C.H.N.). 31

Content Page

3.1.3. UV-vis spectra. 32

3.2. Kinetic studies. 33

3.3. Conclusion. 37

REFERENCES. 38

APPENDIX.. 51

Abstract and Title Page in Persian

List of Tables

Table Page

Table 3.1.The infrared frequencies of the complexes (in cm^-1). 31

Table 3.2.Elemental analysis data of complexes. 31

Tables 3.3.UV-vis bands of the Schiff bases complexes. 32

Table 3.4.Pseudo-first-order rate constants10²k₂(M^-1s^-1), 10⁴k_obs^a for the reaction of [Co(compen)] with Cl^– at different temperatures. [complex]= 2×10^-5M… 35

Table 3.5.The activation parameters ∆G^#, 10⁴∆H^# and ∆S^#for the reaction of [Co (campen)] with various anions in DMF.^(a) 36

Table 3.6.Second-order rate constants10²k₂(M^-1s^-1) for [Co(campen)] and [Co(capten)] in the presence of various anions at 298 K. 37

List of Figures

Figure Page

Figure 1.1. Type of the ligands used in this work. 5

Figure 1.2.Complexes of the tetradentate Schiff base. 6

Figure 1.3.Cu(II) Schiff base complexes with N₄ donor. 7

Figure 1.6. The structure of some Schiff bases and their abbreviations. 11

Figure1.7. The four most common coordination modes of the Salen complexes, a= square planar, b= square pyramidal, c= octahedral and d= pentagonal bipyramidal coordination. L= charged or neutral ligand. 12

Figure 1.8.Planar metal salophen structure. 13

Figure.1.9. Stepped (a) and umbrella (b) conformations in Salen type complexes. 13

Figure 1.10. R, R² = H, alk, Ar, hal, NO₂, COOH, CN ; R¹ = H, OHR³ = H, alk, Ar 14

Figure 1.11. Cobalt(III) Schiff base complexes: X = NH₃, Im, 2-MeIm ; R = CH₃, CF₃; Y = H, Cl. 16

Figure 1.12. Schematic representation of Vitamin B₁₂. 20

Figure 1.13. Changing the equatorial ligand system from (left to right) amine to cobaloxime to porphyrin and corrin. 20

Figure 2.1. The UV-vis spectra of [Co(campen)] with Cl^– at T = 40ºC in DMF. 28

Figure Page

Figure 3.1. The FT- IR spectrum of [Co(campen)]. 31

Figure 3.2. The UV-vis spectrum of [Co(campen)]. 32

Figure 3.3.UV–vis spectra changes for [ Co(campen)] (2.4×10^-4M)
with excess [Cl^–] in DMF at 293 K. 33

Figure 3.4.The plots of k_obsvs. [Cl^–] for [Co(campen)] at different temperatures. 34

Figure 3.5. The Eyring plot for the reaction of [Co (campen)]
with [Cl^–]. 36

List of Scheme

Scheme Page

Scheme 1.1 Condensation reaction of a carbonyl compound with
a primary amine. 3

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