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COMPLEX IONS AND COORDINATION COMPOUNDS

COMPLEX IONS AND COORDINATION COMPOUNDS. COLOR AND COLORS OF COMPLEXES ASPECTS OF COMPLEX ION EQUILIBRIA ACID-BASE REACTIONS OF COMPLEX IONS SOME KINETIC CONSIDERATIONS APPLICATIONS OF COORDINATION CHEMISTRY. ff. COLOR AND THE COLOR OF COMPLEXES. Nature of Color Mixing.

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COMPLEX IONS AND COORDINATION COMPOUNDS

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  1. COMPLEX IONS AND COORDINATION COMPOUNDS • COLOR AND COLORS OF COMPLEXES • ASPECTS OF COMPLEX ION EQUILIBRIA • ACID-BASE REACTIONS OF COMPLEX IONS • SOME KINETIC CONSIDERATIONS • APPLICATIONS OF COORDINATION CHEMISTRY

  2. ff COLORANDTHE COLOROF COMPLEXES

  3. Nature of Color Mixing Additive Mixing = the primary colors when combine yield white light R+G+B=W = the secondary colors are those that produced by com bining primary colors. Example: yellow (Y=R+G), cyan (C=G+B), and magenta (M=B+R). = the complementary colors is the opposite of either primary or secondary color. Example:cyan is the complementary of red. Subtractive Color Mixing = some of the wavelength components of white light are removed by absorption, and the reflected light or transmitted light is deficient in some wavelength.

  4. Color and the Color of Complex Colored solution contains species that can absorb photons of visible light and use the energy of these photons to promote electrons in the species to the higher energy levels. The energy of the photons must just match the energy differences through which the electrons are to be promoted. Because the energy of the photons are related to the frequencies (and wavelength) of light only a certain wavelength components are absorbed as white light passes through the solution. The emerging light, because it is lacking some wavelength components, is no longer white; it is colored.

  5. Ions that do not have electron transitions in the energy range corresponding to the visible light are: 1. A noble gas electron configuration 2. An outer shell of 18 electrons, 3. The “18+2” configuration (18 electron in the n-1 shell and two in the n, or outermost, shell) White ligth passes through these solutions without being absorbed;these ions are colorless in solution.

  6. BEAM OF DIFFERENT WAVELENTHS OF LIGTH TRANSMITTED LIGTH [Cu(H2O)4]2+ [Cu(H2O)4]2-

  7. Color and the colors of complexes Table 25.5 Some coordination compounds of Cr3+ and their colors Color Isomer [Cr(H2O)6] Cl3 violet [CrCl(H2O)5]Cl2 blue-green [Cr(NH3)6]Cl3 yellow [CrCl(NH3)5]Cl2 purple

  8. Table 25.5 Some Coordination Compounds of Cr3+ and their colors Isomer Color [Cr (H2O)6] Cl3 Violet [CrCl(H2O)5] Cl2 Blue-green [Cr(NH3)6] Cl3 Yellow [Cr(NH3)6] Cl2 Purple

  9. Cobalt (III) Chloride Amines Solids compound color Inized Cl- Formulation as Complex CoCl3.6NH3 Yellow Purple Green Violet 3 2 1 1 [Co(NH3)6]Cl3 CoCl3.5NH3 [Co(NH3)5Cl]Cl2 CoCl3.4NH3 Trans- [Co(NH3)4Cl2]Cl CoCl3.4NH3 Cis- [Co(NH3)4Cl2]Cl

  10. Cobalt (III) Chloride Amines Solids compound color Inized Cl- Formulation as Complex CoCl3.6NH3 Yellow Purple Green Violet 3 2 1 1 [Co(NH3)6]Cl3 CoCl3.5NH3 [Co(NH3)5Cl]Cl2 CoCl3.4NH3 Trans- [Co(NH3)4Cl2]Cl CoCl3.4NH3 Cis- [Co(NH3)4Cl2]Cl Cl Cl Co Cl Co Cl trans-dichlorodiaminecobalt Cis-dichlorodiaminecobalt

  11. Cobalt (III) Chloride Amines Solids compound color Inized Cl- Formulation as Complex CoCl3.6NH3 Yellow Purple Green Violet 3 2 1 1 [Co(NH3)6]Cl3 CoCl3.5NH3 [Co(NH3)5Cl]Cl2 CoCl3.4NH3 Trans- [Co(NH3)4Cl2]Cl CoCl3.4NH3 Cis- [Co(NH3)4Cl2]Cl Cl Cl Co Cl Co Represent NH3 Ligands Represent NH3 Ligands Cl trans-dichlorodiaminecobalt Cis-dichlorodiaminecobalt

  12. Aspects of Complex Ion Equilibria Complex ion formation can have a great effect on the solubilities of substances, in fact, cations in aques solution exist mostly in hydrated form. When an anion molecules bond to a cation to form another complex ion, they do not enter an empty coordination sphere. They must displace H2O molecules, and this occurs in a step-wise fushion. The reaction: Zn2+(aq) + 4 NH3(aq) [Zn(NH3)4]2+(aq) [[Zn(NH3)4]2+] Kf 4.1 x 108 = = [Zn2+][NH3]4

  13. Aspects of Complex Ion Equilibria Complex ion formation can have a great effect on the solubilities of substances, in fact, cations in aques solution exist mostly in hydrated form. When an anion molecules bond to a cation to form another complex ion, they do not enter an empty coordination sphere. They must displace H2O molecules, and this occurs in a step-wise fushion. The reaction: Exist as [Zn(H2O)4]2+ Zn2+(aq) + 4 NH3(aq) [Zn(NH3)4]2+(aq) [[Zn(NH3)4]2+] Kf 4.1 x 108 = = [Zn2+][NH3]4

  14. [Zn(H2O)4]2+ + NH3 [Zn(H2O)3NH3]2+ + H2O For which [[Zn(H2O)3NH3]2+] = K1= 3.9 X 102 [[Zn(H2O)4NH3]2+] [NH3] Is followed by [Zn(H2O)3]2+ + NH3 [Zn(H2O)2NH2]2+ + H2O [[Zn(H2O)2 (NH3)2]2+] = K2= 2.1 X 102 [[Zn(H2O)3NH3]2+] [NH3] And so: The value of K1 is often designated as 1 and called the formation constant for the complex ion [[Zn(H2O)3NH3]2+]

  15. The formation of [Zn(H2O)2(NH3)2]2+ is represented by the sum of equations (25.3) and (25.5) [Zn(H2O)4]2+ + 2NH3 [Zn(H2O)2(NH3)2]2+ + 2H2O And the formation constant 2, in turn, is given by the product of equation (25.4) and (25.6). 2 = [[Zn(H2O)2(NH3)2]2+] =k1x k2 = 8.2x 104 [[Zn(H2O)4]2+][NH3]2 For the next ion in the series,[Zn(H2O)(NH3)3]2+,3=k1x k2 x k3.

  16. Acid-Base Reactions of Complex Ions -Metal cations usaually form complexes with from 2 to 12 donor molecules at once, depending on the sizes and electronic structures of the cation and donor molecules. The bound donor molecules are called Ligand (from the Latin Ligare,,to bind), and the acceptor and donor species may be regarded as Lewis Acids and Lewis Bases, respectedly. -In general, then, metal ions in solution form complexes (frequently six coordinate) with the solvent molecules, their counter ions,and other donor melecules that happen to be in the solution.

  17. Acid-Base Reactions of Complex Ions Complex ions may exhibit acid-base properties in the Bronsted-Lowry sense, that is, they may act as proton donors or acceptors, the poton donor may come from a ligand water molecule and is transferred to a solvent water molecule. the H2O ligand is converted to OH-. [Fe(H2O)6]3+ + H2O FeOH(H2O)5]2+ + H3O+ ka1=9x10-4

  18. 3+ H H O H H H H O O Fe3+ + O H H O O H H H H O H H Ionization of [Fe(H2O)6]3+

  19. 2+ H H O H H H O O + H Fe3+ + O H H H O O H H H O H H Ionization of [Fe(H2O)6]3+

  20. Some Kinetic Considerations [Cu (H2O)4]2+ + 4NH3 [Cu (NH3)4]2+ + 4H2O Very deep blue Pale blue These reaction occurs very rapidly-as rapidly as the two reactants can be brought together. [Cu (H2O)4]2+ + 4Cl-[Cu Cl4]2- + 4H2O Yellow Pale blue This reaction precedes slowly, the addition of HCl to an aqueous solution of Cu2+ to produces an immediate color change from pale blue to green, or even yellow if the HCl is sufficiently concentrated.

  21. Applications of Coordination Chemistry

  22. H R R C Porphyrin Structure R R N N H C H H C H N N R R C R R H

  23. H R R C Structure of Cholorophyll a. R R Sequestered metal ion N N Mg C H H C N N R R C O=C R CH

  24. CH2COO- -OOCCH2 NCH2CH2N 4Na+ -OOCCH2 CH2COO- Ethylenediaminetetraacetic acid (EDTA)

  25. O +n-4 C CH2 O- O CH2 C N CH2 O- Mn+ N CH2 O- C CH2 O CH2 O- C O

  26. The End

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