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LECTURE 4

LECTURE 4. THEME: Complex compound in biological systems. associate prof. Dmukhalska Ye. B. Outline. Concept of complex compounds and complexing process. Nomenclature of complex compounds. Types of complexes.

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LECTURE 4

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  1. LECTURE 4 THEME: Complex compound in biological systems. associate prof. Dmukhalska Ye. B.

  2. Outline • Concept of complex compounds and complexing process. Nomenclature of complex compounds. Types of complexes. • Structure of complex compounds. Isomerism of complex compounds. Chemical bonds in complex compounds molecule. • Stability of complexes and influence of different factors on it. • Biological role of complex compounds.Usage of complexing in chemistry.

  3. A coordination complex • Coordination compounds are the compounds in which the central atom (usually metallic), is linked to а number of ions or neutral molecules by coordinate bonds i.е. by donation of lone pairs of electrons by these ions or neutral molecules to the central metal atom. • nickel tetracarbonyl, [Ni(CO)4]

  4. Complex compounds А) Structure CuSO4 + 4 NH3 = [Cu (NH3)4] SO4 [Cu (NH3)4] SO4 Complex compound • Cu2+ - central atom • NH3 – ligand • [Cu (NH3)4]2+ - complex ion • SO42- -anion

  5. Aqueous solutions that contain [Ni(H2O)6]2+, [Ni(NH3)6]2+ and [Ni(en)3]2+ (from left to right). The two solutions on the right were prepared by adding ammonia and ethylenediamine, respectively, to aqueous nickel(II) nitrate.

  6. Werner’s Theory • Alfred Werner suggested in 1893 that metal ions exhibit what he called primary and secondary valences. • Primary valences were the oxidation number for the metal (+3 on the cobalt at the right). • Secondary valences were the coordination number, the number of atoms directly bonded to the metal (6 in the complex at the right).

  7. Co-ordination Werner’s theory Charge coordination number example of the metal ion +1 2 Ag+, Cu+ +2 4, 6Cu2+, Zn2+, Pd2+, Pt2+ +3 6, 4Pt4+, Cr3+, Co3+, Fe3+ +4 8 Sn4+

  8. The species formed by linking of а number of ions or molecules by co-ordinate bonds to the central metal atom (or ion) carries positive or negative charge, it is called a complex ion (coordination sphera). [Fe(СN)6]4-, [Cu(NH3)4]2+, [Ag(CN)2]-

  9. Coordination sphere. • The central atom and the ligands which are directly attached to it are enclosed in square brackets and are collectively termed as the coordination sphere.

  10. Metal-Ligand Bond • This bond is formed between a Lewis acid and a Lewis base. • The ligands (Lewis bases) have nonbonding electrons. • The metal (Lewis acid) has empty orbitals.

  11. Lewis base Complex ion Lewis acid Lewis base Lewis acid Complex ion • Transition metals act as Lewis acids • Form complexes/complex ions Fe3+(aq) + 6CN-(aq)  [Fe(CN)6]3-(aq) Ni2+(aq) + 6NH3(aq)  [Ni(NH3)6]2+(aq) Complex with a net charge = complex ion Complexes have distinct properties

  12. Coordination compound • Compound that contains 1 or more complexes • Example • [Co(NH3)6]Cl3 • [Cu(NH3)4][PtCl4] • [Pt(NH3)2Cl2]

  13. The donor atoms, molecules or anions, which donate а pair of electrons to the metal atom and form co-ordinate bond with it are called ligands.

  14. Ligands • classified according to the number of donor atoms • Examples • monodentate = 1 • bidentate = 2 • tetradentate = 4 • hexadentate = 6 • polydentate = 2 or more donor atoms chelating agents

  15. Ligands • Monodentate • Examples: • H2O, CN-, NH3, NO2-, SCN-, OH-, X- (halides), CO, O2- • Example Complexes • [Co(NH3)6]3+ • [Fe(SCN)6]3-

  16. Ligands • Bidentate • Examples • oxalate ion = C2O42- • ethylenediamine (en) = NH2CH2CH2NH2 • ortho-phenanthroline (o-phen) • Example Complexes • [Co(en)3]3+ • [Cr(C2O4)3]3- • [Fe(NH3)4(o-phen)]3+

  17. Ligands oxalate ion ethylenediamine * * * * ortho-phenanthroline Donor Atoms:* * *

  18. Ligands oxalate ion ethylenediamine H C C O M N M

  19. Ligands

  20. Chelation is a process in which a polydentateligand bonds to a metal ion, forming a ring. The complex produced by this process is called a chelate, and the polydentateligand is referred to as a chelating agent. • ethylenediaminetetraacetate (EDTA) = (O2CCH2)2N(CH2)2N(CH2CO2)24- • Example Complexes • [Fe(EDTA)]-1 • [Co(EDTA)]-1

  21. Ligands * Donor Atoms EDTA * * * * * *

  22. Ligands O EDTA H C N M

  23. Ligands EDTA

  24. Some important characteristics of chelates. • (i) Chelating ligands form more stable complexes than the monodentate analogs. This is called chelating effect. • (ii) Chelating ligands, which do not contain double bonds e.g. ethylenediamine form five membered stable rings. The chelating ligands such as acetylacetone form six membered stable ring complexes. • (iii) Ligands with large groups form unstable rings than the ligands with smaller groups due to steric hindrance.

  25. The complexes formed by Cu (II) and Pt (II) ions with ethylenediamine are metal chelates represented as follows:

  26. Coordination number • The number of ligand donor atoms that surround a central metal ion in a complex is called the coordination number of the metal • Originally, a complex implied a reversible association of molecules, atoms, or ions through weak chemical bonds. • [Ag(СN)2]-, [Cu(NН3)4]2+ and [Cr(Н2О)6]3+

  27. Common Geometries of Complexes Coordination Number Geometry 2 Linear Example: [Ag(NH3)2]+

  28. Common Geometries of Complexes Coordination Number Geometry 4 tetrahedral Examples: [Zn(NH3)4]2+, [FeCl4]- square planar Example: [Ni(CN)4]2-

  29. Common Geometries of Complexes Coordination Number Geometry 6 Examples: [Co(CN)6]3-, [Fe(en)3]3+ octahedral

  30. Charge on the complex ion. • The charge carried by а complex ion is the algebraic sum of the charges carried by central metal ion and the ligands coordinated to the central metal ion. • [Ag (CN)2]- • [Cu (NH3)4]2+

  31. Complex charge = sum of charges on the metal and the ligands [Fe(CN)6]3-

  32. Complex charge = sum of charges on the metal and the ligands [Fe(CN)6]3- +3 6(-1)

  33. Neutral charge of coordination compound = sum of charges on metal, ligands, and counterbalancing ions [Co(NH3)6]Cl2 +2 6(0) 2(-1) neutral compound

  34. Oxidation number or oxidation state. • It is а number that represents an electric charge which an atom or ion actually has or appears to have when combined with other atoms, • oxidation number of copper in [Cu(NH3)4]2+ is +2 but coordination number is 4. • oxidation number of Fe in [Fe(СN)6]3- is + 3 but the coordination number is 6. • (i) [Cu (NНЗ)4]SO4. • (ii) Fe in [Fe (СN)6]3- • (iii)К3[Fe(С2О4)3]. • (iv) [Ni(CO)4].

  35. Neutral charge of coordination compound = sum of charges on metal, ligands, and counterbalancing ions [Co(NH3)6]Cl2 +2 6(0) 2(-1) neutral compound

  36. Nomenclature of Coordination Compounds: IUPAC Rules • The cation is named before the anion • When naming a complex: • Ligands are named first • alphabetical order • Metal atom/ion is named last • oxidation state given in Roman numerals follows in parentheses • Use no spaces in complex name

  37. Naming Coordination Compounds

  38. Names of Some Common Metallate Anions

  39. Names of Some Common Ligands

  40. Examples of Complexes withVarious Coordination Numbers

  41. [Co(NН3)6]Cl3, hexaamminecobalt (III) chloride. • K2[PtCl6], potassium hexachloroplatinate (IV). • [Co(NO2)(NH3)3], triamminetrinitrocobalt (III) • [PtCl4(NH3)2], diamminetetrachloroplatinum (IV).

  42. Types of complexes. • (i) А complex in which the complex ion carries а net positive charge is called cationic complex: [Co(NН3)]3+, [Ni(NH3)6]2+ • (ii) А complex in which the complex ion carries а net negative charge is called anionic complex: [Ag(CN)2]-, [Fe (CN)6]4- • (iii) А complex carrying no net charge is called а neutral complex or simply а complex: • [Ni(CO)4], [CoCl3 (NН3)3]

  43. CH2 CH2 H2C HOOC COOH CH2 N N Me CH2 H2C O O C C O O NH2 CH2 O O C Me Me NH2 CH2 O C O Main types of complex compounds • 1. With one central atom • Ammonia complex [Cu(NH3)4]SO4 • Aqua complex[Al(H2O)6]Cl3 • acidic complex K2[PtCl4] • complexwith difference ligandsK[Pt(NH3)Cl3] • cyclic (chelates) • Polycentral compoynds • Chain [Cr(NH3)5 – OH – (NH3)Cr]Cl3 • chelaes (CO)5Mn – Mn(Co)5

  44. Isomerism • Isomers • compounds that have the same composition but a different arrangement of atoms • Major Types • structural isomers • stereoisomers

  45. Structural Isomers • Structural Isomers • isomers that have different bonds • Coordination-sphere isomers • differ in a ligand bonded to the metal in the complex, as opposed to being outside the coordination-sphere • Example [Co(NH3)5Cl]Br vs. [Co(NH3)5Br]Cl

  46. Coordination-Sphere Isomers • Example [Co(NH3)5Cl]Br vs. [Co(NH3)5Br]Cl • Consider ionization in water [Co(NH3)5Cl]Br  [Co(NH3)5Cl]+ + Br- [Co(NH3)5Br]Cl  [Co(NH3)5Br]+ + Cl-

  47. Coordination-Sphere Isomers • Example [Co(NH3)5Cl]Br vs. [Co(NH3)5Br]Cl • Consider precipitation [Co(NH3)5Cl]Br(aq) + AgNO3(aq)  [Co(NH3)5Cl]NO3(aq) + AgBr(s) [Co(NH3)5Br]Cl(aq) + AgNO3(aq)  [Co(NH3)5Br]NO3(aq) + AgCl(aq)

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