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Coordination Chemistry

Coordination Chemistry. Paper III Unit 1 No. of Classes - 12. Complexes. A central metal atom bonded to a group of molecules or ions is a metal complex . Metal complexes are coordination compounds . Example Complexes [Co (NH 3 ) 6 ]Cl 3 K 4 [Fe(SCN) 6 ] [Cu(NH 3 ) 4 ][PtCl 4 ]

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Coordination Chemistry

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  1. Coordination Chemistry Paper III Unit 1 No. of Classes - 12 www.smitaasthana.com

  2. Complexes • A central metal atom bonded to a group of molecules or ions is a metal complex. • Metal complexes are coordination compounds. • Example Complexes • [Co (NH3)6 ]Cl3 • K 4 [Fe(SCN)6 ] • [Cu(NH3)4][PtCl4] • [Pt(NH3)2Cl2] www.smitaasthana.com

  3. Coordination Chemistry Metal Complex Central meal Atom – Ligands [ M – L ] Metals – Acceptors – • take lone pair of electrons from Ligands • Small size & High positive charge density • Vacant orbital of suitable energy • Example – transition metals Ligands – Donors • They are usually anions, sometimes cations or polar molecules. • The must have lone pairs to interact with metal www.smitaasthana.com

  4. What is Coordination? • When an orbital from a ligand with lone pair overlaps with an empty orbital from a metal a coordinate covalent bond is formed M L So ligands musthave lone pairs of electrons. www.smitaasthana.com

  5. 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. Fe3+(aq) + 6CN- (aq)  [Fe(CN)6]3-(aq) Lewis base Ni2+(aq) + 6NH3(aq)  [Ni(NH3)6]2+(aq) Lewis acid Complex ion www.smitaasthana.com

  6. Ligands are classified according to the number of donor atoms *If the complex has a closed ring structure it is called Chelate And the ligand is called Chelating ligand. www.smitaasthana.com

  7. Ligands • Monodentate • H2O, CN-, NH3, NO2-, SCN-, OH-, X- (halides), CO, O2- • Bidentate • oxalate ion = C2O42- • ethylenediamine (en) = NH2CH2CH2NH2 • ortho-phenanthroline (o-phen) www.smitaasthana.com

  8. Ligands oxalate ion ethylenediamine * * * * ortho-phenanthroline * * *Donor Atoms www.smitaasthana.com

  9. Ligands EDTA * * * * * * *Donor Atoms www.smitaasthana.com

  10. Chelating Agents • Porphyrins are complexes containing a form of the porphine molecule shown at right. • Important biomolecules like heme and chlorophyll are porphyrins. www.smitaasthana.com

  11. PolydentateLigands Ethylenediaminetetraacetate, abbreviated EDTA, has six donor atoms. Wraps around the central atom like an octopus www.smitaasthana.com

  12. Coordination Chemistry - Terms Coordination sphere - Metal and ligands bound to it. [ M L (n) ] Coordination number - Number of donor atoms bonded to the central metal atom or ion in the complex • The atom that supplies the lone pairs of electrons for the metal-ligand bond is the donor atom. • The number of these atoms is the coordination number. www.smitaasthana.com

  13. Coordination Chemistry - Terms Complex ion = sum of charges on the metal and the ligands [Fe(CN)6]3- +3 6(-1) Neutral complex molecule = sum of charges on metal, ligands, and counterbalancing ions is zero www.smitaasthana.com

  14. Nomenclature of Coordination Compounds: IUPAC Rules 1. One word or Two words- • Molecular complex – One word name [Pt(NH3)2Cl2] Diamminedichloroplatinum(II) • Ionic complex – Two words -Name of cation &Name of anion The cation is named before the anion a) Cationic complex – [ ML ] Y  [ML]+ + Y - cpx. cation [Co (NH3)6 ]Cl3Hexaamminecobolt(III) Chloride [Cr(NH3)3(H2O)3]Cl3 Triamminetriaquachromium(III) chloride www.smitaasthana.com

  15. Nomenclature b) Anionic complex – X [ ML ]  X + + [ ML ]- Cpx. Anion K 4 [Fe(CN)6 ] Potassium hexacyanoferrate(II) c)When there aretwo coordination spheres the cation is named first followed by anion and each coordination sphere is named separately. [Ag(NH3)2][Ag(CN)2] Diamminesilver(I) dicyanoargentate(I) [ www.smitaasthana.com

  16. Nomenclature • 2. Naming the Central metal atom – • 2.1 Name - • For neutral and cationic complex – Name of metal is as it is. • For anionic complex - suffix -ate appended to the name of the metal www.smitaasthana.com

  17. 2. Naming the Central metal atom • 2.2 Oxidation state - Name followed by its oxidation state in Roman numerals in parenthesis. Knowing the charge on a complex ion and the charge on each ligand, one can determine the oxidation number for the metal. • Ex. [Pt(NH3)2Cl2] - x + (0*2) + (-1*2) = 0 • x +0-2 = 0, x = +2 • Diamminedichloroplatinum(II) • Na2 [NiCl4] Sodium tetrachloronickelate(II) www.smitaasthana.com

  18. Nomenclature 3. Naming the Coordination sphere - • In the coordination sphere the ligands are named first and Metal is named last and its oxidation state given in Roman numerals follows in parentheses. Use no spaces in name of complex ion. • [Pt(NH3)5Cl]Br3Pentaamminechloroplatinum(IV) bromide • (NH4)2[Ni(C2O4)2(H2O)2] Ammonium diaquadioxalatonickelate(II) • The oxalate ion is a bidentateligand. www.smitaasthana.com

  19. Nomenclature 3.1 Name of the Ligand – a) The names of anionic ligands end with the suffix -o www.smitaasthana.com

  20. Nomenclature –3.1Name of the Ligand • b) Neutral ligands are referred to by the usual name for the molecule • Example – ethylenediamine, Pyridine, Ethanol, Methyl amine. • Exceptions • Water, H2O : Aqua • Ammonia, NH3 :Ammine • Carbon monoxide, CO :Carbonyl • Nitric oxide, NO : Nitrosyl c) Positive ligands – Their name ends with a suffix of - ium Pyridinium. Nitronium NO+ www.smitaasthana.com

  21. Nomenclature – 3.2 - No. of ligands a) Greek prefixes are used to indicate the number of each type of ligand when more than one of same type is present in the complex di-, 2; tri-, 3; tetra-, 4; penta-, 5; hexa-, 6 [Fe(NH3)6](NO3)3 Hexaammineiron(III) nitrate Prefixes denoting the number of ligands are ignored when alphabetizing. b) If the ligand name already contains a Greek prefix, use alternate prefixes like bis-, 2; tris-, 3; tetrakis-,4; pentakis-, 5; hexakis-, 6 The name of the ligand is placed in parentheses f) Ligands are listed alphabetically [CoClBr(NH3)4]SO4Tetraamminebromochlorocobalt(III) sulfate www.smitaasthana.com

  22. Nomenclature • 3.3 Bridging ligands have the prefix m • [(NH3)4Co(OH)(NH2)Co(NH3)4]4+ • m-amido-m-hydroxobis(tetraaminecobalt(III)) • When a complex has two or more metal atoms it is called Polynuclear • and the metals are bonded through the bridging ligands. • (NH3)4Fe Fe(Cl)4 • Tetraammineiron(III) -m- dihydroxotetrachloroiron(III) • 4. Isomer designations come before the rest of the name and in italics • cis-diamminedichloroplatinum(II) • trans-diamminedichloroplatinum(II) OH OH www.smitaasthana.com

  23. Examples K3[Fe(CN)6] = potassium hexacyanoferrate(III) K4[Fe(CN)6] = potassium hexacyanoferrate(II) Na3[AlF6] = sodium hexafluoroaluminate(III) [Co(NH3)3F3] = triamminetrifluorocobalt(III) [Fe(NH3) 6] NO3Hexaammineiron(III) nitrate (NH4)2[CuCl4] Ammonium tetrachlorocuprate(II) Na3[FeCl(CN)5] Sodium chloropentacyanoferrate(III) K3[CoF6] Potassium hexafluorocobaltate(III) [Co(SO4)(NH3)5]+. Pentaamminesulfatocobalt(III) ion [Fe(OH)(H2O)5]2+ Pentaaquahydroxoiron(III) ion [Fe(NH3)6][Cr(CN)6]Hexaammineiron(III) hexacyanochromate (III) [Fe(CO)5 ]Pentacarbonyliron(0) www.smitaasthana.com

  24. A chemical mysterySame metal, same ligands, different number of ions when dissolved

  25. Werner’s Theory • Metal ions have primary and secondaryvalences. • Primary valence equal the metal’s oxidation number • Secondary valence is the number of atoms directly bonded to the metal (coordination number) • Primary valences are ionizable and non – directional. • Secondary valences are non – ionizableand directional and give the geometry and shape of the molecule. • Sometimes ions satisfying the primary valence play a dual role and also satisfy the sec. valence.

  26. Werner’s Theory • The central metal and the ligands directly bonded to it make up the coordination sphere of the complex. • In CoCl3 ∙6 NH3, all six of the ligands are NH3 and the 3 chloride ions are outside the coordination sphere.

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  29. Werner’s Theory & Isomerism Co(NH3)4Cl2]Cl – Coord. no. 6 Theoretically 3 shapes possible • Hexagonal Planar - 3 isomers • Trigonal Prism – 3 isomers Cl Cl Cl NH3 NH3 NH3 NH3 NH3 Cl NH3 NH3 Cl NH3 NH3 NH3 NH3 NH3 Cl NH3 Cl Cl NH3 NH3 NH3 Cl Cl NH3 NH3 NH3 NH3 Cl NH3 NH3 Cl NH3 NH3

  30. 3. Octahedra - Cl Cl NH3 NH3 NH3 Cl Pt Pt NH3 NH3 NH3 NH3 Cl NH3 Two isomers possible. Werner could isolate TWO isomers hence concluded that the complex is Octahedra www.smitaasthana.com

  31. Cis – trans – isomers in Octahedra shape Cis - Trans - www.smitaasthana.com

  32. Sidwick's theory of effective atomic number In complexes, metal atom accept lone pair of electrons donated by the ligand for bond formation. It proposes that a metal ion will continue to accept lone pair of electrons till its effective atomic number becomes equal to the atomic no. of the next higher noble gas. ( Effective atomic number - it is the total no. of electrons present on a metal atom i.e. no. of electrons present on the metal atom – e lost during formation of ion + those gained from the ligands. Each monodentateligand gives one lone pair of electron.) Calculation of EAN - [Co(NH3)6]Cl3 - atomic no. of cobalt = 27, oxidation state of Co = +3 no. of electrons on Co3+ ion = 27 - 3 = 24 Each ammonia ligand gives one pair of electron, no. of electrons given by 6 ammonia molecules = 6 * 2 = 12 Total no. of electrons present on Co3+ now = 24 + 12 = 36 EAN of Co3+ = 36 36 is atomic no. of Krypton. www.smitaasthana.com

  33. Examples of EAN rule Though EAN rule is applicable to a number of cases, there are several complexes which do not follow this rule. • Deffects in Sidwick's theory - • Many well known complexes do not follow EAN rule. • The theory does not predict magnetic behaviour of the complexes. • The theory does not comment on the geometries of the complexes. www.smitaasthana.com

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