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Coordination Compounds: Understanding Chemistry Concepts

Exploring coordination complexes - bonding, color, stability, metal & ligands, nomenclature, isomerism, and theories such as Valence Bond and Crystal Field. Learn about different isomers and shapes of complexes with detailed examples.

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Coordination Compounds: Understanding Chemistry Concepts

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  1. Co-ordination compounds or complexes Presented By:- Mrs. Gurvinder Kaur PGT (Chemistry) K V SURA NUSSI

  2. topics • Introduction • Nomenclature • Isomerism • Bonding in coordination compounds • Colour of complexes • Stability of complexes

  3. introduction Central metal ion Ligand K4[Fe(CN)6] Counter ion Co-ordination no. Co-ordination sphere

  4. A Coordination compound consist of a complex ion and necessary counter ions. [Co(NH3)5Cl]Cl2Complex ion: [Co(NH3)5Cl]2+Counter ions: 2 Cl- For example -

  5. Complex ion is a species where transition metal ion is surrounded by a certain number of ligands. Transition metal ion : Lewis acid Ligands : Lewis bases e.g. [Co(NH3)6]3+ [Pt(NH3)3Br]+

  6. The molecules or ions coordinating to the metal are the Ligands. • They are usually anions or polar molecules having lone pair of electrons to donate. • Example :

  7. Monodentate ligands bond using the electron pairs of a single atom. • Bidentate ligands bond using the electron pairs of two atoms. • Polydentate ligands bond using the electron pairs of many atoms • Chelating ligands includes bidentate, Polydentate ligands capable of forming ring with the metal atom or ion.

  8. Polydentate Ligands • Some ligands have two or more donor atoms. • These are called polydentate ligands or chelating agents. • In ethylenediamine, NH2CH2CH2NH2, represented here as en, each N is a donor atom. • Therefore, en is bidentate

  9. Lewis base: Lewis acid: Co3+ The formation of a coordinate complex is a Lewis acid-basereaction Lewis base i.e., the electron pair donor ligand atom is coordinated to a Lewis acid i.e., the electron pair acceptor metal atom or ion. The number of ligand bonds to the central metal atom is termed the coordination number

  10. Nomenclature • Cation • Anion • Naming complex ions: • Ligands in alphabetical order • Central metal ion • Oxidation no. of metal ion in Roman nos.

  11. Examples : K[PtCl3(NH3)] : Potassium amminetrichloridoplatinate(II) K3[Fe(C2O4)3] : Potassium trioxalatoferrate(III) [CoCl2(en)2]Cl : dichloridobis(ethane-1,2-diamine) cobalt(III)chloride [Pt(NH3)4][PtCl4] : tetraammineplatinum(II) tetrachloridoplatinate(II)

  12. BONDING IN CO-ORDINATION COMPOUNDS • VALENCE BOND THEORY • CRYSTAL FIELD THEORY

  13. Features of valence bond theory : • Presence of vacant orbitals • Hybridization of suitable number of orbitals • Co-ordinate covalent bond between ligand and metal atom • Outer or inner orbital complex depending on d-orbitals used in hybridisation

  14. Features of valence bond theory: contd… • Valence Bond Theory predicts that in metal complexes bonding arises from overlap of filled ligand orbitals and vacant metal orbitals. • Resulting bond is a coordinate covalent bond.

  15. Complex ions-Three common structural types Octahedral: Most important Tetrahedral Square planar What determines why a metal takes one of these shapes?

  16. Features of crystal field theory : • Ligands and metal ion are point charges • Electrostatic attraction between ligands and metal ion • Splitting of d-orbitals in the presence of ligand fields • Nature of ligands affects the extent of splitting

  17. Crystal Field Splitting • Splitting of d-orbitals depends on • Nature of Ligand • Metal Oxidation state • Group Position • Geometry of the coordination entity

  18. Nature of ligands affects the extent of splitting • Stronger the ligand greater is the splitting between d-orbitals High spin Low spin

  19. Metal Oxidation state • Greater Oxidation no., (e.g. Fe+3 vs Fe+2) attracts Ligand in closer and results in greater Ligand-Metal interaction and hence greater splitting of d-orbitals

  20. Group Position • Further down group, greater Δ • d orbitals more diffuse, interact more with ligand

  21. Geometry of the coordination entity Δt = 4/9 Δo

  22. The five d-orbitals in an octahedral field of ligands

  23. Splitting of d-orbitals in octahedral field

  24. tetrahedral Splitting of d-orbital energies by a tetrahedral field of ligands.

  25. Splitting of d-orbital energies by a square planar field of ligands.

  26. Square Planar & Linear Complexes Approach along x-and y-axes Approach along z-axis

  27. ISOMERISM IN COMPLEXES Isomers: same atomic composition, different structures

  28. Ionization isomers [Co(NH3)Br]SO4 & [Co(NH3)SO4]Br [PtCl2(NH3)]Br2 & [PtBr2(NH3)]Cl2

  29. Hydrate isomers Water in outer sphere i.e., water is part of solvent. Water in the inner sphere i.e., water is a ligand in the coordination sphere of the metal.

  30. Example: Linkage isomers Bonding to metal may occur at the S or the N atom Bonding occurs from N atom to metal Bonding occurs from S atom to metal

  31. Linkage Isomers [Co(NH3)5(NO2)]Cl2 Pentaamminenitrito-Ncobalt(III) chloride [Co(NH3)5(ONO)]Cl2 Pentaamminenitrito-Ocobalt(III) chloride

  32. Co-ordination isomers [Co(NH3)6][Cr(CN)6] & [Cr(NH3)6][Co(CN)6] [Pt(NH3)4][PtCl4] & [PtCl(NH3)3][PtCl3(NH3)]

  33. Stereoisomerism

  34. Trans Cis

  35. Geometrical isomerism is not shown by • Complexes with co-ordination no.4 having tetrahedral geometry. • Square planar complexes of the type MA4,MA3B,MAB3 • Octahedral complexes of the type MA6,MA5B.

  36. Octahedral complexes of the type MA3B3 also exist in two geometrical isomers: fac- and mer-. Example : [Co(NO2)3(NH3)3] NO2 NH3 H3N NO2 NO2 NO2 Co Co H3N H3N NO2 NO2 NH3 NH3 fac- isomer mer- isomer

  37. fac-isomer mer-isomer

  38. Stereoisomerism Optical isomerism: Have opposite effects on plane-polarized light (non superimposable mirror images)

  39. Enantiomers: non superimposable mirror images A structure is termed chiral if it is not superimposable on its mirror image Mirror image Of structure Structure Two chiral structures: non superimposable mirror images: Enantiomers!

  40. Chirality: the absence of a plane of symmetry Enantiomers are possible A molecule possessing a plane of symmetry is achiral and superimposible on its mirror image.Enantiomers are NOT possible Are the following chiral or achiral structures? Plane of symmetry Achiral (one structure) No plane of symmetry Chiral (two enantiomer)

  41. Which are enantiomers (non-superimposable mirror images) and which are identical (superimposable mirror images)?

  42. Colour in complexes Bonding Theories attempt to account for the colour and magnetic properties of transition metal complexes.

  43. Colour in co-ordination compounds : Due to d-d transition Example: [Ti(H2O)6]3+ Ti3+ : 3d1

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