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CHEM 522 Chapter 01

CHEM 522 Chapter 01. Introduction. Transition Metal Organometallic Chemistry. Organic versus inorganic chemistry Transition metals Oxidation state d orbitals Ligands (L) Coordination compounds or complexes (ML n ). Werner Complexes. Lewis acids and bases Common types Octahedral ML 6

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CHEM 522 Chapter 01

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  1. CHEM 522Chapter 01 Introduction

  2. Transition Metal Organometallic Chemistry • Organic versus inorganic chemistry • Transition metals • Oxidation state • d orbitals • Ligands (L) • Coordination compounds or complexes (MLn)

  3. Werner Complexes • Lewis acids and bases • Common types • Octahedral ML6 • Tetrahedral ML4 • Square planar ML4 • Trigonal bipyramid ML5 • Square pyramid ML5 • Stereochemistry • cis, trans isomers • optical isomers

  4. Bridging • When the ligand have more than one site for binding it could make a bridge • 3c-2e bond

  5. Chelate Effect • Chelating ligand can bind through more than one donor atom • Example ethylene diamine • Chelating ligands are favored from entropy point of view M(NH3)6n+ + 3en  M(en)3n+ + 6NH3

  6. The Trans Effect • Trans influence: certain ligands make ligands trans to it more labile. • For platinum complexes the order is: OH- < NH3 < Cl- < CN- , CO < PR3 < H-

  7. Hard and Soft Bases • Hard base small and high charge • Soft base large and low charge • Soft-soft and hard-hard interaction is prefer over hard-soft interaction

  8. Effect of ligands on d-orbitals

  9. Octahedral Complex and d-Orbital Energies

  10. Crystal Field Theory

  11. Energy Effects in Octahedral Complexes

  12. Crystal Field Theory

  13. ∆o versus P • Hund’s rule • pairing energy considerations • ∆ > P low spin • ∆ < P high spin

  14. Magnetic Properties of CoordinationCompounds and Crystal Field Theory.

  15. Magnetic moment • Magnetic moment μs μs = √n(n+2) Where n = number of unpaired electrons n μs 11.73 2 2.83 3 3.87 4 4.90 5 5.92

  16. Colors of Transition-Metal Complexes • Transition-metal complexes can be red, purple, blue, green, yellow, orange, etc. • Most other compounds are colorless (or, white). • Why are transition-metal complexes special?

  17. Absorption of Light • If a compound is colored, it must absorb visible light. • To absorb visible light a compound must have an empty (or partially filled) electronic energy level that is just a little higher in energy than another filled (or partially filled) level. • The d orbitals in transition-metal ions often meet this test.

  18. t2g1eg0 –> t2g0eg1

  19. Spectrochemical Series • Ligands can be arranged into a spectrochemical series according to the magnitude of splitting of the d-orbitals • Large splitting is associated with strong field ligands • Small splitting is associated with weak field ligands • CN-1>en>NH3>H2O>F->SCN-> Cl-> Br-> I-

  20. Crystal field splitting

  21. Weak and Strong Field Ligands

  22. Tetrahedral Crystal Field

  23. ∆O>∆T thus no strong field vs. weak field cases Tetrahedral Splitting Pattern of d-Orbitals

  24. Square Planar Crystal Field

  25. Pi Bond Donor

  26. Pi Bond Acceptor

  27. Interaction with л-donor ligands

  28. Interaction with л-acceptor ligands

  29. л-donor ligandsл-acceptor ligands

  30. MO diagram of M(CO)6

  31. Types of Ligands • Simple sigma (σ)donor M-Cl M-NH3 • M can also bond to C=C л bond and H-H σ bond • This is known as hapticity (η) • η2 H2CCH2 • η2 H2

  32. M-H2 Bond (η2)

  33. Interaction with Double Bond (η2)

  34. Interaction with Double Bond

  35. (η5) (η1)

  36. Type of Ligands • σ bonding electron pair donors (always consider 2-e are donated by ligand so ligand will be NH3, H-, R3C-, • σ bonding, strong л-acceptor CO, CN-, PR3, • σ bonding л-donor Cl-, F-, • л-bonding electron pair donor л-acceptor C2H4, O2,

  37. Common Ligands • Table 1.10 • CO, CN- • Cp • PR3 • bipy • dpe • acac

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