A. Electronic Spectra of Coordination Compounds 1. We

A. Electronic Spectra of Coordination Compounds 1. We

A. Electronic Spectra of Coordination Compounds 1. We know how to determine Free Ion Terms; d-electron configurations given below a. Determining Lowest Energy Free Ion Term 1. From Table above: highest multiplicity, largest L if more than one (d 3 = 4F) 2. Selection Rules a. Laporte Selection Rule: transitions between states of same parity (g/u) are forbidden gg and uu forbidden (all dd transitions); gu allowed (dp allowed) b. Spin Selection Rule: transitions between different spin multiplicities are

forbidden 4A24T1 are allowed; 4A22A2 are forbidden c. 3. Seem to rule out almost all transitions in metal complexes: Why Colored? Mechanisms that relax the selection rules a. Vibronic Coupling: vibrations of bonds cause loss of the center of symmetry Relaxes Laporte Selection Rule and allows 5-50 M-1 cm-1 metal transitions b. Tetrahedral complexes strongly absorb 1. No center of symmetry, so no Laporte forbideness 2. sp3/sd3 hybridization mixes p orbitals (u) with d orbitals (g) to relax Laporte 3. Spin-Orbit Coupling relaxes Spin Selection Rule in some case (<1 M -1cm-1) Most important for 2nd and 3rd row transition metals 4. [V(H2O)6]3+ d2 Example 5.

Correlation Diagrams a. Free Ion (no ligand field) Term Symbols (Previous Lecture) shown on left b. Strong Ligand Field Term Symbols shown on the right: overcomes LS coupling a. Possible d2 electron configurations (t2g2 is ground state lowest energy) b. Actual complexes lie in between these weak and strong field limits c. Free ion terms can be reduced to constituent irreducible representations d. 6. Each Free Ion Term irreducible representation Correlates with one from the strong-field limit e. Transitions from Ground State must match same Spin Multiplicity (Bold Lines) f. Non-Crossing Rule: lines connecting states of same symmetry do not cross

Tanabe-Sugano Diagrams g. Special correlation diagrams useful for interpreting electronic spectra h. Lowest energy state plotted along horizontal axis i. Vertical distance above is correlated to energy of transition Horizontal Axis: Do /B Do = ligand field splitting ch 10 B = Racah parameter = repulsion between terms of same multiplicity Vertical Axis: E/B E = energy of excited state above n ground state 1 n2 n3

7. More on Tanabe-Sugano Diagrams a. Simplified Tanabe-Sugano Diagrams show allowed transitions for Octahedral Geom d2 and d8 opposite order d3 and d7 opposite order d4 and d6 opposite order b. c. d4-d7 configurations have High Spin and Low Spin possibilities 1. d4 example S = 2 (mult = 5) S = 1 (mult = 3) 2.

Weak Field limit defined as Do /B = 27 3. Weak Field (High Spin): ground state d4 = 5Eg 4. Strong Field (Low Spin): ground state d4 = 3T1g Weak Field Aqua Complex Spectra for 1st-Row Transition Metal Ions: compare number of peaks to Tanabe-Sugano Diagrams 8. Jahn-Teller Distortions and Electronic Spectra a. d1 and d9 electron configurations are Jahn-Teller distorted b.

c. Cu2+ and Ti3+ spectra show some splitting of single expected absorption Jahn-Teller distortion break degenerate electronic states (strongest if e g like d9) Two absorbances in Cu2+ spectrum. B1gA1g too low E to be observed. d. Electron Configurations can be symmetry labelled based on degeneracy e. Ti3+ d1 spectrum also shows splitting, but t2g Jahn-Teller effects are small? 1. f. g.

Excited state (with eg Jahn-Teller distortion) is responsible for splitting Distortion from pure Octahedral Geometries are common, so Electronic Spectra are often more complex than the Tanabe-Sugano Diagrams indicate Example: [Fe(H2O)6]2+ has split peak at 1000nm. Use Tanabe Sugano Diagram to Transition is 5T2g5Eg account for transition and explain splitting Splitting due to Jahn-Teller Distortion of Doubly Degenerate eg 9. Determining Do from Electronic Spectra a. b. Not always possible, as overlapping bands and complex math limits utility

Often possible to calculate Do and/or B directly from spectrum c. d1, d4(hs), d6(hs), d9 complexes give only one band = Do d. d3, d8 have ground state F terms. Do is found from lowest energy transition e. d2, d7(hs)Complicated by splitting into many states. See text for complex explanation of estimate of Do, but we will not cover these. f. d5(hs), d4-d7(ls) 1. d5(hs) has no excited states with the

correct multiplicity, so all transitions are Spin Forbidden. Very weak absorptions 10. Tetrahedral Complexes a. More intense absorptions due to no center of symmetry making Laporte Selection Rule moot b. d-orbitals are split in opposite direction than octahedral c. Hole Formalism: d1 Oh treated similarly as d9 tetrahedral 1. Use Correlation Diagram for the d10-n Oh configuration to describe dn Td 2. Example for d2 Td case, use d8 Oh diagram 11. Orgel Diagrams (L. E. Orgel, J. Chem. Phys., 1955, 1004.) a. dn (Oh) and dn5 have the same diagram

b. dn (Td) and dn5 have the same diagram c. dn and dn5 (Oh) is the reverse of dn and dn5 (Td) d. dn (Oh) is the reverse of d10-n (Oh) g. Orgel Diagrams h. Simple tool (can memorize them) to predict # of bands and Term Symbols

LMCT 12. Charge Transfer Spectra a. Exchange of an electron from one Ligand to Metal or Metal to LigandMLCT b. c. d. Often in UV, but can be in visible region Much more intense (50,000 M-1cm-1) than dd bands because Laporte Allowed LMCT: MnO4- dark purple color, O ligand orbitals to empty Mn+7 d-orbitals e. f. MLCT: Usually with p-acceptor ligands (CO, CN-, SCN-) Both can occur in same complex: Cr(CO)6

g. h. i. Not always possible to determine LMCT vs. MLCT May cover up dd bands Often have to collect spectra at two different concentrations 1. Low concentration to get CT bands on scale 2. High concentration to get dd bands on scale 13. Intraligand Bands a. Some ligands absorb light themselves (sp* or pp*)

Recently Viewed Presentations

  • Conformation Specific Spectroscopic Investigation of - and /-peptides:

    Conformation Specific Spectroscopic Investigation of - and /-peptides:

    Points: Conformation Specific IR ….mass selected…..tuning range Points: This is our worst case for making assignments…but we can still make firm assignments based on what we know about amide NH….use this as a foundation for what to expect in carbonyl...
  • The Church-Turing Thesis Explained Away

    The Church-Turing Thesis Explained Away

    The Church-Turing Thesis is a Pseudo-proposition Mark Hogarth Wolfson College, Cambridge * * * * * * * * * * T will also give an account of how, e.g., the machine computes 3+4=7 Arithmetic has a physical side 'Pure...
  • Can You Save Fred? - QuestGarden.com

    Can You Save Fred? - QuestGarden.com

    Can You Save Fred? Can You Save Fred (The Situation) Poor Fred! He was sailing along on a boat (the plastic cup) when a strong wind blew it upside down. Fred (the Gummi Worm) ended up on top of the...
  • Analytical Skills Training at CALHR: Problem Solving ...

    Analytical Skills Training at CALHR: Problem Solving ...

    Analytical Skills Training at CALHR: Problem Solving, Critical Thinking, and Decision Making . Bruce Winner. Los Rios CCD. [email protected] Introduce myself and Linda. The three hands symbolize the three partners for CALHR. UCD, CSUS, and Los Rios
  • Kinematics Graphs One-Dimensional Motion Graphs provide an easy

    Kinematics Graphs One-Dimensional Motion Graphs provide an easy

    One of them is housed at the Addison Wesley textbook site called Activphysics. Take time to go out and play with the various problem set examples. It is free and has proven to be useful to a number of students...
  • teterborousersgroup.org

    teterborousersgroup.org

    TERPS vs Pans-Ops. DP Gross . Gradient. Things get more complex when a climb gradient is required. Note that the first example utilizes Pre-change 19 TERPS criteria. Note that the gradient starts at 35 feet above the runway surface.
  • Osmosis - elysciencecenter.com

    Osmosis - elysciencecenter.com

    Osmotic Pressure. Why is osmotic pressure important? Monday, July 20, 2009. Use students to illustrate the differences in pressure. Five on side A and 2 on side B—most pressure going forward will be on side A giving a net pressure...
  • Windows Store apps with HTML + Facebook integration

    Windows Store apps with HTML + Facebook integration

    HTML5 History API. HTML5 Parser. HTML5 Sandbox. HTML5 Selection. HTML5 semantic elements. HTML5 track. HTML5 video and audio. JavaScript Typed Array. ICC Color Profiles. IndexedDB. Page Visibility. Pointer (Mouse, Pen, and Touch) Events. RequestAnimationFrame. Navigation Timing. Selectors API Level 2....