Coordination Chemistry Chapter 7
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Questions and Answers

What is the significance of a larger K value in complex formation?

  • Bonding with incoming ligands is more favorable than H2O (correct)
  • Bonding with incoming ligands is less favorable than H2O
  • The complex is less stable
  • The complex is more labile

    • What is the HSAB concept related to in coordination chemistry?

  • Chelate Effect
  • Redox Reactions
  • Ligand Exchange Reactions
  • Hard-Soft Acids and Bases (correct)

    • What is the equation that allows the calculation of free energy, entropy, and enthalpy of a reaction from stability constants?

  • ΔG = -RTlnK = ΔH – TΔS (correct)
  • ΔG = RTlnK = ΔH – 2TΔS
  • ΔG = RTlnK = ΔH + TΔS
  • ΔG = -RTlnK = ΔH + 2TΔS

    • What is a characteristic of labile complexes?

    <p>They undergo substitution with t½ &lt; 1 minute</p> Signup and view all the answers

    What is the significance of the chelate effect in coordination chemistry?

    <p>It increases the stability of complexes</p> Signup and view all the answers

    What is the primary goal of studying reaction mechanisms in coordination chemistry?

    <p>To synthesize predicted products</p> Signup and view all the answers

    What is the significance of the water exchange rate constants in labile complexes?

    <p>They are correlated to the electronic configuration of the starting complex</p> Signup and view all the answers

    What is the primary difference between inert and labile complexes?

    <p>Their kinetic stability</p> Signup and view all the answers

    What is the significance of the work of Werner and Jorgensen in coordination chemistry?

    <p>They discovered many basic reactions</p> Signup and view all the answers

    What is the limitation of studying reaction mechanisms in coordination chemistry?

    <p>We can only disprove a mechanism, not prove it</p> Signup and view all the answers

    What is the primary characteristic of a labile complex?

    <p>Very low activation energy for ligand substitution</p> Signup and view all the answers

    Which of the following compounds was studied by Werner for being inert?

    <p>Co(III) compounds</p> Signup and view all the answers

    Inert compounds react slower due to which of the following?

    <p>Higher activation energy for ligand substitution</p> Signup and view all the answers

    Which transition metal complex is considered to be inert and undergoes water exchange slowly?

    <p>[Cr(H2O)6]3+</p> Signup and view all the answers

    What type of complexes are generally thermodynamically more stable due to the chelate effect?

    <p>Polydentate complexes</p> Signup and view all the answers

    Which factor contributes to the slower ligand substitution in chelated ligands compared to monodentate ligands?

    <p>Higher ΔH associated with removal of the first bound atom</p> Signup and view all the answers

    Which vanadium complex reacts slower with ligands?

    <p>[V(H2O)6]2+</p> Signup and view all the answers

    What characteristic of inert octahedral complexes is often associated with their slower reaction rates?

    <p>High LFSE</p> Signup and view all the answers

    What makes a compound inert in the context provided?

    <p>It is slower to react with a higher activation energy</p> Signup and view all the answers

    Why are compounds with high LFSE generally inert?

    <p>They undergo ligand substitution slowly</p> Signup and view all the answers

    Why is the dissociation of a chelating ethylenediamine ligand expected to be slower than the dissociation of ammonia?

    <p>Ethylenediamine must bend and rotate to move the free amine away from the metal.</p> Signup and view all the answers

    What does the kinetic barrier for the reattachment of a multidentate ligand depend on?

    <p>Proximity to the metal center</p> Signup and view all the answers

    Which ligands in square-planar Pt(II) compounds are most easily replaced?

    <p>Ligands trans to chloride</p> Signup and view all the answers

    Why does chloride have a stronger trans effect than ammonia?

    <p>Chloride creates a weaker Pt-X bond, making substitution easier.</p> Signup and view all the answers

    In Pt(II) compounds, which factor stabilizes the 5-coordinate transition state?

    <p>Interaction from Pt-T</p> Signup and view all the answers

    Which ligand is expected to have the strongest trans effect?

    <p>CO</p> Signup and view all the answers

    What is one result of the trans influence on a Pt(II) compound?

    <p>Weakening of the Pt-X bond</p> Signup and view all the answers

    What is a key characteristic of ligands with high trans-directing ability in Pt(II) complexes?

    <p>They are typically π-acceptors.</p> Signup and view all the answers

    How does the trans effect lower the energy of the Pt-X bond?

    <p>By stabilizing the 5-coordinate transition state</p> Signup and view all the answers

    What is the effect of π-acceptors on Pt in the context of the kinetic trans effect?

    <p>They remove electron density from Pt, making association with Y more likely.</p> Signup and view all the answers

    Study Notes

    Kinetic Barrier

    • Lower kinetic barrier for subsequent reattachment in chelate ligands compared to monodentate ligands due to proximity to the metal center

    Chelate Effect

    • Dissociation of ethylenediamine ligand is slower than that of ammonia due to necessary bending and rotation to move the free amine away from the metal
    • Chelate effect causes polydentate complexes to be thermodynamically more stable than their monodentate counterparts
    • Substitution for a chelated ligand is generally a slower reaction than that for a similar monodentate ligand

    Trans Effect

    • In square-planar Pt(II) compounds, ligands trans to chloride are more easily replaced than those trans to ammonia
    • Chloride has a stronger trans effect than ammonia
    • The trans effect controls the substitution of ligands in Pt(II) compounds
    • Ligands trans to certain other ligands are easily substituted, with the controlling ligands being CO, CN-, olefins, H-, PR3, NO2-, I-, SCN-, Br-, Cl-, NH3, py, OH-, and H2O

    Lability of Cl-

    • The lability of chloride controls the substitution of ligands in certain reactions

    Contribution of Two Factors

    • Thermodynamic effect (trans influence): weakening of the Pt-X bond
    • Kinetic effect (trans effect): stabilization of the 5-coordinate transition state

    Trans-Influence

    • The strong Pt-T sigma bond prevents the trans leaving group Pt-X bond from being strong
    • The weak Pt-X bond corresponds to a high energy ground state
    • The Ea required to get X to leave is small

    The Kinetic Effect (Trans Effect) Contribution

    • π-acceptors remove e- density from Pt, making association with Y more likely
    • This interaction from Pt-T lowers the energy of the 5-coordinate intermediate
    • Ea is lowered and the Pt-X bond is more easily broken
    • The metal center becomes more electrophilic for nucleophilic attack

    Chapter 7: Thermodynamic and Non-Redox Kinetic Factors in Coordination Chemistry

    • Objectives: mechanisms of substitution reactions of octahedral and square planar complexes

    Hard-Soft Acids and Bases

    • HSAB concept: Ag+ is soft and strongly bonds with Br- relative to F- and Cl-

    Factors that Affect Stability of Complexes

    • ∆G = -RTlnK = ∆H – T∆S allows calculation of free energy, entropy, and enthalpy of a reaction from stability constants

    Reactions of Coordination Compounds

    • Types of reactions: substitution, oxidation/reduction, ligand reactions, etc.
    • Werner and Jorgenson discovered many of the basic reactions
    • Experimentation over many years has yielded proposed mechanisms

    Substitution Reactions

    • Inert and labile complexes (kinetic stability)
    • Labile complexes: those undergoing substitution with t½ < 1 minute
    • Labile metal ions: those with small or zero LFSE
    • Examples: d1, d2, d7, d9, d10 and high-spin d4-d6

    Kinetic Stability versus Thermodynamic Stability

    • Stability (formation) constant = 2.0 x 10³¹

    Substitution Reactions

    • These reactions can produce colored products used to identify metal ions
    • Water exchange rate constants vary widely as a function of the metal ion
    • Labile complexes: those with a very low activation energy for ligand substitution

    Inert and Labile Complexes

    • Inert complexes: those that react more slowly, with a higher activation energy for ligand substitution
    • Werner studied Co(III), Cr(III), Pt(II), and Pt(IV) compounds because they are inert and more readily characterized than labile compounds

    Inert Octahedral Complexes

    • Inert octahedral complexes are generally those with high LFSE, specifically those with d3 or low-spin d4 through d6
    • Examples: [Cr(H2O)6]3+ undergoes water exchange exceedingly slowly relative to the high-spin d4 [Cr(H2O)6]2+

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    Coordination Chemistry PDF

    Description

    Learn about thermodynamic and non-redox kinetic factors in coordination chemistry, including mechanisms of substitution reactions and equilibrium constants of complex formation. Understand HSAB concept and factors affecting stability of complexes.

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