Chapter 20 Coordination chemistry: reactions of …...Chapter 20 Coordination chemistry: reactions...
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Chapter 20 Coordination chemistry: reactions of complexes Redox reactions Ligand substitution in octahedral complexes Ligand substitution in square-planar complexes Ligand substituton reactions Photochemical reactions
Transcript of Chapter 20 Coordination chemistry: reactions of …...Chapter 20 Coordination chemistry: reactions...
Chapter 20 Coordination chemistry: reactions of complexes
Redox reactions
Ligand substitution in octahedral complexes
Ligand substitution in square-planar complexes
Ligand substituton reactions
Photochemical reactions
20-1 Thermodynamic considerationsFormation Constants
20-1 Thermodynamic considerationsFormation Constants
20-1 Thermodynamic considerationsTrends in successive formation constants
Stepwise formation constants typically lie in the order Kn > Kn+1, as expected statistically; deviations from this order indicate a major change in structure.
20-1 Thermodynamic considerationsTrends in successive formation constants
Stepwise formation constants typically lie in the order Kn > Kn+1, as expected statistically; deviations from this order indicate a major change in structure.
20-1 Thermodynamic considerationsThe chelate effect
The chelate effect is the greater stability of a complex containing a coordinated polydentate ligand compared with a complex containing the equivalent number of analogous monodentate ligands; it is largely an entropic effect.
20-1 Thermodynamic considerationsSteric effects and electron delocalization
The stability of chelate complexes of d metals involving diimine ligandsis a result of the chelate effect in conjunction with the ability of the ligands to act as π acceptors as well as σ donors.
20-1 Thermodynamic considerationsThe Irving-Williams series
The Irving-Williams series summarizes the relative stabilities of complexes formed by M2+ ions, and reflects a combination of electrostatic effects and LFSE. The order is relatively insensitive to the choice of ligands.
Ionic radius
20-2 Rates of ligand substitution
Labile vs inert or nonlabile
20-2 Rates of ligand substitution
20-3 The classification of mechanismsAssociation, dissociation, and interchange
The mechanism of a nucleophilic substitution reaction is the sequence of elementary steps by which the reaction takes place and is classified as associative, dissociative, or interchange; an associative mechanism is distinguished from an interchange mechanism by demonstrating that the intermediate has a relatively long life.
20-3 The classification of mechanismsThe rate-determining step
The rate-determining step is classified as associative or dissociativeaccording to the dependence of its rate on the identity of the entering group.
Ligand substitution in square-planar complexes20-4 The nucleophilicity of the entering group
The nucleophilicity of an entering group is expressed in terms of the nucleophilicity parameter defined in terms of the substitution reactions of a specific square-planar platinum complex; the sensitivity of other platinum complexes to changes in the entering group is expressed in terms of the nucleophilic descrimination factor.
20-5 The shape of the transition stateThe trans effect
A strong σ–donor ligand or π–acceptor ligand greatly accelerates substitution of a ligand that lies in the trans position.
Trans influenceTransition state effect
20-5 The shape of the transition stateSteric effects, stereochemistry
Steric crowding at the reaction centre usually inhibits associative reactions and facilitates dissociative reactions.
Substitution of a square-planar complex preserves the original geometry, which suggests a trigonal-pyramidal transition state.
20-5 The shape of the transition stateTemperature and presure dependence,The first-order pathway
Negative volumes and entropies of activationsupport the view that the rate-determining step of square-planar Pt(II) complexes is associative.
The first-order contribution to the rate law in eq. 20.7 is in fact a pseudo-first-order process in which the solvent participates.
Rate = (k1 + k2[Y])[PtL4]
20-6 Rate laws and their interpretationThe Eigen-Wilkins mechanism
In the Eigen-Wilkins mechanism, an encounter complex is formed in a pre-equilibrium step and the encounter complex forms products in a subsequent rate-determining step.
The Fuoss-Eigen equation
The Fuoss-Eigen equation provides an estimate of the pre-equilibrium constant based on the strength of the Coulombicinteraction between the reactants and their distance of closest approach.
20-7 The activation of octahedral complexes
A large effect of the leaving group X is expected in Id reactions; a linear relation is found between the logarithms of the rate constants and equilibrium constants.
The effects of spectator ligands
Steric effects
Leaving-group effects
20-7 The activation of octahedral complexesThe effects of spectator ligands
A large effect of the leaving group X is expected in Id reactions; a linear relation is found between the logarithms of the rate constants and equilibrium constants.
20-7 The activation of octahedral complexes
20-7 The activation of octahedral complexes
20-7 The activation of octahedral complexesAssociative activation
20-8 Base hydrolysis
20-9 Stereochemistry
20-10 Isomerization reactions
Template synthesis
Redox reactions20-11 The classification of redox reactions
20-12 The inner-sphere mechanism
20-13 The outer-sphere mechanism
20-13 The outer-sphere mechanism
20-13 The outer-sphere mechanism
Photochemical reactions20-14 Prompt and delayed reactions
20-16 Transitions in metal-metal bonded systems
Photochemical reactions20-15 d-d and charge-transfer reactions
