Exam 3 Inorganic Chemistry

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Laporte selection rule

Transition between states of same parity (symmetry with respect to a center of inversion) are forbidden. d to d is not formally allowed since both are centrosymmetric. D to p is allowed since p is non centrosymmetric.

Spin selection for forbidden transition

allowed when 2s+1 is the same between states. But transition between states are different spin multiplicity are forbidden

UV-vis transitions and circular dichroism (CD) and magnetic circular dichroism (MCD)

UV-vis transitions and circular dichroism (CD) and magnetic circular dichroism (MCD)

Electric dipole allowed: x, y, z are polarization with UV-vis; Rx, Ry, Rz are polarization with CD and MCD

Ligand to Metal Charge Transfer (LMCT) 

When metal is in high oxidation state and ligands contain non bonding electrons. 

Metal to ligand charge transfer (MLCT)

when the metal is in a low oxidation state and ligands have low-lying acceptor levels. Metal center can more easily donate electrons to pi*.

Fluorescence

no change in multiplicity

Phosphorescence

excited state undergoes intersystem crossing to a state of different multiplicity and then radiatively decays

labile

Electrons in antibonding orbitals means faster water exchange. Gaps in t2g

inert

No electrons in antibonding orbitals means slower water exchange. d3/d6 low spin

Jahn-Teller distortion (elongation)

weakens M-L bonds, resulting in faster exchange

Dissociative (D)

has intermediate with decreased coordination number (5)
Rate limiting step is dissociation of initial ligand to form activated complex/transition state
First order. Logk (rate constant) varies linearly with LogKeq depending on identity of initial ligand

Associative (A)

second order has intermediate with increase coordination number. Rate limiting is the formation of increase coordination activated complex/transition state. Rate constant stays stays the same regardless of identity of initial ligand as logKeg changes (depends on incoming ligand) 

Interchange (I)

has incoming ligand assist but no intermediates appear

Dissociative mechanism evidence

• Higher oxidation state have slower ligand exchange rates

• Ionic radius: smaller ions have slower exchange rates(more charge density and electrostatic attraction with ligands)

• Rate of reaction changes slightly with changes in incoming ligand 

• Greater positive charge decrease rate of dissociation 

• steric crowding increases rate of dissociation 

• Volume of Activation I sportive 

Associative mechanism

• Rate of reaction changes with the incoming ligand 

• steric crowding decreases the rate of association 

• volume of activation is negative since two species combine in one 

Linear free energy relationship

• when the bond strength of a metal -ligand bond (thermodynamic) plays a role in determining the dissociation rate of a ligand (kinetic) 

• If log(rate constant) vs log(equilibrium constant) is linear there is evidence for a strong influence on the thermodynamic parameter on the activation energy of the reaction 

Excited state is polar

with polar solvent addition, the energy of the polar excited state decreases as solvent aligns with the excited state which lowering the energy of transition

Ground state is polar

is ground state is sentive to the addition of polar solvent and is lowered in energy since the neutral =, excited state is unaffected and the results will be higher energy transition 

ground and excited states are polar

the solvent aligned with the polar ground state will be in the world orientation to align with the polar excited state this will raise the energy of that state increase the energy of that transtop even further. 

Blue shift

increase polarity of solvent better salvation of electron pair (n level has lower E) peaks shift to the blue This means the hap gets bigger

red shift

increasing polarity of solvent then increase the attractive polarization forces between solvent and absorber. Decreases the energy of the excited state greater than the ground state.  energy gap gets smaller

Hypsochromic Shift

absorption peak moves to shorter wavelength (higher energy)

Red Shift (Bathochromic Shift)

Absorption peak moves to longer wavelength (lower energy). becuasepolar solvent stabilize the excited state more than ground states and reduces delta E 

Bigger Gap 

higher energy and shorter wavelength 

Square Pyramidal (SPY)

• Occurs in d⁸ (e.g., Pt(II)) or low-spin octahedral systems.

• Substitution proceeds via dissociative (D) mechanism → loss of ligand first.

• Stereochemistry retained because ligand leaves and incoming ligand enters opposite the same site.

Trigonal Bipyramidal (TBP)

• Typical for associative (A) mechanisms (e.g., Pt(II), Ni(II)).

• A 5-coordinate TBP intermediate forms when a new ligand binds before one leaves.

Stereochemistry:

• If entering ligand (B) is bulky, it stays away from the leaving site → retention.

• If small, it can approach closely → possible stereochemical scrambling (inversion).

Trans Effect

The ability of a ligand trans to the leaving group to increase the rate of substitution (without necessarily changing equilibrium).

σ-donor (σ-trans effect):

• Strong σ donation weakens the bond trans to it (Pt–X).

• Example: PR₃, H⁻, CH₃⁻.

• Effect: Lowers activation energy (Ea) by destabilizing ground state → faster substitution.

π-acceptor (π-trans effect):

• Ligand withdraws electron density from the metal (backbonding into π* orbitals).

• Metal becomes electron-poor → more susceptible to nucleophilic attack.

• Effect: Stabilizes the 5-coordinate TS → faster substitution.

Trans Effect depend on

Kinetic effect so so activation energy

Strong σ-donor

Pushes a lot of electron density into the metal’s σ orbitals so, Weakens the metal–X bond across from it → easier to break

Strong π-acceptor

Pulls electron density out of the metal via backbonding (into its π* orbitals). Lowers electron density on metal → stabilizes the 5-coordinate transition state during substitution

Ligands like CO, CN⁻, and C₂H₄ are σ-donors + π-acceptors at the same time.

• They σ-donate through their lone pair or π bond, and

• They π-accept through their empty π* orbitals.

Chelating ligands increase kinetic stability

slower substitution.

Vibronic coupling

Molecular vibrations temporarily distort symmetry → mix g/u characters

Orbital mixing

p and d orbitals mix in Td or π-bonding complexes

Spin–orbit coupling

Electron’s spin interacts with orbital motion

Maximum spin multiplicity first (2S + 1 largest).

Parallel spins reduce repulsion (exchange stabilization).
→ Example: ³P < ¹P

For equal spin multiplicity, largest L (orbital angular momentum) next. true or false 

correct

If subshell less than half-filled

lowest J → lowest energy

If more than half-filled

highest J → lowest energy