Inorganic chemistry year 3

Labile

Low charge density (small charge, big radii)

TM gains stability (+ve change in CFSE) going to 5- or 7- coord, lower E barrier

d0, d1, d2, d4 HS (c4v), d5 HS, d6 HS, d7, d9 HS (c4v)

Inert

High charge density (high charge, small radii)

TM loses stability (-ve change in CFSE) upon forming coord - higher E barrier

d3, d4 HS (d5h), d4 LS, d5 LS, d6 LS, d8, d9 (d5h)

A mechanism

Limiting rates not observed

D mechanism

Ligands react faster than rate for solvent exchange

Small variation in rates

Ia mechanism

Rate dependence on nature of Y (bond formation dominates)

Rates can vary by big amounts

Id

Independent of Y

Limiting rate slower than solvent exchange

Thermodynamic activation parameters for A mechanism

negative -delta S activation

negative - delta V activation

Thermodynamic activation parameters of D mechanism

positive + delta S activation

positive + delta V activation

Reactions of square planar complexes

Solvent interactions = reaction accelerated by Nu, slowed by sterically bulky co-ligands

2 consecutive A exchanges

Trans influence

Sigma donors

More effectively donates e density to M

Exerts repulsion on LG, weakening M-X

Trans effect

Strong pi acceptor ligands

Pull e density away from M, stabilising 5 coord intermediate

If you want a trans isomer you have to start with adding…

The less labile ligand

Labilising series

Pi acceptor ligands prefer M in…

Low Oxn states

Sigma bonding ligands prefer…

M in high oxn state

Ligands that donate 1e-

H, Cl, Br, CN, bent NO, Me, Ph, COMe

Ligands that donate 2e-

, CO, PR3, P(OR)3, CNR, N2, O2, CR2, C2H4, NH3, CN

-charge ligands (wouldn’t exist by themselves)

Me, Et, Cl, Br, Cl, RO, RS, HO, R2P, R2N, Ph, C5H5, C(O)R

Neutral ligands

I2, R2O, H2O, R2S, PR3, NH3, NR3, CO2, CO, N2, C2H4, C6H6

pi acceptors

EWGs increase pi acidity

phosphines can be affected by…

steric factors - cone angle, bulkier R groups on P, bigger cone angle

electronic factors - e.g. if R = EWG, less backdonation of e density from M to pi* of CO - CO bond stronger

heterogeneous vs homogeneous catalysis

TM with carbonyls

TM with phosphines

ASSEMBLY - transmetallation

• no change in anything

• TM-X + M-R e.g.: Cl + PhLi → Ph + LiCl

ASSEMBLY - substitution

• no change in anything

• one 2e donor replaced by another

ASSEMBLY - addition

• 2e donor added

• VE increase by 2

• CN increase by 1

ASSEMBLY - oxidative addition

• adddition of X-Y (add separately)

• 2e addition

• VE increase by 2

• OS increases by 2

• CN changes by 2

• Me-I (easiest to break) > H-H > Me-Me > Me - H

MODIFICATION - 1,1 ME

• R inserted into CO ligands

• MUST BE CIS

• VE decrease by 2

• CN decreases by 1

MODIFICATION - 1,2 ME

• R inserted into alkene

• MUST BE CIS

• H inserts at more sub end of double bond, reducing steric hindrance on M

• VE decreases by 2

• CN decreases by 1

MODIFICATION - nucleophilic attack

• alkene bound to TM (e density pulled away by TM) can react with nu

• REQ TM w high oxn state, formal +charge, other EWGs coord

• trans attack - attack at more subbed end of alkene

• attack at M (req e deficient M that can add another ligand) - cis addition at less subbed end of alkene

EXPULSION - 1,1 RE

• elimination of X-Y

• MUST BE CIS

• VE decreases by 2

• OS decreases by 2

• CN decreases by 2

EXPULSION - B-hydride elimination

• M-C-C-H → alkene ligand

• can then undergo 1,1 RE

EXPULSION - a-hydride elimination

• M-C-H → carbene M=C-R

Vibronic coupling

• relaxation of laporte rule

• g-g transition allowed

• e.g.: asymmetric vibration destroys inversion centre

Why are d-d transitions allowed in Td complexes?

dp mixing

Spin orbit coupling

• relaxation of spin selection rule

• good for 2nd and 3rd row TMs (heavy atom effect)

Pi donors have _ Δo

• small

• weak field ligands

• high spin

Pi acceptors have _ Δo

• high

• strong field ligands

• low spin

1st row TMs have _ Δo

• low

• high spin

Free ion terms *

• θ = 360/no of axis

B - racah parameter

• B(free ion) > B(complex)

• e repulsions weaker in complexes

• small B = signif delocalisation of e to ligands

• softer ligands (pi acceptor)= smaller B

What happens when there’s a tetragonal distortion from Oh → D4h

• symmetry change

• additional transitions possible

• LINE BROADENING → shoulder peak

LMCT (general)

• more intense than d-d (Laporte allowed)

• more likely when ligands have lone pairs - PI DONORS

• OR M has high oxn state - RHS d-block, 2nd+3rd row TMs

LMCT Oh

• E decreases across TM series (3d orbital E decreases w increase in Zeff)

• E decreases down triad (d orbital-ligand overlap increases)

LMCT Td

• E decreases as ligands are less electronegative (E of p orbitals increases)

• E decreases as no of ligands decreases (less e repulsion - E of M orbitals decreased)

MLCT (general)

• most likely when ligands have low pi* - PI ACCEPTORS

• m is in low oxn state

• E increases across TM series (d orbital E decreases as Zeff increases)

• E increases down triad (d-orbital-ligand overlap decreases?)

Spin forbidden d-d transitions can give rise to sharp abs bands when…

• transitions involve spin flip in orbitals

• d3 and d5?

Spin crossover (LS→HS)

• change in number of bands (d-d transitions) - d6 LS = multiple bands, d6 LS = one band?

• increase in bond length (e occupy Eg antibonding)

• increase in mag moment

• ligands remain the same

• usually only in 1st row TMs

• d4 to d7 only - can be high or low spin

Spin-only magnetic moment

• 1st row only - no signif orbital contribution

• u = 2(S(S+1))^1/2

why is ΔV activation easier to calculate than ΔS activation?

• gradient rather than intercept (subject to larger error)

• harder to obtain experimentally

Outer sphere electron transfer

• e transfer occurs bw two molecules w/o bond breaking

Inner sphere electron transfer

• single ligand links 2 M ions

• bond breaking occurs

Fermi energy

E at which the probability of the levels being occupied is 0.5

Group 2 band structure

• S band filled

• In 3D, s and p overlap (top of s band higher E than bottom of p band)

Group 2 change w pressure

• Down group, as P increases, conductivity decreases

• Start of group, overlap good > sp gap small (avoided crossing)

• Increased P, atoms closer together (more overlap) → bonding E lowered, antibonding E raised → band separation/gap increases → bands overlap less in 3D → conductivity decreases

Group 12 band structure w increased P

• orbital overlap bad < s-p gap - no avoided crossing

• under P, band gap narrows → bands overlap more in 3D → conductivity increases

Bloch function

• periodic functions defining the wavefunctions for a 1-D chain of N atoms

• value of the wavelengths must be the same on both ends of the chain

• wavefunction must have periodicity that reflects the regular repeat spacing a bw atoms

• wavefunction must be normalised

Sizes of bandgap…

Insulator > semiconductor > metal

Fermi level for metal

E up to which energy band is filled

Fermi level for a semiconductor

Midpoint energy in bandgap

Band theory

• extension of MO theory

• overlap of valence orbitals creates closely spaced E levels that forms bands

Jahn-Teller effect

• Distortion when orbitals aren’t degenerate

• e.g.: d3, d5 excused

Huckel theory (a and b)

• a = E of relevant AO

• B = interaction of AOs

• important for describing (in)stability of bonding

Energy level diagram (band theory)

Band structure diagram (E vs k)

Density of states diagram (1D)

Band structure of group 1

• Half filled s orbitals overlap → half filled band

• Therefore metals

What is k (adrian)

• WAVENUMBER - potential E levels bw all antibonding/bonding

• all linear combos of AOs characterised by a value of k

Why can only a small amount of e near Ef access higher E levels?

kBT (energy in environment) at 300K ~ 0.025eV - only small % can access higher E level

s and p band mixing scenarios for group 2 (1D)

• band dispersion (broadness of band from overlap of orbitals) < s-p gap → separate s + p bands exist

• band dispersion (broader bands) > s-p gap →1xsp bonding, 1xsp antibonding band w gap → avoided crossing

2D band structure

Why can metals absorb a wide spectrum of energies in the visible spectrum?

• band widths E > E of visible light

Resistivity scattering (optical properties of metals)

• electrical resistance caused by collisions in the metal lattice w imperfections in lattice (lattice imperfections or lattice vibrations, increase w T)

• causes rapid re emission of light as e drop back to ground state

How can some TMs show ferromagnetism?

• TMs w a d-band at the fermi level have a high density of states (many degenerate levels)

• nearly full, narrow 3d band (d orbitals less diffuse more localised)

• E favourable to have high number of e w parallel spins →

• allows significant no e to move to unpaired states above fermi level

B (interaction integral) is _ for d (compared to s+p)

Much smaller

At 0K, group 4 allotropes w diamond structure are…

Insulators - no electrical conductivity

• band gap at 0K - no thermal E to promote E to CB

Above 0K, for group 4 elements…

• thermal excitation is possible

• depends on thermal E available and band gap

Band gap of insulators

Band gap > 3-4eV

Band gap of semiconductors

0-3/4eV

Band gap of metals

~0

The bigger the band gap…

The lower the conductivity

Conductivity increases with T for…

• Semiconductors

• Insulators

Conductivity decreases with T for…

• Superconductors

• Metals

Extrinsic semi-conductor (n-type)

• e.g. Si doped w P

• extra e remains near P

• donor level formed just below conduction band

• e can be easily ionised into CB

• *add image

Extrinsic semiconductors (p type)

• e.g.: dope Si w B

• each group 3 provides one less e to VB than Si

• e promoted from VB to acceptor level just above VB (where conductivity occurs)

• *add image

Down group 4…

• down group, r increases (covalent bond strength decreases) → decreased orbital overlap → decreased band gap (sp3 bonding raised, sp3 antibonding lowered) → bands overlap more in 3D → better conductance

Upon increasing temp Ef…

Goes from an extrinsic region to intrinsic region

What are most insulators?

• Ionic compounds (oxides, halides)

• (filled valence bands)

What are most semiconductors?

• covalent e.g.: sulphides

• (filled valence bands)

Increased difference in electronegativities

• increased charge transfer

• increased E of band gap

• more insulator character

• decreased colour

Why do energies of donor/acceptor levels in extrinsic semiconductors not depend on dopant species?

• e delocalised over many host atoms

• overall lattice properties more important

Van Arkel and Ketelaar diagrams

• Low avg electronegativity = metallic

• High avg electronegativity + big difference = ionic

• High avg electronegativity + small difference = covalent

How does a p-n junction act as a diode?

• allows current to flow in 1D

• e move from n-type through junction

• holes move from p-type through junction

• if electric field reversed, current can’t flow, e and h move away from junction

LEDs vs PVs?

• LEDs - voltage applied → e + h recombine at junction + emit light

• PVs - absorb light → voltage to power external work

Change of Ef with T in semiconductors

B = (adrian)

B = uH

• B - response of volume (magnetic induction - Tesla)

• H - mag field strength (amps m-1)

• u or uo = permeability of volume/free space (vacuum)

What happens to a diamagnet in a magnetic field?

• decreased density of lines of force - repelled by mag field

• Magnetisation is negative (-)

What happens to a paramagnet in a magnetic field?

• increased density of lines of force - attracted by mag field

• Magnetisation (M) is positive (+)

B = (when mag field applied)

B = uoH + uoM