d block chemistry

get a hint

hint

describe the splitting of a tetrahedral complex

describe the splitting of a tetrahedral complex

describe the splitting of an octahedral complex

describe the Jahn Teller distortion - elongation

describe the Jahn Teller distortion - compression

describe the Jahn Teller effect

occurs when valence electron has choice of degenerate orbitals, further distortion of d orbitals from tetrahedral/octahedral arrangement creates non-degenerate orbitals, either compression or elongation: dz2 and dx2-y2 both become higher in energy

describe the splitting of a square planar complex

name some strong field ligands, (and their charges) what does this mean for the arrangement of electrons in a complex, why?

CN-, NO+, CO, > NO2(2-) > py, NH3 > NCCH3 strong field ligands cause large splitting between t(2g) and e(g) making them low spin because the E difference between eg and tg is greater than the E requirement to pair an electron (e repulsion)

name some weak field ligands (and their charges), what does this mean for the arrangement of electrons in a complex, why?

I- < Br-< SCN- < Cl- < F-, OH- < OH2

weak field ligands cause small splitting between e(g) and t(2g) so the energy requirement to pair an electron is greater than the energy between t(2g) and e(g), they are usually high spin

list the selection rules

Spin-spin selection

Laporte/parity

describe the Laporte/parity selection rule

for molecules with centre of symmetry, electronic transitions can only be made between u and g. g to g and u to u is forbidden. d orbitals are all g orbitals (have symmetry) so effectively d to d orbital transitions are not allowed.

this rule is not super strict as donation from lone pairs of electrons are allowed (charge transfer) e.g. in MnO4, oxygen reduces Mn and then donates electrons back (non-bonding e = lone pairs on O) so technically d to d transition but passed off as p to d transition

other exceptions: distorted octahedral complexes don't have as great symmetry, vibrations of bonds mean centre of symmetry can be lost temporarily, hybridisation of orbitals mean p to d transitions can occur

octahedral complexes are the only complexes with symmetry so this rule does not apply to tetrahedral/square planar complexes

describe the spin-spin selection rule

states electrons cannot change spin during a transition. e.g. when all orbitals singly occupied and electron promoted to higher orbital: changes spin

forbidden for all types of complexes

e.g. high spin d5

state the order of colour intensity dictate by rules (octahedral/tetrahedral/which rule etc.), which complex is usually more intensely coloured?

1. just spin-spin selection allowed (not d-d transitions) - octahedral

2. octahedral d-d transitions + spin

3. tetrahedral d-d transitions allowed + spin

tetrahedral complexes usually more intensely coloured

what are the exceptions to the usual d shell filling and why?

Cr, Mo = have 1 electron away from being half-filled, d orbitals are d orbitals which are less than one from half-filled/full are less stable than when half-filled/full

changes from [Ar] 4s2 3d4 to [Ar] 4s1 3d5 (half-full)

Cu, Ag = same principle applies except for full d shell

changes from [Ar] 4s2 3d9 to [Ar] 4s1 3d10

what is special about the SCN ligand? is it strong/weak, what's its charge?

charge = -1

strong field ligand, so produces low spin complexes

special because can coordinate from either S or N - produces linkage isomers

describe/explain trans/cis isomerism in TM complexes?

cis = when molecule is on the same side of central atom, only occurs with one molecule e.g. one Cl ligand, 3 NH3 ligands

trans = must cross central atom to get to other molecule

describe/explain fac/mer isomerism in TM complexes?

fac = in an octahedral complex 3 of the same ligands consecutively to make a triangle when connected

mer = broken up e.g. 2 NH3, then H2O, then NH3 to make a curved line

(see pic)

does the type of metal affect the spin of the complex?

yes - heavier (and bigger) metals with higher oxidation states tend to form only low spin complexes as their orbitals are more diffuse so overlap is stronger, making the energy gap bigger. bigger energy gap > electron repulsion energy so complexes are usually low spin.

only exception: PF2

how do you tell which colour a complex is?

the bigger the CFSE, the smaller the wavelength absorbed so the longer the frequency colour shown

bigger CSFE = octahedral and stronger field ligands (tetrahedral always smaller than octahedral and SF ligands always bigger than WF ligands)

E = hλ, c = vλ so E = ch/v - wavelength is small when E is big

c = vλ, so small λ = big frequency (v)

give the ranges of red wavelengths absorbed and what colour it will be

620 - 800 nm

appears blue

give the ranges of blue wavelengths absorbed and what colour it will be

430 - 490nm

appears red/pink/orange-y

give the ranges of green wavelengths absorbed and what colour it will be

490 - 560nm

appears violet - red (pink)

give the ranges of yellow wavelengths absorbed and what colour it will be

560 - 580nm

appears violet

give the ranges of violet wavelengths absorbed and what colour it will be

400 - 430nm

appears yellow

give the ranges of orange wavelengths absorbed and what colour it will be

580 - 620 nm

appears blue

what is the equation for ΔG involving the stability constant?

ΔG = -RTlnK

what is the equation for the overall stability constant?

β(initial) - β(final) (β is the same as K basically)

logβn = logK1 + logK2 + logK3 ... logKn

describe the chelate effect in terms of the stability constant, why does this happen?

the enhanced stability of a complex containing (polydentate) ligands over one containing similar monodentate ligands e.g. NH3 vs en (en 10 magnitudes larger)

most stable when 5/6 membered rings

increase in species on the right hand side = entropically favourable so eqm lies to the right

what is the macrocyclic effect

complexes of macrocyclic ligands show even greater stability than chelated complexes

what are the metals that have anomalous trends in stability constants?

Cu(OH2)6 when replaced by 6NH3 ligands, K5 has sudden drop to a low value and K6 too small to measure

what is the usual trend in stability constants when 6H2O are replaced by 6NH3?

steadily decreasing because each intermediate has less H2O ligands to displace so less likely to be replaced

NH3 is bulkier and pushed electron density onto metal - less electrophilic so less likely to gain NH3

what reaction has a very unusual trend in K values? and why? (S)

6H2O being replaced with 4Br-

K decreased rapidly from K1 to K2, then slower from K2 to K3, increase from K3 to K4

different due to change in geometry, K4 more favourable due to entropy change

what reaction has a very unusual trend in K values? and why? (ss)

ligand substitution with ligands of different field strengths e.g. water to bipy, different due to change in spin state

what are the 4 factors that can affect stability constants in ligand substitution

1. size of ligand (steric hindrance/bulky)

2. electronegativity of ligand (EW or ED to make M more Nu-/El+)

3. change in geometry of complex

4. change in spin state of complex when ligands have different field strengths

what is a lewis acid

electron pair acceptor

what is a lewis base

electron pair donor

what determines the acidity of a hexa aqua complex?

charge density (oxidation state and size) of metal, polarises bond - protons more easily lost in solution to form partial/full OH- complex

do hard bases interact more strongly with soft or hard acids? what type of interaction is this?

hard acids

interactions are more electrostatic (+/- charges)

do soft bases interact more strongly with soft or hard acids? what type of interaction is this?

soft acids

interactions are more covalent (donor/acceptor orbitals)

define ambidentate ligands and give examples

ligands which have two possible centres of donation/attachement

e.g. SCN - S = soft, N = hard

SMe2O (DMSO), use O or S

what is a hard Lewis base?

small, low polarisability, high electronegativity

what is a hard Lewis acid?

small, large positive charges or high charge density

what is the Irving Williams series

trend in CFSE due to variation of the M(II) central ion on the stabilities of transition metal complexes

CFSE increase till d3, decrease to d5, increases until d8, decreases to d10 due to ionic radius

why are certain TM complexes certain colours?

equation: E = hv, c = vλ

the larger the energy (CFSE) the larger the frequency absorbed (shorter wavelength) so the smaller the frequency emitted and the longer the wavelength

what types of transition metals form linear complexes? why?

TMs with electron configuration of d10 e.g. Ag+

because CFSE has no effect on geometry so ligands can sit as far apart from one another like normal due to electron repulsion

how to calculate βn?

K1 x K2 x K3... x Kn = βn