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Inorganic Chemistry > Transition metal chemistry > Flashcards

Transition metal chemistry Flashcards

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1
Q

oxidation states

A

[earlier transition metals]
+3 = more common than +2
= strongly reducing

[later transition metals]
+2 = more common than +3
+3 oxn state = strongly oxidising

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2
Q

trend in oxidation states

A

increasing 3rd and higher I.E. across series

d-orbitals become more core-like (closer to nucleus)

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3
Q

halides - stability of oxn states

A

decreases in order of F- > Cl- > Br- > I-

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4
Q

Ti(IV)

A

high covalent character

high charge density on metal (v. polarising)

TiCl4 = covalently bonded liquid + soluble in benzene
TiCl2 = ionic solid

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5
Q

thermodynamically unfavourable oxidation states

A

[intermediate = below line]

can still be observed (disproportionation reaction may be slow)
= kinetically stable

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6
Q

scandium

A

Sc3+ (d0)

colourless

strong Lewis acid

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7
Q

titanium

A

+4 (d0) - TiO3 2-, TiO 2+

not Ti4+ -> charge = so high (would pull hydrogens from water ligand - TiO2+)

strong Lewi acid

Ti3+ = strong reducing agent

No Ti2+ aq chem - TiCl2 reacts violently with water, reducing it to H2

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8
Q

vandium

A

VO4 3- at pH 14
VO2 + at pH 0

reduced to VO2+ (blue), V3+ (green) and V2+ (violet) - all stable rwt disproportionation

VO2+ = square planar

V2+ = strongly reducing and oxidised by air (needs to be kept in inert atmosphere)

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9
Q

chromium

A

Cr(IV) = powerful oxidising agent

Cr2O7 2- (orange) in acidic solutions
CrO4 2- (green) in alkaline solutions

Cr2O7 2- + 3H2O -> CrO4 2- + 2H3O+

Cr(III) d3 - high CFSE; kinetically inert

Cr(II) = strongly reducing

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10
Q

manganese

A

Mn(VII) = powerful oxidising agent

MnO4- = tetrahedral anion

intense colour due to M->L transfer band

Mn(III) = distorted octahedral due to J-T distortion

Mn(II) = v. pale (d->d = forbidden by all selection rules)

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11
Q

iron

A

Fe3+ + e- -> Fe2+

position of equilibrium + stability of oxn state determined by ligands

Fe3+ = acidic solutions - high charge on metal

equilibrium affects by pH
-Fe3+ stable at pH <2

Fe2+ + O2 + 4H3O+ -> 4Fe3+ + 6H2O (stable but slowly oxidises due to presence of dissolved oxygen)

strongly coloured - M->M transfer bands

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12
Q

cobalt

A

Co(III) = strong oxidising agent

LS complex - kinetically inert despite thermodynamic driving force

N-donor ligands (e.g. NH3) greatly stabilise Co3+ rwt reduction

Co(II) - colour depends on geometry
octahedral = pink
tetrahedral = intense blue

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13
Q

pale -> intense colour

A

no longer have centre of symmetry

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14
Q

pink -> blue

A

Δoct = smaller for tetrahedral compared to octahedral

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15
Q

nickel

A

Ni(II) = stable to oxidation + reduction

range of geometries (depends on counter ion)

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16
Q

copper

A

Cu2+ (cupric) and Cu+ (cuprous)

octahedral = distorted due to J-T effect

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17
Q

zinc

A

Zn2+

colourless (no d-d e- transition possible)

wide range of geometries

not really a transition metal - neither metal nor compound has partially filled d orbitals

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18
Q

transition metal triads - chromium, molybdenum + tungsten

A

CrO3 + [CrO4]2- = strong oxidising agents

WO and [WO4]2- = not readily reduced

high oxn states: 1st row < 2nd row < 3rd row

Mo(IV) and W(IV) = common
Mo(III) and W(III) = sparse

high coordination numbers possible for larger metals (1st row - ions not big enough)

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19
Q

transition metal triads - nickel, palladium + platinum

A

Ni and Pd = +2
Pt = +4

Pd + Pt = square planar (high Δoct)

M-M bonds and low oxn states (+1,0) = more important down group

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20
Q

why don’t t2g orbitals interact with any ligand orbitals?

A

don’t have correct symmetry

directed between axis

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21
Q

evidence for covalency

A

pairing energies have been shown to be lower in metal complexes than in gaseous Mn+ ions

indicates inter-electronic repulsion is less in complexes so effective size of metal orbitals has increased

= nephelauxetic effect

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22
Q

Lenz’s law (MD)

A

in absence of any magnetic moment (i.e. unpaired e-)
= induced magnetic field that opposes main field
=diamagnetism (MD)

*repelled by magnetic field

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23
Q

MP

A

if there’s a magnetic moment (unpaired e-) and moments don’t interact with each other, they align to give overall magnetic moment (MP)

*attracted to magnetic field

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24
Q

effect of metal on Δ - charge

A

as charge on M increases, Δ increases

[reason]

ionic radius decreases

∴ M-L decreases

greater interaction between M and L orbitals

increases energy of antibonding eg orbitals ∴ t2g-eg gap increases

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25
Q

effect of metal on Δ - going down group

A

Δ increases

[reason]

size of orbital increases

greater interaction between M and L orbitals

increases energy of antibonding eg orbitals ∴ t2g-eg gap increases

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26
Q

change in orbital size from 3d to 4d compared to 4d to 5d

A

bigger

due to lanthanoid contraction

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27
Q

why are 4d and 5d complexes low spin?

A

due to increasing orbital size and decrease in pairing energy

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28
Q

dipole moment of CO

A

0.40 Debye

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29
Q

how does CO coordinate to a metal centre ?

A

via δ+ carbon atom

σ-donation from filled orbital on CO to empty M d-orbital

π-donation from filled d-orbital on M to empty π* on CO = BACKBONDING

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30
Q

backbonding

A

π-donation from filled d-orbital on M to empty π* on CO

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31
Q

effect of backbonding

A

strengthens M-C bond

[reason]

e- density is put into CO antibonding orbital

weakens C-O bond

decreases in v(CO) from 2143 cm-1 for CO(g)

32
Q

thermodynamics

A

[extent of reaction]

relates to ΔG

quantified by equilibrium constant = K

stable vs unstable

33
Q

kinetics

A

[speed of reaction]

relates to activation energy

quantified by rate constant = k

inert vs labile

34
Q

substitution reactions

A

K1 > K2 > K3 [step-wise formation constants decrease]

less likely to be sub. as number of H2O ligands decreases (being replaced with NH3)

35
Q

formation constant

A

β6 = K1K2K3K4K5K6

high = large CFSE (means ligand being subbed onto molecule is a stronger field ligand)

36
Q

chelate effect

A

bidentate/polydentate = enhanced stability

ΔS = +ve (increase in disorder) = large K

+ less rearrangement required

37
Q

hard

A

high charge density

non-polarisable

38
Q

soft

A

low charge density

polarisable

39
Q

ligand sub. reactions

A

MLxX + Y ⇌ MLxY + X

X = leaving group
Y = entering group
L = spectator ligand

L + X covalently bonded to metal = inner-sphere ligands

outer sphere of solvent molecules loosely associated

40
Q

why is Pd(II) used for kinetic work on square planar complexes?

A

relatively inert to oxidation/reduction

virtually always square planar

rate of ligand sub. = slow (t1/2 > 60s) - easy to study

41
Q

what type of mechanism do square planar complexes undergo?

A

associative mechanisms

42
Q

evidence for associative mechanisms

A
  1. k values for displacement of Cl- by H2O in [PtCl4]2-, [PtCl3(NH3)]-, [PtCl2(NH3)2], [PtCl(NH3)3]+

suggests associative pathway since dissociative pathway would be expected to be dependent on charge of complex

  1. most reactions occur with stereoretention at Pt (3-coordinate intermediate = all ligands same; no cis/trans)
  2. all reactions accompanied by large, -ve ΔS = loss of molecular freedom approaching transition state
  3. if pressure increases, sub. accelerated and large -ve vol. of activation (ΔV) observed
43
Q

k(obs) vs [Y] graph - effect of solvent

A

changes intercept

polar = increases
non-polar = decreases

44
Q

substitution reactions - influence of spectator ligands

A

more steric bulk = slower reaction

effect is more prominent when bulky ligand = cis to leaving group

45
Q

substitution reactions - trans effect

A

effect of ligand on sub. rate for ligand trans to it

46
Q

trans effect - cause of increased RoR

A
  1. destabilisation of ground state
  2. stabilisation of transition state
47
Q

σ-effects on trans effect

A

trans ligand and leaving group, X, compete for same metal orbitals

competition = relaxed in trigonal bipyramidal state

if trans ligand = strong σ-donor = less orbital for interaction with X

48
Q

π-effects on trans effect

A

if ligand = π-acceptor, charge delocalisation eases formation of 5-coordinate transition state/intermediate

strong π-acceptor ligands accept e- density donated by incoming Nu

helps spread charge over complex = more stable

= lower energy of transition state

49
Q

trans influence

A

effect of ligand on ground state properties

i.e. bond angles + NMR

just σ-components that have influence

50
Q

sub. in octahedral complexes - effect of charge

A

higher charge = less labile ligands

stronger M-L bond strength (suggests it’s RDS)

51
Q

sub. in octahedral complexes - CFSE

A

loss of CFSE going from ground state -> transition state

= increased in activation energy

= decrease in rate

=CFAE (crystal field activation energy)

52
Q

evidence for dissociative mechanisms

A
  1. rates generally unaffected by nature of entering group
  2. rates depend on nature of leaving group - correlates with M-X bond strength

[easiest to displace] NO3- > I- >Br- > Cl- > MeCo2- NCS- ~ NH3 > OH-

  1. rate increases by increasing bulk of spectator ligands
  2. increasing pressure slows reaction (ΔV = +ve)
53
Q

which type of sub. mechanism does square planar undergo?

A

associative

54
Q

which type of sub. mechanism does octahedral undergo?

A

dissociative

55
Q

acid catalysis

A

protonates leaving group

**leaving group must have lone pair that’s not bonded to metal

56
Q

base catalysis

A

ion doesn’t attack metal centre

instead, ligand is deprotonated to give base complex

57
Q

what is tunnelling?

A

complexes get close and e- “hops” from 1 M to another

58
Q

tunnelling - requirements

A

Ea must overcome electrostatic repulsion between ions of like charge

when reactants have different bond lengths, vibrationally excited states with equal bond lengths must be formed (allows e- transfer to occur)

greater change in bond lengths = slower rate of e- transfer

59
Q

inner sphere e- transfer

A

covalently-bound bridging ligand that may transfer with e-

  1. bridge formation
  2. e- transfer
  3. bridge cleaving
60
Q

bioinorganic chemistry - roles

A
  1. structural - stabilising protein structures
  2. functional - metal ion involved in reactivity

[transport, enzymes, metal storage/transport, photoredox]

61
Q

oxygen transport and storage

A

Hb = metalloprotein

Mb = monomer of Hb (only contains iron atom)

in both compounds, iron is bound to porphyrin ring = HAEM GROUP

each haem group can absorb 1 molecule of O2 = red colour

62
Q

haemoglobin - coordination of oxygen

A

O2 = π-acceptor

enters 6th coordination site

configuration changes to LS

since antibonding orbitals are no longer occupied, ion = smaller -> therefore moves to haem ring

O2 coordinated in bent, end-on manner + supported by H bond to distant a.a.

63
Q

haemoglobin - binding of O2 vs CO

A

O2 - reversible [when conc. of O2 decreases in blood, it’s released from haem group]

CO = irreversible

64
Q

haemoglobin - cooperative binding

A

as O2 binds to 1 iron, affinity of other iron atoms for O2 increases

due to conformational changes in protein chains [movement into porphyrin ring - HS->LS]

65
Q

myoglobin

A

binds O2 better at low conc.

in tissues, O2 is released by Hb and taken up by Mb

66
Q

haemoglobin - pH

A

low pH - O2 released more readily

metabolism => CO2 released = lower pH; helps transfer O2 from Hb to Mb

67
Q

haemocyanin

A

copper containing

present in molluscs + anthropoids

blue colour

68
Q

haemoerythrin

A

non-haem di-iron protein

present in marine worms

purple colour

69
Q

cis-platin - function

A

anti-tumour agent

70
Q

trans-plantin?

A

trans-platin = inactive

unable to bridge between guanine-N atoms

71
Q

Pd cis/trans complexes

A

cis = inactive

ligands = more labile (break bonds more readily

cis-trans isomerism occurs more readily - rapid interconversion to thermodynamically trans complexes

72
Q

problems with cis-platin

A
  1. affects narrow range of tumours
  2. toxic - lots of side effects
  3. not v. soluble in water (can’t be taken orally)
  4. development of resistance in tumour cells
73
Q

2nd and 3rd generation of Pt drugs

A

[carboplatin]

-dicarboxylate = less labile than Cl
-lower toxicity (larger doses possible)
-hydrolysis = slower

[satraplatin]

-Pt(IV) = more soluble

[JM335]
-no cis-amines (different mechanism?)

74
Q

key features of Pt anti-tumour drugs

A

cis amines

at least 1 amine group

optimised leaving group

good water solubility and stability in 0.1M NaCl

reactions with competing S-donors suppressed

ability to cross cell boundary

75
Q

cis-platin - mechanism

A

conc. of Cl- inside cells = lower than outside (why hydrolysis only occurs inside cells)

labile H2O replaced by N atoms from 2 of DNA base pairs - occurs w/o breaking H bonds linking strands together

Pt bridges are between 2 neighbouring guanine bases

chelation tilts guanine rings from normal stacked position - disrupts helix + interferes with replication

76
Q

why is H bonding important in cis-platin?

A

stabilises both intermediate + platinated DNA

no N-H = no anti-tumour activity

H bonding occurs both the P-backbone and carbonyl O of guanine = explanation for preference of G over A

Inorganic Chemistry (15 decks)

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