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Inorganic Chemistry > Transition metal chemistry > Flashcards

Transition metal chemistry Flashcards

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
effect of metal on Δ - going down group
Δ increases [reason] size of orbital increases greater interaction between M and L orbitals increases energy of antibonding eg orbitals ∴ t2g-eg gap increases
26
change in orbital size from 3d to 4d compared to 4d to 5d
bigger due to lanthanoid contraction
27
why are 4d and 5d complexes low spin?
due to increasing orbital size and decrease in pairing energy
28
dipole moment of CO
0.40 Debye
29
how does CO coordinate to a metal centre ?
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
30
backbonding
π-donation from filled d-orbital on M to empty π* on CO
31
effect of backbonding
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
thermodynamics
[extent of reaction] relates to ΔG quantified by equilibrium constant = K stable vs unstable
33
kinetics
[speed of reaction] relates to activation energy quantified by rate constant = k inert vs labile
34
substitution reactions
K1 > K2 > K3 [step-wise formation constants decrease] less likely to be sub. as number of H2O ligands decreases (being replaced with NH3)
35
formation constant
β6 = K1K2K3K4K5K6 high = large CFSE (means ligand being subbed onto molecule is a stronger field ligand)
36
chelate effect
bidentate/polydentate = enhanced stability ΔS = +ve (increase in disorder) = large K + less rearrangement required
37
hard
high charge density non-polarisable
38
soft
low charge density polarisable
39
ligand sub. reactions
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
why is Pd(II) used for kinetic work on square planar complexes?
relatively inert to oxidation/reduction virtually always square planar rate of ligand sub. = slow (t1/2 > 60s) - easy to study
41
what type of mechanism do square planar complexes undergo?
associative mechanisms
42
evidence for associative mechanisms
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 2. most reactions occur with stereoretention at Pt (3-coordinate intermediate = all ligands same; no cis/trans) 3. all reactions accompanied by large, -ve ΔS = loss of molecular freedom approaching transition state 4. if pressure increases, sub. accelerated and large -ve vol. of activation (ΔV) observed
43
k(obs) vs [Y] graph - effect of solvent
changes intercept polar = increases non-polar = decreases
44
substitution reactions - influence of spectator ligands
more steric bulk = slower reaction effect is more prominent when bulky ligand = cis to leaving group
45
substitution reactions - trans effect
effect of ligand on sub. rate for ligand trans to it
46
trans effect - cause of increased RoR
1. destabilisation of ground state 2. stabilisation of transition state
47
σ-effects on trans effect
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
π-effects on trans effect
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
trans influence
effect of ligand on ground state properties i.e. bond angles + NMR just σ-components that have influence
50
sub. in octahedral complexes - effect of charge
higher charge = less labile ligands stronger M-L bond strength (suggests it's RDS)
51
sub. in octahedral complexes - CFSE
loss of CFSE going from ground state -> transition state = increased in activation energy = decrease in rate =CFAE (crystal field activation energy)
52
evidence for dissociative mechanisms
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- 3. rate increases by increasing bulk of spectator ligands 4. increasing pressure slows reaction (ΔV = +ve)
53
which type of sub. mechanism does square planar undergo?
associative
54
which type of sub. mechanism does octahedral undergo?
dissociative
55
acid catalysis
protonates leaving group **leaving group must have lone pair that's not bonded to metal
56
base catalysis
ion doesn't attack metal centre instead, ligand is deprotonated to give base complex
57
what is tunnelling?
complexes get close and e- "hops" from 1 M to another
58
tunnelling - requirements
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
inner sphere e- transfer
covalently-bound bridging ligand that may transfer with e- 1. bridge formation 2. e- transfer 3. bridge cleaving
60
bioinorganic chemistry - roles
1. structural - stabilising protein structures 2. functional - metal ion involved in reactivity [transport, enzymes, metal storage/transport, photoredox]
61
oxygen transport and storage
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
haemoglobin - coordination of oxygen
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
haemoglobin - binding of O2 vs CO
O2 - reversible [when conc. of O2 decreases in blood, it's released from haem group] CO = irreversible
64
haemoglobin - cooperative binding
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
myoglobin
binds O2 better at low conc. in tissues, O2 is released by Hb and taken up by Mb
66
haemoglobin - pH
low pH - O2 released more readily metabolism => CO2 released = lower pH; helps transfer O2 from Hb to Mb
67
haemocyanin
copper containing present in molluscs + anthropoids blue colour
68
haemoerythrin
non-haem di-iron protein present in marine worms purple colour
69
cis-platin - function
anti-tumour agent
70
trans-plantin?
trans-platin = inactive unable to bridge between guanine-N atoms
71
Pd cis/trans complexes
cis = inactive ligands = more labile (break bonds more readily cis-trans isomerism occurs more readily - rapid interconversion to thermodynamically trans complexes
72
problems with cis-platin
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
2nd and 3rd generation of Pt drugs
[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
key features of Pt anti-tumour drugs
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
cis-platin - mechanism
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
why is H bonding important in cis-platin?
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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