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Inorganic Chemistry > Crystal field theory > Flashcards

Crystal field theory Flashcards

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1
Q

what makes a metal a ‘d block element’ ?

A

partially filed d-orbital

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2
Q

Coinage metals

A

Cu, Ag, Au

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3
Q

Platinum group elements

A

Ru, Os, Rh, Ir, Pd, Pt

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4
Q

organometallic compounds

A

ligands that are C based

e.g. CO, CH3

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5
Q

5-bond compound?

A

quintuple bond

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6
Q

metathesis

A

swapping reaction

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7
Q

inner sphere ligands

A

bonded directly to metal

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8
Q

outer sphere ligands

A

electrostatically associated with inner sphere complex

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9
Q

primary valency

A

value that never changes

oxidation number

satisfied by -ve ions

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10
Q

secondary valency

A

no. of groups covalently bonded to M

coordination number

directed to fixed positions in space about central M ion

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11
Q

trend in oxidation state across group

A

increasingly less favoured L->R

Zeff increases

IE increases

harder to move away from nucleus

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12
Q

trend in oxidation ability across group

A

becomes increasingly oxidising - wants to be removed

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13
Q

trend down group in oxidation state

A

increasingly favoured

RDF more diffuse

less electron repulsion

M easier to oxidise

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14
Q

crystal field theory

A

[simple]

based on electrostatics

treats ligands as point charges

ignores possibility of metal d-electrons being removed in bonding

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15
Q

ligand field theory

A

[more complex]

allows for covalent bonding

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16
Q

3d orbital degeneracy

A

as ligands approach more closely along x/y/z axis, 3d orbitals lose degeneracy

dxy, dxz, dyz = t2g (less electron repulsion; stabilised as they lie between x/y/z axis)

dx2-y2 + dz2 = eg (destabilised)

17
Q

Δoct

A

[crystal field stabilisation energy]

represents stabilisation relative to spherical field

= 0 (stabilisation must offset destabilisation) -> centre of gravity/barycentre

18
Q

t2g e- value

A

-2/5

19
Q

eg e- value

A

3/5

20
Q

Δoct in Dq

A

Δoct = 10Dq

21
Q

evidence for CF theory

A

[double humped plot of hydration for octahedral M2+ ions]

hydration = M2+(g) + H2O -> [M(H2O)6]2+

expected trend = increased favourable (exothermic) L->R as Zeff increases; ion size decreases ; M-L interaction increases

measured trend = Ca2+, Mn2+, Zn2+ sit on line - others vary significantly

related to Δoct (makes favourable contribution to hydration energy of system - more exothermic)

22
Q

filling orbitals

A

d1-d3 = no choice

d4 = either keep filling or double one of t2g sets
-although t2g gives -2/5 Δoct, filling doubly filled orbital increases e- repulsion

23
Q

high spin

A

[weak field arrangement]

energy to put e- in eg set < e- repulsion

24
Q

low spin

A

[strong field arrangement]

energy to put e- in eg set > e- repulsion

25
Q

effects on radii metals - iron

A

Fe2+/Fe3+ = high spin (choice)
Fe2+ = low spin

low spin = smaller
-more e- repulsion in HS arrangement (2e- in eg orbital)
-ion = bigger
-closer ligand approach in LS - smaller

26
Q

barycentre

A

energy before split

27
Q

where does colour arise from?

A

t2g -> eg orbital transition

= direct measure of Δoct

only works with d1 systems

28
Q

∈

A

measure of the probability of a transition taking place

bigger ∈ = more likely for transition to take place

29
Q

selection rules

A
  1. spin can’t change
  2. change in parity required (i.e. symmetry)
  3. implies ΔI (OAM quantum number) = +/- 1
30
Q

LMCT

A

[ligand -> metal charge transfer band]

transfer of e- of oxygen lone pair to M-centred orbital

31
Q

MLCT

A

[metal -> ligand charge transfer band]

32
Q

Lenz’s Law

A

in absence of any magnetic moment (i.e. any unpaired e-), a magnetic field is induced that opposes the main field

= MAGNETIC MOMENT/MOLE from diamagnetic effect MD

33
Q

what does ueff relate to?

A

no. of unpaired e-

= √n

34
Q

temperature dependent paramagnetism

e.g.[Ni(Et3)2Cl2

A

8 d electrons - √8 = 2.83BM

Ueff (80K) = 3.2BM
Ueff (300K) = 3.8BM

higher than expected = effect from orbital angular momentum

as temperature increases, so does effect of orbital angular momentum

Inorganic Chemistry (15 decks)

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