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Year 3 - Chemistry > Inorganic Concepts > Flashcards

Inorganic Concepts Flashcards

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1
Q

What is the inert pair effect?

A

Increased stability of N-2 oxn state over N oxidation state down the main group

Where N is the group number

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2
Q

What are some examples of the inert pair effect?

A
  • In group 15 (N=5) PCl5,is stable but AsCl5 unstable to AsCl3, SbCl5 stable
  • H2SO4 stable but H2SeO4 unstable
  • CO2 stable, PbO2 decomposes to PbO
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3
Q

What is the relativistic effect?

A

As nuclear mass increases then orbiting e- move faster and closer to speed of light
Means relativistic mass of e- increases, so become stabilised, so higher IE
Also mixes more with d orbitals, so increase SO couploing

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4
Q

What is the ionic and covalent justification of the inert pair effect?

A

Ionic:
High IEs of ns orbitals so not used in bonding (not compensated by extra lattice enthalpy)

Covalent:
ns2 not involved as poorer s-p hydbridisation - as sig size and energy mismatch between ns and np for post 3d and post-5d elements (6s sig contracted due to relativistic)
Direct consequence of this lesser s-p hybridisation seen in bond angles and lone pair

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5
Q

What occurs to bond angles due to inert pair effect?

A

If s-orbitals not used then trans-bending occurs for better p-use (SH2 smaller angle than H2O)

Trans-bent structure seen in C2R2 structure comparing to down the group

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6
Q

How does stereochem inactive lone pairs seen in inert pair effect?

A

s is non-directional, so lp is stereochem inactive
Hybridisation of ns/p makes it active as gives it a direction

Hybridisation less favourable for post-3d/5d non-metals

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7
Q

What are the structures of SnO, PbO, and SnS, PbS?

A

Distorted rocksalt due to 5s/6p mixing with 5p/6p via the O2p/S3p
Results in a stereochem active lp

Not seen in PbS as energy gap between Pb 6s and S 3p too large so undistorted rocksalt and lp inactive

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8
Q

What is the alternation effect?

A

Describes oscillating trend in Zeff down the main group

From main and lanthanide contractions and relativistic effects

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9
Q

How is the alternation effect seen in group 13?

A

B -> Al sees IE decrease explained by Zeff2/n2
Al -> Ga sees IE increase, as TM contraction for Ga, 3d has no nodes and poorly shield 4s
Ga -> In sees IE decrease explained by 4d has an inner max so shields 5s e-
In -> Tl sees IE increase, as relativistic effects of 6s

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10
Q

What factors other than atomic radii does alternation effect affect?

A

Bond lengths and electronegativity

Stability of group 15 pentachlorides (PCl5 stable but others unstable)

Causes inert pair effect

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11
Q

Why does relativistic effect only seen in s-orbital?

A

Only orbitals with a non-0 coefficient on the nucleus

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12
Q

How does relativistic effect cause colour and shape of Au?

A

Due to s-dz2 mixing as 6s lower in energy
Means smaller gap absorbs in visible and “gold” colour

Au compounds: mixing effects causes d9/10 complexes to be linear

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13
Q

What is a frustrated lewis pair?

A

Lewis acid-base pair that cannot form an adduct due to steric hindrance

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14
Q

How do frustrated lewis pairs cause small molecule activation?

A

They have unquenched reactivity and can activate small molecules

Can heterolytically cleave H2 or activate CO2

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15
Q

What are the radius ratio rules?

A

Rules to predict structures/coord geometries of ionic solids based on ratio of radii of cation and anion (r+/r-)

Stable structure will have cation with largest number of anions possible before anions come into contact - max lattice enthalpy and min coulombic repulsions
Explains structures (coord numbers and etc)

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16
Q

What is an example of the radius ratio rules?

A

All 3d MOs with rocksalt except ZnO as Zn2+ too small
ZnO adopts zinc blende

TiO2 6-coord rutile and ZrO2 8-coord fluorite

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17
Q

What are the limitations of radius ratio rules?

A

Assumes completely ionic

  • Most alkali halides adopt rocksalt despite radius rules predicting otherwise - Br-/I- is more polarisable and so can be compressed so have a larger effective radius, meaning radius lower than expected
  • Silver halides defy due to covalency, AgI wurtzite allows for closer Ag-Ag, and at higher T then changes structure to get 8-coord bcc
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18
Q

What is agostic bonding?

A

e- deficient (coord unsat) metals gain stabilisation by intra chelation
2 e- in C-H bond are donated into metal d-orbital

Usually β but can see α

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19
Q

What is the evidence of agostic bonding?

A

Neutron diffraction gives H location
Coupling const 1JCH reduced
C-H IR reduced
Increases C-H

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20
Q

When is neutron or X-ray diffraction used?

A

Can’t use X-ray for H atoms as small number of e- at H centre

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21
Q

What are the limitations of the agostic bonding theory?

A

Driving force is increase VE - which doesn’t make sense in early TM

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22
Q

How is agostic bonding seen in catalysis?

A

Increases “rigidity” of TS

Seen in Ziegler-Natta catalysis - highly electrophilic metal centre has agostic interactions with growing polymer chain
Incrased rigidity influences stereochem

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23
Q

What is an overview of the chelate effect?

A

Described increased stability of complexes with chelate ligands relative to stability of systems with monodentate

There are enthalpic and entropic contributions, and a probability factor

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24
Q

What is the entropic contribution to the chelate effect?

A

Binding of chelate releases many molecules per ligand, so increase # of molecules in product
So large and positive entropy change, and more -ve G and larger stability const (K)

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25
Q

What is the enthalpic contribution to chelate effect?

A

lp-lp repulsion between donor atoms overcome in chelate synthesis, so doesnt need to overcome during binding of multiple ligands

Less desolvation energy for chelate ligands

RNH2 more basic than NH3 due to inductive effect

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26
Q

How does prob factor affect the chelate effect?

A

After one site occupied then prob of second binding is greater when chelate as higher effective contribution of donor atoms in vicinity

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27
Q

What is the macrocyclic effect?

A

Macrocycle ligand complexes more stable than open chain acyclic analogues

Macrocycle - at least 3 donor atoms in cculic structure

Enthalpic and entropic contributions

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28
Q

What is the enthalpic contribution to the macrocyclic effect?

A

Initial enthalpy for macrocycle more +ve due to lp-lp repulsions stronger in cyclic
Change in complexation larger and more -ve, so complexation more stable

Less strongly solvated than acyclic analogues

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29
Q

What is the entropic contribution to macrocyclic effect?

A

Macro less conformationally flexible so lose fewer dof on complexation (S larger and more +ve than the acyclic)

Coord of metal cation release solvent molecules (same for acyclic but still better than monodentate)

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30
Q

What is the trans effect?

A

Ligand trans to leaving-group has an effect on rate of substitution

Series orders ligands by their effect on rate const of sub

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31
Q

When is the trans effect series most observed?

A

Most often for square planar, but can observed in Oct species

Combination of sigma gs and π-TS effects

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32
Q

How does trans effect explained by the effect on ground state?

A

Ligand higher in series if raises E of gs - seen with strong σ-donor ligands

Trans ligands bonded to same metal orbital as LG, so stronger the trans ligand the weaker the bond to LG

This can then effect the rate or strength of the bond (completely different)

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33
Q

Wha tis the trans influence series?

A

Bond-weaking effect due to the σ-bonding of a trans ligand to a leaving-group

If high in trans influence then not necessarily high in trans effect - doesnt include π donor effectiveness and other factors

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34
Q

How can the trans influence be observed?

A

X-ray crystallography for M-X bond lengths
IR stretching freq
NMR coupling const

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35
Q

What occurs to TS to give trans effect and influence?

A

Must lower energy of TS to be high in series, done by π-acceptor ligands

Because in TBP TS then LG and trans ligand share a d-orbital so extra e- density on metal on metal from new group accomodated by π-acceoptor of trans ligand

Pi-acceptors are low in trans inflence as they dont weaken M-LG bond

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36
Q

What is the Racah parameter?

A

Measure of interelectronic repulsion in a complex

Smaller for complexes than free ions as e- have more atoms to spread over

Smaller for 4/5d as e- further apart
Increases across a period as higher Zeff

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37
Q

What is the nephelauxetic effect?

A

Explains decrease in Racah (B) when TM free ion forms a complex

Decreases for complexes as e- more spread out and ligands have -ve charge so decreases +ve charge on metal and orbitals expand

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38
Q

How does B change in complexation for Mn2+ compared to V2+?

A

B reduced less for Mn2+ as prefers to keep electrons localised due to exchange stabilisation

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39
Q

How is covalency involved in the nephelauxetic effect?

A

Covalency delocaises e-

Softer ligands therefore more delocalisation so reduced e- density

Means small B and ligands high in nephelauxetic effect series

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40
Q

How is π-donor/acceptor involved in nephelauxetic effect?

A

π-donors/acceptors high in nephelauxetic effect series as both spread the elec charge

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41
Q

What is the nephelauxetic effect series?

A

Extent of reduction of B for different ligands

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42
Q

What are the 1st row anomalies?

A

Chemistry of 1st row main group v different to later rows

Effects:
Oxn staes, hybridisation, multiple bonds, electronegative effects

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43
Q

How does oxn states of 1st row differ from main group?

A

Difference between 2p and later np is due to lack of radial nodes in 2p RDF

Means 2p more sensitive to charge so stabilises rapidly on oxn compared to 3p

Limits oxn states of 1st row as successive IE increase dramatically

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44
Q

How does 1st row hybridisation compare to rest of main group?

A

More sp hybridisations with 1st row as 2s/p have similar radial extents (diverges down the group)

Not favoured down the group as poorer size/energy match (decreasing S2/ΔE for hybridisations)

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45
Q

How can you see change in hybridisation down the group?

A

MeLi has tetramic with covalency, NaMe is ionic rocksalt

Trans-bent structures of E2R2

Bond angle in H2O larger than SH2

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46
Q

How is multiple bonds seen down the group?

A

π-overlap decreases faster than σ-ovelap down group

Means multiple bonds rather than double bonds becomes more common

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47
Q

What are oxoacids?

A

E(OH)qOp

where E is non-metal or early TM

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48
Q

How does the χ of a central atom affect acidity of oxoacids?

A

More χ makes O-H bond more polar and stabilises conj base

Opposite to HX - which is based on bond strength

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49
Q

How does # of O effect acidity of oxoacids?

A

Inductive effect and increased stability of conj base as p increases, so more resonance structures

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50
Q

What is Pauling’s main rule?

A

E(OH)qOp

pKa = 8 - 5p

As succesive ionisations, the pKa increases by 5 each time

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51
Q

When does Pauling’s rules fail?

A

H2CO3 less acidic than expected, as in eqm with H2O + CO2

Dont include solvation

HClO4 more acidic than HClO3 by a larger margin than expected. Due to VII oxn state much less stable than V, so Cl draws e- density towards itself, polarising OH bond & increasing acidity

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52
Q

What is the Kapustinskii equation?

A

Equation to calc lattice enthalpy

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53
Q

How is the Kapustinskii equation dervied?

A

Derived from Born-Lande

Define madelung constant A=0.87, account for repulsive interaction at short distance (1/n), and assume n=9 for rock-salt structure

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54
Q

What are the assumptions for the Kapustinskii?

A

Assumes ionic model:
* hard, incompressible spheres
* integer charges
* only elecrostatic forces

Breaks down when any covalency

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55
Q

What can the Kapustinskii equation be used to determine?

A
  • Stability trends of different compounds and oxn states
  • Solubilities - find in combination with born equation, solubility increases as the difference in the radii increases
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56
Q

What is intercalation?

A

Intercalation of guest species into a host lattice, which remains largely unchanged

Weak vdW interactions between layers make intercalation possible

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57
Q

Why/how does intercalation into graphite occur?

A

Graphite - semimetal, no bandgap but no density of states (dos) at Fermi. Can make into metal via two methods

Empty states above fermi easily filled via reductive intercatalation (KC8)

Filled states below Ef emptied via oxidative intercalation (C8Br)

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58
Q

What are some examples of layers to interacalate into?

A

Sulfides:
TiS2 + Na -> NaxTiS2
Others:
C60
ReO3 and WO3
Li-ion batteries

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59
Q

What is the intercalation into C60?

A

Solid C60 has fcc
K+ can occupy all Oh/Td sites within ccp array of C603-

Can measure redn of C60 to C603- via voltammetry

Superconductor below 40K

60
Q

What is intercalation like in ReO3?

A

2nd/3rd row TM oxides with ReO3 can intercalate Li

Li2ReO3 structural distortion converts 12-coord cavity into 2x edge-sharing 6-coord sites occupied by Li

61
Q

What is intercalation like in WO3?

A

Li insertion leads to:
12-coord cavity -> 4x planar 4-coord sites

Lower level Li than ReO3

But can have more Na inserted

62
Q

What is the intercalation which occurs in Li-ion batteries?

A

Reversible electrochem oxn of LiCoO2 <-> Li0.5CoO2

Reductive intercalation highly favourable and has an almost constant driving force, generates electric potential

63
Q

What are Mott-Hubbard insulators?

A

Solids where the electrons are localised, whereby the band at the fermi level splits due to e- repulsion

64
Q

What is a band?

A

Large number of crystal orbitals which are approx to be continuous

Greater overlap of orbitals then the wider the band

65
Q

Why is there repulsion in a band?

A

e-s have random spins so experience greater e- e- repulsion than if on one atom

Strength of repulsion measued by parameter U

66
Q

What is the advantage of band formation?

A

Greater the length of box (in particle in a box) means lower curvature of wavefn so lower KE of e-s

Strength of this favourable bonding is by W

67
Q

What is W and U for mott-hubbard?

A

Mott-hubbard insulator: W<U

Simple-band so metallic:
W>U

68
Q

What occurs to U across the group?

A

d orbitals contract as Zeff increases
This gives narrower bands and increased e-e- repulsion

e.g. TiO/VO metallic and MnO/NiO Mott-hubbard insulating

69
Q

Which of 3/4/5d metal compounds are more likely to be Mott-Hubbard insulating?

A

4/5d unlikely to be Mott-Hubbard insulating

As more radially diffuse orbital so better overlap (larger W) and wider bands (smaller U)

70
Q

Are lanthanides likely to be Mott-Hubbard insulators?

A

4f contracted in core so don’t participate in bonding, and e- localised (U»W)
V. narrow band so this band is Mott-Hubbard insulating

Only conduct when d-band contains e-

71
Q

What is the conductivity of EuS and GdS?

A

EuS: 4f75d0 is insulating

GdS: metallic, 4f75d1 is favouted over 4f8 due to pairing energy

72
Q

How can the Mott-Hubbard state be avoided?

A

Introduce mixed valency

e.g. react NiO with O2 to give Ni1-xO, which has Ni3+ sites and e- can hop between them

73
Q

What are fast ion conductors and their use?

A

Solid electrolytes - conductors with highly mobile ions

Used in batteries and sensors

74
Q

Name some structures which are fast ion conductors

A

AgI
Na2O.nAl2O3
ZrO2
Bi2O3

75
Q

What is the structure of AgI?

A

β-form is wurtzite
Upon heating Ag+ “melts” to give α form - bcc of I- and Ag+ distrbuted across different cation sites

low activation energy for hopping between sites leads to increase in conductivity

entropy change from β->α about 1/2 associated with melting of typical ionic solid

Addition of Rb gives low T ionic conductivity

76
Q

What is the structure of Na2O.nAl2O3?

A

Spinel-like blocks of Al2O3
Al3+ in Td and Oh sites and every 5th layer has 3/4 O2- missing

Na+ in layer and mobile within it, makes it conducting

Used in Na-S battery

77
Q

What is the structure of
ZrO2?

A

7-coord at low T, distorted fluorite at high T

Used in O sensors in ICE engines

78
Q

What is the structure of
Bi2O3?

A

Low T:γ-phase with low symm at low T
High T: δ-phase, anion melts to adopt disordered array within fcc Bi cations

Based on fluorites but AB1.5 instead fo AB2, as disordered anion vacancies
O2- occupy many frankel defect sites, polarizability of Bi leads to high anion mobility

79
Q

What is the curie law?

A

Molar mag susceptibility of a complex containing a metal ion
χ = C/T

where C α effective mag moment

Therefore T independent

80
Q

What are the assumptions of the Curie Law?

A

Must obey spin-only formula (TM) or lande (lanthanides) so must be no thermally excited states

2nd order mixing can allow for obeying curie

81
Q

When is the spin-only formula followed?

A

No thermally excited states

TM ions with A2 E gs

82
Q

What is 2nd order zeeman effect in magnetism?

A

2nd order mixing of es into gs by B when small ΔE

A2 and E in TM are close in energy for this to occur

83
Q

When do metals not follow curie law?

A

TM states which have gs orbital have L=1

84
Q

Why does angular momentum prevent curie law (mag is T independent)?

A

A.m leads to spin-orbit coupling where different J levels have energy splitting ~ kT (as SO coupling const small)

Boltzmann distribution amongst these levels so mag moment is T dependent
χ-1 against T plotted - curves up at low T (as μ increases with T) but straightens at high T as effects of SO equalise (all equal energy states)

85
Q

Do lanthanides follow Curie law?

A

Mostly do - even though gs orbital has am (4f contracted and not perturbed by ligand field)

SO occurs but only ground J level is occupied as splitting between J levels is much larger than kT as λ α Z4

86
Q

When do lanthanides not follow curie law?

A

4f6 and 4f5 including Eu3+ or Sm2+

As have thermally accessible es so mag moments vary with T

87
Q

What is the spin only formula?

A

Predicts mag moment of complexes with para metal ions

n = unpaired e-
S = spin quantum number

88
Q

What are the assumptions of the spin-only formula?

A
  • L=0 in gs
  • No thermally accesible es
  • No 2nd order Zeeman effect in an applied mag field
  • No spin-orbit coupling
89
Q

When is the spin-only formula followed?

A

hs d5 and d7 (e.g. Fe3+)

90
Q

Why do TM with T states not follow spin-only formula?

A

Gs orbital am L=1
Leads to spin-orbit coupling so different J levels have similar energy splitting to kT

Boltzmann distribution amongst those levels so mag moment T dependent

91
Q

Why does low d e- TMs not follow Curie law?

A

when d<1/2 filled then λ +ve and 2nd order spin-orbit coupling decreases effective mag moment below spin-only

Counteracts TIP

92
Q

Why do most high de- TMs not follow Curie law?

A

as d>1/2 the λ is -ve and so the 2nd order spin orbit coupling increases mag moment above spin only

enforces TIP

93
Q

What is fluxionality?

A

Requires a stereochem non-rigid molecule which has <1 themally accessible structure and can pass between them under certain cond

94
Q

What are the common examples of fulxionality?

A

Functionality interchange
Berry pseudorotation
Ring whizzing

95
Q

How does variable T NMR work?

A

k = rate const for exchange, and Δv = difference in shift between 2 forms

when k»Δv then fast exchange so indistinguishable
when k«Δv then slow exchange and they are distinguishable

k ~ Δv then at coalescence point

96
Q

Why do peaks broaden in NMR when T increases from low-T limit?

A

Due to energy-time uncertainty principle

Forms exist for shorter period of time, so uncertainty in their energy is greater

97
Q

How can ring-whizzing be explained by NMR?

A

Can show if 1,2 or 1,3 ring shifts as the chemical environment that is maintained through a single shift differs

98
Q

How can IR probe fluxionality?

A

Fast technique so for rapid exchange processes
E.g. berry pseudorotation

99
Q

What is the 19F NMR of PF5?

A

Doublet at all T - not complex splitting as expected
Due to berry pseudorotation process which has a low Ea

100
Q

What is the structure of Co4(CO)12?

A

Interchange between bridgind/terminal CO
C NMR:
Low T - 4 peaks, bridging and 3xterminal
High T - 1 peak, all are equivalent

101
Q

What is the structure of TiCp4?

A

2xη-5 and 2xη-1 rings

H NMR:
Low T - 4 peaks
High T -2 peaks, ring whizzing so all protons in η-1 rings are equivalent
V high T - 1 peak, hapicity can change

102
Q

What is the stability of 1/2 filled shell?

A

p3, d5, f7 elements comparatively stable to ionisation and keep e- localised in compounds

103
Q

How does Mn being 1/2 filled change properties?

A

Prefers to keep e- localised rather than delocalised so weaker metal bonding and easier atomisation

MnO is mott-hubbard insulator whereas other early 3d MO are conductors due to this localisation

104
Q

What is hard-soft acid base (HSAB) theory?

A

Predicts stability of compounds and reaction pathways

Hard - small and charge dense, electrostatic
Soft - large and charge diffuse, covalent bonding

105
Q

What are the limitations on HSAB?

A

Qualitative, is a big oversimplification

Difficult to predict/compare reactivity of species on border between soft and hard - like TM

106
Q

What is the 18e- rule?

A

TM complexes kinetically stable when 18 VE

Due to all M-L bonding and low-energy nb d orbitals filled
Anti orbitals empty

107
Q

How many orbitals are there is TM metals?

A

9 valence MOs

If σ-only MLx:
x bonding MOs
x anti MOs
9-x nb MOs

108
Q

What are the 3 complexes for following 18VE rule?

A

Class 1: 3d metals and/or weak field ligands, t2g nb and eg anti so range of VE possible

Class 2: 4/5d metals with weak field ligands and/or σ donors, t2g nb but eg strongly anti, only up to 18 VE

Class 3: most organometallics, t2g is π-bonding and eg strongly anti, follows 18 VE

109
Q

Why do early TMs not follow 18 VE rule?

A

Low neutral VE so to form 18 VE would be difficult sterically

best example being group 4 metallocenes (like Ti - which give 16/14 VE compounds)

110
Q

Why do square-planar complexes follow 16 VE?

A

pz not used in bonding (by D4h symm) so only 8xM-L bonding and metal based non-bonding MOs to fill
Adds up to 16 VE

Donation into this would cause strong steric repulsion from filled dz2, which is contracted

111
Q

How does 18 VE rule compare to octet rule?

A

Directly analogus - but octet rules has almost no exceptions unlike 18 VE

As 18 VE relies on using valence orbitals in bonding which is unrealistic due to different radial extent of the d orbitals to s/p

Octet only relies on using valence s/p which have similar radial extents

112
Q

What is the exception to octet rule?

A

Heavy main group elements where 6s contracted due to relativity so different to p

Example of inter pair effect

113
Q

What does M-M bonding depend on?

A

Overlap (RDF) and electron occupancy

Observed in TM as have more extended overlap

Limited in s/f blocks are core-like orbitals which don’t overlap

114
Q

How does M-M bonding change down the group?

A

Orbitals down group get nodes and get more diffuse (with lower e-e- repulsion)
Better overlap and greater bond strength when better overlap

115
Q

What is the structure of 3/4/5d carbonyl compounds?

A

3d - bridging COs

4/5d - M-M more common and fewer bridging CO

Can find by IR - bridging CO have a lower stretching freq

116
Q

How does M-M bonding change across a period?

A

Decreases as Zeff, so more contracted d-orbitals so worse overlap and higher e- repulsion

U>W across the period

117
Q

Why can Li form cubane-type clusters in MeLi?

A

Li 2s and 2p same radial extent so s-p mixing possible
Gives directional hybrid orbitals with good overlap in a cluster

Doesnt happen in MeCs which is ionic rocksalt

118
Q

What does the general term lanthanide contraction mean?

A

Term which describes the decrease in ionic radii across the lanthanide elements

119
Q

What causes the lanthanide contraction?

A

Increased Zeff across series at same n lowers their energy

120
Q

Why is the lanthanide contraction smooth?

A

Absence of ligand field effects
4f shielded from external charge by 5s/5p

121
Q

How does the lanthanide contraction effect the lanthanides?

A

Lanth chem dominated by ionic interactions, 1/r relationship

Seen in water exchange mech for Ln3+, 1st half undergo Id 2nd half undergoes Ia
This is because contraction causes ideal coord number to switch from 9 to 8 by Gd (sterics)

122
Q

How does the lanthanide contraction effect TM?

A

Chem of 4d similar to 5d instead of 3d

5d has similar radii to 4d, both form high oxn states
Similar structures and orbital energies (found from LMCT)

123
Q

What is the effect of lanthanide contraction on main group chemistry?

A

Causes alternation effect down main group in IEs
This has knock-on effect for stability of group 15 pentachlorides, P/SbCl5 stable and As/BiCl5 unstable due to the TM and lanthanide contraction in term

124
Q

Why do clusters compounds form?

A

Formed due to e- deficiency and facilitates e- sharing

125
Q

What is the concept Wade’s rules?

A

Set of rules for predicting structures of borane cluster compounds
Can be applied to many other clusters

126
Q

What are skeletal e- pairs?

A

Skeletal e- pair = [total VE - 2xB-H subunit]/2

where the total VE = (# of B * 3) + (# of H * 1)

127
Q

What are the structures in Wade’s rules?

A

n vertices = closo
n-1 vertices = nido
n-2 verticies = arachno
n-3 verticies = hypho

128
Q

How do you apply Wade’s rules?

A

1) Determine VE
2) Subtract 2 for each B-H subunit
3) Divide by 2 to get # of SEP
4) SEP = n+1, so then find n and the structure via how many boron atoms
5) n B is closo, n-1 B is nido, n-2 B is arachno, n-3 hypho

e.g. if SEP = 8 and it is B5H11
then n=7 and the structure is n-2 so arachno

129
Q

What is the isolobal analogy?

A

A fragment can be replaced by another if:
* same # of fronteir orbitals, and they have same symm and similar energies
* Fronteir orbitals filled with same # of e-

e.g. BH isolobal in C,Sn,Pb, means that the equivalent can be synthesised starting from B

130
Q

What is the limitation of wade’s rules?

A

Must be an e- deficient cluster
Condition is: SEC < 2x # of bonds

131
Q

What observations are there about oxides across the table?

A

O forms diverse range of compounds

Almost always O2- and brings out high oxn states as small size and favourable formation enthalpy (only F- better)

Structures of them shows trends in radii, orbital overlap, e-e- repulsion, etc

132
Q

What is the bonding in main group oxides?

A

Dominated by covalency/orbital overlap

133
Q

What are the structures of 1st row main group oxides?

A
  • B forms B2O3
  • C/N oxides dominated by C=O/N=O
  • OF2 is example when has a +1 oxn state
  • XeO3 has trig bipyrimidal structure, cant make others as more accessible IEs
134
Q

What is the general structure of main group oxides lower down the groups?

A

More extended structures with E-O bonds, pi bonds derease in strength faster than sigma as p-orbitals more sensitive to distance
E.g. CO2 molecular but SiO2 has extended cristobalite

135
Q

What are the structures of SnO/PbO?

A

SnO/PbO - layered structure, the cation charge density is polarisable by O2-

ns orbitals interact with O 2p which interacts with metal np, hybridisation drives structural dist to form a stereochem lone pair

136
Q

What are the M2O notable structures?

A

Group 1 oxides - antifluorite, M in all Td holes of ccp array of O2-

Cs2O is the exception - large and polarisable so layered oct structure, anti-CdCl2

137
Q

What is the structure of 1st row TM monoxides?

A

Rocksalt - M in all Oh holes of ccp O2- array

138
Q

What are the elec properties of 1st row MO?

A

Metallic to Mott-Hubbard insulating as 3d contracts across the series

139
Q

What the difference between TiO compared to standard rocksalt?

A

15% Schottky defects (anion and cation) gives short Ti-Ti distances

extended Ti orbitals capable of Ti-Ti bonding (Nb equivalent will have more M-M bonding)

140
Q

Why is the structure of NiO notable?

A

Partial oxn to Ni(III) when heated
Ni1-xO has e- hopping doesnt form d9 config with high e-e- repulsion

141
Q

What causes defect formation in 1st row TM MO?

A

Driving force early and late in series

Is M-M bonding vs reducing repulsion

142
Q

When is rocksalt not observed in 1st row TM MO?

A

ZnO and BeO has ccp zinc blende / hcp wurtzite

Small cations so Td rather than Oh coord

143
Q

What are the structures of MO2?

A

Most TM adopt Oh rutile structure (TiO2)

VO2 rutile at high T but undergoes Pierl’s distortion at lower T, then becomes banmd gap insulator as e- localised in V-V bonds
NbO2 same as VO2 but stronger M-M so always distorted

MoO2 distorts but still conducts, d2 so 1e- in M-M bond and 1 to conduct

144
Q

What are the higher oxn state O salts?

A

Higher oxn state more stable down group

RuO4 and OsO4 stable, but FeO4 unstable

CrO3 high oxidising, WO3 not oxidising

145
Q

What are the structures of lanthanide oxides?

A

Mostly Ln2O3 as +3 oxn state dominates lanthanides

LnO not as common - Ln(III) O2- e-, v good conductor as e- is mobile in 5d conduction band
Not case for EuO/YbO - exchange energy keep e- localised on metal

CeO2 is rare Ln(IV), fluorite

146
Q

What are binary spinels?

A

A3O4

Normal - ccp O2- with A(III) in 1/2 Oh holes and A(II) in Td holes

Inverse - A(II) Oh and 1/2 A(III) Td, which max LFS. Occurs when A(III) has 0 LFSE, for example Fe(III)

147
Q

Why is Fe3O4 a good conductor and Co3O4 a poor conductor?

A

Fe3O4 metallic as Fe(II) and Fe(III) belong to edge-sharing octahedra, so HAB good and small FC barrier to ET (as t2g to t2g)

Co3O4 normal spinel (LFSE), poor conductor as eg-eg ET

Year 3 - Chemistry (12 decks)

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