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Year 3 - Chemistry > Compounds of Interest > Flashcards

Compounds of Interest Flashcards

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1
Q

Why is Li3N of interest?

A

Only stable nitride of alkali metals

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2
Q

What are features of Li3 synthesis?

A
  • Li + N2 @ high T in a dray environment
  • Possible as lattice enthalpy large enough due to small Li+ to overcome endo formation enthalpy N3- ion
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3
Q

How do alkali metals (other than Li) react with N2?

A

Form azides which have a lower formation enthalpy

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4
Q

What is the structure of Li3N?

A

Alternating layers of (Li2N)- and Li+

Li+ ions are 2 or 3 coord (as small), 2x different N-Li distances

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5
Q

What are the properties of Li3N?

A

Ionic conductivity in 2 dimensions, as Li+ can move between interstitial sites and causes cation vacancies

Functions as fast ion conductor

Small band gap

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6
Q

What is the reactivity of Li3N?

A

Explosive reaction with water: Li3N + 3H2O -> NH3 + 3LiOH

Spacings mean intercalation of small molecules like H2 or Li+
LiCoO2 can also do this

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7
Q

Why is MeLi interesting?

A

Due to tetramic structure and use as a reagent in organic synthesis

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8
Q

What is the synthesis of MeLi?

A

MeX + 2Li -> LiMe + LiX
X = Cl, Br

Metal-halogen exchange

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9
Q

What is the structure of MeLi?

A

Connected (LiMe)4 tetramic units, with CH3 capping each face of Li4 tetrahedron

Li-Li similar to Li2 in gas (smaller than metal so more covalent)

Cluster forms as e- deficient bonding model

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10
Q

How can you spec probe MeLi?

A

C13 NMR shows high T fluxionality

6Li I = 2
Low T: slow exchange, 7 lines (C couples to 3Li)
High T: fast exchange, 9 lines (C couples to 4 Li)

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11
Q

What is the MO diagram of MeLi?

A

t2 bond polarised on C

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12
Q

What are the reactions of MeLi?

A

Nucleophlic equivalent of Me-

Transmetallated into organocopper reagents, for use as softer nucleophiles

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13
Q

What can you compare the structure of MeLi to?

A

NaMe rockstalt structure - more polarised as poorer orbital energy match

KMe has the NiAs structure

Grignard also covalent

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14
Q

Why is LixCoO2 a compound of interest?

A

Used in rechargeable batteries

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15
Q

How are LixCoO2 compounds synthesised?

A

Li2CO3 + 2CoCO3 + heat -> Li2CoO2

then deintercalation using X2

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16
Q

What is the structure of LixCoO2?

A

Layered structure consiting of sheets of edge-sharing Co(III) octahedra separated by layers of Li cations

This can be deintercatalated

Oxide lattice has ABCA cubic stacking (CdI)

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17
Q

What is the structure of LixCoO2?

A

Layered structure consiting of sheets of edge-sharing Co(III) octahedra separated by layers of Li cations

This can be deintercatalated

Oxide lattice has ABCA cubic stacking (CdI)

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18
Q

Why are LixCoO2 good batteries?

A

Electrochem oxn is reversible so rechargable

Reductive intercalation highly favourable

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19
Q

What is the band structure of LixCoO2 states?

A

Oxidation of Co(III) to Co(IV) lowers energy of Co 3d so O 2p depleted which can lead to a fire risk as O2 released

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20
Q

Why is Na2(2.2.2-cryptand) of interest?

A

Binding of Na+ to cryptand strong enough to drive disproportionation to sodide anion, Na-
2Na <-> Na+ + Na-

Good reducing agent (not as strong as Cs equivalent)

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21
Q

How is Na2(2.2.2-cryptand) synthesised?

A

2Na + 2,2,2-cryptand -> Na2(2.2.2-cryptand)

Done in ethylamine

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22
Q

What is the structure of Na2(2.2.2-cryptand)?

A

HCP array of Na(2.2.2-cryptand)+ with Na- in octahedral holes
NiAs structure

Na+ is 8-coord

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23
Q

Why can Na2(2.2.2-cryptand) form?

A

Cryptand effect

Entropic - preorganised, so fewer dof lost on complexation, Na- not well solvated so little H2O organisation

Enthalpic - lone pair repulsion overcome in complexation

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24
Q

Why is Na β-alumina a compound of interest?

A

Very high electrical conductivity and use as a solid electrolyte in Na-S battery system

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25
Q

What is the synthesis of Na β-alumina?

A

Na2CO3 + Al2O3 -> NaAl11O7

Within a sealed vessel to avoid loss of Na2O

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26
Q

What is the structure of Na β-alumina?

A

Al3+ occupies Td and Oh holes in close-packed layers (similar to spinels)

Every 5th layer has 3/4 of oxide ions missing

Layered structure with Na within layers

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27
Q

Why is Na β-alumina a good conductivity?

A

Na+ mobility

Mobile in oxide-deficient layers as smaller than O2- and many states to occupy

Only in 2 dimensions

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28
Q

What occurs to Na β-alumina if you exchange for larger cations?

A

As radii increases they are less mobile as cannot move as freely within oxide layers

BUT Li+ has v low conductivity as so small it occupies smaller sites so higher activation energy for motion

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29
Q

Why is K3C60 a compound of interest?

A

Superconductor at temperatures as high as 40K

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30
Q

How is K3C60 synthesised?

A

Intercatalation of K vapour into C60

N-style doping

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31
Q

What is the structure of K3C60?

A

C60 by itself are fcc
With K+ cations in all Oh and Td with C603- ccp

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32
Q

What is the band structure of K3C60?

A
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33
Q

How is K3C60 a superconductor?

A

BCS theory - movement of pairs of e- (cooper pairs) coupled by lattice vibrations

Tc = ωe1/λ
λ = VN(Ef)

Tc also depends on lattice parameter a0 (as separation increases then bandwith increases)

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34
Q

Why is α-AgI/RbAg4I5 interesting?

A

Fast-ion conductor

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35
Q

How do you synthesise α-AgI/RbAg4I5?

A

KI + AgNO3 -> α-AgI

RbAg4I5 can be made by inserting some RbI

only α-AgI at higher temp

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36
Q

What is the structure of α-AgI?

A

Body-centered array of I-

Ag+</sub> ions distributed across different sties and this mobility leads to being a conudctor?

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37
Q

How is the structure of RbAg4I5 similar to α-AgI?

A

Rb+ and I- form a rigid lattice
Ag+ randomly distributed between Td Sites

Has higher ionic cond at low T but comprises overall response

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38
Q

Why is Rb9O2 interesting?

A

Fast-ion conductor

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39
Q

How do you synthesise Rb9O2?

A

Partial oxn of Rb @ low T gives Rb6I which then decomposes to Rb9O2 and Rb

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40
Q

What is the structure of Rb9O2?

A

2x ORb6 face-sharing octahedra

e- delocalisation between Rb ions, so good ion conductor (and coloured)
Short Rb-Rb distance

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41
Q

What is the reactivity of Rb9O2?

A

Melts to form Rb2O & Rb

Reacts with water to produce fully oxidised RbOH

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42
Q

Why is TiCp4 an interesting compound?

A

Due to fluxonality of protons in NMR

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43
Q

How is TiCp4 synthesised?

A

TiCl4 and 4NaCp

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44
Q

What is the structure of TiCp4?

A

2x η5 CP and 2x η1 Cp to avoid exceeding 18VE rule

16 VE - poor overlap of 3d orbitals so only small stabilisation of bodning orbitals. Means doesnt follow 18 e- rule (like 4/5d)

Makes sense as Ti(IV) is majority of Ti chemistry

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45
Q

What is the NMR of TiCp4?

A
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46
Q

Why can ring wizzing occur in TiCp4?

A

16VE so can form suitable TS

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47
Q

Why is TiO1+x interesting?

A

Abnormal structure

they didnt even give a reason

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48
Q

Why is TiO1+x interesting?

A

Abnormal structure

they didnt even give a reason

49
Q

How can TiO1+x be synthesised?

A

TiO2 and Ti at 1500C

50
Q

What is the structure of TiO1+x?

A

when x=0, 15% of cation and anion sites vacant, means ordered monoclinic structure

Change in stochiometry changes vacancy conc, but total conc same

Vacancies reduce Ti-Ti distances and max M-M bonding, which is good for early TM as more extended d-orbitals

51
Q

What is the reactivity of TiO1+x?

A

Reacts with acid to form Ti3+ and H2

Because stable oxn states are 3/4, as early in period and compensated by electrostatic interactions with anions

52
Q

How does TiO1+x compare to NbO/NiO?

A

NbO - 25% vacancies, more M-M as better 4d overlap so wider bands and more metallic

NiO - cation vacancies, Ni1-xO gives mixed valence (2/3). Mott-hubbard insulator to metallic conductor

53
Q

Why is BaTiO3 interesting?

A

Perovskite structure

54
Q

How do you synthesise BaTiO3?

A

React TiO2 and BaCO3 at high T

55
Q

What is the structure of BaTiO3?

A

Cubic perovskite with corner-sharing TiO6 octahedra

Large Ba expands lattice along with the 2nd order JT, displaces Ti(IV) from centres of octahedra

Leads to ferroelectric polarisation - charge accumlates in material while thermally stable

56
Q

Why is VO an interesting compound?

A

Structure comparison with 3d MOs and VO2

57
Q

How do you synthesise VO?

A

V2O3 and V(s)

58
Q

What is the structure of VO?

A

Distorted rocksalt with weak V-V

varies between VO0.8-1.3

59
Q

What is the band structure of VO?

A

Broad band (W>U) as early 3d TM

Metallic conductor as partially filled t2g

60
Q

How does VO compared to 3d MOs?

A

Later MOs - more contracted 3d, U>W, mott-hubbard insulators

Early MOs - more extended 3d, M-M leads to more defective structure

61
Q

Why is VO2 of interest?

A

Undergoes Pierl’s distortion where it changes from metallic to insulating

62
Q

How is VO2 synthesised?

A

V2O5 + CO -> CO2 + VO2

63
Q

What is the electron count of VO2?

A

V(IV) is t2g1

Would expect metallic behaviour

64
Q

What is the structure of VO2?

A

> 340K is undistorted metallic
<340K undergoes Pierls distortion, by which V-V dimers formed and e- localised in V-V bonds

65
Q

What is a Pierls’ distortion?

A

1D chain of equally spaced ions with 1 e- is unstable
Leads to distortion

66
Q

Why can the Pierls distortion occur in VO2?

A

Early in 3d, orbital overlap good and V-V bonds outweighs loss of lengthening V-O bonds

67
Q

How does the structure of VO2 compare to similar??

A

TiO2 - rutile band gap insulator, d0

CrO2 - 3d overlap not sufficient, undistrorted rutile

NbO2 - distortion occurs to higher temp as better overlap, insulating

68
Q

How is CrO2 synthesised?

A

Thermal decomp of CrO3

69
Q

How is CrO2 ferromagnetic?

A

Rutile structure - dyz and dxz able to mix with O 2p
Leads to delocalisation in this band

70
Q

Why is [2,6-Dipp2C6H3]Cr2 a compound of interest?

A

Quintuple Cr-Cr

71
Q

How is [2,6-Dipp2C6H3]Cr2 synthesised?

A
72
Q

What is the structure of [2,6-Dipp2C6H3]Cr2 ?

A

Trans-bent with quintuple bond
1xσ - dz2
2xπ - dyz, dxz
2xδ - dxy, dx2-y2

Confirmed by X-ray, IR, and NMR (no Cr-H bonding)

73
Q

What type of ligands stabilise multiple metal bonds?

A

Bulky ones-
Limit intermolecular reactions which yields

Also want few ligands as too many reduces VE available to form M-M

74
Q

Why is Cr2(OAc)4.2H2 of interest?

A

Quadruple bonds

75
Q

How is Cr2(OAc)4.2H2 synthesised?

A

CrCl3 + Zn/HCl -> CrCl2

CrCl2 + NaOAc -> Cr(OAc)2

All under N2

76
Q

What is the bonding in Cr2(OAc)4.2H2?

A

Quadruple bonding
All e- paired in dimer, so diamagnetism (Cr 2+ is JT distorted)

Red due to δ-δ* transitions

77
Q

What is the structure of Cr2(OAc)4.2H2?

A

Dimer with eclipsed config - as allows for quadruple bonds even if bad sterics
C4V point group

78
Q

What is the reactivity of Cr2(OAc)4.2H2?

A

Strong reducing agent Cr(II) - Cr(III)

Reduces atmospheric O2 so can used as scrubber for oxygen

79
Q

How can you compare Cr2(OAc)4.2H2?

A

Mo - shorter quadruple bonds as better overlap of 4d, and stronger bonding so δ-δ* gap larger so lesser thermal δ* population

Re - same number of VE and eclipsed

Os - not eclipsed as δ* fully occupied so sterics outweighs

80
Q

Why is M(CO)5(C(R)OMe) interesting?

(when M= Mo, W and R = Me, tBu)

A

Fischer carbene

81
Q

How is M(CO)5(C(R)OMe) synthesised?

A
82
Q

What is the reactivity of M(CO)5(C(R)OMe)?

A

Reacts with nulceophiles as C in carbene electrophilic

83
Q

What is the elec structure of M(CO)5(C(R)OMe)?

A

d-orbitals rel low energy due to π-acceptor co-ligands (CO)

CR2 has O/R sub which destabilises C 2p, leading to singlet carbene formation
But C 2p empty, so C is electrophlic

HOMO metal d-bsaed, LUMO is C-based

84
Q

How is a Fischer carbene compare to a schrock alkylidene?

A

Schrock:
no π-acceptor co-ligands, d-orbitals rel high in energy, no π-donors on C

Triplet carbene

85
Q

Why is Fe2Cp2(CO)4 interesting?

A

Interest due to fluxionality

86
Q

How can you synthesise Fe2Cp2(CO)4?

A

Reaction between Fe(CO)5 and cyclopentadiene dimer C10H12

87
Q

What is the reactivity of Fe2Cp2(CO)4?

A

React with Na/Hg amalgam to form v nucleophilic [CpFe(CO)2]- anion

Reacts with Br2 or I2 by OX -> CpFe(CO)2X

88
Q

What is the structure of Fe2Cp2(CO)4?

A

Fluxional - between cis and trans via a non-bridged intermediate

NMR: 1 CO in fast exchange, 2 in slow exchange (bridged & terminal)

89
Q

Why is Fe3O4, called magnetite, interesting?

A

Due to structure, elec conductivity, and magnetic properties

90
Q

How can you synthesise Fe3O4 (magnetite)?

A

6Fe2O3 + high heat -> 4Fe3O4 + O2
Heat is 1400C

Also produced in the body but can be poisonous

91
Q

What is the structure of Fe3O4 (magnetite)?

A

Fe(II)Fe(III)2O4 has the inverse spinel structure
ccp arrangement of O2- with Fe(III) in 1/8 Td holes and 1/4 Td Oh, and Fe(II) in 1/4 Oh holes

Fe(III) - hs d5, LFSE is 0 (no preference for Oh or Td)
Fe(II) - hs d6, favours an Oh coord as 0.4ΔOh > 0.6ΔTd

92
Q

How does Fe3O4 (magnetite) compare to Co3O4?

A

Co3O4 adopts normal instead of inverse
Co(III) in 1/2 Oh holes and Co(II) in 1/8 Td holes

93
Q

Why is magnetite, Fe3O4, a good electron conductor?

A

Above 120K: e- transfer between Oh Fe(II) and Oh Fe(III) which are in edge-sharing octahedra. This is good as transition is t2g -> t2g, so no change in σ* and small franck-condon barrier to e- transfer

Below 120K: Verwey distortion occurs which reduces conductivity

94
Q

How is Fe3O4, magnetite, ferromagnetic?

A

Ferro - can form a naturally occuring magnet

95
Q

How does Fe3O4, magnetite, react?

A

Decomposes with CO in blast furnace to Fe + CO2

Binds to impurities in water and sediments, for purification

96
Q

Why are Fe(NCS)2(bipy/phen)2 a compound of interest?

A

They are spin crossover compounds

Which are compounds within which high-spin-to-low-spin transition at a TM centre, in response to a change in temperature or pressure

97
Q

What are the spin properties of Fe(NCS)2(bipy/phen)2?

A

ls at low T, hs at high T

Due to maximising vib entropy in higher T
As in hs - weaker bonding, so vib energy levels closer together so more populated, more vib entropy

98
Q

What is the ligand field strengths in Fe(NCS)2(bipy/phen)2?

A

Both bipy/NCS- have intermediate field strengths

Means hs/ls spin states are similar energies

99
Q

Why is KFe2(CN)6, prussian blue, interesting?

A

Intense blue colour
This arises from intravalent charge transfer (IVCT)

100
Q

How can you synthesise KFe2(CN)6, prussian blue?

A

K4[FeII(CN)6] + FeIII(H2O)6 3+</sub> -> KFe2(CN)6 + 6H2O

101
Q

What is the structure of KFe2(CN)6, prussian blue?

A

FCC of FeII(CN)6 with FeIII in Oh holes and K+ in 1/2 Td holes

CN- linear between Fe ions, aligned so softer C adjacent to FeII and N next to FeIII

102
Q

Why is CoCO4 of interest?

A

Eqm between bridged and non-bridged structures

Also used in org synthesis

103
Q

How is CoCO4 synthesised?

A

CoIII(OAc)3 + H2 + CO @ high T and p

H2 reduces Co

104
Q

What is the structure of CoCO4?

A

Major isomer has 2xbridging CO and eclipsed terminal CO (C2v)

Unbridged has staggered CO (D3d)

Distinguished by IR

105
Q

How does CoCO4 react?

A

Reacts with alkyne

Also reacts with Na then acidification to give a pre-catalyst used in hydroformylation reactions (HCo(CO)4)

106
Q

Why is YBa2Cu3O7 of interest?

A

Superconducting material

107
Q

How can you synthesise YBa2Cu3O7?

A

Sol-gel precursor - dry and heat to form product

High T ceramic synthesis with heating and grinding cycles

108
Q

What is the structure of YBa2Cu3O7?

A

CuO4 square-planes separated by layers of CuO3 which insert or remove e-, which partially oxidises Cu(II) to Cu(III)
This gives a superconducting metal

If just Cu(II) then would be Mott-Hubbard insulator

109
Q

How is superconduction explained in YBa2Cu3O7?

A

Low T - BCS theory

Higher T - not clearly explained but involves stronger e-/phonon coupling

110
Q

Why is ZrO2 of interest?

A

Reaction with Y2O3 to give fast-ion conductor

This is called yttria stabilised zirconia

111
Q

How can you synthesise ZrO2?

A

Exists naturally

Or heat Zr(OH)4

112
Q

What is the coord of Zr in ZrO2?

A

Low T: 7-coord in monoclinic

High T: 8-coord in dist fluorite

Show in x-ray

113
Q

hat is the band structure of ZrO2?

A

Band gap insulator - O 2p valence filled and conduction 4d band empty

114
Q

What is the conductivity of ZrO2 at different T?

A

High T is sig more conductive

As low T (monoclinic) has 2 distinct anion sites whereas fluorite has 1 anion sites

More randomly distributed in high symm structure, so easier hoppijng between sites and faster conductivity

115
Q

How does ZrO2 react with Y2O3?

A

ZrO2 + (x/2) Y2O3 -> Zr1-xYxO2-2/x

Y stabilises fluorite as Y(3+) larger than Zn(4+) which leads to O2-</sub> vacancies to maintain charge neutrality
Gives good ionic conduction at high T

116
Q

How is the product of ZrO2 reacting with Y2O3 useful?

A

Solid electrolyte in oxygen sensors in internal combustion energies

117
Q

What is the structure of ZrO2 compared to other MO2?

A

TiO2 - rutile at all T, Ti(IV) 6-coord as smaller

SiO2, GeO2 - 4 coord system

118
Q

Why is the structure of Cp2ZrCl2 interesting?

A

Precursor to an alkene polymerisation catalyst

119
Q

How do you synthesise Cp2ZrCl2?

A

ZrCl4 + 2NaCp -> Cp2ZrCl2 + 2NaCl

Zr(II) to Zr(IV)

Year 3 - Chemistry (12 decks)

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