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Knowledge from Past Papers > 2017 PP > Flashcards

2017 PP Flashcards

1
Q

Cubic Crystal System

A

a=b=c alpha=beta=gamma=90degrees

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2
Q

Orthorhombic system

A

a does not = b does not = c BUT alpha=beta=gamma=90degrees

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3
Q

Multiplicity in Orthorhomic systems

A

We say that in orthorhombic systems the peaks (h00) have a multiplicity of 2, the peaks (0k0) have a multiplicity of 2, and the peaks (00l) have a multiplicity of 2.

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4
Q

Describe an octahedral splitting diagram

A

Split into 3 lower degenerate t2g d orbitals and 2 higher eg orbitals- separated by energy delta O (^2)

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5
Q

What effects delta O/T

A

Identity of ligand- same order of splitting is followed regardless of identity of metal ion

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6
Q

Examples of strong field ligands that give rise to high energy transitions

A

py-NH3 CN- CO (pi acceptors)

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7
Q

Examples of weak field ligands that give rise to low energy transitions

A

I- Br- SCN- CL- (pi donors)

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8
Q

Ligand field strength also depends on- that CFT doesn’t explain .. explain effect

A

Identity of central metal ion- Value of delta O increases with oxidation state of central metal atom- and increases down a group. Variation in OX states reflects smaller size more highly charged ions therefore shorter ML distances and stronger interaction energies. Increase down group due to larger size of d orbitals therefore stronger interaction with Ls

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9
Q

Ligand field stab E (CFSE)

A

Treats ligands as point charges/ dipoles- does not take into account overlap of ligand/ metal orbitals NEED LIGAND FIELD THEORY
Additional stab relative to the barycentre

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10
Q

Pairing energy

If delta O/T is smaller than P

A

Coulombic repulsion when pair electrons

Weak field case

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11
Q

When is Octa complex low spin and high spin

A

3d4 configuration is low spin if CF is strong but high spin if CF is weak- same applies to 3d5,6,7

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12
Q

Deviation of hydration enthalpies from straight line arises from

A

additional LFSE in oct. complexes formed from the free ion

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13
Q

Describe tetra splitting diagram:

explain why Delta O > delta T

A

3 higher in t2, 2 lower in e…. delta T < delta O as complex with fewer ligands none of which are directly orientated at d orbitals

FOR TETRA ONLY HIGH SPIN COMPLEXES

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14
Q

What favours Square Planar complexes

A

d8, strong CF- tendency enhanced for 4d/4d metals because of larger size and greater ease of electron pairing

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15
Q

Jahn Teller effect

A

If the ground electronic configuration of a non linear complex is orbitally degenerate, and asymmetrically filled, then the complex distorts so as to remove the degeneracy and achieve a lower energy level.
Oct. axial elongation more common than compression

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16
Q

Jahn Teller possible for?

A

Oct= d1,2,4 low spin….d5,6,7 high spin

Tetra: d1,,3,4,6,8,9

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17
Q

Pi donor ligands

A

decrease delta O whereas pi acceptor ligands increase delta O
Has filled orbitals of pi symmetry abound the ML axis
Halides- OH-, O2-, H2O, SCN-
Pi Base
E lower in energy than M d Os ONLY interact with t2g Os
Decrease delta O

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18
Q

Pi Acceptor Ligand

A 
Empty Pi Os
Pi Acid
vacant anti bonding Os (LUMO)
higher in energy than M d Os
Increase delta O
py-NH3, CN-, CO
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19
Q

Microstate

A

Different ways in which electrons can occupy the orbitals specified in the configuration

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20
Q

Terms

A

Group together microstates that have same energy when take into account e-e repulsions- spectroscopically distinguishable energy levels
Use Clebsch-Gordan series to determine L,S
L=0(s), 1(P)…

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21
Q

Hund’s Rule

A

Identifies ground term of gas-phase atom or ion
For a given configuration- the term with the greatest multiplicity lies at the lowest energy
For terms of given multiplicity, the term with the greatest value of L lies at lowest in E

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22
Q

Selection rules

A

Electronic transitions with a change of multiplicity are forbidden
Laporte selection rule: Trabsitions between d Os are forbidden in oct complexes- asymmetrical vibrations relax this restriction

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23
Q

Chatt Dewar Duncanson model vs Metallacyclopropane model

A

draw

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24
Q

Perovskite structure

A

ABO3
A= large CN= 12
B CN= 6

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25
Q

Ilmenite Structure

A 
ABO3
A, B Both SMALL cations
HCP
draw it with o layers
A and B occupy 2/3 of oct holes, occurring in alternate layers
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26
Q

Normal spinel

A

A in Tetra holes
B in Octa holes
1/2 oct holes filled
1/8 tetra holes filled

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27
Q

inverse spinel

A

B in tetra sites

A+B in octa sites

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28
Q

Biofuels

A

Reduce dependence on oil, gas, coal

competition with food production, changing land use, extra fertilizers/ pesticides

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29
Q

Sustainable chem

A

Environment, energy, health, economics

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30
Q

12 principles Green Chem

A
  1. Better to prevent waste than to treat and clean up
  2. synthetic methods designed to use all materials for product
  3. Synthetic methodologies little or no toxicity to human health and environment
  4. chem products designed to preserve efficacy of function while reducing toxicity
  5. use of auxiliary substances made unnecessary
  6. E minimized- synthetic methods at ambient temp and pressure
  7. chemical products designed so at end of function do not persist in environment
  8. substances in chem processes should be chosen to minimize potential for chem accidents
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31
Q

Atom economy- design factor of chem process- additional consideration to yield, ease of product isolation and purity requirements

A

even if 100% yield still can have more waste than product
= MR desired/ MR all *100
E factor considers solvents as well= mass of by product/ mass product

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32
Q

Friedel-Crafts reactions

A

Zeolite
Serious safety concerns
catalytic

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33
Q

Considerations for Biofuels/plastics

A

life cycle

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34
Q

Recycling

issues

A

element may be highly dispersed
alloys
contamination during recycling

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35
Q

Element concerns

A

companion metals

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36
Q

Energy- reduction in chem processes

alternative energy sources

A 
Ultrasoniction
microwave reactors
photochemistry
electrochemistry
hydrothermal/solvothermal
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37
Q

Risk and Hazard
major consideration in Green Chem
how to reduce risk

A

Risk = hazard*exposure
1. reduce exposure- tighter regulations, more safety equipment
2. reduce hazard
design out hazard and won’t need to worry about exposure

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38
Q

Chitin

A

Skeletal structure made purely from organic material
polysaccharide
requires a lot of energy to make

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39
Q

Problems with organic skeletal tissue/ inorganic

A

not very hard BUT tough and flexible…. hard but brittle

ideal solution if a composite

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40
Q

Composite + example

A

Organic matrix filled with inorganic mineral
Crab shell- Chitin + CaCO3
tough and flexible and hard

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41
Q

main functions of biominerals

A

Protection, motion, cutting grinding, buoyancy, optical/magnetic/gravity sensing/ storage
mostly crystalline

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42
Q

Define a polymorph

give example

A

Different crystalline structures of the same material

CaCO3

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43
Q

Two most stable polymorphs of CaCO3

A

Calcite and aragonite and they are the most common

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44
Q

What are bones and teeth made out of

A

Hydroxyapatite HAP- calcium phosphate
often sub CO3(2-) and F- for PO4(3-)
with has smaller sol. product therefore phase less soluble- prevents tooth decay

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45
Q

Amorphous

A

disordered- does not have long range order and cannot diffract X-Rays
atoms are irregularly arranged and bond lengths and angles vary throughout the structure

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46
Q

Describe Silica and why under ambient conditions is it amorphous

A

Contains v stable Si-O-Si bond which has a lot of variability in the bond angle, leads to disorder, much higher temps needed to generate crystalline form- quartz

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47
Q

Diatom

A

Living organism that uses Silica to make shells

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48
Q

Why does grass incorporate silica into its structure

A

uses in leaves but also in husks around the seeds to make them less palatable to a hungry animal

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49
Q

Anisotropic

A

Crystalline materials have distinct fracture planes

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50
Q

Isotropic

A

Amorphous, disordered- do distinct directions in material- easier to mould into certain shapes

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51
Q

Uses of Iron Oxides

A

Magnetotactic bacteria- mixed valence iron oxide- magnetite (FeO4) allow them to navigate using Earth’s magnetic field

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52
Q

Ox states in Magnetite

A

Fe3+ Ferric ion

Fe2+ Ferrous ion

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53
Q

Purpose of Ferritin

A

Protein- found in almost all living organisms, acts as ion buffer, providing ion to critical biological systems in a controlled way- preventing toxic build up of soluble ion

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54
Q

How do Molluscs use iron oxide

A

Limpet teeth- goethite and chiton teeth- mix of lepidocrite and magnetite- crystalline iron oxide mineral forms hard cutting edge to teeth used to scrape algae from rocks

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55
Q

Describe mother of pearl
and what is the structure called
how effective

A

layer in many shells composed of tablet blocks of aragonite (CaCO3) that are apporx. 0.5um thick, sandwiched between 30nm sheets of organic protein- polysaccharide matrix. called NACRE
effective in resisting crack propagation- 3000x stronger than pure aragonite

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56
Q

Bone

why known as a living material

A

Organic matrix with organized crystals of hydroxyapatite
organic matrix- fibrils of collagen (protein)
Responds to internal and external signs and is continually growing, dissolving and remodelling. Composition depends on animal and where in body.

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57
Q

How do living organisms employ method to control formation if inorganic materials?

A

Intarcellular (compartments within cells)
Intercellular (spaces between closely packed cells)
extracellular (Within insoluble macromolecular framework)

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58
Q

2 main processes of biomineralization

A
  1. Boundary organized biomineralization

2. Organic matrix-mediated biomineralization

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59
Q

Define solubility of an inorganic salt

A

The amount (moles/ mass) of a pure solid that will dissolve in a litre of solvent at a given temperature

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60
Q

When does dissolution occur

A

when the free energy required to disrupt the lattice bonding is smaller than the free energy released in the formation of aqueous species

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61
Q

Define the solubility product

A

an equib constant- related to the solubility on an IO salt- generally ionic solid containing monovalent ions
Ksp = aM+*aM- (activity product)
a is the effective conc.s (activities) of ions in sol. in equib. with the solid phase

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62
Q

define saturation

A

state of equib. with the undissolved solute in equib with the dissolved solute

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63
Q

define equib.

A

dissolution = precipitation

saturated solution

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64
Q

Define supersaturation

A

if the actual conc. (activity product) is higher that the solubility product, then precipitation will occur until Ksp = actual conc.
determination difficult in biological fluids as presence of many organic molecules

indicates how much solution is out of equib. and is a measure of TDY driving force for inorganic precipitation

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65
Q

Explain Ostwald Ripening

A

Sol. not contant but increases with diminishing crystal size- because small crystals have high surface to volume ration. This means that the surface energy begins to outweigh the lattice energy. Effect in mixture of crystal sizes- smaller crystals are dissolved but larger ones grow.

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66
Q

define SS by equation

A

ratio of the activity product to the equib. sol. product
= (aM+*aM-)/Ksp
at equib. =1
if greater than 1 then material will precipitate from solution

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67
Q

The TDY driving force is … + equation

A

the difference in chemical potential between a supersaturated solution and a solution in equib. with solid
delta u = kTlnS

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68
Q

Define nucleation

A

when SS>1 sol in state of SS, solid phase can begin to precipitate

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69
Q

define homogeneous nucleation

A

spontaneous formation of nuclei in solution- not realistic given that most solutions contain contaminants such as dust

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70
Q

define heterogeneous nucleation

A

formation of nucleus on existing surface
surface energy- interfacial energy term (delta GI) is decreased- overall energy demand for nucleation is decreased. therefore occurs at lower SS than HOMO

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71
Q

Explain Epitaxy

A

growth of IO crystalline phase onto pre-existing substrate also crystalline- can direct the orientation of the new phase so both phases are crystallographic ally oriented.
requires high level of lattice matching

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72
Q

Explain classical crystal growth theory

A

adsorption of solute atoms, molecules, ions onto crystal face- unit then able to move freely in two dimensions until reaches step/ kink and integrates into crystal lattice. Step and kink sites have higher binding energies than a flat face so new units will keep adding to these sites until one layer is completed.

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73
Q

Explain evolution of new layer in CC growth

A

once one face completed- generation of new nucleation site- requires more energy- evolution of new layers depends linearly on SS. Higher S enables nucleation of new layers.
V high SS can lead to Polynucleation

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74
Q

What is the morphology of a crystal dependent on

A

surface energy of different crystal faces which in term are dependent on the growth environment.

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75
Q

Rate of growth of a crystal face related to

A

surface energy- faces that have high energy will grow quickly and disappear whereas faces with low energy will grow slowly and dominate the final shape

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76
Q

Why do different crystal faces have different energies

A

Different surface atoms
different unsaturated/ dangling bonds
different polarity, hydrophilicity and solvent interactions

Some additives can absorb selectively onto certain faces- this slows down/ prevents growth in that direction

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77
Q

Non classical crystal growth

A

systems go via intermediate polymorphs
for SS for a less soluble crystalline polymorph, the eqib sol product will be lower
involves aggregation of primary nanoparticles

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78
Q

Different polymorphs of Calcium Carbonate from soluble (TDY stable)–> less soluble

A

Amorphous CaCO3
Varerite
Aragonite
Calcite

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79
Q

On TDY grounds expect crystalline phase to be the one that precipitates

A

SS is higher than non classical

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80
Q

Kinetic control of crystal growth

A

not lowest energy product (TDY) - kinetic control
formation of a less stable polymorph
trap phases

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81
Q

TDY control most important at

Kinetic at

A

low SS

High SS –> intermediate phaes

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82
Q

Kinetic effect on Crystal growth

A

High SS therefore big driving force for precipitation- the kinetically favoured crystal forms- intermediates first to be precipitated— results in aggregation pathways.

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83
Q

TDY pathway for Crystal growth

A

Single/ low number of nucleation events and subsequent slow growth to single crystals

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84
Q

2 different processes for aggregation

A

oriented attachment

mesocrystals

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85
Q

oriented attachment

A

primary nanoparticles self-organize to a superstructure with a common crystallographic orientation
particles then fuse together to produce a single crystal
driving force = minimization of high energy surfaces
Increase in entropy as molecules displaced that were adsorbed on the fusing surfaces

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86
Q

Mesocrystals

A

3D superstructures of nanoparticles that are crystallograhically aligned
nanoparticles remain distinct separated by organic of amorphous IO material or by porous space

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87
Q

What happens if surfaces of nanoparticles in mesocrystals are not stabilised

A

may transform into single crystals via oriented attachment

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88
Q

example of stable mesocrystal

A

Sea urchin- nanoparticles of calcite separated by amorphous material

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89
Q

Describe boundary organized mineralization

A

Living organisms create enclosed spaces which are separated from the general environment of the cell-
functions-
control shape of mineral phase
control diffusion of ions
stab minerals against dissolution or phase transformation
transporting minerals to different sites

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90
Q

Type of compartments in BOBioMin

A

Vesicles- fluid filled compartments surrounded by phospholipid bilayer or protein shell.

Or cells can join together to create sealed space where surrounding cells control the chem of inner space through diffusion- osteoblasts in bone growth

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91
Q

How do spatial boundaries control SS

A

Ion pumping- biological membranes contain sites for selective ion transport

ion complexation- binding cations with ligands such as citrate lowers SS by reducing activity

Enzymatic regulation- enzymes can control the formation of solid IO species by influencing reaction equib. or directly providing crucial ions

proton pumping- change in pH can change acid base equib of anions/ hydrolysis of metal ions.

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92
Q

Describe organic matrix- mediated BioMin

A

Insoluble macromolecular frameworks to control mineralization- function of matrix-

modification of physical properties of the material such as strength and toughness- e.g. collagen in bone

stab of minerals against dissolution or phase transformation

controlling nucleation sites or directing crystallographic orientation- lower Eact by reducing interfacial energy… organize direct nulceation

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93
Q

briefly describe sol gel chem

A

soft material synthesis, refers to hydrolysis and condensation of metal alkoxides

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94
Q

define a gel

A

non-fluid colloidal network or polymer that is expanded throughout its volume by a fluid

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95
Q

What are the 4 types of gels and their bonding

A

Metal-oxo or hydroxo polymer- Covalent bonds- extended networks

Metal complex (urea) - M complexes weakly connected by VDW or HB often viscous solutions rather than gels

Polymer complex- Organic polymers corsslinked by VDW or HB

Collodial- network or particles linked by electrostatic VDWs

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96
Q

Sol gel process

A

Formation of sol ( stable suspension of colloidal particles or polymers)

Gelation through polycondenstaion/ esterification- extended network of covalent bonds

Aging- syneresis- continued Polycondensation to solid network- contraction and expulsion of solvent pores

Drying- remove solvent

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97
Q

Sol gel process of silica

A

Hydrolysis (acid base catalysed)

Condensation- formation of siloxane bond. acid/ base catalysed

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98
Q

The structure of silica gel depends on.

A

The relative rates of hydrolysis and condensation, any factor that effects the reaction rates will affect how the gel develops

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99
Q

high pH- basic conditions- give:

Low pH- acidic conditions- give

A

colloidal, or particle gels

networks of interconnected chains

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100
Q

Rate of hydrolysis and condensation depends on-

A

sterics - hindrance by bulky groups inhibits attack by water

and inductive effects- electronic stab/destab of TS

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101
Q

Hate of hydrolysis decreases as…

A

more alkoxy groups are hydrolysed. Therefore, condensations starts to occur before hydrolysis is complete and condensation tends to occur on terminal silicons- resulting in linear products- eventually tangle and crosslink to form gel

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102
Q

the rate of hydrolysis decreases as…

A

more alkoxy groups are hydrolysed. Therefore, condensations starts to occur before hydrolysis is complete and condensation tends to occur on terminal silicons- resulting in linear products- eventually tangle and crosslink to form gel

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103
Q

Acid Catalysed summary

A

Positive TS- Stab by EDGs - Progressive hydrolysis steps slower- condensation on terminal silicons- linear products- network gels

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104
Q

the rate of hydrolysis increases as…

A

more alkoxy groups are hydrolysed

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105
Q

base catalysed summary

A

Negativ TS- stab by EWGs- progressive hydrolysis steps faster- multiple condensation steps- particle gels

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106
Q

other factors affecting rates in sol gel

A

Solvent- allows immiscible reactions
water- small = slow since water is a reactant… large = slow due to dilution… highest rate at intermediate point
substituents- inductive and steric effects

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107
Q

how to form an xerogel

A

fast and uncontrolled drying

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108
Q

how to form an aerogel

A

slow and controlled drying but can collapse to xerogel

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109
Q

Why is surface tension a problem in drying?

A

when put silica gel in oven to dry off solvent the water and alcohol mixture has to move through tiny gaps in the network. Capillary forces are significant and they cause gel network to collapse. Therefore, need to leave gel sealed for a while to allow syrenesis to progress- more resistant to collapse

110
Q

How do you get an open porous network

A

dry gel carefully- using supercritical fluids- decompress fluid allowing it to escape without collapsing network- aerogel

111
Q

explain crsytallization in solgel

A

final heating- dehydrate gel - remove surface silanol groups- further heating- more densification and eventually the formation of crystalline silicon dioxide phase- all porosity collapsed

112
Q

why use silica over other metals

A

they don’t have range of chem and high level of control over gel structure
other metals oxides crystallize a lot sooner
SiO2 remains amorphous to v high temps
restrict exposure to water
chelating ligands stab. against hydrolysis

113
Q

Why hydrolysis so much faster for other metal alkoxides

A

partial- charge model- electronegativity and k

114
Q

how does partial charge explain hydrolysis rates

A

TMs have much lower electronegativities than Si therefore the partial charge on the metal is higher- higher +ve charges stab the TS… TMs have higher rate of hydrolysis

115
Q

alternatives to alkoxides in solgel

problems

A

Metal chlorides, acetates, nitrate
Crystallization- might just precipitate out M salt- mixture of large particles of metal oxide product- no good when trying to make a high surface area catalyst
Hydrolysis- of aqueous cations- weakens OH bond- deprotonation can occur
change hydrolysis by addition of ligands

116
Q

The Pechini method

A

Chelator molecules- linked by covalent bonds- form much stronger network around metal ction, further stab to form something more gel like. Transesterification between glycol and citrate

form interpenetrating covalent network which is much stronger than a weak association of metal citrate complexes.

117
Q

Advantages of Pechini method

A

stays around long enough to control how the metal oxide crystallites nucleate and grow
two or more metals can be mixed homogeneously- start with homogeneous mixture

118
Q

disadvantages of Pechini method

A

Amount of organic material- pure oxide required then mixture will need heating for quite a while to remove all the carbon
little control over particle shape- normally spherical or irregularly shaped particles
sintering- heating over time causes particles to sinter together- no good for forming discrete particles

119
Q

Colloid

emulsions are a type of colloid

A

dispersion of one phase in another. Different from a suspension as the particles in the dispersed phase are 1-1000 nm in size

120
Q

how to make emulsions

stable microemulsion?

A

mix aqueous phase and organic phase and amphiphile

5-50 nm droplets

121
Q

What is the difference between an emulsion and a microemulsion

A

Emulsions are kinetically stable- surfactant is just slowing down the phase separation
Microemulsions are thermodynamically stable

122
Q

Theory behind microemulsions

what happens if precipitation reaction?

A

Collisions between reverse micelles- A and B content mix then break appart–> equib distribution of all reactants

get nanoparticles

123
Q

What factors can affect particle size in microemulsions

A

solvent- if surfactant tail reacts well with solvent it may be able to stab the particle better- restricting growth

W-value ([water]/[surfactant]

Type of surfactant and cosurfactant

reagent concentration

124
Q

what chemistry can you do inside a microemulsion

A

metals by reduction
metal oxides by coprecipitation
many others

125
Q

describe hydrothermal/ solvothermal methods

A

in a sealed vessel- bring solvents to well above their boiling point a lot of autogeneous pressure, above ambient temp (200). pressure above 1 atm
chem mostly occurs below supercritical point
many metals exhibit higher solubility and reactivity under these conditions
many solid materials can be generated in crystalline form at much lower temps

126
Q

advantages and disadvantages of solvothermal synthesis

A 
Ads:
low reaction temps
fast kinetics
phase purity and high crystallinity
homogeneous product
potentially environmentally benign

Disads:
expensive autoclaves with Teflon liners
safety
closed system

127
Q

Types of templating and what is it

microemulsion synthesis is a type

A

use of solid templates and directed growth of minerals by soluble additives

infilling- remove by dissolving or burning

surface coating

direct replication- template becomes part of new material

128
Q

types of template

A

hard template- silica spheres, wood

soft template- gel, self-assembled surfactant phase

Biotemplating- use of material of biological origin- biomass

129
Q

How does templating work

A

Hard-provides surface for nucleation and growth- best will have surface chem that facilitates metal adsorption

soft- growing/precipitating an inorganic mineral inside an organic gel

130
Q

rule for filling 3d orbitals

A

3d orbitals are higher in energy than the 4s in neutral atoms but lower in E in cations

131
Q

Describe ML bonding

A

L is a lewis base- e pari donated to the metal- stronger base = stronger bond

132
Q

Paulings electronegativity principle

A

charge on any one atom in a species always must be less than 1- therefore Cr3+, Al3+, Fe3+ are all acidic in solution- nick explained loss of hydrogen to you

133
Q

What is the Tolman cone angle

A

Angle from M to outer shell of L

134
Q

What is a hard metal

A

Bonding mainly electrostatic
polarizing
H+, Li+, Na+, K+

135
Q

Soft Metals

A

Not v polarizing
0 ox state
bonding mainly covalent- good orbital overlapCu2+, Ag+, Au+, Pd2+

136
Q

Hard donor

A

Electronegative- not easily polarised F, O, N, Cl

ligands are either sigma or pi donors

137
Q

Soft donor

A

Medium electronegativity, easily polarized, alkenes, I, S, P, H, OH-
pi acceptors

138
Q

Example of ambidentate ligand

A

NCS- / -NCS

139
Q

Examples of square planar

A 
d8- Ni2+ with strong field (pi acceptor) ligands- [Ni(CH)4] 
Pd and Pt2+ with weak field ligands- Cl-
Rh(1)
Ir(1)
Au(3)
always low spin diamagnetic
imposed by macrocycles
140
Q

Chelate effect

A

Polydentate ligands found to be more TDY stable- mainly entropy effect- often additional stabilisation is gained by enthalpy changes

141
Q

macrocyclic effect

A

Chelate effect enhanced by cyclic conformation of ligand
crown ether
porphyrins

142
Q

How do you prepare Macrocycles

A

metal template reactions- components of a ligand only assemble to form ligand in presence of a metal ion
self assembly of metal cages

143
Q

What influences the colour of a compound

A

The size of the crystal field splitting

144
Q

Is blue light high energy?

A

Yes- red light is low energy

145
Q

factors that influence magnitude of splitting

A

No of ligands already dealt with
distance of L from M (larger for greater charge)
Size of d orbitals 5d>4d
Nature of ligands

146
Q

4 examples of pi donor ligands

LOW FIELD SMALL SPLITTING

A

I-
Br-
SCN-
Cl-

147
Q

4 examples of sigma donor ligands

MEDIUM FIELD MEDIUM SPLITTING

A

F-
H2O
OH-
NCS-

148
Q

3 examples of pi acceptor ligands

HIGH FIELD LARGE SPLITTING

A

py-NH3
CN-
CO

149
Q

special about d5

A

NO LFSE

150
Q

Why is ligand field theory better than CFT

A

Disregards idea of point charges- takes into account covalency- applies MO theory

151
Q

Sigma donor ligand

A

L-M through sigma bond
H-
NH3 (Sp3 lp)
no nodal surface containing bond

152
Q

Pi donor ligand

A

one nodal surface containing internuclear ML bond
Ligand pz orbital filled with a lp
X-, NH2-, O2-
decrease splitting (pi bases)

153
Q

Pi acceptor ligands

A 
CN-, CNR, CO, NO+
increase splitting (pi acids)
154
Q

Kinetic liability

A

result of the ready availability of low energy decomposition routes
presence of partially filled valence electrons
coordinative unsaturation
OCTET rule
18 ELECTRON RULE

155
Q

Octet rule and the 18 e rule state that

A

stability is connected with the presence is a complete valence shell

156
Q

explain reactivity of O2 towards M

A

Low lying empty orbitals

presence of non bonding pairs of electrons

157
Q

What does the rate of hydrolysis depend on- PIko

A

Nu- attack on the organometal by H2O- facilitated by presence of low lying orbitals on M- rate also dependent on MC bond polarity

158
Q

1 e donor ligands

A

H, Cl, CN, COMe, Bent NO, OR

consider bridging ligands e.g. CO to provide 1 e to each metal

159
Q

2 e donor ligands

A

CO, PR3, P(OR3), CNR, N2, O2, C2H4

160
Q

how can you classify sigma donors

A

by hybridisation

161
Q

2 types of synergic bonding

A

pi donor/ pi acceptor

sigma donor/ pi acceptor

162
Q

factors affecting v(CO)

A

Bonding mode of CO ligand- free, terminal, semi-bridging, bridging, capping

charge on the complex- increasing -ve charge on a complex increases the electron density- expansion of d orbitals (more electron rich)

other donor ligands

symmetry of the molecule

163
Q

2 bonding models for ethane and M

A

Chatt Dewar Duncanson CDD model
Metallacyclopropane MCP model
Sp2 –> Sp3

164
Q

Oxidation addition

A

Neutral ligand adds to M and oxidzes metal by 2e-

reductive elimination does the opposite

165
Q

1,1/2 migratory insertion

beta hydride elimination

A

No change in ox state

166
Q

Two methods of synthesis of Binary Carbonyls

A

I) Direct reaction of M with CO- only applies to [Fe(CO)5] and [Ni(CO)4]
2) reductive carbonylation- remaining carbonyls are prepared by high temp reduction of metal salt under CO pressure
100-200c, 200-300atm, reductants H2, Na, Mg, Al, CO
3) photolysis or thermolysis
4) Metal- atom synthesis- special equipment- condensation of metal vapour with CO at very low tempertures

167
Q

Reactivity of Metal Carbonyls

A

1) sub. reactions
2) Metal carbonyl halides
3) Metal carbonyl anions or carbonyl metallates

168
Q

Why are tetrahedral complexes always high spin

A

CFS is small and therefore pairing energy is always higher

169
Q

Why does Jahn teller distortion occur

A

to remove degeneracy of electronic states

170
Q

delta G =

A

-nFE

171
Q

If E is +ve

A

The reaction as written is spontaneous

172
Q

if E is -ve

A

The reverse reaction is spontaneous

173
Q

E of reducing agents

A

-ve and magnitude correlates to how strong an agent

174
Q

E of oxidising agents

A

+ve and magnitude correlates

175
Q

How to construct a latimer diagram

A

Most highly oxidised species on the RHS
can add branches to determine which oxidation is more favourable
conventional to construct for the two extremes of pH

176
Q

What alters delta G/ redox potentials

A

Conc
temp
other reagents which are not inert
pH

177
Q

Interpreting a frost diagram- high up species on LHS and RHS

A

High are oxidising to LHS
High are reducing to RHS
strength can be determined by steepness of slope
lowest species are the final thermodynamic product

178
Q

How do ligands effect stability

A

Strong field CN- = greater therefore greater stability- stronger bond than with weak field e.g. H2O as pi backbonding

179
Q

High Ox states

how to stab

A

v strong oxidising agents and highly susceptible to reduction

complexed by other species which are even stronger oxidising agents e.g. O2-, F-

180
Q

Describe a solid state reaction and give an example

A

Direct reaction of a mixture of solid starting materials
most widely used method for synthesis of organic solids
high temps, above 900C
long reaction times hours-days
intermediate regrinding

SrCO3 + MnO2 –> SrMnO3 + CO2

Easy to perform and mostly effective

Disads- high temps and long reaction times
imputities
volatile products
some phases only stable at low temperatures

181
Q

Synthesis of YBa2Cu3O(7-x)

A 
Need materials in correct ratio otherwise cannot remove impurities
930C
12 hr air/O2 *2
regrind
cooled
anneal, 400C, O2
182
Q

LiCoO2 battery material synthesis

A 
1:1
1/2Li2CO3 + 1/2Co2O3 --> LiCoO2 + 1/2CO2
700C
24 hrs
intermediate regrind

if use high temp may lose Li through volatility of LiO2

183
Q

LiFePO4 Battery material synthesis

A 
1:1:1
Fe2+
Heat treatment under N2
700C
24 hrs
intermediate regrind

1/2Li2CO3 + 1/2Fe2O3 + H3PO4 + 0.25C –> LiFePO4 +1.5H2O + 0.75CO2

184
Q

Solid State reaction- why need high temp and long reaction times

A

Formation of product nuclei is difficult- distances- reorganisation

growth of product layer may be even more difficult

185
Q

Solid state reaction- 3 possibilities for RDS

A

Transport of matter to the reaction interface
reaction at surface/ interface
transfer of matter away from reaction interface

slow kinetics can lead to metastable products

186
Q

Alternative synthesis methods to solid state

A

Coprecipitation- lower reaction temp- not widely used

sol-gel synthesis- lower temp- synthesis of new phases possible- capacity to form films or fibres and control particle size and shape BUT high cost, longer processing times, alkoxides in diff hydrolysis rates

Hydrothermal synthesis

mechanochemical synthesis - ball milling- cannot be used for all

187
Q

Hydrothermal synthesis

A

Utilises water under pressure and at temps above boiling point to speed up solid state reactions 100-200C
reactions in autoclaves
for compounds not stab at high temps

188
Q

Chimie Douce reactions

A 
lower reaction temps that SS
intercalation
deintercalation
ion exchange
for compounds not stable at high temps
189
Q

Cation intercalation

A

insertion of cations into 1/2/3 D channels

insertion into 1D –> Solids with Rutile structure: MoO2 –> LiMoO2 (Mo3+)

chemical/ electrochemical methods

190
Q

Anion intercalation

A

the graph with metastable states with lower activation energies

191
Q

Why is metal stoichiometry important

A

if incorrect weights used then impurities will result

192
Q

Describe NaCL (AX) structure

A

CCP
Cations (A) occupy ALL oct. holes
TiO, VO (metallic conductors)
NiO (insulator)

193
Q

NiAs (AX)

A

HCP
Cations (A) occupy ALL oct. holes
large anions

194
Q

Rutile structure (AX2)

A

HCP
Cations (A) occupy 1/2 oct. holes

remove alternate of octahedral cations within same layer

distorts slightly from HCP therefore UC is tetragonal

MX6 share edges to form infinite chains- link together to form 3D network

Os are 3 coordinate

195
Q

CdI2 (AX2)

A

Same as Rutile but remove alternate layers of oct. cations

layered HCP

M2+ iodides/ bromides/ chlorides/ OH-/ sulphides

196
Q

CdCl2

A

Layered structure CCP

M2+ chlorides/ bromides/ iodides

197
Q

AX3 (ReO3)

A

Primitive cubic lattice

198
Q

Perovskite ABX3 CaTiO3

A

A cation large and of low charge 12 coordinate e.g. Ca2+

B cation 6 coordinate - small high charge Ti4+

sizes of A and B determine whether will form and distortion from cubic symmetry –> hexagonal perovskites if t>1.06

superconductors
ionic and electronic conductor (NaxWO3)

199
Q

Tolerance factor

A
  1. 9-1 usually cubic

0. 75-0.9 usually lower symmetry orthorhombic

200
Q

Ilmenite

A

ABO3
A and B are both small (FeTiO3)

HCP, Fe and Ti occupying 2/3 of oct. holes in alternate layers

201
Q

Ruddlesden Popper Phases

A

Perovskites and rock salt type intergrowths

layer separated by rock salt units

202
Q

Octahedral and tetrahedral sites in a CCP UC

A

CCP=FCC
4 atoms in UC, between atoms-
4 octahedral holes
8 tetrahedral holes

203
Q

AB2O4

A

Spinel
FCC/CCP

1/2 oct. holes filled
1/8 tetra. holes filled

204
Q

Normal Spinel

A

A in tetra holes
B in oct holes
MgAl2O4

205
Q

Inverse Spinel

A

ABAO4
B in tetra holes
A + B in oct sites

206
Q

What influences which structure type a given structure will adopt

A

1) Attractive and repulsive forces, Attractive maximised by high CN but CN limited by Size of Cations and anions
2) Radius Ratio- limiting ratio r+/r-
3) Shared edges and faces- unfavourable, especially for cations with high charge and low CN
4) Non-ionic effects

207
Q

5 Non-Ionic effects on structure

A

1) Covalency- favours lower CN as O overlap more efficient when cations and anions are closer
2) VDW- higher CN more polarisable ions
3) M-M bonding- stab. strucutres
4) CFEffects- CFSE can influence structure- dictates ordering of AB between tet and oct sites- e.g. spinels
5) H bonding- stab structures- layered- e.g. CdI2

208
Q

How to work out if would prefer normal or inverse spinel

A

Work out CFSE for delta O and T using splitting diagram and dn configuration
delta T is 4/9 of delta O
which ever bigger is more stable
then also look at cation sizes

209
Q

Jahn teller distortions

A

CFEffects

1st row TM difluorides adopt the rutile structure which allows distortions from octahedral geometry

210
Q

Oxo-cations and Oxo-anions

A

Mononuclear oxo complexes- high oxid states are stab by the )2- ligand
low oxid states have simple aqua ions
strong polarisation of e- density on water by high ox state cations- increases Brinsted acidity of H2) and OH-

vanadyl phosphates- uses as catalysts

211
Q

Define Polyoxometallates

A

an oxoanion which contains more than one metal atom
formed by condensation of mononuclear oxoanions at low pH
only corner sharing tetrahedral observed

focusing on Mo- can control nuclearity of oxoanions by precisely adjusting the pH- connected by O bridges

212
Q

Isopolyoxometallates

A

where all metals are the same

213
Q

Heteropolyoxometallates

A

Mixing metals/ inc. non metals in anions- kegging/ Dawson structure

214
Q

Properties and applications of polyoxometallates

A

High bronsted acidity- use as acid catalysts

redox activity

215
Q

Discrete M-M bonded clusters

A

Low Ox S 2/3rd TM chlorides

216
Q

Extended Lattice structures M-M bonding

A

Early 2/3rd TM chlorides

higher multiple bonds formed y overlap of identical d orbitals

217
Q

How to determine Metal Bond Order

A

1) Calculate the dn configuration of the metal cations present (n)
2) Determine the number of M-M connections within the cluster (b)
3) Bond Order - (n*No. of M atoms)/ 2b

DOES NOT APPLY if pi acceptor ligands are coordinated to M

218
Q

Examples of extended Lattice Chlorides

A

1) Sc7CL10- single and multiple chains of SC atoms

2) ZrCL graphitic hexagonal nets of Zr sandwiched between bridging Cl layers

219
Q

Why is TiO a metal whereas NiO is an insulator?

A

Metallic character of TiO associated with direct MM bonding that extends over the whole of the material- not present in NiO-
orientation of t2g and eg
Ti2+ t2g patially filled- direct overlap of dxy orbitals- MM bonding that extends all over the structure diagonal

Ni2+ t2g6 eg2 partially filled eg orbitals can only interact indirectly via O2p orbitals so no direct MM bonding square dx2-y2

220
Q

Colour differences in Cu, Ag, Au

A

chanfe in relative energies of the d and s orbitals in the atoms
Ag- Ef larger
Au Ef smaller
Cu corresponds to adsorption in visible region

221
Q

Difference between single and powder crystal XDR

A

single for determination of structure- powder for phase identification, purity, quantitative analysis, estimation of particle size

222
Q

All crystalline structures posses

A

Translational symmetry

223
Q

How many crystal systems?

A

7

224
Q

Triclinic

A

No restrictions

none

225
Q

Monoclinic

A

alpha=gamma=90

1, 2 fold axis

226
Q

Orthorhombic

A

alpha=beta=gamma=90

3, perpendicular 2 fold axis

227
Q

Tetragonal

A

a=b
alpha=beta=gamma=90
4 fold rotation axis
1, 4 fold axis

228
Q

Cubic

A

a=b=c
alpha=beta=gamma
4, 3 fold axes in tetr. arrangement

229
Q

trigonal

A

a=b=c

1, 3 fold axis

230
Q

Hexagonal

A

a=b
alpha=beta=90
gamma=120
1, 6 fold axis

231
Q

fractional coordinates

A

dimensionless

allow direct compariaon of positions in UCs

232
Q

Glide planes

A

Mirror + translation

233
Q

Screw axes

A

Rotation + translation

234
Q

Body centred- I

A

2 LP/ UC

x,y,z) (x+1/2,y+1/2,z+1/2

235
Q

Face centred- F

A

4LP/ UC

236
Q

Base Centred- C, A or B

A

2 LP/ UC
(x,y,z)
(x+1/2,y+1/2, z)

237
Q

define a space group

A

collection of symmetry elements in a crystal structure- because symmetry operations can only be combined in certain ways
e.g. P1 = Primitive lattice type, only symmetry element is an inversion centre

238
Q

define d spacing

A

inter-planar distance, one members of the set must pass through the origin of the UC

239
Q

Miller indicies

A

reciprocals of the fractional coordinates

240
Q

Diffraction of light

how works with crystalline solids

A

if wavelength smaller than diffraction slit then no change but if similar then appears as if new wave emanating from a point in the centre of the slit (diffraction grating)
X-Rays = 0.01-
crystalline solids are composed of planes with interplanar d spacings of 1-2A upwards therefore crystal can act as diffraction grating for X-Rays

241
Q

1 A =

A

1*10^-10 m

242
Q

Bragg’s Law

A

For constructive interference to occur beams must be in phase therefore the path length diff. must be a whole number

243
Q

There is one peak for..

A

every set of planes in the crystal lattice

244
Q

Cubic systems with peaks (h00) have multiplicity of

A

6

6 planes have the same d spacing and peak position

245
Q

Primitive hkl

A

all values observed

246
Q

Face hkl

A

either all odd or all even observed

247
Q

I (body) h+k+l

A

Odd numbers are absent

248
Q

Base (c) h+k

A

Odd numbers are absent

249
Q

Systematic absences

A

can distinguish lattice types by identifying hkl reflections that are missing from the diffraction pattern

space groups may also lead to additional systematic absences

250
Q

How do you report a structure

A

Space Group
a=
where are anions and cations?

251
Q

Z=

A

no. of empirical formula units in UC = lattice points

252
Q

Atomic scattering factor f =

A

quantitative measure of how effectively an atom scatters X-rays
as f decreases (overall intensity)- 2theta increases
f= no of electrons in the atom/ ion

253
Q

Structure factor

A

Resultant of the waves scattered by ALL of the atoms in the unit cell in the 2theta direction
every atom contributes to every peak- not like in spec

254
Q

Intensity of peak hkl is proportional to

A

modulus of F ^2

multiplicity also determines peak intensity

255
Q

modulus of F

A

= square root of (A^2 + B^2)
angles in radians NOT degrees

if = 0 then the peak hkl has no intensity/ absent

256
Q

Electron density

A

from structure factor

intensities give us the exact atom locations

257
Q

density=

A

mass/ volume
Mass of UC/ UC volume
VOLUME convert A to cm (*10^-8)

258
Q

Mass of UC=

A

sum of (ne * RMMe)/ NA

259
Q

Interatomic distances=

A

a*sqrt (deltax^2 +deltay^2 +deltaz^2)

260
Q

In order for the diffraction patterns from two different crystalline materials to be identical they must have exactly the same:

A

UC (lattice) parameters = Peak positions
UC centring and space group = pattern of systematic absences
Electron density distribution = intensities

as the odds of this are extremely small, PXRD can be confidently used for the identification (fingerprinting) of crystalline phases

261
Q

Determination of purity

A

Qualitative analysis

262
Q

determination of crystal size

A

for constructive interference to occur the parts o beams a and b that reach detector must be completely in phase- if slightly out complete destructive interference

263
Q

When would you see intensity either side of Bragg’s diffraction angle

A

Crystallite v small- less than 1um in size, then not enough planes in set so some intensity will be either side of Bragg diffraction angle 2theta- smaller crystallites give broader peaks
FWHM

264
Q

Beta tilde, peak broadening =

A

FWHMsmall- FWHMlarge

265
Q

instrumental effects

A

intrinsic peak width
upper size limit for crystallites beyond which no measurable particle size broadening will occur
typically around 1um for a lab diffractometer

266
Q

Scherrer equation

A

relates crystal size peak broadening to mean crystallite dimension=
tilde = (Crystallite shape constant*wavelength)/ (Peak broadening *tilde-particle size cos theta)

267
Q

The Rietveld method

A

calculate the powder diffraction pattern of a model crystal structure and minimise the diff between that and the raw diffraction pattern

268
Q

WHat is needed to produce silica via sol gel route

A

Acid/base catalyst
Alcohol to make sure mixes
water to hydrolyse

269
Q

Structure of silica gels produced under acidic conditions- how do acidic conditions lead to this structure?

A

Linear chains and network gels
Build up of +ve charge around TS
+ve charge stab by EDGs more than OR/H
As hydrolysis progresses there are more OH so the rate slows down
Condensation starts before hydrolysis is complete
condensation tends to occur on terminal silanol groups
leads to linear siloxanes which eventually crosslink to give network gel

270
Q

Why is hydrolysis dangerous

A

Exothermic- energy management is a concern for the actual reaction.

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