2017 PP Flashcards
Cubic Crystal System
a=b=c alpha=beta=gamma=90degrees
Orthorhombic system
a does not = b does not = c BUT alpha=beta=gamma=90degrees
Multiplicity in Orthorhomic systems
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.
Describe an octahedral splitting diagram
Split into 3 lower degenerate t2g d orbitals and 2 higher eg orbitals- separated by energy delta O (^2)
What effects delta O/T
Identity of ligand- same order of splitting is followed regardless of identity of metal ion
Examples of strong field ligands that give rise to high energy transitions
py-NH3 CN- CO (pi acceptors)
Examples of weak field ligands that give rise to low energy transitions
I- Br- SCN- CL- (pi donors)
Ligand field strength also depends on- that CFT doesn’t explain .. explain effect
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
Ligand field stab E (CFSE)
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
Pairing energy
If delta O/T is smaller than P
Coulombic repulsion when pair electrons
Weak field case
When is Octa complex low spin and high spin
3d4 configuration is low spin if CF is strong but high spin if CF is weak- same applies to 3d5,6,7
Deviation of hydration enthalpies from straight line arises from
additional LFSE in oct. complexes formed from the free ion
Describe tetra splitting diagram:
explain why Delta O > delta T
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
What favours Square Planar complexes
d8, strong CF- tendency enhanced for 4d/4d metals because of larger size and greater ease of electron pairing
Jahn Teller effect
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
Jahn Teller possible for?
Oct= d1,2,4 low spin….d5,6,7 high spin
Tetra: d1,,3,4,6,8,9
Pi donor ligands
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
Pi Acceptor Ligand
Empty Pi Os Pi Acid vacant anti bonding Os (LUMO) higher in energy than M d Os Increase delta O py-NH3, CN-, CO
Microstate
Different ways in which electrons can occupy the orbitals specified in the configuration
Terms
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)…
Hund’s Rule
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
Selection rules
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
Chatt Dewar Duncanson model vs Metallacyclopropane model
draw
Perovskite structure
ABO3
A= large CN= 12
B CN= 6
Ilmenite Structure
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
Normal spinel
A in Tetra holes
B in Octa holes
1/2 oct holes filled
1/8 tetra holes filled
inverse spinel
B in tetra sites
A+B in octa sites
Biofuels
Reduce dependence on oil, gas, coal
competition with food production, changing land use, extra fertilizers/ pesticides
Sustainable chem
Environment, energy, health, economics
12 principles Green Chem
- Better to prevent waste than to treat and clean up
- synthetic methods designed to use all materials for product
- Synthetic methodologies little or no toxicity to human health and environment
- chem products designed to preserve efficacy of function while reducing toxicity
- use of auxiliary substances made unnecessary
- E minimized- synthetic methods at ambient temp and pressure
- chemical products designed so at end of function do not persist in environment
- substances in chem processes should be chosen to minimize potential for chem accidents
Atom economy- design factor of chem process- additional consideration to yield, ease of product isolation and purity requirements
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
Friedel-Crafts reactions
Zeolite
Serious safety concerns
catalytic
Considerations for Biofuels/plastics
life cycle
Recycling
issues
element may be highly dispersed
alloys
contamination during recycling
Element concerns
companion metals
Energy- reduction in chem processes
alternative energy sources
Ultrasoniction microwave reactors photochemistry electrochemistry hydrothermal/solvothermal
Risk and Hazard
major consideration in Green Chem
how to reduce risk
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
Chitin
Skeletal structure made purely from organic material
polysaccharide
requires a lot of energy to make
Problems with organic skeletal tissue/ inorganic
not very hard BUT tough and flexible…. hard but brittle
ideal solution if a composite
Composite + example
Organic matrix filled with inorganic mineral
Crab shell- Chitin + CaCO3
tough and flexible and hard
main functions of biominerals
Protection, motion, cutting grinding, buoyancy, optical/magnetic/gravity sensing/ storage
mostly crystalline
Define a polymorph
give example
Different crystalline structures of the same material
CaCO3
Two most stable polymorphs of CaCO3
Calcite and aragonite and they are the most common
What are bones and teeth made out of
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
Amorphous
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
Describe Silica and why under ambient conditions is it amorphous
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
Diatom
Living organism that uses Silica to make shells
Why does grass incorporate silica into its structure
uses in leaves but also in husks around the seeds to make them less palatable to a hungry animal
Anisotropic
Crystalline materials have distinct fracture planes
Isotropic
Amorphous, disordered- do distinct directions in material- easier to mould into certain shapes
Uses of Iron Oxides
Magnetotactic bacteria- mixed valence iron oxide- magnetite (FeO4) allow them to navigate using Earth’s magnetic field
Ox states in Magnetite
Fe3+ Ferric ion
Fe2+ Ferrous ion
Purpose of Ferritin
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
How do Molluscs use iron oxide
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
Describe mother of pearl
and what is the structure called
how effective
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
Bone
why known as a living material
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.
How do living organisms employ method to control formation if inorganic materials?
Intarcellular (compartments within cells)
Intercellular (spaces between closely packed cells)
extracellular (Within insoluble macromolecular framework)
2 main processes of biomineralization
- Boundary organized biomineralization
2. Organic matrix-mediated biomineralization
Define solubility of an inorganic salt
The amount (moles/ mass) of a pure solid that will dissolve in a litre of solvent at a given temperature
When does dissolution occur
when the free energy required to disrupt the lattice bonding is smaller than the free energy released in the formation of aqueous species
Define the solubility product
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
define saturation
state of equib. with the undissolved solute in equib with the dissolved solute
define equib.
dissolution = precipitation
saturated solution
Define supersaturation
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
Explain Ostwald Ripening
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.
define SS by equation
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
The TDY driving force is … + equation
the difference in chemical potential between a supersaturated solution and a solution in equib. with solid
delta u = kTlnS
Define nucleation
when SS>1 sol in state of SS, solid phase can begin to precipitate
define homogeneous nucleation
spontaneous formation of nuclei in solution- not realistic given that most solutions contain contaminants such as dust
define heterogeneous nucleation
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
Explain Epitaxy
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
Explain classical crystal growth theory
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.
Explain evolution of new layer in CC growth
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
What is the morphology of a crystal dependent on
surface energy of different crystal faces which in term are dependent on the growth environment.
Rate of growth of a crystal face related to
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
Why do different crystal faces have different energies
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
Non classical crystal growth
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
Different polymorphs of Calcium Carbonate from soluble (TDY stable)–> less soluble
Amorphous CaCO3
Varerite
Aragonite
Calcite
On TDY grounds expect crystalline phase to be the one that precipitates
SS is higher than non classical
Kinetic control of crystal growth
not lowest energy product (TDY) - kinetic control
formation of a less stable polymorph
trap phases
TDY control most important at
Kinetic at
low SS
High SS –> intermediate phaes
Kinetic effect on Crystal growth
High SS therefore big driving force for precipitation- the kinetically favoured crystal forms- intermediates first to be precipitated— results in aggregation pathways.
TDY pathway for Crystal growth
Single/ low number of nucleation events and subsequent slow growth to single crystals
2 different processes for aggregation
oriented attachment
mesocrystals
oriented attachment
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
Mesocrystals
3D superstructures of nanoparticles that are crystallograhically aligned
nanoparticles remain distinct separated by organic of amorphous IO material or by porous space
What happens if surfaces of nanoparticles in mesocrystals are not stabilised
may transform into single crystals via oriented attachment
example of stable mesocrystal
Sea urchin- nanoparticles of calcite separated by amorphous material
Describe boundary organized mineralization
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
Type of compartments in BOBioMin
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
How do spatial boundaries control SS
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.
Describe organic matrix- mediated BioMin
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
briefly describe sol gel chem
soft material synthesis, refers to hydrolysis and condensation of metal alkoxides
define a gel
non-fluid colloidal network or polymer that is expanded throughout its volume by a fluid
What are the 4 types of gels and their bonding
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
Sol gel process
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
Sol gel process of silica
Hydrolysis (acid base catalysed)
Condensation- formation of siloxane bond. acid/ base catalysed
The structure of silica gel depends on.
The relative rates of hydrolysis and condensation, any factor that effects the reaction rates will affect how the gel develops
high pH- basic conditions- give:
Low pH- acidic conditions- give
colloidal, or particle gels
networks of interconnected chains
Rate of hydrolysis and condensation depends on-
sterics - hindrance by bulky groups inhibits attack by water
and inductive effects- electronic stab/destab of TS
Hate of hydrolysis decreases as…
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
the rate of hydrolysis decreases as…
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
Acid Catalysed summary
Positive TS- Stab by EDGs - Progressive hydrolysis steps slower- condensation on terminal silicons- linear products- network gels
the rate of hydrolysis increases as…
more alkoxy groups are hydrolysed
base catalysed summary
Negativ TS- stab by EWGs- progressive hydrolysis steps faster- multiple condensation steps- particle gels
other factors affecting rates in sol gel
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
how to form an xerogel
fast and uncontrolled drying
how to form an aerogel
slow and controlled drying but can collapse to xerogel
Why is surface tension a problem in drying?
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
How do you get an open porous network
dry gel carefully- using supercritical fluids- decompress fluid allowing it to escape without collapsing network- aerogel
explain crsytallization in solgel
final heating- dehydrate gel - remove surface silanol groups- further heating- more densification and eventually the formation of crystalline silicon dioxide phase- all porosity collapsed
why use silica over other metals
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
Why hydrolysis so much faster for other metal alkoxides
partial- charge model- electronegativity and k
how does partial charge explain hydrolysis rates
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
alternatives to alkoxides in solgel
problems
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
The Pechini method
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.
Advantages of Pechini method
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
disadvantages of Pechini method
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
Colloid
emulsions are a type of colloid
dispersion of one phase in another. Different from a suspension as the particles in the dispersed phase are 1-1000 nm in size
how to make emulsions
stable microemulsion?
mix aqueous phase and organic phase and amphiphile
5-50 nm droplets
What is the difference between an emulsion and a microemulsion
Emulsions are kinetically stable- surfactant is just slowing down the phase separation
Microemulsions are thermodynamically stable
Theory behind microemulsions
what happens if precipitation reaction?
Collisions between reverse micelles- A and B content mix then break appart–> equib distribution of all reactants
get nanoparticles
What factors can affect particle size in microemulsions
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
what chemistry can you do inside a microemulsion
metals by reduction
metal oxides by coprecipitation
many others
describe hydrothermal/ solvothermal methods
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
advantages and disadvantages of solvothermal synthesis
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
Types of templating and what is it
microemulsion synthesis is a type
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
types of template
hard template- silica spheres, wood
soft template- gel, self-assembled surfactant phase
Biotemplating- use of material of biological origin- biomass
How does templating work
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
rule for filling 3d orbitals
3d orbitals are higher in energy than the 4s in neutral atoms but lower in E in cations
Describe ML bonding
L is a lewis base- e pari donated to the metal- stronger base = stronger bond
Paulings electronegativity principle
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
What is the Tolman cone angle
Angle from M to outer shell of L
What is a hard metal
Bonding mainly electrostatic
polarizing
H+, Li+, Na+, K+
Soft Metals
Not v polarizing
0 ox state
bonding mainly covalent- good orbital overlapCu2+, Ag+, Au+, Pd2+
Hard donor
Electronegative- not easily polarised F, O, N, Cl
ligands are either sigma or pi donors
Soft donor
Medium electronegativity, easily polarized, alkenes, I, S, P, H, OH-
pi acceptors
Example of ambidentate ligand
NCS- / -NCS
Examples of square planar
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
Chelate effect
Polydentate ligands found to be more TDY stable- mainly entropy effect- often additional stabilisation is gained by enthalpy changes
macrocyclic effect
Chelate effect enhanced by cyclic conformation of ligand
crown ether
porphyrins
How do you prepare Macrocycles
metal template reactions- components of a ligand only assemble to form ligand in presence of a metal ion
self assembly of metal cages
What influences the colour of a compound
The size of the crystal field splitting
Is blue light high energy?
Yes- red light is low energy
factors that influence magnitude of splitting
No of ligands already dealt with
distance of L from M (larger for greater charge)
Size of d orbitals 5d>4d
Nature of ligands
4 examples of pi donor ligands
LOW FIELD SMALL SPLITTING
I-
Br-
SCN-
Cl-
4 examples of sigma donor ligands
MEDIUM FIELD MEDIUM SPLITTING
F-
H2O
OH-
NCS-
3 examples of pi acceptor ligands
HIGH FIELD LARGE SPLITTING
py-NH3
CN-
CO
special about d5
NO LFSE
Why is ligand field theory better than CFT
Disregards idea of point charges- takes into account covalency- applies MO theory
Sigma donor ligand
L-M through sigma bond
H-
NH3 (Sp3 lp)
no nodal surface containing bond
Pi donor ligand
one nodal surface containing internuclear ML bond
Ligand pz orbital filled with a lp
X-, NH2-, O2-
decrease splitting (pi bases)
Pi acceptor ligands
CN-, CNR, CO, NO+ increase splitting (pi acids)
Kinetic liability
result of the ready availability of low energy decomposition routes
presence of partially filled valence electrons
coordinative unsaturation
OCTET rule
18 ELECTRON RULE
Octet rule and the 18 e rule state that
stability is connected with the presence is a complete valence shell
explain reactivity of O2 towards M
Low lying empty orbitals
presence of non bonding pairs of electrons
What does the rate of hydrolysis depend on- PIko
Nu- attack on the organometal by H2O- facilitated by presence of low lying orbitals on M- rate also dependent on MC bond polarity
1 e donor ligands
H, Cl, CN, COMe, Bent NO, OR
consider bridging ligands e.g. CO to provide 1 e to each metal
2 e donor ligands
CO, PR3, P(OR3), CNR, N2, O2, C2H4
how can you classify sigma donors
by hybridisation
2 types of synergic bonding
pi donor/ pi acceptor
sigma donor/ pi acceptor
factors affecting v(CO)
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
2 bonding models for ethane and M
Chatt Dewar Duncanson CDD model
Metallacyclopropane MCP model
Sp2 –> Sp3
Oxidation addition
Neutral ligand adds to M and oxidzes metal by 2e-
reductive elimination does the opposite
1,1/2 migratory insertion
beta hydride elimination
No change in ox state
Two methods of synthesis of Binary Carbonyls
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
Reactivity of Metal Carbonyls
1) sub. reactions
2) Metal carbonyl halides
3) Metal carbonyl anions or carbonyl metallates
Why are tetrahedral complexes always high spin
CFS is small and therefore pairing energy is always higher
Why does Jahn teller distortion occur
to remove degeneracy of electronic states
delta G =
-nFE
If E is +ve
The reaction as written is spontaneous
if E is -ve
The reverse reaction is spontaneous
E of reducing agents
-ve and magnitude correlates to how strong an agent
E of oxidising agents
+ve and magnitude correlates
How to construct a latimer diagram
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
What alters delta G/ redox potentials
Conc
temp
other reagents which are not inert
pH
Interpreting a frost diagram- high up species on LHS and RHS
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
How do ligands effect stability
Strong field CN- = greater therefore greater stability- stronger bond than with weak field e.g. H2O as pi backbonding
High Ox states
how to stab
v strong oxidising agents and highly susceptible to reduction
complexed by other species which are even stronger oxidising agents e.g. O2-, F-
Describe a solid state reaction and give an example
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
Synthesis of YBa2Cu3O(7-x)
Need materials in correct ratio otherwise cannot remove impurities 930C 12 hr air/O2 *2 regrind cooled anneal, 400C, O2
LiCoO2 battery material synthesis
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
LiFePO4 Battery material synthesis
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
Solid State reaction- why need high temp and long reaction times
Formation of product nuclei is difficult- distances- reorganisation
growth of product layer may be even more difficult
Solid state reaction- 3 possibilities for RDS
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
Alternative synthesis methods to solid state
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
Hydrothermal synthesis
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
Chimie Douce reactions
lower reaction temps that SS intercalation deintercalation ion exchange for compounds not stable at high temps
Cation intercalation
insertion of cations into 1/2/3 D channels
insertion into 1D –> Solids with Rutile structure: MoO2 –> LiMoO2 (Mo3+)
chemical/ electrochemical methods
Anion intercalation
the graph with metastable states with lower activation energies
Why is metal stoichiometry important
if incorrect weights used then impurities will result
Describe NaCL (AX) structure
CCP
Cations (A) occupy ALL oct. holes
TiO, VO (metallic conductors)
NiO (insulator)
NiAs (AX)
HCP
Cations (A) occupy ALL oct. holes
large anions
Rutile structure (AX2)
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
CdI2 (AX2)
Same as Rutile but remove alternate layers of oct. cations
layered HCP
M2+ iodides/ bromides/ chlorides/ OH-/ sulphides
CdCl2
Layered structure CCP
M2+ chlorides/ bromides/ iodides
AX3 (ReO3)
Primitive cubic lattice
Perovskite ABX3 CaTiO3
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)
Tolerance factor
- 9-1 usually cubic
0. 75-0.9 usually lower symmetry orthorhombic
Ilmenite
ABO3
A and B are both small (FeTiO3)
HCP, Fe and Ti occupying 2/3 of oct. holes in alternate layers
Ruddlesden Popper Phases
Perovskites and rock salt type intergrowths
layer separated by rock salt units
Octahedral and tetrahedral sites in a CCP UC
CCP=FCC
4 atoms in UC, between atoms-
4 octahedral holes
8 tetrahedral holes
AB2O4
Spinel
FCC/CCP
1/2 oct. holes filled
1/8 tetra. holes filled
Normal Spinel
A in tetra holes
B in oct holes
MgAl2O4
Inverse Spinel
ABAO4
B in tetra holes
A + B in oct sites
What influences which structure type a given structure will adopt
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
5 Non-Ionic effects on structure
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
How to work out if would prefer normal or inverse spinel
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
Jahn teller distortions
CFEffects
1st row TM difluorides adopt the rutile structure which allows distortions from octahedral geometry
Oxo-cations and Oxo-anions
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
Define Polyoxometallates
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
Isopolyoxometallates
where all metals are the same
Heteropolyoxometallates
Mixing metals/ inc. non metals in anions- kegging/ Dawson structure
Properties and applications of polyoxometallates
High bronsted acidity- use as acid catalysts
redox activity
Discrete M-M bonded clusters
Low Ox S 2/3rd TM chlorides
Extended Lattice structures M-M bonding
Early 2/3rd TM chlorides
higher multiple bonds formed y overlap of identical d orbitals
How to determine Metal Bond Order
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
Examples of extended Lattice Chlorides
1) Sc7CL10- single and multiple chains of SC atoms
2) ZrCL graphitic hexagonal nets of Zr sandwiched between bridging Cl layers
Why is TiO a metal whereas NiO is an insulator?
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
Colour differences in Cu, Ag, Au
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
Difference between single and powder crystal XDR
single for determination of structure- powder for phase identification, purity, quantitative analysis, estimation of particle size
All crystalline structures posses
Translational symmetry
How many crystal systems?
7
Triclinic
No restrictions
none
Monoclinic
alpha=gamma=90
1, 2 fold axis
Orthorhombic
alpha=beta=gamma=90
3, perpendicular 2 fold axis
Tetragonal
a=b
alpha=beta=gamma=90
4 fold rotation axis
1, 4 fold axis
Cubic
a=b=c
alpha=beta=gamma
4, 3 fold axes in tetr. arrangement
trigonal
a=b=c
1, 3 fold axis
Hexagonal
a=b
alpha=beta=90
gamma=120
1, 6 fold axis
fractional coordinates
dimensionless
allow direct compariaon of positions in UCs
Glide planes
Mirror + translation
Screw axes
Rotation + translation
Body centred- I
2 LP/ UC
x,y,z) (x+1/2,y+1/2,z+1/2
Face centred- F
4LP/ UC
Base Centred- C, A or B
2 LP/ UC
(x,y,z)
(x+1/2,y+1/2, z)
define a space group
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
define d spacing
inter-planar distance, one members of the set must pass through the origin of the UC
Miller indicies
reciprocals of the fractional coordinates
Diffraction of light
how works with crystalline solids
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
1 A =
1*10^-10 m
Bragg’s Law
For constructive interference to occur beams must be in phase therefore the path length diff. must be a whole number
There is one peak for..
every set of planes in the crystal lattice
Cubic systems with peaks (h00) have multiplicity of
6
6 planes have the same d spacing and peak position
Primitive hkl
all values observed
Face hkl
either all odd or all even observed
I (body) h+k+l
Odd numbers are absent
Base (c) h+k
Odd numbers are absent
Systematic absences
can distinguish lattice types by identifying hkl reflections that are missing from the diffraction pattern
space groups may also lead to additional systematic absences
How do you report a structure
Space Group
a=
where are anions and cations?
Z=
no. of empirical formula units in UC = lattice points
Atomic scattering factor f =
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
Structure factor
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
Intensity of peak hkl is proportional to
modulus of F ^2
multiplicity also determines peak intensity
modulus of F
= square root of (A^2 + B^2)
angles in radians NOT degrees
if = 0 then the peak hkl has no intensity/ absent
Electron density
from structure factor
intensities give us the exact atom locations
density=
mass/ volume
Mass of UC/ UC volume
VOLUME convert A to cm (*10^-8)
Mass of UC=
sum of (ne * RMMe)/ NA
Interatomic distances=
a*sqrt (deltax^2 +deltay^2 +deltaz^2)
In order for the diffraction patterns from two different crystalline materials to be identical they must have exactly the same:
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
Determination of purity
Qualitative analysis
determination of crystal size
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
When would you see intensity either side of Bragg’s diffraction angle
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
Beta tilde, peak broadening =
FWHMsmall- FWHMlarge
instrumental effects
intrinsic peak width
upper size limit for crystallites beyond which no measurable particle size broadening will occur
typically around 1um for a lab diffractometer
Scherrer equation
relates crystal size peak broadening to mean crystallite dimension=
tilde = (Crystallite shape constant*wavelength)/ (Peak broadening *tilde-particle size cos theta)
The Rietveld method
calculate the powder diffraction pattern of a model crystal structure and minimise the diff between that and the raw diffraction pattern
WHat is needed to produce silica via sol gel route
Acid/base catalyst
Alcohol to make sure mixes
water to hydrolyse
Structure of silica gels produced under acidic conditions- how do acidic conditions lead to this structure?
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
Why is hydrolysis dangerous
Exothermic- energy management is a concern for the actual reaction.
