Handouts Flashcards
When do you get high spin?
Always for tetrahedral as Pairing Energy always higher than CFS. Octahedral 1st series
Spontaneity of reaction, what does E show
E = +ve the reaction as written is spontaneous
E = -ve the REVERSE reaction is spontaneous
delta G = -nFE
What do electrodes show?
-ve = reducing agent, +ve = oxidising agent… magnitude shows strength
Latimer diagram
Highly oxidised on the left e.g. +7 –> +1
Standard potential for overall reaction
E RHD - E LHS
Can conclude that species is unstable if pot. on right of species is more +ve than left
Anything that alters delta G will change the redox potentials- 4 things
Conc. Temp. Other reagents which are not inert. pH
pH is most important so construct Latimer diagrams for two extremes of pH=0 and pH=14 (1M acid, 1M base)
In a Frost Diagram the most stable species…
lie lowest
plot a Frost Diagram
vE vs Oxidation no.
slope = standard potential, more +ve means more liable to undergo reduction, less +ve more liable to undergo oxidation
What do Frost Diagrams show?
Species high on rhs are oxidising agents towards species on lhs and vis versa
if line connecting two species is +ve the higher lying is oxid agent
if line has -ve slope higher species is reducing agent
species likely to undergo Disproportionation
species lying above line connecting neighbours- TDY unstab. towards disproportionation
How can you stabilise High oxidation state TMs
Complex by other species which are even stronger oxid. agents- O2-, F-
Conditions for Standard Solid State Reaction
Direct reaction of a mixture of solid starting materials
most widely used method for synthesis of organic solids
High temperatures- over 900C
Long reaction times- several hours/ days with intermediate grinding
need correct ratios otherwise will have impurities
controlled atmosphere- o2, air, n2 or vacuum
why need high temp and long times?
Formation of product nuclei is difficult- large distance between reactants and products- large amount of structural reorganisation
2- growth product layer may be even more difficult
3 possibilities for RDS in SS reaction
- Transport of matter (IONS) to reaction surface
- reaction at the surface/ interface
- Transfer of matter away from reaction interface
Ad. of SS
Disad.
+ easy, effective
- high temp + long therefore, lots of energy
- inhomogeneity of mixture- impurities (regrind + reheat)
- volatile products (high temp can lead to loss of reactant)
- some phases only stable at low temperatures
Pechini Method
Dissolve metal salts (nitrates) in water then add dicarboxylic acid and dialcohol
Sol Gel Ad, Disad
Ad. Lower temps, synthesis of new phases possible (metastable phases), capacity to form films/ fibres and control particle size and shape
Disad. High cost, long processing times- weeks- longer than SS, problems with use of alkoxides if diff. hydrolysis rate, problems getting homogeneous gel
Hydrothermal Synthesis
Suited to phases unstable at high temperature e.g. zeolites, metal organic frameworks- sample must be stable in water
Mechanochemical synthesis
Ball milling –> local heating of powders
several hours
NaCl AX
CCP
Cations A occupy all oct. holes
TiO, VO, NiO
NiAS AX
HCP
Cations occupy all oct. holes
Rutile structure AX2
HCP
X sublattice distorts slightly from ideal HCP- UC actually tetragonal
common for M4+ oxides
M2+ Fluorides
Cations occupy 1/2 oct. holes
1) remove alternate rows of octahedral cations within same layer (rutile)
2) Remove alternate layers of oct. cations (CdI1 structure)
CdI2
Layered HCP
M2+ Iodides, bromides, chlorides, hydroxides, M4+ Sulphides
CdCl2
Layered CCP
M2+ Chlorides, bromides, iodides
AX3 ReO3
Primitive Cubic Lattice
ABX3
Perovskite
A cation 12 coordinate and will be large and of low charge
B cation 6 coordinate and small with high charge
Tolerance factor
1 for ideal perovskite
t= (rA+rx)/ sqrt 2 (rB + rx)
lower = lower symmetry - orthorhombic
Technological importance of Perovskites
Superconductor, ionic and electronic conductor, fuel cell material
ABO3 Ilmenite
A, B small cations
HCP Fe, Ti occupy 2/3 of oct. holes, Fe and Ti occurring in alternate layers
Ruddlesden popper phase
Perovskite and rock salt- type intergrowths
A(n+1)BnO(3n+1)
AB2O4 Spinel
Normal
Inverse
CCP, 1/2 oct. filled, 1/8 tetr. filled
Normal: A in tetra. B in oct.
Inverse: B in tetr. A+B in oct.
Coordination number to shape
2,3,4,6,8
Linear, trig. planar, tetra, oct, cubic
Use of Oxocation Material
Vanadyl phosphates - catalysts- oxidation of butane to maleic anhydride
Polyoxometallate
An oxoanion which contains more than one metal atom- formed by condensation of mononuclear oxoanions at low acidic pH
When all metals are the same: Isopolyoxometallate
Mixing- Heteropoluoxometallate (kegging/ Dawson Structure)
Properties and Applications of Polyoxometallates
High Bronsted Acidity- used as acid catalysts
redox activity- catalysis- oxidation reactions
How to determine BO
= n* No. of M atoms/ 2b
n= dn configuration of metal cations present
b= no. of M-M connections within cluster
example of extended lattice chlorides
Scandium Chloride: Sc7Cl10
Zirconium Chloride ZrCl
