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