Chemistry Y2: Coordination Chemistry Flashcards
What are the 5 d orbitals
dxy, dxz, dyz, dz². dx²-y²
How many e can fit in d shell
2 e in each shell =10e
what is the electronic configuration of Cr
[Ar]4s1 3d5
Stable half shell takes priority
what is the electronic configuration of Cu
[Ar]4s1 3d10
Stable full shell takes priority
How do TMs exist in many oxidation states
Early TMs can lose all valence e
In metal/atom - ion coordination complexes which electrons are removed first 3d or 4s
4s
what bonds to TMs and ligands form?
Coordinative/ dative/ donor/ metal-ligand
Which is true?
TMs are Lewis acids
Ligands are lewis acids
TMs are lewis acids- accept e
Ligands are Lewis bases- donate e
what is a mono-dentate ligand?
A ligand that can only form a single coordinate bond with the metal centre
What is a Bi-dentate ligand?
A ligands that is capable of forming 2 coordinate bonds with a central metal ion
What is a poly-dentate ligand?
A ligands that can form multiple coordinate bonds with a central metal ion e.g. tetra-dentate
What 3 factors affect number of ligands in a complex
- Size of the atom
- Steric interactions between ligands
- Electronic interactions between metal and ligand = BONDING
What is structural isomerism in coordination complexes?
Same molecular formula, different order of bonds
*Ionisation isomerism
*Hydration isomerism
*Coordination isomerism
*Linkage isomerism
What is stereoisomerism in coordination complexes?
Same molecular formula/ sequence of bonds but different spatial arrangement
*Geometrical isomerism (Cis and Trans)
*Optical isomerism (Chiral centre)
e.g. [M(L-L)₃] , [M(L-L)₂] and (L-L chelate ligands)
What coordination does a 7-coordinate complex have
Pentagonal Bipyramidal
or
Square faced monocapped trigonal prism
What coordination does a 8-coordinate complex have
Square antiprism
What coordination does a 9-coordinate complex have
Square faced tricapped trigonal
What does chelate mean?
A bidentate ligand bonded to a single metal ion
How do ligands approach the metal ion? and why?
Along the X,Y and Z axis
So they’re evenly spaced
How Do ligands contribute to the spherical electrical field around the metal ion
Each ligand has its own electrical field which contributes to the spherical electrical field
How does the d orbital increase in energy and become destabilised?
The ligands are drawn towards the +ve metal ion causing the electrical fields to become smaller
Ligands become close enough to bond to the ion
If an orbital points at a ligand what happens?
The orbitals get destabilised. Raised in energy
If an orbital points between ligands what happens?
The orbitals are stabilised. Lowered in energy
What is the crystal field splitting energy (Δ0)
It’s the energy gap between the orbitals
In octahedral splitting which orbitals are shifted +3/5 Δ0
d͓x²-y² and dz² orbitals
In octahedral splitting which orbitals are shifted -2/5 Δ0
dxy, dxz, dyz orbitals
Octahedral splitting what are the orbitals labeled and how degenerate is each
Higher 5d = doubly degenerate =eg
Lower 5d = triply degenerate = t2g
How do you calculate CFSE
CFSE= (m x +3/5) + (n x -2/5)
m= no. e in eg
n= no. e in t2g
What configuration comes with HIGH spin
Low configuration
What configuration comes with LOW spin
Hight configuration
What is ligand field splitting a measure of?
Strength of the ligand
Which spin in Co(III) always
Low spin
Unless bonded to F
What does a larger CFSE mean for the size of electrical field?
Larger electrical field
Why do weaker ligands have a smaller CFSE?
The weaker ligands don’t have enough energy to lift the energy of eg as much
What is pairing energy
The energy required to flip and electron with a spin up e in the same orbital
Why in weak field is CFSE < pairing energy?
Makes it easier to promote e to the eg orbitals rathe than flipping e to pair electrons
Why in strong field is the CFSE > Pairing energy?
Easier to pair electrons than to raise them to eg
Is High spin weak field or strong field?
WEAK FIELD
Which d configurations can have either High spin and Low spin?
d4, d5, d6, d7
For the other configurations there is only 1 possibility
What makes a complex high spin or low spin?
The metal ion
The metal ion ox state
The ligands
what is the spectrochemical series in order of increasing Δ0
I-, Br-, SCN-, Cl-, F-, OH-, C2O4²⁻, OH2, NCS-, py, NH3, en, bipy, CN-, CO
As Δ0 increases, field strength increases
TRUE OR FALSE
TRUE
WHAT does HONC stand for
It’s a means to remember the electrochemical series
H<O<N<C
H= Halides
O= Oxygen
N= nitrogen
C=Carbon
What do the colours of coordination complexes relate to?
To the energy gap between t2g and eg
A certain energy gap relates to a specific colour
How to coordination complexes have colour?
Electrons are excited by visible light energy. The colour is created by the transition from t2g to eg
Equation for the energy gap between t2g and eg
λ(nm)=10^7/Δ0(CM^(-1))
what is the complementary colour rule
Whatever colour is absorbed its complementary colour is reflected-this is the colour we see
HOW DOES CFSE INCREASE WITH OX STATE?
-changes based on the metal
-Increased pull on ligands
-Greater e-e repulsion
=Greater CFSE
How does CFSE increase down a group?
-Radius of metal ion increases
-Electronic repulsion increases
-Larger Δ0
What makes a complex colourless?
A filled or half filled d subshell
e.g. Zn²⁺ (d10) or Mn²⁺ (d5 and typically white)
That geometry is formed when 4 ligands approach a central metal ion?
TETRAHEDRAL
In a cubic space where are the ligands located in tetrahedral complexes
At the corners
The triply degenerate t2 orbitals in tetrahedral all point to where?
So dxy is closer to the ligand that dx-y²
the sides of the cube
The double degenerate orbitals of e in tetrahedral geometry point to where?
the faces
In tetrahedral geometry which orbitals are t2 and which are e? And what fraction of Δt are they?
t2g = +2/5 = dxy, dxz, dyz
eg = -3/5 = dz², dx²-y²
Why is there no (g) in t2 and e in tetrahedral crystal field splitting
No g = cause there is no inversion symmetry
Why are dxy, dxz, dyz raised in Δt?
Because these orbitals face the ligands- destabilising them = increased energy
The 4 ligands all don’t exactly point at the ligands in tetrahedral. What is Δt as a fraction of Δo?
Δt = ~ 4/9 Δo
approx
less that half
What is the Δt CFSE equation?
(m x +2/5) + (n x -3/5)
m= no. e in t2
n= no. e in e
Are all tetrahedral geometries HIGH spin or LOW spin?
They’re all HIGH spin
=small splitting
What is the order of orbitals from most destabilised to least in SQUARE PLANAR?
- dx²y²
- dxy
- dz²
- dxz, dyz
In SP how do the ligands approach the metal ion?
Along the X axis
Why is the dx²-y² orbital the most destabilised?
2 ligands along the x axis have been removed. But dx²-y² still point at a ligand- destabilising it
Why is the dxy orbital in SP raised?
It is in plane with the ligands
How do you calculate ΔSP looking at ΔSP splitting diagram?
difference between dx²-y² and (dxz and dyz)
Does SP splittng favour HIGH spin or LOW spin?
LOW SPIN
-suited for heavier metals
Which metal ions have SP geometry?
2nd and 3rd row d8 metal ions
Rh(I), Pd(II), Pt(II), Au(III)
*For 1st row ions SP isn’t guaranteed it depends on the strength of the ligand
-STRONG LIGAND =SP
-WEAK LIGAND = TETRAHEDRAL
How would you differentiate between [NiCl⁴]²⁻ and [PdCl⁴]²⁻?
Both are 8d
[NiCl⁴]²⁻ is High spin TETRAHEDRAL and therefore has 2 unpaired e
[PdCl⁴]²⁻ is low spin SP and therefor has 0 unpaired e
- this gives the 2 complexes different MAGNETIC MOMENTS which can distinguish them
What is the linear crystal field splitting diagram
Ligands approach along z axis
- dz²
- dxz, dyz
- dxy, dx²y²
- No ligands in xy plane
6 coordinate crystal field splitting,
which orbitals are stanilised and destabilised?
Dx²y² and dz²= destabilised and degenerate
dxy, dxz, dyz = stabilised and degenerate
Jahn -Teller effect
How do we decide where to put an e if 2 orbitals are degenerate?
We need to make them become non-degenerate
How do we break degeneracy?
J-T effect
*We need to stabilise 1 d orbital relative to the other
*distortion
*by changing bond distance, by changing E REPULSION WITHIN THE LIGANDS
what are the 2 ways we can achieve the Jahn-teller effect?
- The 2 ligands on the Z axis can move further away from the metal= increased bond distance
-equatorial bonds get closer
-Stabilising dz² relative to dx²y²
-e added to dz² first - 4 ligands in equatorial plane push back from the metal
-lengthening these bonds
-dx²y² stabilised relative to dz²
-e added to dx²y² first
What is the effect of breaking bond degeneracy?
*Changes the geometry -> tetragonal
*easier to move 2 ligands rather than 4
*Most distortions occur along x-axis - elongated TETRAGONAL as x-axis is stretched
Which configurations apply to Jahn-Teller?
d9, Low d7, HIGH d4
All Cu(II) complexes, Low spin Co(II), High spin Mn(III) and CR(II)
what does small distortion (e.g along Z axis) in octahedral complexes mean?
The bond distances arn’t altered that much
*dx²-y² is raised compared to dz²
*dxy is raised but not enough to be above dz²
what does large distortion (e.g along Z axis) in octahedral complexes mean?
The bond distances are altered largely
*dx²-y² is raised compared to dz²
*dxy is raised above dz²
If bond distortion happens too extremely in OCTAHEDRAL complexes what happens?
Ligands detach on that specific axis
*Gives 4 coordinate SP complex
What distortion tendency does Cu have
*Lose an axial ligand
*Breaks degeneracy
*Forms a 5-coordinate SQUARE PYRAMIDAL complex
Does Jahn-Teller increase or decrease stability of a complex
It increases stability as it allows e to be added at lower energy levels
In J-T if geometry changes do we keep or change the electronic configuration
We keep the octahedral electronic configuration
How do we know if it’s Jahn-Teller from the electronic configuration
if the electron count in eg is 1 or 3
-As eg orbitals need to become non-degenerate in these instances
What techniques can be used to tell us more about the Jahn-teller effect?
- x-ray crystallography
- Electronic absorption spectra
-A J-T distorted complex will have 2 peaks as the energy levels are NOT degenererate
Why is the Jahn-Teller effect negligible when there is uneven occupancy of the t2g orbital
Because the orbitals point between the ligands
even though J-T in negligible for t2g why do we sometimes see 2 peaks in electronic absorbtion
Caused by excited e jumping from t2g to either dx²-y² or dz²
what are the 3 electronic configurations with we need to know for Jahn-Teller effect?
d9, Low d7, high d4
what is the macrocyclic effect
*Involves rings of at lease 9 atoms with at least 3 donor atoms
*cyclic ligands are a lot more stable - they’re too rigid to dissociate arms to attach donor atoms
*They lock metal ions in enzymes and proteins
e.g. nitrogen donors
what is denticity?
the number of donor atoms through which ligands bind
What is chelation?
When 2+ donor atoms bind to a metal ion:
Formation of a chelate ring
5-membered ring is most stable
What dictates if and x-membered ring is favourable
the bite angle varies depending on x
*Best bite angle is 5 membered
*Above 6 becomes unstable
*3 and 4 are unfavourable
What conditions for entropy and enthalpy are needed to favour a chemical process
+ve change in entropy
-ve enthalpy
what is Gibbs free energy?
How likely a chemical process is
ΔG°=–RTlnK=ΔH°–TΔS°
ΔG°= gibbs free energy of a reaction
ΔH = enthalpy of reaction
ΔS° = entropy of reaction
T = temp (K)
R = 8.314
K= equilibrium constant
what is entropy and what is its relation to the chelate effect?
Entropy is an increase in disorder
*More favourable reaction = increase in disorder (ΔS°> 0)
If ΔS is more +ve, ΔG is more -ve
*CHELATE EFFECT WORKS BY REPLACING MONODENTATE LIGANDS WITH POLYDENTATE LIGANDS
-driven by increase in entropy
What is supramolecular chemistry
How molecules interact with each other through non-covalent bonds
e.g.
Molecular recognition in DNA
Non-covalent bonds include:
*H-bonds
*Electrostatic force sof attraction
*Van derWaals
*Pi-Pi stacking
*matal-ligand bonds
What do we get if we add 2 bipy ligands to Cu+?
TETRAHEDRAL COMPLEX in double helix
*Cu+ ensures bipys stay orthogonal to each other = Bite angle of 90⁰
what do we get if we add 3 bipy ligands to Fe2+
A triple helix
Bipy ligands are orthogonal to each other
How are molecular grids formed
2 terpy units combines with Fe2+
2 by 2 moleculare grid
Grid is planar
Multidentate ligands can have 2,3or 4 terpy pockets
but grids can only ever by 2’2, 3’3, 4’4 not mixed
What is the molecular formular of magnetite/
Fe3O4
what causes magnetism
Unpaired e
What are the 2 types of magnetism? and which is bigger?
Paramagnetism»_space; Diamagnetism
1.Paramagnetism- a material that aligns with a magnetic field because it has unpaired e
2.Diamagnetism- A substance without unpaired e and is repelled by a magnetic field
What is spin angular momentum
*e rotates on its axis
*The electrons dipole has 2 orientations PARALLEL and ANIT-PARALLEL to the magnetic field
What are the parallel and antiparallel spin quantum numbers?
Parallel =ms +1/2
Anti-parallel = ms -1/2
in terms of energy, which is bigger parallel or antiparallel
Antiparallel»_space; Parallel
what are the 2 parts of the magnetic moment
- Apin angular momentum
- Orbital angular momentum
what is orbital angular momentum? Give equation
the momentum given to the e while is circles the nucleus
μSo=√n(n+2)
μ= Magnetic moment
S = total spin
Spin only formula can be written in terms of n
n=Number of u unpaired e
Why do paramagnetic compounds weigh more than diamagnetic compounds?
They’re repelled by the magnetic field
Why are magnetic moments useful?
They can help distinguish between HIGH. and LOW configurations in octahedral complexes
How to calculate total spin, S
S=n/2
where n= number of unpaired e
