Coordination Chemistry Flashcards
What are the 5 d-orbitals?
dxy
dyz
dxz
dz^2
dx^2 - dy^2
Which 4 d-orbitals are similarly shaped?
dxy
dyz
dxz
dx^2-dy^2
What is the shape of the 4 similarly shaped orbitals?
They are all clover shaped, but oriented on different planes
What is the shape of dz^2?
A dumbbell shape with donut shaped electron cloud around the centre
How can you deduce the number of electrons in d-orbitals of an ion?
Subtract the oxidation state from the group number of the element
Which is the Lewis acid, and which is the Lewis base between transition metals and ligands?
Transition metals = Lewis acid (accepts electrons)
Ligands = Lewis base (donates electrons)
How many lone pairs does Dien donate?
3 lone pairs (terdentate)
How many lone pairs does Tren donate?
4 lone pairs (tetradentate)
How many lone pairs does Porphyrin donate?
4 lone pairs (tetradentate)
How many lone pairs does EDTA donate?
6 lone pairs (hexadentate)
If a complex has CN 2, what is it’s structural geometry?
Linear
If a complex has CN 3, what is it’s structural geometry?
Trigonal planar
If a complex has CN 4, what is it’s structural geometry?
Tetrahedral or Square planar
If a complex has CN 5, what is it’s structural geometry?
Trigonal bipyramidal or Square pyramidal
If a complex has CN 6, what is it’s structural geometry?
Octahedral
What is the chelate effect?
Complexes of multidentate ligands have a greater stability than those of monodentate ligands
What is coordinative/ionisation isomerism?
Isomers that differ in which ligands are bonded to the metal, or which act as counterions (different transition metal but same ligands)
What is linkage isomerism?
Isomers that differ in which donor atom the ligands use to bond to the metal
Where does linkage isomerism occur, give two examples?
Linkage isomerism occurs in ambidentate ligands, in which there is more than one possible donor atom.
For example:
Cyanato ligand (OCN-) and NO2- ligand can both be O or N bonded
What is stereoisomerism?
Isomers in which the same ligands are bonded to the metal, but in different spacial arrangements
Which structural geometries can have cis/trans isomerism?
Square planar and octahedral species can have cis/trans isomerism
When does facial/meridional structural isomerism occur?
In octahedral complexes where there are two sets of monodentate ligands
What does a fac isomer look like?
Where 3 same ligands are on the octahedral face, which looks like all on the bottom right hand side of the metal, and the other 3 are on the top left.
What does a mer isomer look like?
Where 3 same ligands are on the octahedral meridial, which looks like two on the right and one bottom left, and the other 3 same are in the other positions
In what 2 complexes would you find chirality (and hence enantiomers)?
- In octahedral complexes with three bidentate ligands
- In octahedral complexes with two bidentate ligands and one monodentate ligand, the cis molecule is chiral
What is the name of the lower energy orbitals, and what orbitals are at this energy level (oct)?
t2g:
- dxy
- dyz
- dxz
What is the name of the higher energy orbitals, and what orbitals are at this energy level (oct)?
eg:
dz^2
dx^2-y^2
What is the energy difference between t2g and eg called (oct)?
Delta octahedral
How will electrons fill the orbitals in high-spin configuration (oct)?
Electrons will enter eg before pairing in t2g
How will electrons fill the orbitals in low-spin configuration (oct)?
Electrons will pair in t2g before entering eg
If delta oct is greater than electron pairing energy (in t2g), what configuration will be favoured (oct)?
Low spin, so electrons will pair in t2g before entering eg
What is the CFSE equation for oct?
(no. electrons in t2g x -2/5) + (no. electrons in eg x +3/5)
On the colour wheel, what is the lowest energy colour, and what is the highest energy colour?
Red is the lowest energy, and it increases in energy counter-clockwise until you get to violet, which is the highest
How does ligand strength correspond to the colour on the spectrochemical series?
The stronger the ligand, the higher the energy of the colour; so the strongest ligands correspond to purple/violet, and the weakest to red/orange
How can you work out the colour of a compound from the strength of the ligand?
The colour of the compound will be opposite the corresponding colour to the ligand. For example:
CN- is a strong ligand that corresponds to purple/violet, and will hence produce a yellow/orange compound, as yellow is opposite purple on the colour wheel
What possible reasons can cause a compound to appear colourless?
- Filled (d-10) or half filled high spin (d-5), meaning there are no possible electrons to be excited
Or - Very strong ligand field, meaning delta oct wave number is outside the visible spectrum
What 3 factors affect delta oct value?
- Strength of ligand (greater strength, greater delta oct)
- Oxidation state (larger positive oxidation state, the greater delta oct)
- Down a group (down the group = larger the radii, the greater delta oct)
What is the higher energy group of orbitals called (tetra), and what orbitals are at this level?
t2:
- dxy
- dyz
- dxz
What is the lower energy group of orbitals called (tetra), and what orbitals are at this level?
e:
- dz^2
- dx^2 -y^2
Why are the t2 orbitals higher energy (tetra)?
Because the orbitals (dxy, dyz, dxz) sort of point at the ligands, making them destabilised
Why are the e orbitals lower energy (tetra)?
Because the orbitals (dz^2, dx^2-y^2) point between the ligands, making them more stable
What is the difference between e and t2g called (tetra)?
Delta tetrahedral
What is the delta tetrahedral value wrt delta octahedral?
Delta tetrahedral = 4/9 delta oct
What is the CFSE equation for tetrahedral splitting?
CSFE = (no. electrons in t2 x +2/5) + (no. electrons in e x -3/5)
What is the configuration of tetrahedral complexes and why?
Tetrahedral complexes are always high spin, as the delta T is small, so it is pairing energy in e is greater than delta T.
This means electrons always enter t2 before pairing in e
In square planar geometry, what is most destabilised orbital and why?
dx^2 -y^2 is the most destabilised, as it points at all four ligands
In square planar geometry, what is second most destabilised orbital and why?
dxy is the second most destabilised, as it is in the same plane as the ligands
What is the crystal field splitting of square planar complexes?
dx^2-y^2
dxy
dz^2
dxy dyz
2 1 1 1
For what transition metals does square planar geometry occur?
For 4d8 and 5d8 transition metals.
For it to occur in 3d8 metals, a strong field ligand is required
How is square planar configuration different to tetrahedral?
Tetrahedral complexes = always high spin
Square planar complexes = usually low spin
How can you differentiate tetrahedral and square planar complexes experimentally?
By measuring the magnetic moment.
Tetrahedral complexes will have a higher magnetic moment, as there are more unpaired electrons
What is the Jahn Teller effect?
When degeneracy of orbitals is broken; one d orbital is stabilised relative to the other
For what octahedral complexes does Jahn Teller distortion occur?
d9
low spin d7
high spin d4
What can a larger Jahn Teller distortion result in for octahedral complexes?
A larger enough distortion will result in 2 ligands detaching from the metal, resulting in a 4 coordinate square planar complex
What does Cu (II) have a tendency to become due to the Jahn Teller effect?
Cu (II) has a tendency to become a 5-coordinate complex by losing one ligand along the z-axis (to break the degeneracy).
The result of this is a square pyramidal complex
How can Jahn Teller distortion be measured?
By measuring bonds lengths through crystallography. The greater the difference in absorption peaks, the greater the distortion
Is Jahn Teller effect present in t2g?
Yes, but it is negligible as the orbitals point inbetween ligands
What is the most stable chelate ring?
5 membered chelate rings (such as ox2-) are the most stable
What do 4 or >6 membered rings tend to form?
They tend to bridge two metal atoms
What is a macrocycle?
A ring of at least 9 atoms, with at least 3 donor atoms
What is the macrocyclic effect?
Macrocyclic complexes are far more stable
What are the two types of magnetism?
Paramagnetic- attracted by a magnetic field (i.e unpaired electrons present)
Diamagnetic- repelled by a magnetic field (i.e. no unpaired electrons present)
What is a larger force out of para and dia magnetism?
Paramagnetism is a much larger force than diamagnetism
What is ferromagnetism?
A form of paramagnetism, in which the alignment of unpaired electrons extends throughout the material, making it a permanent magnet
What are the two possible ms values of electrons in a magnetic field?
+1/2 or -1/2
What is the orientation of +1/2 electrons?
+1/2 ms electrons will be aligned with the magnetic field
What is the orientation of -1/2 eletrons?
-1/2 electrons will be aligned against the magnetic field
Which have a higher energy out of +1/2 and -1/2 ms electrons?
-1/2 electrons have a higher energy2
What is the formula to work out magnetic moment?
square root of: no. unpaired electrons x (no. unpaired electrons + 2)
What is the unit of magnetic moment?
B.M.
What can you use magnetic moment to deduce?
Whether it is a high or low spin complex.
From this you can also deduce complex geometry
What is the only ligand that can push Co2+ into a square planar geometry?
CN-
[Co(CN)4]2- is square planar
