Mary Flashcards
What block of elements contains the transition metals?
The D block
Why are they called transition metals?
Because they contain partially filled d orbitals
For a given principle quantum number how many d orbitals are there with the same radial wavefunction?
5
What is the principle quantum number and the secondary quantum number l for the 3d and 4d orbitals?
Principle 3 and 4
Secondary l = 2 for both
What is the value of 1 x r or the Bohr radius?
0.529 armstrongs
Why does the 3d orbital have 0 nodes at r>0 ?
N=3 is the first appearance of the d-orbital type
Why does each d orbital have a different spatial shape and/or orientation?
Because each of the 5 d orbitals have a different angular function
Why does the 4s orbital fill before the 3d?
3d orbitals are higher in energy than the 4s.
What is the RDF max?
Most likely distance of finding an electron in the orbital
Why does the 4s fill before the 3d when the rdf max for 4s is higher than that for 3d?
When empty the 4s has lower energy than the 3d orbital because it penetrates it.this means that the 4s electron can sometimes get closer to the nucleus than the 3d electron and this lowers the energy of the 4s below the 3d and hence the 4s fills first.
Why do the 4s electrons get lost first when forming cations?
When occupied the 4s has higher energy than 3d in energy, so w hen forming ions the 4s are lost first
Transition metal compounds have n d electrons. What are the limits for n?
0
When would a transition metal have free radicals?
When the value of n is odd
When does paramagnetism result?
When there is an odd number of electrons
Unpaired electrons in d block elements gives rise to what type of behaviour?
Paramagnetic
Colour in d block elements is characteristic of what
Incompletely filled d orbitals
How are lower energy arrangements achieved when transition metals are involved in compounds?
The outer s electrons will move to the d orbitals to give a lower energy arrangement
What year and by who was crystal field theory developed?
1929 by Hans Bethe
In what year by who used crystal field theory used to interpret some properties of transition metals?
In 1932 by John Hasbrouck Van Vleck
What 3 assumptions are made with crystal field theory?
- Interactions between ligands and metals are purely electrostatic
- The metal and ligands are point charges; lone pairs of ligand electrons are treated as negative charges and the metal centres treated as point positive charges
- No metal ligand covalent interactions are considered
What happens when you introduce a spherical field of ligands to a free metal ion?
The energy of the d Orbitals remains the equivalent (they are degenerate) the overall energy of the orbitals and the electrons within them are uniformly raised (relative to the free metal ion)
What happens to the d orbitals when the ligands come into bonding distance from the metal ion?
The ligands point directly at the lobes of the metal dz2 and dx2-y2 orbitals
The electron electron repulsions will raise the energies of these orbitals with respect to the barycentre
By the same token the energy of the electrons in metal d orbitals whose lobes point in between then ligands dxy, dxz and dyz is lowered with respect to the spherical field
The total energy of the orbital remains the same
What are the stabilised dxy, dxz and dyz orbitals labelled as in an octahedral complex
The t2g set
What is the label given to the dz2 and the dx2-y2 orbitals in an octahedral complex?
Eg set
What is the difference in energy between the eg and t2g set called?
Delta oct
How much energy is the t2g orbital stabilised by
-2/4 x delta oct
How much energy is the eg set stabilised by?
3/5 delta oct
What are the two possible geometries for ML4 complexes containing d block metals?
Tetrahedral and square planar
How is a tetrahedral crystal field created?
When the four ligand point charges are placed at alternate corners of the cube on the same axis frame
Why is the splitting of orbitals in tetrahedral arrangements not as large as in octahedral arrangements?
Because none of the ligands in a tetrahedral arrangement point directly at the lobes of the orbitals
What are the symmetry labels for tetrahedral sets of orbitals and why?
No symmetry label as the arrangement of ligands around the metal centre does not have inversion symmetry.
What is the label given to the dxy, dxz and dyz orbitals in a tetrahedral split and what amount of energy is this set raised by from the barycentre?
T2 set
Raised by 2/5 delta get
What is the label given to the dz2 and dx2-y2 orbital? And how much energy is this set lowered by from the barycentre
E set
-3/5 delta tet
Is delta test higher or lower than delta oct for the same metal ion and M-L distances?
Lower
Why is delta tet lower than delta oct?
Because the ligands don’t point directly at the lobes
What is the general equation for delta tet and delta oct?
Delta tet is 4/9 of delta oct
For what transition metals is square planar geometry more common?
D8 metals
What is the crystal field like for square planar geometry?
The metal-ligand e-e repulsions along the z-axis are removed and orbitals with a z component are stabilised.
The dx2-y2 and dxy orbitals are further destabilised with respect to the octahedral case
What orbitals change over in energetic ordering in the square planar case?
Dxy and dz2
What equation relates delta sp and delta oct
Delta sp is equal to 1.3 x delta oct
What type of distortion is seen in between octahedral and square planar geometry?
Tetragonal distortion
What happens in a tetragonal distortion?
There is a M-L extension along the Z axis and an M-L compression along the x and y axes
Describe what the CF splitting diagram for tetragonal distortion?
Similar to that of square planar except the dz2 and the dxy do not cross over energetically. The energy of the dz2 is higher than dxy. Because there are ligands in the z axis
What property of ligands changes the colour of a complex?
Increase in frequency and therefore an increase in energy
What does the spectrochemical series of ligands show?
The increasing order of ability to split the crystal field
Why do delta oct and delta tet increase with increasing oxidation state?
Higher charged cations have smaller radii and hence shorter M-L distances
Why does delta tet and delta oct increase as you go down a group?
M-L bonding improves due to expanded 4d and 5d orbitals
What is the CFSE or LFSE given by?
(-0.4x+0.6y) x delta oct
What is a high spin configuration?
The arrangement with the highest number of parallel spins
What is a low spin configuration?
The arrangement with the fewest parallel spins
What is the strong coloumbic repulsion called that occurs between electron pairs in an orbital?
Pairing energy, P
When does a high spin configuration occur?
When delta oct is less than the pairing energy
When does a low spin configuration occur?
When delta oct is greater than the pairing energy
How would you calculate the number of P(pairing energies) in the CFSE?
No of electron pairs in the crystal field - no of electron pairs in the spherical field
Why will a low spin complex not form for a d3 tetrahedral complex?
Because delta tet is small and so will be less than the pairing energy
When is a high spin and low spin configuration observed for d8 complexes?
High - when ligand on the metal is lower in the soectrochemical series resulting in a tetrahedral complex being formed so delta tet is small
Low - when ligand on the metal is high in the spectrochemical series resulting in a square planar complex being formed because the CFSE is large enough delta sp is large
Why do transition metal complexes appear coloured?
Transitions occur in the visible and ultraviolet regions of the EM spectrum
What region of the electromagnetic spectrum is ultraviolet?
200-740 nm
Why does a ‘yellow’ complex appear yellow?
Because it absorbs more of the other spectral wavelengths than yellow in its electronic transitions
What transition types can occur?
Ligand spectra
Counter ion spectra
Charge stransfer spectra
Crystal field transitions
What is happening when E is greater than delta oct in a uv via experiment? (Before lambda max)
The ligands are closer to the metal than at lambda max so more electron electron repulsions
What is happening when E is less than delta oct in a uv vis experiment? (Before lambda max)
Ligands move further away from the metal than delta oct due to less electron electron repulsions
How do you calculate the delta oct from a uv-vis experiment?
hc1/lambda = E
Who came up with the rule of average environment?
Jorgensen
What does the rule of average environment state?
The position of a peak in a complex TiL3X3 will be midway between the other two complexes TiL6 and TiX6
How is the Jain-teller effect defined?
If the ground state electronic configuration of a non-linear molecule is orbitally degenerate, then the molecule will distort so as to remove the degeneracy and achieve lower energy
When does orbital degeneracy arise?
Where there is more than one electronic configuration possible with equal energy
For what configurations would you get a Jahn-Teller distortion?
d1, d2, d4, d6, d7 and d9
What do the biggest Jahn-Teller effects have been noted for ground state electronic configurations that have…
Degeneracy in eg orbital occupancy
How are absorption bands described?
In terms of wavelength corresponding to the absorption maximum
What is the molar extinction coefficient?
The measure of intensity (strength) of a transition at Amax
What is the Beer-Lambert Law?
Emax=Amax/conc x l
For what low spin configurations would you expects the Jahn-teller effects be greatest?
When the degenerate orbitals are in the eg set
What does a bigger molar extinction coefficient mean?
The more intense the colour of the sample
How many selection rules are there?
3
What is the equation for delta spin?
Sum of ms values for the ground state - sum of the ms values for the excited state
What is the spin selection rule?
Delta S is equal to 0
The spin of the electron before and after the selection must be the same
What is the orbital/Laporte selection rule?
Delta L is equal to +-1 for allowed orbital transitions
What is the parity rule?
In a molecules /ion with a centre of symmetry, a transition must invoke s change in parity
Is g to u parity allowed?
Yes
Is g to g or u to u parity allowed?
No it is disallowed or parity forbidden
Are d to d transitions in octahedral complexes parity allowed?
Parity forbidden
Are d to d transitions in tetrahedral complexes parity allowed?
Yes they are parity allowed
What happens to the colour of a complex as the number of selection rules met increases?
The intensity will increase
What is the transition from a ligand to metal?
Ligand to metal charge transfer
What is the Emax of spin, orbital and parity forbidden complex?
1
What is the Emax of spin allowed, orbital and parity forbidden complex?
10-100
What is the Emax of spin allowed, orbital forbidden and parity allowed complex?
500
What is the Emax of spin and orbital allowed complex?
1000-50000
Which complexes are more intensely coloured generally octahedral or tetrahedral?
Tetrahedral
Why do d to d transitions occur at all?
-octahedral complexes can undergo asymmetrical vibrations which destroy the centre of inversion
-complexes may not be perfectly octahedral and hence there is no real inversion centre
-orbitals can mix with each other which means transitions may not be d to d in nature
A spin forbidden transition has more impact on reducing the colour intensity than an orbital forbidden transition
What is the molar susceptibility a measure of?
The amount of magnetism induced per unit volume of sample and is usually expressed in units of cm3 mol-1.
How is magnetisation achieved?
By the alignment of the electron spins
What does mew b have a value of and what does it represent in terms of magnetism on a buoy balance?
9.294x10-24 J T-1 and it represents the magnetic moment of a single electron orbiting a nucleus
What does a large mew eff value mean
High levels of paramagnetism and more unpaired electrons
What is temperature dependant paramagnetism?
When a ground state electronic configuration has triple orbital degeneracy, the magnetic moment varies with temperature
What are spinels?
Beautiful gemstones which are quite rare. They come in many colours the most common being red
What is the William Irving series?
Refers to the stability especially of complexes formed by divalent transition metal ions in the first row.
Mn Fe Co Ni Cu Zn
What is the explanation for the William Irving series?
The ionic radius decreases from Mn to Zn
CFSE increases from 0 for Mn to maximum for nickel
Although CFSE OF Cu is less than Ni. Octahedral Cu is subjected or the Jahn-Teller effect which gives it more stability
Recent study of metal thiolate complexes shows the interplay between electrostatic and covalent interactions
What is the spin selection rule?
Delta S is equal to 0
The spin of the electron before and after the selection must be the same
What is the orbital/Laporte selection rule?
Delta L is equal to +-1 for allowed orbital transitions
What is the parity rule?
In a molecules /ion with a centre of symmetry, a transition must invoke s change in parity
Is g to u parity allowed?
Yes
Is g to g or u to u parity allowed?
No it is disallowed or parity forbidden
Are d to d transitions in octahedral complexes parity allowed?
Parity forbidden
Are d to d transitions in tetrahedral complexes parity allowed?
Yes they are parity allowed
What happens to the colour of a complex as the number of selection rules met increases?
The intensity will increase
What is the transition from a ligand to metal?
Ligand to metal charge transfer
What is the Emax of spin, orbital and parity forbidden complex?
1
What is the Emax of spin allowed, orbital and parity forbidden complex?
10-100
What is the Emax of spin allowed, orbital forbidden and parity allowed complex?
500
What is the Emax of spin and orbital allowed complex?
1000-50000
Which complexes are more intensely coloured generally octahedral or tetrahedral?
Tetrahedral
Why do d to d transitions occur at all?
-octahedral complexes can undergo asymmetrical vibrations which destroy the centre of inversion
-complexes may not be perfectly octahedral and hence there is no real inversion centre
-orbitals can mix with each other which means transitions may not be d to d in nature
A spin forbidden transition has more impact on reducing the colour intensity than an orbital forbidden transition
What is the molar susceptibility a measure of?
The amount of magnetism induced per unit volume of sample and is usually expressed in units of cm3 mol-1.
How is magnetisation achieved?
By the alignment of the electron spins
What does mew b have a value of and what does it represent in terms of magnetism on a buoy balance?
9.294x10-24 J T-1 and it represents the magnetic moment of a single electron orbiting a nucleus
What does a large mew eff value mean
High levels of paramagnetism and more unpaired electrons
What is temperature dependant paramagnetism?
When a ground state electronic configuration has triple orbital degeneracy, the magnetic moment varies with temperature
What are spinels?
Beautiful gemstones which are quite rare. They come in many colours the most common being red
What is the general composition of a spinel structure?
A2+B3+)2 O4
What is the parent spinel structure of a Ruby?
MgAl2O4
If the CFSE of the B is greater than A what type of spinel do you get?
Normal
If the CFSE of the A is greater than Bwhat type of spinel do you get?
Inverse Spinel
What happens in an inverse spinel structure?
The divalent ions swap places with half of the trivalent ions
