Bonding in Tranisiton Metal Compounds - Part 2

Bonding in Transition Metal compounds
Part 2:
Other Geometries:
-> tetragonal
-> square-planar

2
Which set of d-orbitals comes in closer contact to the ligands
(and is therefore de-stabilized) ?
(draw typical orbitals into this picture and estimate the
distances)

Energy Level Splitting
3
How do we expect the d-energy levels to split up
in a tetrahedral field ?
How many d-electrons are OK for tetrahedral ?

Tetrahedral complexes
4
Write ox.number of the metal and no. of d electrons:
[MnO4]
- (permanganate)
[CrO4]2- (chromate)
[FeCl4]2-
[CoCl4]2-
[NiCl4]2-
[ZnCl4]2-
Ni(CO)4
Which 2 factors determine the geometry ??

Square planar from Octahedral
5
How would the d-orbitals split from an octahedral complex ?
How many d-electrons are OK for square-planar ?

6
d-orbital energy split according to the ligand coordination:
Identify the d-orbitals for each coordination !

Trigonal bipyramidal ML5
7
For example
(refer to VSEPR Theory !)

Example: Ru(CO)3(PPh3)2
8
Which possible structures can we draw from this compound
and which one is most likely to form ?

Coordination 2 and 3
• Occurs rarely
• Most for Cu(I), Ag(I), Au(I) and Hg(II)
which are all d__ (?)
Why are these complexes variable in their
coordination geometry ?
example: Hg(CN)2 linear – HgI3(-) trigonal planar
9

Crystal Field Splitting Energy
10

CFSE
+ 2 P
So it depends on the magnitude of ∆ and P
which configuration is more stable

12
Draw the energy level diagram for both answers and state if
high- or lowspin

13
End of Part 2
Summary:
• Two factors determine the geometry of a compound:
• CFSE
• Steric influences
• Most common compounds are octahedral ML6 (middle of
the TM block) and trigonal-bipyramidal
• Tetrahedral ML4 are common for the first row TM’s
• Square-planar ML4 are typical for 2nd and 3rd row TM’s
• d10 ions arrange ligands according to their ox.numbers and
max. distance of the ligands to each other
THANKS FOR WATCHING … SEE YOU LATER !

UV/VIS Spectroscopy
LIght absorption by electron transfers
14

Spectrum of d1 complex
Only one allowed electron transition:
Ground state:
- triple degenerated => “T”
- Spin ½ => S= (2s+1) = 2
- Name: “2T2g”
Excited state:
- double degenerated => “E”
- Spin ½ => S= (2s+1) = 2
- Name: “2Eg”

Selection Rules
(a) Laporte rule:
we should have a change in parity (g u , u g)
(b) Spin selection rule:
spin multiplicity must not change (3A  3T ok)
Rule (a) is always NOT fulfilled for d-d transitions,
therefore these are only of moderate intensity !

19
How to convert between cm-1 and nm ?
Why do we use wavenumber ν instead of wavelength λ ?

Questions
• Which colour will the complex have ?
• How many electron transitions are happening and why ?
• How will the colour change if we add ammonia to the
aqueous solution ? And why ?
20

d1 and d9
Electronic states in Cu(2+):
We look at the state of the
electron-”hole”

d5 high spin case
The only possible transition is “spin-forbidden”
=> Only very small peak in the spectrum
 Only weak colour of the compound
 Which transitions are possible for the low spin case ?

d2 case
the 2 electrons are in
orthogonal orbitals
the 2 electrons are in
orbitals in the same plane
=> 2 different energies of the 2 states !

Tanabe-Sugano
 3 transitions are possible
 3 peaks in spectrum
One peak at 38000 cm-1 is in UV

Compare 2 Ni-compounds
25
Ni(H2O)6 (2+)
Colour:
Ni(NH3)6 (2+):
Colour:
Which compound absorbs
light at higher energy ?
http://jchemed.chem.wisc.edu/JCEWWW/Articles/JCENi/JCENi.html
Find the ground- and excited
electron states

Simulation
(from: http://firstyear.chem.usyd.edu.au/calculators/dd.shtml )
Ground state d8:
Excited states d8:

Possible d8 d-d transitions
3A
Multiplicity 3
-> 2 unpaired
electrons +1
Single
degenerated
3T
8’500 cm-1
3T
14’000 cm-1
3T
26’000 cm-1

Jahn-Teller Effect
28
The Jahn-Teller effect is generally
only important for odd number
occupancy of the eg level.
The effect of Jahn-Teller
distortions is best documented
for Cu(II) complexes (with 3
electrons in the eg level) where
the result is that most complexes
are found to have elongation
along the z-axis.

Compression
Why could we expect elongation instead of compression
for d9 compounds ?

Example Ti(3+)
If we look carefully, we detect 2 absorptions in
the VIS spectrum:
32

33
Which kind of Jahn-Teller Effect do you expect for a d1 complex ?
And which electron transitions can be observed then ?

Problem solving
Compare the 2 compounds: Fe(H2O)6 2+ and Fe(CN)6 4-
∆o = 10’400 cm-1 and 32’850 cm-1
Paring energy P is 17’600 cm-1 for both
Which is the electron configuration (low- or high-spin) for both compounds ?
Compare the 2 compounds: Co(F)6 3- and Co(NH3)6 3+
∆o = 13’000 cm-1 and 23’000 cm-1
Paring energy P is 21’000 cm-1 for both
Which is the electron configuration (low- or high-spin) for both compounds ?
Which d-electron configuration(s) always have zero CFSE ?

Consider a d8 compound (like Pt(II)).
What is more likely to form - a 4
coordinate or a 6 coordinate compound.
Explain using VB theory and CFT.

Bonding in Tranisiton Metal Compounds - Part 2

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