Transition Metals Flashcards
What is a transition metal?
An element with partially filled d-orbital shell
What are base metals?
Metals that oxidise or corrode easily
What are 3 examples of base metals?
- Fe
- Cu
- Zn
What are noble metals?
Metals that resist oxidisation or corrosion
What are 2 examples of noble metals?
- Au
- Ag
What is the general rule for filling of metal atom orbitals?
4s fills before 3d
What are 2 exceptions to 4s filling before 3d, and why?
- Cr will have a half filled 4s orbital to give each 3d orbital 1 electron
- Cu will have a half filled 4s orbital to give fully fill each 3d orbital
For metals atoms/ions in coordination complexes, where are electrons first removed from?
The 4s orbital
How can you easily work out the number of electrons in the d-orbital of a metal ion?
Group number - oxidation state = number of d electrons
What is coordination number?
The number of donor atoms around the metal species
Does coordination number include counter ions?
No
What are ligands?
Molecules which donate a lone pair to the metal to form a dative bond (i.e ligands donate electrons)
What charge are ligands?
Ligands can be neutral, or negatively charged
Do all ligands correspond to the same bond strength with the metal?
No. Different ligands correspond to different bond strengths: e.g. CN- forms a much stronger bond that Cl-
What are monodentate ligands?
A lone pair donated from one donor atom
What are some examples of monodentate ligands?
- Acetato
- Hydroxo
- Pyridine
- Carbonyl
What are bidentate ligands?
Ligands which can donate lone pairs from 2 donor atom
What are some examples of bidentate ligands?
- En
- Bipy
- Ox2-
- Acac-
What is the chelate effect?
Complexes of multi dentate ligands have a greater stability that monodentate ligands.
The result is that multidentate ligands readily display monodentate
What is coordinative/ionisation isomerism?
Isomers which differ in which of the ligands are bonded to the metal, and/or which act as counterions
What is linkage isomerism?
Isomers which differ by which atom on the ligand is used to bond to the metal (i.e which acts as the donor atom).
Only occurs with ambidentate ligands
What ambidentate ligands?
Ligands with more than one potential donor atom.
E.g. in the OCN- ligand, either the O or the N could act as the donor atom
What is stereoisomerism of ligands?
Isomers which are bond by the same donor atoms to the metal, which differ in spatial arrangement
What are some types of stereoisomerism?
- Fac/mer
- Cis/trans
- Optical
Where does fac/mer isomerism occur?
In octahedral complexes with 2 sets of monodentate ligands
What are fac isomers?
Where the same 3 ligands are on the same octahedron face (i.e all next to each other)
What are mer isomers?
Where the same 3 ligands are on different octahedron faces (i.e not all next to each other)
What shapes of complexes have cis/trans isomerism?
Square planar and tetrehedral
What are the two energy levels in octahedral crystal field?
- t2g
- eg
What orbitals are included in t2g?
3 orbitals between axis
dxy
dxz
dyz
What are the properties of the t2g orbitals?
Less ligand interaction
Lower in energy
What orbitals are included in eg?
2 orbitals along axis
- dx^2 -y^2
- d2^2
What are the properties of the eg orbitals?
Greater ligand interaction
Higher in energy
What is delta octahedral?
The difference in energy between t2g and eg
What will happen to electron 1 to 3 in d orbital filling?
They will all go into t2g, and eg will remain empty
What are the two possible configurations for the filling of 4+ electrons in d orbitals?
High spin config
Low spin config
What is the high spin configuration?
Electrons fill eg before pairing in t2g
What is the low spin configuration?
Electrons will pair in t2g before filling eg
What configuration does a high delta O favour (delta O > electron pairing energy)?
Low spin configuration
What does the size of delta O depend on?
The strength of the ligand field, as according to the ‘spectrochemical series’
Small delta O =
Weak field, high spin configuration
Large delta O =
Strong field, low spin configuration
What are 3 elements that will have a weak field, and what configuration will this result in?
Cl-
F-
H2O
This will result in a high spin config
What are 3 elements that will have a strong field, and what configuration will this result in?
CN-
CO
en
This will result in a low spin config
Where does octahedral crystal filling apply?
It only applies to first row transition metals
What can be used to measure magnetic moment?
A Gouy balance
What can magnetic moment value tell us?
Whether a complex is high or low spin config
What does paramagnetic mean?
Magnetic moment > 0, so complex has unpaired electrons
What does diamagnetic mean?
Magnetic moment ~ 0, so complex has no unpaired electrons
If the complex is diamagnetic, the complex must be….
Low spin configuration
What does crystal field stabilisation (CSFE) quantify?
The stabilisation of the electronic configuration in a complex
How do you calculate CSFE?
(no. electrons in t2g x -2/5) + (no. electrons in eg x +3/5)
What will the values of CSFE always be?
Less than or equal to 0
How does CSFE relate to colour in transition metal complexes?
The energy gap between t2g and eg is in the visible range of the EM spectrum, so when photons of appropriate energy are absorbed, electrons are promoted from t2g to eg; the energy gap corresponds to a certain wavelength/colour of light
