1. Transition Metals

2. Definitions Complex: A metal ion surrounded by ligands.
Ligand: an electron pair donor i.e. a molecule or ion joined onto the metal ion by a dative covalent bond to the metal.
Coordination number: The number of atoms directly joined to a transition metal by a coordinate (dative covalent) bond.

3. Typical ligands Unidentate H2O: :NH3 :Cl-
Bidentate C2O H2NCH2CH2NH2
Multidentate EDTA4-
Watch out for the chelate effect.

4. Shapes
Six-coordinate complexes are octahedral. eg Cu(H2O)62+ Co(NH3)63+
Four-coordinate complexes are usually tetrahedral eg CoCl42- but a few are square planar eg Ni(CN)42-.
Two-coordinate complexes are linear eg AgCl2-.

5. Colour
Most transition metal colours are due to d-d electron transitions. The energy gap between the split d-orbitals corresponds to visible light (E=hf).
Some of the really strong colours are due to charge transfer (such as in MnO4-).

6. Changing colour
Anything that changes the energy difference between the d-orbitals causes a change in colour:
Oxidation state
Ligand
Coordination number

7. Measuring concentration by colour
A measurement of colour intensity (using a colorimeter) can measure the concentration of a solution.
Sometimes a special complex is formed so that the colour is more intense.
This is known as UV/visible spectroscopy.
eg Fe(H2O)63+ + SCN Fe(H2O)5(SCN)2+ + H2O

8. Reaction types
The reactions of the transition metals come under three headings (but sometimes more than one occurs at the same time!).
Ligand substitution
Hydrolysis (the acidity reaction)
Redox

9. Cu(H2O)62+ + 4Cl- → CuCl42- + 6H2O
Ligand substitution
One kind of ligand is replaced by another.
For example,
Cu(H2O) Cl- → CuCl H2O

10. Hydrolysis (the Acidity reaction)
One or more hydrogen ions is removed.
For example,
Cu(H2O)62+(aq) + 2OH-(aq) →
Cu(H2O)4(OH)2(s) + 2H2O(l)

11. Redox
The oxidation state of the metal is changed by adding or removing one or more electrons
For example,
Co(NH3)62+ → Co(NH3)63+ + e-

12. Titanium
Mainly known for its chloride, TiCl4, as part of the Kroll process for extraction of titanium from its ores.
The chloride is covalently bonded.
Titanium oxide, TiO2 , is used as a white pigment.

13. VO2+ → VO2+ → V(H2O)63+ → V(H2O)62+
Vanadium
Most stable form is V(IV) eg as VO2+.
V(V) can be reduced in acidic conditions (eg Zn / HCl)
VO2+ → VO2+ → V(H2O)63+ → V(H2O)62+
V(H2O)62+ is unstable in air since it is oxidised by oxygen.

14. Chromium Cr(H2O)63+ Cr(H2O)3(OH)3 Cr(OH)63-
>>>>Increasingly alkaline conditions>>
Cr2O CrO42-
<<<<Increasingly alkaline conditions<<<<

15. Manganese Mn(H2O)62+ MnO2 MnO42- MnO4- II IV VI VII
v. pale pink brown deep purple
MnO4- is a very strong oxidising agent.
Use acidic conditions. For titrations, make sure you add
sufficient sulfuric acid to take Mn all the way to Mn2+.
Otherwise you get incomplete reduction
(the brown solid, MnO2 is formed, rather than Mn2+).

16. Iron Fe(H2O)62+ is non-acidic in water (green).
Pure Fe(H2O)63+ is a lilac colour but on contact with water goes rusty brown.
Fe(H2O)62+ forms Fe(OH)2 (a green solid) with NaOH but it goes brown (forming Fe(OH)3 on standing in air.

17. Cobalt Co(H2O)62+ → Co(NH3)62+ → Co(NH3)63+ CoCl42- Co(OH)2
add ammonia solution add hydrogen peroxide (or air)
Co(H2O)62+ → Co(NH3)62+ → Co(NH3)63+
pink brown / yellow orange
CoCl Co(OH)2
blue blue-grey
Add conc HCl
Add NaOH or NH3 (aq)

18. Nickel Ni(H2O)62+ Ni(NH3)62+ NiCl42- Ni(OH)2 Ni(CN)42-
add ammonia solution
Ni(H2O) Ni(NH3)62+
green blue
NiCl Ni(OH) Ni(CN)42-
blue pale green a square planar complex!
Add NaOH or NH3 (aq)
Add NaCN (aq)
Add conc HCl

19. Copper CuCl42- Cu(OH)2 add ammonia solution
Cu(H2O) Co(NH3)4(H2O)22+
blue deep blue / violet
CuCl Cu(OH)2
yellow-green pale blue
Add conc HCl
Add NaOH or NH3 (aq)

20. Silver Ag+(aq) Ag2O(s) Ag(NH3)2+ Cl- AgCl(s)
Small quantity of NaOH, NH3(aq) excess NH3 (aq)
Ag+(aq) Ag2O(s) Ag(NH3)2+
Cl-
AgCl(s)
excess Cl-
AgCl Ag(S2O3) Ag(CN)2-
NaCN(aq)
Na2S2O3(aq)

21. Uses of transition metals and their complexes
V2O5 is used as a catalyst in the Contact Process (manufacture of sulfuric acid).
Cis-platin (a platinum complex) is a very effective anti-cancer drug.
Fe2+ is an important part of haemoglobin.
Ag(NH3)2+ is Tollen’s reagent (test for aldehydes).
Ag(S2O3)23- is formed during photographic processing.
Ag(CN)2- is used in electroplating.