1. Complex Formation Do Now: What is a coordinate bond?
What is a covalent bond?
What does Fe3+(aq) mean?

2. What is a Complex? Some definitions ...
Ligand ion/ molecule with a lone pair that forms co-ordinate bond with a metal
Complex metal ion with ligands co-ordinately bonded to it
Co-ordination number
number of co-ordinate bonds from ligand(s) to metal ions
Remind pupils of co-ordinate bonds – covalent bond where one atom donates BOTH electrons
Make it clear that Lewis acids and Lewis bases are NOT the same as Bronsted-Lowry acids and Bases (opposite way around and involve

3. Formation of complex
Transition metals have a smaller radii than non-transition metals
Due to the smaller radii, they can attract electron-rich species more strongly e.g. water molecules
The water molecules are attracted to the TM ions strongly so they form a specific number of bonds

5. Complexes
A complex is an ion or molecule with a central atom or ion surrounded by ligands joined by co-ordinate bonds so that the number of ligands exceeds the oxidation state of the central atom. e.g.,
[Cu(H2O)6]2+

6. Complexes
It is a well known fact that copper(II) sulphate is not a blue solid!
Anhydrous copper(II) sulphate is a white solid but becomes blue in solution because of the formation of this complex.
Cu2+ + 6H2O  [Cu(H2O)6] 2+
white(s) blue(aq)
Demo CuSO4 anhydrous and hydrated

7. Ligands These can be: Negative ions: Cl-, OH-, CN-
Uncharged molecules that have one or more lone pairs of e-:
NH3, H2O

8. Complexes 6 4 The co-ordination number of the complex is the number of
co-ordinate bonds attached to the central atom or ion.
[Cr(NH3)6]3+ co-ord no. =
[CuCl4]2- co-ord no. = 6 4

9. Naming Complexes

10. Naming Complexes Formulas give us a lot of info ... [Cu(H2O)6]2+
[CuCl4]2-
Brackets:
() = ligands comprising more than 1 element (H2O, NH3, OH-, CN-). NOT needed if ligand is ion formed from 1 element.
[] = to enclose the complex. Overall charge on the outside.
Name also gives a lot of info ...
[Cu(H2O)6]2+ Overall charge = +2, central Cu ion, 6 water molecules as ligands, Cu ox state = +2
[CuCl4]2- Overall charge = -2, central Cu ion, 4 chloride ions as ligands, Cu ox state = +2

11. Naming Complexes Name gives info on ... Number of each type of ligand
The identity of each ligand
The identity of the central metal ion and its oxidation state

12. Naming Complexes Number of ligands Prefix 2 Di 3 Tri 4 Tetra 5 Penta 6
1. Number of each type of ligand
Number of ligands
Prefix 2 Di 3
Tri 4
Tetra 5
Penta 6
hexa

13. Naming Complexes Ligand Name in complex Water Aqua Ammonia Ammine
2. The identity of each ligand
Ligand
Name in complex
Water
Aqua
Ammonia
Ammine
Chloride
Chloro
Hydroxide
Hydroxo
cyanide
Cyano
Ammine is with 2 “m” – not to be confused with “amine”
Also Diammine and diamine

14. Name in anionic complex
Naming Complexes
3. The identity of the central metal ion and its oxidation state
Name changes depending on whether complex is positively or negatively charged.
POSITVELY Charged: Metal has normal name and ox state in brackets
e.g., [Cu(H2O)6]2+ hexaaquacopper(II) ion (Cu in ox state +2)
NEGATIVELY Charged: Ox state still in brackets. Add suffix “-ate” to end of metal
e.g., [CuCl4]2- tetrachlorocuprate(II) ion(Cu in ox state +2)
Metal
Name in anionic complex
Chromium
Chromate
cobalt
Cobaltate
Copper
Cuprate
Iron
Ferrate
Manganese
Manganate
Nickel
Nickelate
Silver
Argenate
Vanadium
Vanadate
Aluminium is not a TM, but included here for completeness

15. Examples [Ag(NH3)2]+ [Co(NH3)6]2+ [Co(H2O)6]2+ [CuCl4]2- [AgCl2]-
Diamminesilver(I)
Hexaamminecobalt(II)
Hexaaquacobalt(II)
Tetrachlorocuprate(II)
Dichloroargenate(I)

16. Naming Complexes
If 2 or more different ligands are present – name in alphabetical order (of the ligand, not the number prefix)
[Cu(H2O)5(OH)2]+
Pentaaquadihydroxocopper(II)
[Cu(H2O)2(NH3)4]2+
Tetraamminediaquacopper(II)

17. Notes on naming ... 1. Oxidation state NOT charge:
The number in brackets in the name is the oxidation state of the central TM ion, NOT the charge on the complex.
[Cu(H2O)6]2+Hexaaquacopper(II)
[CuCl4]2-Tetrachlorocuprate(II)
2. When writing formula, put the central metal ion first, then the ligands:
They are written in alphabetical order of first symbol in their formula (not written names)
E.g., tetraaquadichlorochromium(III)
[CrCl2(H2O)4]+ and not [Cr(H2O)4Cl2]+
3. As An aside ... IUPAC Says When writing formula, write the ligand so that its donor atom symbol is nearest to the central metal ion:
So H2O Should be written as (OH2)
BUT to avoid confusion, we will use H2O A Level textbooks and exam papers use the non-IUPAC Convention, athough technically incorrect

18. Quick Check ... Name the following: [Fe(H2O)6]2+ [Cr(NH3)6]3+
[Ag(CN)2]-
[MnCl4]2-
[Fe(H2O)4(OH)2]+
Write the formula of the following:
Diaquasilver(I)
Hexaaquavanadium(III)
Tetracyanonickelate(II)
Tetrachloroferrate(II)
Diaquatetrahydroxoaluminate(III)

19. Quick Check ... Name the following: [Fe(H2O)6]2+ hexaaquairon(II)
[Cr(NH3)6]3+ hexaamminechromium(III)
[Ag(CN)2]- dicyanoargenate(I)
[MnCl4]2- tetrachloromanganate(II)
[Fe(H2O)4(OH)2]+ tetraaquadihydroxoiron(III)
Write the formula of the following:
Diaquasilver(I) [Ag(H2O)2]+
Hexaaquavanadium(III) [V(H2O)6]3+
Tetracyanonickelate(II) [Ni(CN)4]2-
Tetrachloroferrate(II) [FeCl4]2-
Diaquatetrahydroxoaluminate(III) [Al(H2O)2(OH)4]-