1. COMPLEX IONS
Compounds in which metal ion is surrounded by a group of anions or neutral molecules.

2. Metal Ions. . . do not exist in isolation.
are accompanied by anions whose negative charge balances the positive charge of metal ion, producing neutral compounds.
have empty valence orbitals therefore act as electron pair acceptors.

3. Metal Ions. . . act as Lewis acids.
Anions or molecules with unshared pairs of electrons can act as Lewis bases and bind to metal center.
ability to form complexes increases positive charge increases and size decreases.
Weakest complexes formed by alkali metals.
2+ and 3+ ions of transition elements show greatest tendency to form complexes.
Cr 3+ forms more stable complexes than does Al 3+

4. Ligands. . . Molecules or ions surrounding the metal ion.
Are known as complexing agents.
Normally either anions or polar molecules.
Must have at least one unshared pair of valence electrons.
Therefore act as electron pair donors/Lewis bases.

5. The central metal and the ligands.
Coordination Sphere. . .
The central metal and the ligands.
[Cu(NH3)4]SO4
Placed inside brackets to set it off from other parts of the compound.

6. Complex Ions. . . Metal ions in water, the ligand is water.
In aqueous solution, ligands such as SCN- and CN- replace H2O in the coordination sphere.
Different properties than metal or ligands.
Color.
Oxidation state stabilized. Reduction potentials change.

7. Charge. . .
Is the sum of the charges on the central metal and surrounding ligands.
[Cu(NH3)4]SO4
SO4 = 2- (charge of the polyatomic ion)
NH3 = 0 (molecule therefore no charge)
Cu = 2+ (based on what is needed to balance the charges)

8. Practice determining charges
1. What is the oxidation number of the central metal in [Co(NH3)5Cl](NO3)2?
2. What is the charge of the complex formed by a platinum (V) metal ion surrounded by three ammonia molecules and three bromide ions?
Write the formula for this complex ion.
3. Given that a complex ion contains a chromium (III) bound to four water molecules and two chloride ions, write its formula.

9. Nomenclature. . . [Co(NH3)5Cl]Cl2 Ligands are named before the metal.
In naming salts, the name of the cation is given before the name of the anion.
[Co(NH3)5Cl] Cl-
Ligands are named before the metal.
[Co(NH3)5Cl]2+
Ligands named in alphabetical order.
Do not consider charge or prefix.
In writing formula, metal is written first.

10. Anionic ligands end in the letter o
Anionic ligands end in the letter o. Others bear the name of the molecule.
Ligand Ligand Name
Azide,N3- azido
Bromide, Br- bromo
Chloride,Cl- chloro
Cyanide, CN- cyano
Hydroxide, OH- hydroxo
Carbonate,CO3 2- carbonato
Oxalate, C2O4 2- oxalato

11. Neutral Molecules. . . Ligand Ligand Name Ammonia, NH3 ammine
Ethylenediamine, en ethylenediamine
Water,H2O aqua
CH3NH2 methylamine
CO carbonyl
NO nitrosyl

12. [Co(en)3]Cl3 [Co(NH3)5Cl]Cl2
A Greek prefix is used to indicate the number and kind of each ligand when more than one is present.
[Co(NH3)5Cl]Cl2
Pentaammine
If the name of the ligand contains a prefix, then the name of the ligand is enlosed in parentheses. Alternate prefixes are used bis-, tris-, tetrakis, petakis-, and hexakis for the name enclosed in the parentheses.
[Co(en)3]Cl3
Tris(ethylenediamine)cobalt (III)

13. Monodentate Ligand Unidentate Ligand
Form one bond to the metal ion.
H2O
NH3
NO2-
SCN-
OH-
X- (halides)

14. Bidentate Ligand Form two bonds to the metal ion. . . Oxalate
Ethylenediamine
Use bis-, tris-, tetrakis-, etc.

16. If the complex is an anion, its name ends in –ate: K4[Fe(CN)6]
The suffix –ate is added to the latin stem.
[Fe(CN)6] 4- hexacyanoferrate (II) ion.
K4[Fe(CN)6]
Iron Ferrate
Copper cuprate
Lead plumbate
Silver argenate
Gold aurate
Tin stannate

17. hexacyanoferrate (II)
The oxidation number of the metal is given in parentheses in Roman numerals following the name of the metal.
hexacyanoferrate (II)
Tris(ethylenediamine)cobalt (III)

18. Practice. . . [Ni(C5H5N)6]Br2 [Co(NH3)4(H2O)CN]Cl2 Na2[MoOCl4]
Hexapyridinenickel(II)bromide
[Co(NH3)4(H2O)CN]Cl2
Tetraammineaquacyanocobalt(III)chloride
Na2[MoOCl4]
Sodium tetrachlorooxomolybdate(IV)
Na[Al(OH)4]
Sodium tetrahydroxoaluminate