1. Transition metal complexes
central metal ion surrounded by ligands
ligand
molecule or negative ion which bonds to metal ion by donation
of at least one electron pair into unfilled metal orbitals
common ligands
water, H20
ammonia, NH3
cyanide ion, CN-
halides, F-,Cl-,Br- & I-
nitrite ion, NO2-
hydroxide ion, OH-
MM 2005 AH

2. Transition metal complexes 2
ligands
monodentate e.g. CN-, H2O, NH3
bidentate e.g. ethanedioate (oxalate),
1,2-diaminoethane (ethylenediamine)
C-C
O O .. -
H H
H2N C C NH2
H H ..
hexadentate e.g. ethylenediaminetetraacetic acid (EDTA) (p60)
MM 2005 AH

3. Transition metal complexes 3
Number of ligands in a complex ion varies depending on the ligand
e.g. [Cu(H2O)6]2+ & [CuCl4]2- both have ligands around the copper(II) ion
Co-ordination number: number of bonds from the ligand to the central
metal ion e.g. copper(II) above has co-ordination numbers of 6 and 4 ,
respectively .
MM 2005 AH

4. Shapes of metal complexes
X - M - X
Co-ordination
number
Shape of complex 2 4 6
linear
X X M X M
X X X
square planar
tetrahedral
X X M X
octahedral X
MM 2005 AH

5. Formulae of metal complexes
Named according to IUPAC rules
Formula should be enclosed within square brackets
metal symbol written first, then negative ligands followed by
neutral ligands e.g. [CoCl2(NH3)4]
MM 2005 AH

6. Naming metal complexes
If the complex is a salt, the name of the positive ion is written before the name of the negative ion e.g. K3[Fe(CN)6]
The name of the complex part (ion or neutral) consists of 2 parts written as 1 word.
Ligands are named first, in alphabetical order, and the central metal ion second.
If the ligand is a negative ion: ‘ide’ is dropped and replaced with ‘o’ e.g. chloride becomes chloro , cyanide becomes cyano; ‘ate’ and ‘ite’ change to ‘ato’ or ‘ito’ e.g. oxalate becomes oxalato, nitrite becomes nitrito.
MM 2005 AH

7. Naming metal complexes 2
K3[Fe(CN)6]
5. Water becomes aqua; ammonia - ammine; carbon monoxide - carbonyl
6. The ligand name is preceded by a Greek prefix indicating the number of each ligand type (di, tri, etc).
7. The metal name is followed by the oxidation number,in Roman numerals, in brackets. The overall charge on the complex part will be equal to the sum of the oxidation number and the total charge on the ligands
8. If the complex ion is negative, the metal name is followed by ‘ate’ and then the oxidation number in brackets e.g. cobaltate, chromate. Latin name is sometimes used e.g. cuprate, ferrate, plumbate, stannate.
MM 2005 AH

8. Naming metal complexes 3
K3[Fe(CN)6]
[Cu(NH3)4]Cl2
[PtCl2(NH3)2]
[Co(H2O)6]Cl2
Na2[PtCl4]
[CrCl(H2O)5]Cl2
[CoCl2(NH3)4]Cl
[Cu(CN)2(H2O)2]
potassium hexacyanoferrate(III)
tetraamminecopper(II) chloride
diamminedichloroplatinum(II)
hexaaquacobalt(II) chloride
sodium tetrachloroplatinate(II)
pentaaquachlorochromium(III) chloride
tetraamminedichlorocobalt(III) chloride
diaquadicyanocopper(II)
MM 2005 AH