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Transition metal complexes

central metal ion surrounded by ligands

ligandmolecule 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-

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Transition metal complexes 2

ligands

• monodentate e.g. CN-, H2O, NH3

• bidentate e.g. ethanedioate (oxalate), 1,2-diaminoethane (ethylenediamine)

C-CO O

O O.. .... ..- -

H H

H2N C C NH2

H H

.. ..

• hexadentate e.g. ethylenediaminetetraacetic acid (EDTA) (p60)

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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 .

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Shapes of metal complexes

Co-ordination

number

Shape of complex

2

4

4

6

X - M - X

X X MX X

X

M

X X X

X

X X MX X

X

linear

square planar

tetrahedral

octahedral

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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]

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Naming metal complexes

1. 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]

2. The name of the complex part (ion or neutral) consists of 2 parts

written as 1 word.

3. Ligands are named first, in alphabetical order, and the central metal

ion second.

4. 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.

p60

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Naming metal complexes 2

• 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.

K3[Fe(CN)6]

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Naming metal complexes 3

1. K3[Fe(CN)6]

2. [Cu(NH3)4]Cl2

3. [PtCl2(NH3)2]

4. [Co(H2O)6]Cl2

5. Na2[PtCl4]

6. [CrCl(H2O)5]Cl2

7. [CoCl2(NH3)4]Cl

8. [Cu(CN)2(H2O)2]

1. potassium hexacyanoferrate(III)

2. tetraamminecopper(II) chloride

3. diamminedichloroplatinum(II)

4. hexaaquacobalt(II) chloride

5. sodium tetrachloroplatinate(II)

6. pentaaquachlorochromium(III) chloride

7. tetraamminedichlorocobalt(III) chloride

8. diaquadicyanocopper(II)