COORDINATION COMPOUNDS LECTURE NOTES SRM.pdf

Hii

1. iii) Coordination Compounds
J.KAVITHA, M.Pharm.,
Lecturer,
Department of Pharmaceutical Analysis,
SRM College of Pharmacy
SRM University.
UNIT-I

2. Contents
Prentice-Hall ©
2002
General
Chemistry:
Sl
id
1Werner’s Theory of Coordination Compounds:
An Overview
2Ligands
3Nomenclature
4Isomerism
5Bonding in Complex Ions: Crystal Field Theory
6Magnetic Properties of Coordination Compounds and
Crystal Field Theory
25-7Color and the Colors of Complexes

3. Werner’s Theory of Coordination  Compounds: 
An Overview
•Compounds made  up of simpler 
compounds are called  coordination 
compounds.
•CoCl
3
and NH
3
.
–CoCl
3
∙ (NH
3
)
6 
and CoCl
3
∙(NH
3
)
5
.
–Differing reactivity with AgNO 3
.

4. Werner’s  Theory
yTwotypes of valence  or bonding capacity.
◦Primaryvalence.
xBased on the number of e
‐
an atom loses in forming 
the ion.
◦Secondaryvalence.
xResponsible for the bonding of other groups, called  
ligands, to the central metal atom.
[Co(NH
3
)
6
]Cl
3
→ [Co(NH
3
)
6
]
3+
+ 3 Cl
-
[CoCl(NH
3
)
5
]Cl
2
→ [CoCl(NH
3
)
5
]
3+
+ 2 Cl
-

5. Coordination Number

6. Example  
Charge on the metal ion:

7. 2 Ligands
yLigandsare  Lewis bases.
◦Donate electron pairs to metals  (which are Lewis  
acids).
yMonodentateligands.
◦Use one pair of electrons to form one point of 
attachment to the metal ion.
yBidentateligands.
◦Use two pairs of electrons to form two points of 
attachment to the metal ion.
yTridentate, tetradentate…..polydentate

8. Some  Common MonodentateLigands.

9. Some Common  PolydentateLigands(Chelating Agents)

10. 3 Nomenclature
yIn names and formulas of coordination compounds, cationscome 
first,  followed by anions.
yAnions  as ligandsare named by using the ending –o. 
◦Normally 
x–ideendings change to–o.
x–iteendings change  to –ito.
x–ate endings change  to–ato.
yNeutral molecules  as ligandsgenerally carried the 
unmodified name.

11. Nomenclature
•The number of ligands of a given type is given by 
a prefix.
•Mono,  di, tri, tetra, penta, hexa…
–If the ligand name is a composite name itself
•Place it in brackets  and precede it with a prefix:
–Bis, tris, tetrakis, pentakis... 

12. Nomenclature
•Name the ligands  first, in alphabetical order, 
followed by the name  of the metal centre.
–Prefixes are ignored  in alphabetical order 
decisions.
•The oxidation state of the metal centre is 
given  by a Roman numeral.
•If the complex is an anion  the ending –ate is 
attached  to the name of the metal.

13. Nomenclature
yWhen writing the formula
xthe chemical  symbol of the metal is written first,
xfollowed by the formulas of anions,
◦in alphabetical order.
xand then formulas of neutral molecules,
◦in alphabetical order.

14. 4 Isomerism
yIsomers.
◦Differ in their  structure and properties.
yStructural isomers.
◦Differ in basic structure.
yStereoisomers.
◦Same number  and type  of ligandswith the same mode of 
attachement.
◦Differ in the way the ligandsoccupy space  around  the metal ion.

15. Examples of Isomerism
Ionization Isomerism
[CrSO
4
(NH
3
)
5
]Cl[CrCl(NH
3
)
5
]SO
4
pentaaminsulfatochromium(III) chloridepentaaminchlorochromium(III) sulfate
Coordination Isomerism
[Co(NH
3
)
6
][CrCN
6
]
hexaaminecobalt(III) hexacyanochromate(III)
[Cr(NH
3
)
6
][CoCN
6
]
hexaaminechromium(III) hexacyanocobaltate(III)

16. Geometric Isomerism

17. Optical Isomerism

18. 5 Bonding in Complex Ions: 
Pauling’s Valence  bond theory
yConsider  bonding in a complex to be an 
electrostatic attraction between  a positively  
charged nucleus and the electrons of the 
ligands.
◦Electrons  on metal atom repel electrons on ligands.
◦Focus particularly on the d‐electrons on the metal 
ion.

19. DIMERCAPROL
Dimercaprol (or BAL or British Anti ‐Lewisite) is a suphur analogue of glycerol and is
structural 2,3‐dimercaptopropanol. In the trihydric alcohol there are three hydroxyl groups.
But in dimercaprol, two of these hydroxyl groups are converted into –SH groups (thiol or
merdapto groups).
CH
2
OH‐CHOH‐CH
2
OHCH
2
SH‐CHSH‐CH
2
OH
GlycerolDimercaprol
This was introduced in the second world war as an antidote by the British to the war gas
lewisite which was an arsenical. Since it contains the thiol ( ‐SH) groups, it combines with
the arsenic and so prevents or reverses the effect of arsenic on thiol ‐Conainging enzymes.
Dimercaprol forms poorly dissociating complexes also with mercury and cadmium ions.
Actullaydimercaprol is useful in the treatment of acute poisoning due to arsenic, mercury,
gold, antimony. Bismuth and thallium. It is given by injection. The injection is a sterile
solution of dimercaprol in a mixture of benzy I benzoate and arachis oil.

20. D-PENCICILLAMINE
D-penicillamine is chemically B,B-Di methylysteine. It is derived from
the sulphur-containing aminoacid cysteine and is a monothiol. It is
preparedby thealkalinehydrolysisofbenzylpenicillin.
It readily chelates with heavy metals such as mercury, copper and lead. It is used
in the treatment of wilson ’s disease in which the copper content of the liver,
brain and other tissues is grossly increased it is also used in the treatment of
heavy metal poisoning such as acute lead poisoning and acute mercury
poisoning. D-Penicillamine is also used in the treatment of rheumatoid arthritis.

21. 1,10–PHENANTHROLINE
1,10–Phenanthroline is a complexing agent which forms stable, highly coloured complexes
with a metal in two oxidation states with a suitable oxidation –reduction potential. So 1,10–
phenanthroline-metal complex can be used as an oxidation–reduction indicator. 1,10-
orthophenanthroline has the following structure:-
It forms complexes with metals like iron,copper and zinc. Three molecules of 1,10-
phenanthroline dissolve easily in solutions of ferrous salts and combine with one ferrous ion to
give the 1,10-phecanthroline-ferrous complex known as ferroin which is intensely red in colour.
It has the following structure:-
It is oxidised to the pale blue ferric compound by any oxidizing agent such
as ceric ammonium sulphate or nitrate.Since the colour change is very
striking, ferroin is used as an indicator in redox titirations such as the assays
of ascorbic acid tablets, ferrous gluconate tablets, acetomenadione tablets
etc, at the end point ferroin is converted to the pale blue ferric complex.
[Fe(C
12
H
8
N
2
)
3
]
2
+[Fe(C
12
H
8
N
2
)
3
]
3
++e
-

22. EDTA
It has already  been stated that  aminopolycarboxylic acids are very  goodcomplexing agents. 
They complex metals and fix them in uniomsable combination in 5 –or ‐6 membered rings 
which  are quite stable, ethylene diaminetetraacetic acid  is one such.  Its structure is given 
below:‐
It forms water soluble complexes knowns as chelates with metals like Cu
2+
and Mg
2+
Disodium salt of ethylene diaminetetraacetic acid is a white, water- soluble dehydrate which
can be used as a primary standard, it is known as EDTA or disodium edetate or sodium edetate. It is used in complexometric analysis as a titrant. It is non-specific in action and can be used for the estimation of the alkaline earths and transition elements. It is simply known as Na
2
H
2
Y and it ionizes in solution as H
2
Y
2-
which reacts quantitatively with may cations
such as Ca
2+
and Mg
2+
, forming complexes. Other application of EDTA may be found in the
text.