Coordination Chemistry 4 Flashcards
explain bonding in metal carbonyls
The metal-carbon bond in metal carbonyls
possess both s and p character.
The M–C s bond is formed by the donation of lone pair of electrons on the carbonyl carbon into a vacant orbital of the metal.
The M–C p bond is formed by the
donation of a pair of electrons from a filled d orbital of metal into the vacant antibonding p* orbital of carbon monoxide.
The metal to ligand bonding creates a synergic effect which strengthens the
bond between CO and the metal
metal carbonyls
The homoleptic carbonyls (compounds containing carbonyl ligands
only) are formed by most of the transition metals. These carbonyls
have simple, well defined structures.
shape of the carbonyls:
i) [Ni(CO)4]
ii) [Fe(CO)5]
iii) [Cr(CO)6]
iv) [Mn2(CO)10]
v) [Co2 (CO)8]
i) tetrahedral
ii) trigonal bipyramidal
iii) octahedral
(iv) 2 square pyramidal joined at the tips
v) Co – Co bond bridged by two CO groups
uses of qualitative analysis
Coordination compounds find use in many qualitative and
quantitative chemical analysis. The familiar colour reactions given
by metal ions with a number of ligands (especially chelating ligands),
as a result of formation of coordination entities, form the basis for
their detection and estimation by classical and instrumental methods
of analysis. Examples of such reagents include EDTA, DMG
(dimethylglyoxime), a–nitroso–b–naphthol, cupron, etc.
hardness of water
Hardness of water is estimated by simple titration with Na2EDTA.
The Ca2+ and Mg2+ ions form stable complexes with EDTA. The
selective estimation of these ions can be done due to difference in
the stability constants of calcium and magnesium complexes.
extraction of noble metals
Some important extraction processes of metals, like those of silver and
gold, make use of complex formation. Gold, for example, combines with
cyanide in the presence of oxygen and water to form the coordination
entity [Au(CN)2]– in aqueous solution. Gold can be separated in metallic
form from this solution by the addition of zinc.
purification
Similarly, purification of metals can be achieved through formation
and subsequent decomposition of their coordination compounds For example, impure nickel is converted to [Ni(CO)4
], which is
decomposed to yield pure nickel.
coordination cpds in biology
The pigment responsible for photosynthesis, chlorophyll,
is a coordination compound of magnesium. Haemoglobin, the red
pigment of blood which acts as oxygen carrier is a coordination
compound of iron. Vitamin B12, cyanocobalamine, the anti–
pernicious anaemia factor, is a coordination compound of cobalt.
Among the other compounds of biological importance with
coordinated metal ions are the enzymes like, carboxypeptidase A
and carbonic anhydrase (catalysts of biological systems).
catalyst for industrial processes
Coordination compounds are used as catalysts for many industrial
processes. Examples include rhodium complex, [(Ph3P)3RhCl], a
Wilkinson catalyst, is used for the hydrogenation of alkenes.
electroplating
Articles can be electroplated with silver and gold much more
smoothly and evenly from solutions of the complexes, [Ag(CN)2]-and [Au(CN)2]–
than from a solution of simple metal ions.
black and white photography
In black and white photography, the developed film is fixed by washing with hypo solution which dissolves the undecomposed AgBr to form a complex ion, [Ag(S2O3)2]3–
chelate therapy
An example is the treatment of problems caused by the
presence of metals in toxic proportions in plant/animal systems.
Thus, excess of copper and iron are removed by the chelating ligands
D–penicillamine and desferrioxime B via the formation of coordination
compounds. EDTA is used in the treatment of lead poisoning. Some
coordination compounds of platinum effectively inhibit the growth
of tumours. Examples are: cis–platin and related compounds
