Werner 514o1u

Werner's coordination theory & its experimental verification: In 1893, Werner was the first to propose correct structures for coordination compounds containing complex ions , in which a central transition metal atom is surrounded by neutral or anionic ligands . CoCl3•6NH3 This type of representation does not implies any proper geometry around the central metal ion

Primary Valency

Secondary Valency

Primary valency may be defined as +ve charge raised over central metal ion as its oxidation state

Secondary valency may be defined as no of mono dentate or equivalent to mondentate ligand attached to central metal ion. It defines the Coordination No.

It is ionisable and variable

It is non ionisable and fixed

Q. Show Experimental observations of werners theory? Werner showed that his postulates are consistent with experimental observations. He made use of basically three kinds of experiments to justify his conclu8ions. Let us look at some of these experiments. It is well known fact that weaker base in a compound is replaced on reacting with a stronger base. For example, ammonia is released from ammonium salts h) reaction with a strong base like NaOH. However, +3 when a complex containing ammonia molecules like [co(NH3)6] is treated with NaOH, no ammonia is released. It is not released even on treatment with strong acids under mild conditions. A reasonable conclusion would be that the ammonia molecules are bound in a different manner to the metal ion. The qualitative and quantitative presence of halogen in ionic form can be established by treating the compound with silver nitqte, which would give a precipitate of silver chloride. or example, a compound with a composition CoCl3 -5NH3 on treatment with AgN03 gives two mole AgCl precipitate per mole of the compound. From this observation the obvious conclusion is that one chlorine is bound to metal in a different way from the other two. -3

Measurement of molar conductance of a salt solution of approximately 10 M concentration can tell us the -1 number of ions present in solution. For instance a molar conductance value of around 520 ohm mol 1 2 -1 cm indicates the presence of five ions in solution whereas values around 400,230 and I00 ohm mol 1 2 cm indicate 4.3 and 2 ions respectively. Werner analysed a series of platinum arnmine complexes and arrived at correct formulation in each case on the basis of molar conductance measurements. Wemer argued that since the secondary valencies have a definite orientation in space, complexes should show stereoisomerism the case of a six coordinated complex three geometrical shapes are possible namely. Planar prismatic or octahedral. Application Of Werner’s Theory 1.

It could predict the exact formulation of each complex.

2. It could explain the behavior (different properties) of each complex and was able to suggest as to why different complexes of the same metal atom and ligands showed different behavior. 3. It could predict the structures of different complexes with coordination number 4 (tetrahedron or square planar) and 6 (octahedral). 4. It could explain the existence of isomerism in inorganic complexes (i.e., other than due to the presence of carbon). It could predict both geometrical (cis and trans) and optical isomerism in coordination compounds. 5. It could predict other forms of isomerism in coordination compounds, e.g., ionization or coordination isomerism which are different form both geometrical and optical isomerism.