PART-I. Synthesis and Characterization of Cobalt (III) Ammine complexes.

Introduction
Cobalt(III) complexes are almost always low-spin octahedral. Cobalt(II) forms both tetrahedral
and octahedral complexes; square planar complexes are very rare. As a 3d 7 system, cobalt(II)
complexes have 3 unpaired electrons. With moderate to strong-field ligands, cobalt(II)
complexes tend to be easily oxidized to cobalt(III).
When the ligands can bind in only one way, the coordination number of the complex can be
determined from the formula. NH3 and similar ligands can only be monodentate, o-
phenanthroline can only be bidentate, and so forth. But some ligands can bond in more than one
way. For example, NO3- can be uncoordinated (present as an ion), monodentate (coordinating
through one oxygen), or bidentate (coordinating through two oxygens). Thus when nitrate is
present in a complex, its contribution to the coordination number can be 0, 1, or 2 for each NO 3-
and all nitrates do not need to be the same. In such instances, information other than the formula
must be available in order to determine the complex’s coordination number. Similar to nitrate
(NO3 -), carbonate (CO3 2-) can be ionic, monodentate or bidentate.
Some ligands can bond through different atoms; they are ambidentate. For example, a sulfoxide
(R2SO) can coordinate either through the sulfur or through the oxygen but not through both. The
NO2-ion can bond through the nitrogen or through an oxygen but not both to the same metal
center. The thiocyanate ion, SCN-, can coordinate through the sulfur or through the nitrogen but
only through both when it bridges between two metal centers.
The Chemicals
Cobalt(II) chloride is generally obtained as the hexahydrate, in pink to red slightly deliquescent
crystals. The structure is reported to be [Co(H 2O)4]Cl2·2 H2O. All waters are lost on heating to
140oC. Aqueous solutions are pink to red, becoming blue on heating. The compound has been
used in "invisible" inks, humidity indicators, for painting on glass and porcelain and in the
manufacture of vitamin B12.
Ammonium chloride consists of colorless crystals with a saline taste and a tendency to cake. The
compound sublimes when heated. It is very soluble in water and strongly endothermic as it
dissolves.

Hydrogen peroxide can be made from barium peroxide and dilute phosphoric acid. In the 30%
concentration it is a clear, colorless liquid which contains 30% by weight of H 2O2. It is an
extremely strong oxidizing agent and will attack skin and eyes. Drying of spilled solution on
clothing may cause fire. Trace contamination of the solution can cause rapid evolution of oxygen
gas and heat. 90% hydrogen peroxide is used as a rocket fuel while 3% solutions are sold over
the counter as a disinfectant. 6% solutions are used in hair bleaching preparations. Hydrogen
peroxide is also used in the plastics industry, for bleaching and dyeing, artificially aging wines
and liquors, and in pharmaceutical preparations.

Experiment-1. Preparation of Hexaammine Cobalt (III) Chloride

Purpose:
This experiment illustrates the formation of a coordination compound of cobalt. It raises the
question of whether or not chlorine atom is coordinated to cobalt.
Introduction:
The purpose of this experiment was to synthesize a 6-coordinate cobalt (III) compound from
CoCl2 •6H2O. This is made difficult by the fact that Co 2+ ion is more stable than Co3+ for simple
salts. There are only a few salts of cobalt (III), such as CoF 3,that are known. However, cobalt
(III) can be made stable when in octahedrally coordinated compounds. The determination as to
whether or not the chlorine atom is coordinated or ionic can be determined by gravimetric
determination of the chloride precipitated with silver ions. Volumetric determination of the
chloride with silver is difficult because the usual indicators do not work. Volumetric
determinations have been done using mercury (II) nitrate. Because mercury (II) chloride is only
slightly ionized, there are very few mercury (ll) ions in solution as long as there are chloride ions
present.
The excess mercury (II) ions at the end point can be detected by using sodium nitro prusside as
anas an indicator. The mercury (II) nitro prusside which forms the excess mercury (II) ions is
insoluble and separates as a white turbidity. A difficulty in this experiment is the oxidation of
cobalt (II) to cobalt (III). This could be accomplished through the addition of hydrogen peroxide,
but this method is not suitable for this experiment. A more suitable method is the air oxidation of
cobalt with carbon as a catalyst. An additional benefit of carbon as a catalyst is its ability to shift
the equilibrium in favor of the desired product.
indicator. The mercury (II) nitro prusside which forms the excess mercury(II) ions is insoluble
and separates as a white turbidity.
A difficulty in this experiment is the oxidation of cobalt (II) to cobalt (III). This could be
accomplished through the addition of hydrogen peroxide, but this method is not suitable for this
experiment. A more suitable method is the air oxidation of cobalt with carbon as a catalyst. An
additional benefit of carbon as a catalyst is its ability to shift the equilibrium in favor of the
desired product.
CoCl2 •6H2O + 5NH3+ NH4Cl ↔ [Co(NH3)6]Cl3 + 6H2O + H
Experimental Procedure
Add 5.0g of CoCl2 •6H2O and 3.3 g of NH4Cl to 30 mL of DI water in a 250-mL
Erlenmeyer flask. In the hood add 1.0 g activated charcoal and 45mL conc.
aqueous ammonia. Cool the brown slurry in an ice bath to 0°C, then add 4.0 mL
30% H2O2 from a burette. Do not allow the temperature to rise above 10°C. Heat
the resulting red-brown solution to 60°C, and maintain this temperature for 30min.
(The incubation is needed to ensure complete displacement of all aqua ligands.)
Cool the mixture to 0°C; the product will precipitate from the solution. Collect the
product and the charcoal by filtration.
Recrystallization is necessary to separate the product from the activated charcoal.
Place the solid in a 250-mL Erlenmeyer flask, and add 40 mL hot water and 1.0
mL conc. HCl (test the solution with litmus if necessary, add a few more drops of
HCl). Heat the mixture to 70°C, and filter while still hot. Place the filtrate in an ice
bath, and add 1.0 mL cold conc. HCl (it may be precipitated by common-ion
effect). Collect the orange solid by filtration, wash with 25 mL ice-cold ethanol,
and allow to air-dry. Include the following in the entire lab Report:
1. Percentage yield for the prepared compound
2. Characterize the synthesized complex using the following spectroscopic techniques
Melting point.
Solubility
Experiment-2. Preparation of Chloropentaammine Cobalt(III) Chloride
Purpose:
The purpose is to synthesize chloropentaamminecobalt(III) chloride. It raises the question of
whether the chloride atom is coordinated to cobalt or not.
Introduction:
The cobalt 2+ ion is more stable than the cobalt 3+ ion for simple salts of cobalt. Only a few salts
of Co (II) such as CoF3 are known. However, complexation stabilizes the higher oxidation state,
and a number of very stable octahedrally coordinated complexes of cobalt (III) are known.
The equations of the preparation of [Co(NH3)5Cl]Cl2 are written:-

Experimental Procedure

In a fume hood, add 5 g of ammonium chloride to 30 mL concentrated aqueous ammonia 250-

mL Erlenmeyer flask. (The combination of NH 4Cl and NH3 (aq) guarantees a large excess of the
NH3 ligand.) Stir the ammonium chloride solution vigorously using a magnetic stirring plate
while adding 10 g finely divided CoCl 2 •6H2O in small portions. Next, add 8 mL 30% hydrogen
peroxide to the brown Co slurry, using a burette that has been set up in the hood and filled by the
laboratory instructor. An addition rate of about 2 drops per second is usually sufficient, but care
should be taken to avoid excessive effervescence in this exothermic reaction. (If the reaction
shows signs of excessive effervescence, turning off the magnetic stirrer momentarily will usually
prevent overflow of the solution.) When the effervescence has ceased, add 30 mL conc. HCl with
continuous stirring, pouring about 1-2 mL at a time. At this point, the reaction may be removed
form the hood. Use a heater to heat the solution to 60°C with occasional stirring. Hold the
temperature between 55 °C and 65 °C for 15 min.; this incubation period is necessary to allow
complete displacement of all aqua ligands. Add 25 mL distilled water, and allow the solution to
cool to room temperature. Collect the purple product by filtration through a Buchner funnel;
wash it three times with 7.5 mL cold distilled water and twice with 7.5 mL ice-cold ethanol. (The
solutions must be cold to prevent undue loss of product by redissolving.) Transfer the product to
a crystallizing dish, loosely cover with aluminum foil, and allow to dry until the following
laboratory period. Percentage yield for the prepared compound.

Part-II. The Synthesis and Characterization of Ni (II) Complexes

Introduction
Nickel (II) commonly forms complexes with three different geometries: octahedral, tetrahedral,
and square planar. Some five-coordinate complexes are known but are rare. Nickel (II) is a 3d 8
system so octahedral and tetrahedral complexes will have 2 unpaired electrons and square planar
complexes usually will have none. Octahedral complexes can be prepared from both strong field
and weak field ligands (or a mixture of both). Among four-coordinate nickel (II) complexes,
those with strong field ligands tend to be square planar and those with weak field ligands tend to
be tetrahedral.
Experiment-1. The preparation of [ Ni (en)3]Cl2.2H2O.
Experimental Procedure
Dissolve 6.0g of NiCl2.6H2O in 3mL of H2O. A little warming improves the rate of dissolution.
Cool the solution in ice while adding 5.0g (5.6 mL) of ethylene diamine. Add the ethylene
diamine slowly because the reaction is quite exothermic. Cool. Add 15 mL of cold ethanol to
initiate crystallization. Keep cold for 10 min. The collect the product on a Büchner funnel and
wash with two 5 mL portions of ethanol. Dry in air. Record the yield.
Experiment-2.The preparation of [Ni (NH3)6]Cl2.
Experimental Procedure
Dissolve 3.0g of NiCl2 .6H2O in 5 mL of warm H2O in a 125 mL Erlenmeyer flask and add
5.8mL of concentrated NH4OH. Cool with an ice bath and observe the precipitation of large
violet crystals. Add 15 mL of cold ethanol to complete the precipitation. Collect the crystals on a
Büchner funnel and wash with two 5 mL portions of ethanol. Dry in air. Record the yield.