This sem, Semester 4, Dieba terlibat dgn subjek 'inorganic Chemistry 2' @ 'Coordination Chemistry'. So, salah satu daripada assignment ialah mencari 1 experimen, then run experimen tersebut sorang2... Jadi, inilah hasilnya.. betul lab report Dieba kasi ! hehe.. Moga bermanfaat ! Sekadar perkongsian dan mohon perbetul yg mana silap.. thanks !
Cis and Trans Isomers of Dichlorobis(en)Cobalt(III) Chloride
Objective:
1. To synthesis cis and trans isomer of Dichlorobis(en)cobalt(III)Chloride
2. To determine the differences between cis and trans of the complex.
Geometrical isomer are metal complexesin which the coordinating ligands are present in the same proportion but vary in the arrangement of the ligands around the central metal atom. Despite of always having identical chemical formulas, geometrical isomers often have widely different properties, such as magnetic moments, colors, bond strength, and reactivities.
Cobalt complexes that we will investigate are both have six coordinate. There are six ligands bound to the central atom in octahedral structure. Because here, we have a mixed ligand that has two metal binding sites, our molecules will have a distorted octahedral structure.
We need to synthesis Trans-[Co(en)2Cl2] before we can produce cis-[Co(en)2Cl2]
1. Preparation of Trans-[Co(en)2Cl2]
a) Heat 300ml water in 600ml beaker and maintain it at moderate boil.
b) Combine 4.0g of Cobalt(II)Chloride Hexahydrate with 10 ml water in evaporating dish. Add 15ml of
10% enthylenediamine followed by 15ml of 30% hydrogen peroxide.
c) Place this evaporating dish on the top of the beaker of the boiling water. stir the mixture over this steam
bath for 40 minutes. During this process, the cobalt(II) is oxidize to cobalt(III) by oxygen in air.
d) Add 12ml of concentrated 12M of Hydrochloric acid to this mixture. The heating and stirring is continue
until a thin slurry of crystal is form.
e) The slurry is cooled at room temperature for at least 15 minutes.
f) Filter the mixture using vacuum filtration. Wash with 5ml of 6M HCl to the funnel. Repeat washing process
if the product still brown or blue. Skip the washing process when the product is pure green.
g) Dry and weight the product.
2. Synthesis of Cis-[Co(en)2Cl2]
a) Place 0.2g of green crystal produce before in watch glass.
b) Dissolve this solid material in 6 ml of distilled water and allow this solution to stand about 10 minutes at room temperature.
c) place this watch glass in a water bath, heat, and concentrate it to dryness.
d) A deep violet, glassy material is formed on the watch glass.
Results:
 |
Trans-dichlorobis(en)cobalt(III)Chloride
 |
| cis-dichlorobis(en)cobalt(III)chloride |
|
Discussion:
In this experiment,I have learned how to synthesis coordination complexes trans-dichlorobis(en)cobalt(III)chloride to observe the changes occur between the isomer of this complex.
Coordination compound are formed when a neutral atom, cobalt acting as Lewis acid react with lewis base: Cl an en, that are called as a ligands. In the process of synthesis, CoCl2.6H2O is added to ethylenediamine and H2O2. Hydrogen peroxide, H2O2, is a strong oxidizer which is used to oixidize cobalt.
After 40 minutes, a conc. HCl is added until a thin slurry are formed. The solution is the cooled, and for better cool the mixture in ice bath, so that the crystal can formed perfectly. Filter the solution and green solution is recovered. now, I can assume the product formed is ..
The crystal formed then is used to synthesis cis.. by adding small amount of the green crystal of.. into small amount of water and then reheat the solution. From the observation, the greem solution slowly turned to pale violet solution. However, after I evaporation of water, the glassy green material form. This is due to the loss of water during heating causes the cis isomer re-convert to green trans.. [Co(en)2Cl2]producing the mixture of isomer.
The percentage yield that I get is 16.4 % of [Co(en)2Cl2] This product can be improve by taken some precaution steps.
Firstly, during heating process, we need to manually stir the solution. this allowed the solution for splashing and some of the solution got into the side of evaporating dish. Then, during the addition of the HCl, make sure you add it drop by drop. This is because, when we add the acid slowly, it will lower down the counter ion layer , make it easier to approach each other and tends to form crystalline precipitate.
Moreover, the solution should be cooled properly and much better if we cooled the solution on ice bath. After the filtration, wash the crystal properly with 6M HCl. If the product still brown or blue, repeat the washing process. This may due to the Co2+ that not oxidize completely.
For cis- [Co(en)2Cl2], if violet solid unable to isolated, heat the green solution of trans .[Co(en)2Cl2]. over a steam bath until it turn to violet solution. Then cool it in ice bath and observe what happens.
Sekian, wassalam.. :)
