Werner Complex – Preparation and Determination of Structural Formula

A coordination compound is a chemical compound that comprises a metal compound bonded to ligands. Ligands are electron donors of metals and may be photons, ions, or molecules. Metals are Lewis bases, while ligands are Lewis acids. Alfred Werner’s theory of coordination compounds, commonly known as “Werner’s theory,” was published in 1898. Werner conducted experiments with cobalt (III) chloride and ammonia. During the synthesis of Coordination compounds, ligands serve as donor atoms. The synthesis of coordination copmounds, Hexaamminecobalt chloride, Pentaamminechlorocobalt chloride, and Hexaamminenickel chloride require ammonia and chloride as the ligands and cobalt and nickel as the metal cations. The

Preparation of Hexaammine cobalt chloride

Hexaamminecobalt chloride is a metal compound with [Co (NH3)6] Cl3 as its formula. It was named following pioneer companion of three chlorine anions (Cl3-). The identified positive ions is an Ammine complex mental bearing six molecule of Ammonia as dormant ion on Cobalt atom.The origin of this compound has been perceived from its yellow color before contemporary chemistry discarded color as the least important compared to the molecular structure.

Apparatus and materials

Johnson Matthey magnetic susceptibility balance.

Sample of Cobalt chloride divided into 0.05g.

Sample of deionized and distilled water packed in 50ml.

Charcoal, hydrogen peroxide, Hydrochloric acid (6MHCl).

Ice-cold water, beaker and Buchner funnel

Preparation procedure:

Prepare a feverish solution of Hexahydrate cobalt chloride (4.51g) and white ammonium chloride (3.026g) in distilled water (5ml).

Carefully decolorizing charcoal (0.5g).

Add to the mixture 10ml of concentrated ammonia solution.

Cool the compound on tap water while slightly adding Hydrogen peroxide (10ml).

After all hydrogen peroxide is added, burn and maintain a steady temperature of 600 C in a duration of (15-20 min).

After heating, chilly the compound of the mixture in a subsequently ice-cold water, filter the solid and transfer the precipitate in to another beaker with Hydrochloric acid (2ml) and distilled water (40ml).

Filter the suspension once all the solids expect charcoal completely dissolves.

Add to filtration HCl (5ml) and chilly the solution in ice-cold water.

Filter and dry the crystals. Record the weight and calculate the weight of obtained yield (Aspaas and Lindbeck, n.p).

Observation

On additional and heating solution to the charcoal, it didn’t dissolve. Adding more of concentrated ammonia solution, most charcoal dissolved forming a black solution (No Precipitate). However, addition of hydrogen peroxide retained the black solution. Heating after 5min (2:15pm – 2:20pm), the solution was in 600 C and only water vapor appeared at flask’s side and throat. The first filtration, product was black solid. Adding the precipitation to the hot mixture distilled water and hydrochloric acid, it dissolved with exception of charcoal forming a solid layer on top. After second filtration, there was a dark-red filtrate. Addition of HCl into the filtrate formed a dark-brown solution with light brown precipitate. Finally, last filter gave a brown-orange solid (Aspaas and Lindbeck, n.p).

Pentaaminechlorocobalt chloride

This compound complex is busked and arrayed in two-step series beginning with oxidization of ammonia and cobalt chloride solution (Orhanovic and Early, pg. 1479).

2 CoCl2, 6H2O + 2 NH4Cl + H2O2 + 8 NH3 → 12 H2O + 2 [Co (NH3)5(OH2)] Cl3 

The intermediate substance formed as part of the series is heated to trigger coordination of the outer sphere chloride Ions:

[Co (NH3)5(OH2)]Cl3 → H2O + [Co (NH3)5Cl] Cl2

Preparation procedure:

Dissolve Ammonium chloride (7.502g) into a concentrated ammonia (45ml)

Add powdered hydrated cobalt chloride (7.512g) gentily in small portion whleigitating the mixture with magnetic stirrer.

Continue stirring to form a slurry. Slightly add hydrogen peroxide (7.5ml) using a dropper.

After a while, add concentrated hydrochloric acid (45ml), persist on heating holding a steady temperature of 850 C for a duration of about 20min.

Cool the compound formed to a normal room temperature as well as filtering off the precipitate formed on vacuum filtration.

Using 30ml of ice-cold water, wash in several portions the compound so as to eliminate any solid white crystalline) which may be present.

Follow a wash with concentrated hydrochloric acid (30ml), and eventually ethanol (30ml).

Finally, let the product of the compound formed in air exposure to dry (Orhanovic and Early, pg. 1480).

Observation

On the dissolve of the Ammonium chloride to ammonia solution, a colorless solution was formed. Continuous addition of hydrated cobalt chloride while stirring brown, cloudy solution forms as hydrated cobalt chloride dissolves. On adding hydrogen peroxide, solution turned to dark-violent with a lot of effervesces which suddenly subsided. Adding 6MHCl, vapors and bubbles appeared as the solution was turning to dark-red and then dark-purple reddish. On heating the solution, very dark-cloudy purple solution was formed. On pause to stirring and heating, at room temperature, heterogeneous layer were formed (Dark-blue on top and dark-cloudy purple at the bottom). By vacuum filtration, dark-pink solid was obtained (Orhanovic and Early, pg. 1481).

Preparation of hexaamminenickel chloride

This compound is prepared by reacting NiCl2.6H2O with ammonia solution in excess. The hexammine complex precipitates out as the chloride salt since there already chloride anions in the reaction.

This reaction can be represented in the equation shown below;

[Ni (H2O) 6]2+ (aq) + 6NH3 (aq) —> [Ni (NH3)6]2+ (aq) + 6H2O

When the nickel ions are put in the solution, they are dissolved and it becomes hydrated resulting to a green octahedral product [Ni (H2O) 6]2+.The water molecules present in the product, [Ni (H2O) 6]2+ are readily removed by the excess Ammonia hence resulting to formation of hexaamminenickel (ii) chloride (Ingersoll, pg.450).

Procedure

Hydrated nickel chloride of mass 1.214g was put in ethanol solution containing 95% of 10 ml and it dissolved in the solution.

5ml of concentrated ammonia was then added to the solution while stirring,

The precipitate was then filtered by the sunction process, the residue was washed using ethanol and kept to dry on air.

After the product has dried, it is measured to find its weight and the yield of the product is determined

A small part of the sample is put in a labeled test-tube in the oven throughout the night, observe any change on the sample. The other part of the sample is kept in the locker in a protective cover (Ingersoll, pg.453).

Observations

The nickel (ii) chloride was initially green, large irregular solids which was added to 95% ethanol.

On adding the nickel ii chloride to the ethanol, some of the particles dissolves forming a solution, light green in color and no precipitate is formed.

Concentrated NH3 solution was added to the mixture forming a light purple solution with a purple precipitate.

After vacuum filtration was carried out, the product came out as light purple solid chunks (Ingersoll, pg.455).

Discussion

Synthesis of the three coordination compounds; Hexaamminecobalt chloride, Pentaamminechlorocobalt chloride, and Hexaamminenickel chloride involved three main steps which include dissolving the metalsin water to form ions and then adding the ligands or the Lewis bases, heating to remove water of crystallization and then carrying out filtration procedures to obtain the metal complex. In the first phase of the synthesis experiment, the metal salts are formed but contains water molecules. Washing the salt precipitates in excess ammonia removes water molecules because ammonium ions compete with water molecules in binding with the metal ions. Ammonia finally replaces water molecules and binds with the metal ions. Crystallization of the coordination compounds is important to enable analysis and determination of their structural formula.

The structural formula of the complex compounds

Hexaamminecobalt chloride is [Co (NH3)6] Cl3.

Pentaamminechlorocobalt chloride – [Co (NH3)5]Cl3 

hexaamminenickel chloride – [Ni(H2O)6]Cl2

Conclusion

Coordination compounds are usually synthesised as complex salts. Ammonia and chloride ligands use lone pairs of electrons to form bonds with the cations of metals such as cobalt and nickel. Hexaamminecobalt(III) chloride and pentaamminechlorocobalt(III) chloride compounds can be easily obtained in experiments to synthesise complex salts. Synthesis of coordination compounds is essential in industrial applications because these compounds can be used as catalyst in the production organic substances. The brilliant colors of coordination compounds are used as pigments or dyes for fabrics. Coordination compounds are also used in the analysis of various substances such as nickel ions.

Works cited

Aspaas, Andrew, Levi Stanley, and M. Lindbeck.”Synthesis of Hexaammine Cobalt (III) Chloride.” (2000).

Orhanovic, Mato, and Joseph E. Earley.”Kinetics of reduction of pentaamminechlorocobalt (2+) and cis-and trans-bis (1, 2-ethanediamine) dichlorocobalt (1+) by titanium (III).” Inorganic Chemistry 14.7 (1975): 1478-1481.

Ingersoll, J. C., et al. “Catalytic hydrolysis of sodium borohydride by a novel nickel–cobalt–boride catalyst.” Journal of Power Sources 173.1 (2007): 450-457.

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