Oxidation States of Tin. Preparation of Tin (IV) Iodide

The Oxidation States of Tin. Preparation of Tin (IV) iodide and Tin (II) iodide. 

Introduction:

Alfred Werner, a Swedish chemist, determined the octahedral coordination of Werner complexes and gave rise to the field of coordination chemistry. The complexes contained a central transition metal bonded surrounded by a number of negatively or positively charged molecules. The coordination of the structures where unknown until Werner discovered the coordination of Hexaaminecobalt (II) chloride, which is written in many ways, suggesting different coordination of the atoms. The purpose of the experiment conducted is to determine the coordination of three Werner complexes and characterize their structural formulas through a variety of techniques. The techniques utilized are analysis of free chlorides, measuring the conductance, magnetic susceptibility, and of hexaaminecobalt (II) chloride, pentaamine cobalt (II) chloride, and hexaaminemickel (II) chloride.

By titrating the complexes with silver nitrate solution, a precipitate of silver chloride forms and precipitates out of the solution. The non-bonding chlorides in the complexes are reacting with silver forming a precipitate with a low solubility. By calculating the amount of silver nitrate that was used in the titration, we can determine the amount of silver chloride that precipitated out of solution, this results in the amount of free chloride in the solution. Comparing the ratio’s of silver chloride produced to Werner complex in the solution, free chloride ions can be determined.

The conductance of complexes was also determined. The conductance of the complexes corresponds to the ions that are present within the solution. The electrical conductivity the complexes are measured once dissolved in water, the anions and cations dissolve in water. This allows for the determination of structure for metal complexes.

The last technique used was the determination of unpaired electrons in the werner complexes. The Werner complexes were either diamagnetic or paramagnetic, as the contained paired or unpaired electrons which were calculated.

Experimental/Observations:

Part 1: Synthesis of Hexaaminecobalt III chloride (Co(NH₃)₆)Cl₃ :

In an Erlenmeyer flask, a solution containing 4.689g of cobalt III chloride (CoCl₂·6H₂O, a dark purple crystal), 3.005 g of ammonium chloride (NH₄Cl, opaque yellowish crystal) and 5ml of water was heated. The solution started out purple and over time, as it was heated, a color change was noted. Solution turned dark blue over time. Decolorizing charcoal was added, causing the solution to become much dark. 10ml of concentrated ammonia (NH₃) was added to the solution causing it to become brownish/red in color. After the solution was to cooled, 10ml of a 6% hydrogen peroxide (H₂O₂) was added, the solution was heated for 20 minutes at 60C. The solution was then cooled again and vacuum filtered. The bright reddish/brown product was then transferred to a solution containing 2ml of hydrochloric acid (HCl) and 40ml of water. The filtrate was then gravity filtered and another 5ml of concentrated HCl was added. The filtrate was cooled once again and vacuumed filtered. 2.8591g of the bright reddish/brown product was dried and was isolated at a yield of 36%…..

Part 2: Synthesis of Pentaaminecobalt III chloride (Co(NH₃)₅)Cl₃ :

7.5g of NH₄Cl was dissolved in 15ml of 14M NH₃. Finely ground CoCl₂·6H₂O was added the ammonia solution, in small portions, while it was agitated. The solution was initially  purple and transparent and adding the the cobalt crystals resulted in the formation of a brown slurry. 7.5 ml of 30% H₂O₂ was slowly added to the brown slurry, causing an effervescence reaction to occur, releasing a white gas and becoming much darker. Once the effervescence had subsided 45ml of HCl was added to the solution. The solution was heated to 85C and agitated for 20 minutes, then cooled down as a two layered solution was formed. A top blue layer and a bottom dull pink layer. The precipitate was then vacuum filtered and washed with 30 ml of ice cold water, 6M HCl, and 100% ethanol. 6.5729g of the purple product was dried and isolated with a yield of 80%….

Part 3: Synthesis of hexaaminenickel III chloride (Ni(NH₃)₆)Cl₂ :

1.2g of hydrated NiCl₂, a fine light green powder, was dissolved in 95% ethanol. 5ml of 14M NH₃ was added to the nickel solution as it was brought to a boil. The addition of the ammonia lead to the formation of a faint purple precipitate that was vacuum filtered and wash with ethanol. 0.58g was isolated with a … % yield.

Analysis of Compounds:

The products were analyzed to determine their magnetic susceptibility, conductance and the amount of free chloride in solution. The conductance measurements were obtained for all three products through the Sherwood scientific apparatus. 50 ml of 1×10^-3 M aqueous solution of each of the products was prepared by dissolving 0.01570g of Ni(NH3)₆Cl₂, 0.01252 g of Co(NH₃)₆)Cl₃ and 0.01337g of Co(NH₃)₅)Cl₃ in a 50 ml volumetric flask. The conductance measure was then taken.

A Johnson-Matthey magnetic susceptibility balance was used to determine the magnetic moment of each of the three products. The products were packed into a tube and the reading was taken.

The analysis of free chlorides was carried out on both cobalt solutions. 0.05g of the cobalt products was dissolved in a 50ml Erlenmeyer flask and titrated with silver nitrate solution. Fluorescein was used as an indicator and the end point was determined to be a bright pink layer of the cobalt solution.

Data:

Table 1. Results for the synthesis of Co(NH₃)₆)Cl₃, Co(NH₃)₅)Cl₃ and Ni(NH₃)₆)Cl₂

Actual yield	Percent yield A	Theoretical yield B
(Co(NH3)6) Cl3	2.8591g	54.2%	5.272g
(Co(NH3)5)Cl3	6.5729g	83.29%	7.891g
(Ni(NH3)6)Cl2	0.58g	49.23%	1.170g

Sample calculation for percent and theoretical yeild of Co(NH₃)₆) Cl₃ :

Table 2. Results for the analysis of free chlorides for (Co(NH₃)₆)Cl₃ and (Co(NH₃)₅)Cl₃

Volume of AgNO3		Mass of compound	Moles of free Cl-
(Co(NH3)6)Cl3	0.532 ml	0.514ml	0.05g	3
(CO(NH3)5)Cl3	0.417ml	0.515ml	0.05g	2

Sample calculation for moles of free cholride for Co(NH₃)₆) Cl₃ :

Table 3. Results for Conductance Measurements for three compounds

Molar conductance (ohm-1cm2mole-1)	Number of ions C	Lit. ValuesC (ohm-1cm2mole-1)
Co(NH3)6Cl3	297.6	4	235 – 273
Co(NH3)5Cl3	100.8	2	118 – 135
Ni(NH3)6)Cl2	234.3	3	235 – 273

      C) Values obtained from appendix from corresponding molar conductance values.

Table 4. Results for the magnetic susceptibility for the three compounds

Χg (emu mol-1)	ΧMeas	ΧDia	ΧPara	µeff	S	Unpaired electrons
(Co(NH3)5) Cl3	-3.046*10-8	-3.25*10-6	-190.2 * 10-6	0.0001864	0.6625	0.235
(Co(NH3)6)Cl3	-2.603*10-8	-6.507*10-6	-177.2*10-6	0.0001706	0.6326	0.2236
(Ni(NH3)6)Cl2	-1.015*10-7	-2.345*10-5	-166.7*10-6	0.0000713	0.020	0.010

Sample calculation for (Co(NH₃)₅) Cl_{3 :}

Chemical Equations:

In the three-chemical reactions, the metals reacted with the amine forming the products. The chemical reactions are as follows:

Part 1: 2CoCl₂·6H₂O(s) + 2NH₄Cl+10NH₃(aq) + H₂O₂(aq) + 3H₂O(l)  2Co(NH₃)₆Cl₃ + 1/2O_2(g)

Part 2: 2CoCl₂·6H₂O(s) + 2NH₄Cl+8NH₃(aq) + H₂O₂(aq) + 3H₂O(l)  2Co(NH₃)₅Cl₃ + 1/2O_2(g)

Part 3: NiCl₂·6H₂O(s) + 6NH₃(aq)  Ni(NH₃)₆Cl₂(s) + 6H₂O(l)

An oxidation reduction reaction was occurring as hydrogen peroxide was added to the cobalt solutions and used to reduce the cobalt to its 2+ state. The redox reaction is as follows:

R: H₂O₂  H₃O⁺ + 1/2O₂ + e^–      (1)

O: Co³⁺ + e^–  Co²⁺          (2)

Discussion:

To determine the structure of the three complexes, three different techniques where utilized. A magnetic subspecialty measurement, a conductance measurement, and an analysis of free chlorides in each of the three products. Visible color changes were observed in the formation of the brightly colored products indicating that a successful reaction had occurred. The change of color is due to the change in oxidation state. Hydrogen peroxide was used in the reduction of cobalt complexes producing two differently colored cobalt complexes. The in the oxidation reaction we see a change in oxidation state of Co from 3+ to 2+ as hydrogen peroxide is being oxidized. A change in oxidation state causes the solution to change color as the metal complexes contain electrons that absorb light energy and jump to an excited state in a different molecular orbital

Analysis of free chloride. A solution containing 0.05g of Co(NH₃)₆Cl₃ and Co(NH₃)₅Cl₃ was titrated with a silver nitrate solution. The number of moles of free chloride ions was then calculated through their mole ratios. It was determined that Co(NH₃)₆Cl₃ solution contained3 free chloride ions while (Co(NH₃)₅Cl₃ solution contained 2 free chloride ions. The calculated ratios (Table 2) of free chloride ions indicates whether the Chlorine ions are bonded with the cobalt complex, as free chloride ions will precipitate out of the solution in the presence of silver nitrate. From this we can assume that 2 moles of chlorine are not bonded to in cobalt complex in Co(NH₃)₅) Cl₃ while all 3 moles of chlorine are not bonded to the cobalt complex in Co(NH₃)₆)Cl₃. We can conclude that chlorine helps stabilize the positive charge of cobalt complex in Co(NH₃)₆)Cl₃ while a single chloride ions is bonded to the cobalt complex of Co(NH₃)₅Cl₃. Fluorescing, the indicator used in the titration, was added to the solution with 2ml of 2% dextrin solution. The dextrin solution prevents the coagulation of AgCl and the prevention of the AgCl aggregate on the surface of the solution.

Molar conductance. A solution of all three products was prepared with a concentration of 10^-3M. The molar conductance reading was then taken at 20.5C on a Sherwood scientific apparatus. The conductance values were obtained and compared to the literature values and the number ions of each solution can be determined. Co(NH₃)₆Cl₆ had a conductance value of 297.6 ohm^-1cm²mole^-1. From the corresponding literature value, this conductance is due the presence of 4 ions in one mole solution. Similarly, Co(NH₃)₅Cl₅ and Ni(NH₃)₆Cl₂ had molar conductance value of 100.8 and 234.3 ohm^-1cm²mole^-1 which correspond to 2 and 3 ions per mole of solution respectively. From this we can determine the formula of each of the compounds. In hexaaminecobalt (III) chloride, 4 total ions are present which results in one from Co(NH₃)₆²⁺ + 3Cl^–. In pentaaminecobalt (III) chloride, 2 ions are present, one from Co(NH₃)₅²⁺ + Cl^–. In pentaaminenickel (II) chloride, 3 total ions are present, one from Ni(NH₃)₅²⁺ + 2Cl^–. However, for data from the analysis of free chloride does not confer with the molar conductivity of the pentaaminecobalt (II) chloride complex. From the analysis of free chlorides, it was determined that one mole of the complex contained 2Cl^– while the molar conductance suggest 2moles of chloride ion. This discrepancy may be due to the product not being fully dried, and the moisture water may interact and distort the reading of conductance.

Magnetic Susceptibility. The magnetic susceptibility was carried out on a Johnson-Matthey apparatus that determines the magnetic moment of each complex. Through calculating Spin values it was determined that both Cobalt (Co³⁺) complexes, with a d⁶ electron configuration, does not have any unpaired electrons as the spin values were close to 0. From this, we can assume that the electrons are in a low spin state as Hund’s rule of multiplicity suggest that electrons would be paired with altering spin states, and unpairing the electrons would require an increase in energy to overcome Δ_0.

The Nickel (Ni²⁺) complex contain two unpaired electrons. It’s d⁸ electron configuration, with 2 unpaired electrons in a high spin state. The low spin state would not be observed as paring the two electrons was require extra energy.

The three compounds, (Co(NH₃)₆) Cl₃, (Co(NH₃)₅)Cl₃, (Ni(NH₃)₆)Cl₂ were successfully produced and to give yields of 54.2%, 83.29%and 49.23% respectively for the three compounds.

The yields of (Co(NH₃)₆) Cl₃ and (Ni(NH₃)₆)Cl₂ is rather low but it to be expected as the sample may have been lost during the vacuum filtration process while being transferred_. The coordination of the three complexes was determined to be Co(NH₃)₆Cl₃, Co(NH₃)₅Cl)Cl₂ and Ni(NH₃)₅Cl₂.

Conclusion:

The purpose of the experiment was to characterize the structural formulas werener complexes through the synthesis of Co(NH₃)₆Cl₃, Co(NH₃)₅)Cl₃ and Ni(NH₃)₅Cl₂ and the coordination of the compounds was determined to be Co(NH₃)₆Cl₃, Co(NH₃)₅Cl)Cl₂ and Ni(NH₃)₅Cl₂ . The characterizations were conducted with three techniques that determined the moles of free chloride ions, conductance and magnetic moment of the three complexes. The analysis of free chloride ions determined that 3 and 2 chloride ions were present per mole of the two cobalt complexes. Indicating that Cl^– is bonded to Co(NH₃)₆²⁺ complexes, while non-bonded to the Co(NH₃)₅, but function to stabilize the charge on the complex. The molar conductance of the complexes resulted in the presence of 4,2 and 3 total ions for the three Werner complexes. Lastly, the magnetic moment of three complexes was determined and the spin states where calculated. It was determined that both cobalt complexes (Co³⁺) contained 0 unpaired electrons, in a d⁶ diamagnetic electron configuration, in a low spin state. The nickel complex was found to contain 2 unpaired electrons, in a d⁸ paramagnetic electron configuration, with 2 electrons in the high spin state.

References:

1. Simon Fraser University. Inorganic Chemistry, Chemistry 236W laboratory manual: 2016. Vol. 1.81. Print. 9 -10
2. Miessler, G. L.; Tarr, D. A. Inorganic chemistry; Prentice Hall: Boston, 2011.