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Werner Complexes - Preparation and Determination of Structural Formula

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Introduction

Werner Complexes - Preparation and Determination of Structural Formula Abstract: In this experiment three Werner complexes, hexaamminecobalt(III) chloride, pentaamminechlorocobalt(III) chloride and hexaamminenickel(II) chloride were synthesized so their structural formula could be examined through magnetic susceptibility, electronic conductance measurements and the analysis of free chloride in the two cobalt complexes through titrations of silver nitrate. Cobalt (III) coordination compounds usually only form in low spin, octahedral complexes where the all t2g are paired leaving all the eg unpaired; whereas nickel(II) complexes are usually formed in the high spin state1. Through these analytical methods, it was found that: hexaamminecobalt(III) chloride has three free chloride ions to form the complex [Co(NH3)6]Cl3, in the low-spin state. Pentaamminechlorocobalt(III) chloride and hexaamminenickel(II) chloride both have two free chlorine ions to form the complexes [Co(NH3)5Cl]Cl2 and [Ni(NH3)6]Cl2 respectively. As expected, pentaamminechlorocobalt(III) chloride has a low spin electron arrangement, and hexaamminenickel(II) chloride is in a high spin state. Introduction: Alfred Werner was the first to discover the structure for coordination compound in 1893, thus they were given the name "Werner Complexes". For this research he was given the Nobel Prize in 1913. Werner complexes are complex ions that contain a transition metal in the center, which is surrounded by anionic or neutral ligands.2 The metal in this case acts as a Lewis acid (electron pair accepting) and the anionic ligands act as a Lewis base (electron pair donating). ...read more.

Middle

and ethanol (30.6mL, 100%). The product was then dried in an oven at 100 degrees Celsius for one hour. After drying, the product was a dull pink solid(6.421g) at a 81.7% yield. Synthesis of hexaamminenickel(II) chloride: Nickel chloride (1.210g) was dissolved in ethanol (10.2mL, 95%) which produced a lime-green solution. Concentrated ammonia (5.1mL) was added to the solution, which produced a milky-purple color with a light purple precipitate. The precipitate was then vacuum filtered for 20 minutes and washed with ethanol (6mL, 95%). The product was light purple(0.951g) with 78.7% yield. All three substances synthesized were analyzed to find conductance measurements, and magnetic susceptibility. The two cobalt products were titrated with silver nitrate to find the amount of free chloride ions contained in both. Results and Data: Reagent masses used: Reagent Mass CoCl2*6H2O 4.590g for [Co(NH3)6]Cl3 7.365g for [Co(NH3)5Cl]Cl2 NiCl2*6H2O 1.210g NH4Cl 2.946g for [Co(NH3)6]Cl3 7.560g for [Co(NH3)5Cl]Cl2 Mass of products: Product Mass [Co(NH3)6]Cl3 0.123g [Co(NH3)5Cl]Cl2 6.421g [Ni(NH3)6]Cl2 0.915g Balanced Equations: Charcoal 1) 2CoCl2*6H2O(s) + NH4Cl(s) + 10NH3(aq) + H2O2(aq) + 3H2O(l) 2[Co(NH3)6]Cl3(s) + 1/2O2(g) 2) 2CoCl2*6H2O(s) + 2NH4Cl(s) + 8NH3(aq) + H2O2(aq) + 3H2O(l) 2[Co(NH3)5Cl]Cl2(s) + 1/2O2(g) 3) NiCl2(s) + 6NH3(s) [Ni(NH3)6]Cl2(s) 4) Oxidation: Co3+ + e- Co2+ 5) Reduction: H2O2 H3O+ + e- + 1/2O2 Theoretical Yields: Hexaamminecobalt(III) chloride: * = Pentaamminechlorocobalt(III) chloride: = Hexaamminenickel(II) chloride: = % Yields: Hexaamminecobalt(III) chloride: * 100% = 2.38% Pentaamminechlorocobalt(III) chloride: = 81.7% Hexaamminenickel(II) ...read more.

Conclusion

Even though all three compounds were produced successfully, only two of them had a decent yield. Pentaamminechlorocobalt(III) chloride and hexaamminenickel(II) chloride were produced at 81.7% and 78.7% respectively, whereas hexaamminecobalt(III) chloride was only produced at with a 2.38% yield. This was most likely due to inadequate suction while performing the various vacuum filtrations, which would have left some of the compound in the Buchner funnel when the product was in the filtrate. Conclusion: Through various experimental techniques the three coordination compounds, [Co(NH3)6]Cl3, [Co(NH3)5Cl]Cl2 and [Ni(NH3)6]Cl2 can easily be examined and characterized. The three methods were useful in characterizing a different part of each compound. Free chloride titrations can quickly produce the amount of non bonding chloride anions present in a compound's crystal lattice. As shown in the structures above, hexaamminecobalt(III) chloride has three non bonding chloride ions, where pentaamminechlorocobalt(III) chloride and hexaamminenickel(II) chloride both have two non bonding chlorides. Conductance measurements can show the number of total ions available in a solution. Hexaamminecobalt(III) chloride has four total ions, one for the main structure, and three for the charge balancing chloride anions. Pentaamminechlorocobalt(III) chloride and hexaamminenickel(II) chloride both have three total ions, the main cation metal complex, and two chloride anions again to balance the charge Finally, Magnetic susceptibility is a simple way of determining that the compounds were diamagnetic or paramagnetic, and finding out how many lone pairs of electrons are included in the valence shell. Analyzing the results show the two cobalt based products have a low spin, diamagnetic electron arrangement, and the nickel complex has a high spin and paramagnetic electron arrangement. ...read more.

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