Rate of Isomerism of cis[Co(en)2Cl2]Cl
Abstract:
In the course of this experiment the rate of isomerism for the coordination complex cis[Co(en)2Cl2]Cl was determined using UV/Vis spectrometry. Using a range of wavelengths the optimum spectrometer setting for analysis was identified. The corresponding maximum and minimum absorbance of the cis and trans isomers respectively at 540 nm meant that it was selected as the wavelength to determine the rate of conversion between the isomers. The first order rate constant was calculated to be 0.0092 m-1 which is somewhat similar to the literature value of 0.00845 m-1 (Brasted and Hiriyama 1958). The half-life (t 1/2) was found to be 75.34 minutes.
Introduction:
The compound [Co(en)2Cl2]+ is known as a coordination complex, that is, it consists of a Cobalt atom surrounded by an array of molecules to which it is bound, called ligands (Brown 2010). In this case the ligands are Ethylenediamine which are ‘bidentate’, meaning bound in two locations. These ligands are bonded between the two Nitrogen atoms as seen in figure 1 below. This complex occurs in two geometric isomers, cis-[Co(en)2Cl2] + and trans-[Co(en)2Cl2] +. In this experiment the Chloride salt form of the complexes were used i.e. cis-[Co(en)2Cl2]Cl.
Figure 1:
The Trans and Cis isomers of [Co(en)2Cl2]+
Source: Shapter ,J. 2014 Experiment 1: Rate of Isomerism cis[Co(en)2Cl2]Cl, Flinders University, Australia
The Cis- isomer form of the complex which is purple in solution reacts to form the Trans- isomer which is green in solution. This experiment uses spectroscopy to quantify the conversion of the Cis into the Trans isomer due to the fact that the concentration of the Cis isomer is proportional to the difference in absorbance of the two complexes in solution.
This isomerism of the Cis-form is a first order reaction and its rate is expressed in equation 1 below.
Equation 1:
By measuring the optical densities at time 0, t and infinity the rate constant k can be determined with equation 2, a
In the course of this experiment the rate of isomerism for the coordination complex cis[Co(en)2Cl2]Cl was determined using UV/Vis spectrometry. Using a range of wavelengths the optimum spectrometer setting for analysis was identified. The corresponding maximum and minimum absorbance of the cis and trans isomers respectively at 540 nm meant that it was selected as the wavelength to determine the rate of conversion between the isomers. The first order rate constant was calculated to be 0.0092 m-1 which is somewhat similar to the literature value of 0.00845 m-1 (Brasted and Hiriyama 1958). The half-life (t 1/2) was found to be 75.34 minutes.
Introduction:
The compound [Co(en)2Cl2]+ is known as a coordination complex, that is, it consists of a Cobalt atom surrounded by an array of molecules to which it is bound, called ligands (Brown 2010). In this case the ligands are Ethylenediamine which are ‘bidentate’, meaning bound in two locations. These ligands are bonded between the two Nitrogen atoms as seen in figure 1 below. This complex occurs in two geometric isomers, cis-[Co(en)2Cl2] + and trans-[Co(en)2Cl2] +. In this experiment the Chloride salt form of the complexes were used i.e. cis-[Co(en)2Cl2]Cl.
Figure 1:
The Trans and Cis isomers of [Co(en)2Cl2]+
Source: Shapter ,J. 2014 Experiment 1: Rate of Isomerism cis[Co(en)2Cl2]Cl, Flinders University, Australia
The Cis- isomer form of the complex which is purple in solution reacts to form the Trans- isomer which is green in solution. This experiment uses spectroscopy to quantify the conversion of the Cis into the Trans isomer due to the fact that the concentration of the Cis isomer is proportional to the difference in absorbance of the two complexes in solution.
This isomerism of the Cis-form is a first order reaction and its rate is expressed in equation 1 below.
Equation 1:
By measuring the optical densities at time 0, t and infinity the rate constant k can be determined with equation 2, a
References: Brasted, R. Hirayama C. 1958 The cis-trans Isomeration of Dichlorbis-(ethylenediamine)-cobalt(III) Chloride and Dichlorbis-(propylenediamine)-cobalt(III) Chloride in Alcohols, Journal of Chemistry, Department of Chemistry, University of Minnesota. Vol. 80 pp 788 – 794. Brown, T. LeMay H. Bursten, B. Murphy, C. Langford, S. & Sagatys D. 2010. Chemistry: The Central Science, Pearson, Australia. pp 1196 – 1197. Christian, G. 2010. Analytical Chemistry 6th Ed., John Wiley & Sons, USA. pp 159, 270 – 271. Mahaffy, P. Bucat, B . Tasker, R. Kotz, J. Treichel, P. Weaver, G. & McMurry, J. 2011. Chemistry: Human Activity, Chemical Reactivity, Nelson Education, Canada. pp 99, 115 – 116. Appendices: Appendix 1: Figure 3: Absorbance of Cis and Trans Isomers at Various Wavelengths (Varian Car 50 UV-Vis spectrometer)