Chem 1CL Saul Ruiz May 13 2012 Experiment 18 Synthesis of Transition Metal Coordination Complexes The purpose of this experiment is to synthesize isolate and analyze the cis and trans isomers of Co en 2Cl2 Cl as well the synthesis and analysis of the Co NH3 6 Cl3 and Co NH3 5Cl Cl2 compounds Through this the effect of the ligand field strength on the color of a compound can be observed The en is representative of ethylene diamine NH2CH2CH2NH2 Each of these compounds consists of the coordination complex ad a counter ion For example the compound Co en 2Cl2 Cl is a salt which consists of a coordination complex the Co en 2Cl2 ion and the chloride ion Cl The chloride located outside of the square brackets is considered the counter ion which is used to balance the charge in the compound as a solid substance is always neutral The salt of the trans isomer is green and the salt of the cis isomer is purple The reason for this is that the color of a coordination complex is the complementary color of the light it absorbs For instance the trans isomer is green because it absorbs in the red region of the visible spectrum whereas the cis isomer is purple mainly because it absorbs light in the yellow region of the visible spectrum Furthermore yellow light has a shorter wavelength and higher energy than red light which means that the crystal field splitting is greater for cis than it is for trans In can be noted that from the magnetism and absorption spectra of coordination complexes the relative field strength of ligands can be determined meaning the stronger the ligand field strength the greater the splitting The order of ligand field strength is called the spectrochemical series with weak field ligands having small and high spin whereas strong field ligands have a large and low spin Parts 1 and 2 of the experiment deal with the synthesis of Co NH3 6 Cl3 and Co NH3 5Cl Cl2 Due to the fact that NH3 is a strong field ligand and Cl is a weak field ligand the color observed for both of these compounds results to be different In order to determine the limiting reagent theoretical yield and percent yield various formulas for the syntheses of both of these compounds had to be utilized Charcoal NH 3 Co 6 Cl 3 14 H 2 O 2Co Cl 2 6 H 2 O 2 NH 4 Cl 10 NH 3 H 2 O2 2 NH 3 Cl3 12 H 2 O 5 H O Co 2 2Co Cl 2 6 H 2 O 2 NH 4 Cl 8 NH 3 H 2 O2 2 NH 3 NH 3 Co 5 Cl Cl 2 H 2 O Co 5 H 2 O Cl 3 2 2 HCl For both parts the limiting reagent resulted being the CoCl2 6H2O The calculated theoretical yields were 2 251 grams and 2 116 grams for parts 1 and 2 In addition the calculated percent yields were 8 62 and 26 14 respectively A possible reason for obtaining percent yields less than 100 is that every time a component or reaction is transferred to another container some of the compound is lost Another possible reason as to why it can be possible to have less than 100 is due to stopping the reaction before it has completely reacted Thus 100 percent yield is a concept that is impossible to achieve due to limitations in measurement accuracy especially using the equipment that is provided in the laboratory The absorption spectrums show that the Amax for part 1 is around 0 071 Abs and the at Amax for part 1 is around 484 nm The color of the product turned out to be yellow orange which makes sense because the light absorbed was blue which has a wavelength of about 450 nm For part 2 the Amax was around 0 66 Abs and the at Amax was around 528 nm This also makes sense because the light that was absorbed was yellow which has a standard wavelength of 580 nm The color of the Co NH3 6 Cl3 turned out to be dark pink or purple whereas the color of the Co NH3 5Cl Cl2 was dark red or purple looking The color of light absorbed by the complex ion is relative to the electronic energy changes in the structure of the complex i e the electron jumping from a lower energy state to a higher energy state Moreover electronic transitions produce color in the visible region of the electromagnetic process The observed color of the coordination complex appears as the complement of the color it absorbs Strong energy field ligands have a large and are more likely to produce low spin complexes which results in the absorption of high energy light Contrastingly weak field ligands have a small and are more likely to produce high spin complexes which results in the absorption of low energy light Absorbed color versus observed color wheel For example if the compound absorbs yellow light then it will appear violet Parts 3 and 4 of the experiment deal with the synthesis and isolation of the cis and trans Co en 2Cl2 Cl isomers and obtaining the visible spectrum of the two isomers using a spectrophotometer Similar to Parts 1 and 2 the following equations had to be used in order to CH3OH Heat determine the limiting reagent as well as the theoretical and percent yields en 2 Cl Co 2 Cl H 2 O HCl 11 H 2 O 1 2Co Cl 2 6 H 2 O 4 H 2 NCH 2 CH 2 NH 2 4 HCl O2 2 2 en en Co 2 Cl2 Cl HCl H 2 O Co 2 Cl2 Cl H 2 O HCl 2 The results for the limiting reagent for both parts 3 and 4 also ended up being the CoCl2 6H2O One possible reason as to why the CoCl2 6H2O appears to be the limiting reagent throughout the whole lab is that the most expensive element is usually set as the limiting reagent though this can also be proven mathematically The calculated theoretical yield for part 3 was 1 420 grams but unfortunately there was no theoretical yield obtained for part 4 most likely due to the multitude of transfers performed during that section of the experiment The percent yield for part 3 was 13 94 Some possible reasons as to why a percent yield below 100 was obtained could be due to incomplete reactions side reactions losses due to manipulation e g stuff gets stuck in the filter or losses due to physical processes e g evaporation Also the loss of some of the compound because of every time a compound or reaction is transferred to another container can be to blame For this part of the experiment the absorption spectrums revealed that the Amax for trans was around 1 06 Abs and the at Amax was around 625 nm The color of the product was green which goes along with the fact that the light absorbed was red whose wavelength is around …