Synthesis and Characterization of Chloropentaaminecobalt III Chloride and Nitropentaaminecobalt III Chloride Abstract The purpose of this experiment was to synthesize a known compound J chloropentaaminecobalt III chloride Co NH3 5Cl Cl2 and unknown compound M determined to be nitropentaaminecobalt III chloride Co NH3 5NO2 Cl2 Deteriming the compound was the second goal Through the synthesis process of the known J the labile cobalt II was reacted into a coordination complex with amine inner sphere ligands then oxidized to a cobalt III complex The unknown M was then synthesized from the known J by exchanging one labile inner sphere ligand Next four characterization tests were done to find out which ligands attached on the inner and outer sphere of the complex A molar mass test was done by use of creating thiocyanate solutions that had equal volumes then a spec 20 was used to determine the absorbencies which was directly related to moles of the compounds The molecular weight was determined to be 262 318g mol Beer s law was used in the ratio of absorbance with spectroscopy and use of Spec 20 to moles due to the same extinction constant and path length The nonammonia inner sphere ligand was determined by dissolving Compound M in water and finding the lambda max from a UV vis spectrophotometer The charge was also determined by passing dissolved compounds through Dowex 50W X8 cation exchange columns which produced acid to be titrated to find the charge This effluent was titrated and the charge was calculated to be 2 18 This gave the number of counter ions The last test determined the number of ammonia ligands was given by a distillation process into a standardized HCl solution and then a titration with a standardized NaOH solution After calculations the number of ammonia ligands was determined to be 4 77 so approximately five It was then determined that the unknown coordination complex had to be nitropentaaminecobalt III chloride Introduction The general purpose of this lab is to synthesize two cobalt coordination compounds the first is Chloropentaaminecobalt III Co NH3 5Cl Cl2 more easily referred to as compound J and unknown compound M nitropentaamminecobalt III Chloride Co NH3 5NO2 Cl2 The starting cobalt CoCl2 H2O 6 was a 2 oxidation state which was then turned to 3 through a series of reactions that took place The next goal was to characterize the unknown ligands that bonded to the new cobalt 3 compounds Through the series of characterization tests the molar mass non ammonia ligands ammonia ligands and charge can be determined The beginning of meaningful cobalt coordination chemistry was undisputedly in the late 1800 s or early 1900 s8 Before this cobalt had been discovered in 1739 by Georg Brandt in 1739 He discovered it while trying to prove elements could dye glass blue 9 This began with a man named Alfred Werner he is recognized as the father of coordination chemistry and also won a 2 Nobel prize for his works in the field He found that ligands could be replaced by other groups and that often times tetrahedral and octahedral as in Cobalt III complexes complexes were the most likely Because of this discovery he also came to the conclusion that isomers had to be a possibility and brought about what is known as cis and trans isomers of a complex Werner proved and deduced many polynuclear Cobalt III complexes such as ones with NO2 as the one synthesized in this lab Another primary man in coordination chemistry was G S Lewis who proved the nature of covalencies This is that two bonded atoms share two electrons in some way He used this to explain Werner s theory of coordination compounds Later on after World War II new technology was developed which increased knowledge in this area and led to the ability to more easily identify different components of the coordination complexes from X ray and IR spectroscopy The leading scientist in this charge was named Jannik Bjerrum8 A coordination complex has a central atom that has a group of molecules surrounding it on what is called an inner sphere The inner sphere of the complex contains the ligands that bind directly to it These molecules are called ligands Cobalt III is an inert complex while cobalt II is labile with respect to ligand replacement Inert is scientifically defined as a compound that s ligands are replaced very slow while a labile one proceeds very fast Therefore in order to replace the ligands the cobalt II complex is put in an area rich in the ligands which then after ligand attachment it was oxidized to 3 Cobalt is a transition metal that can form a coordination compound This can act as a Lewis acid The electron pair donors that attach to the metal are ligands Monodentate ligands single bonding or chelating ligands many binding or polydentate meaning many toothed can also attach along with bidentate bonding through two atoms A common ligand that attaches is water This happens when a metal salt is dissolved in water Anions can serve as ligands and 3 counter ions ions that balance the charge for example in Co NH3 5Cl Cl2 Chloropentaaminecobalt III Chloride Chlorine acts as both a counter ion and an inner sphere ligand in the metal coordination complex Inner sphere ligands are not easily removed but outer sphere counter ions ones are more easily removed As displayed these metal coordination complexes are octahedral complexes meaning that six ligands can attach to the metal Another common type of complex is the square planar one in which four ligands can attach With these complexes isomers can form which are complexes which have identical formulas within the inner sphere of the complex such as Co NH3 5NO2 Cl2 and Co NH3 5ONO Cl2 Geometric isomers have isomers that lie either next to each other cis or on opposite vertices cis 1 Linkage isomerization is when a ligand can be coordinated to one of two or more different atoms This also shows that NO2 is an ambidente ligand which means it can bind to the cobalt complex by one or more atom in the molecule In this experiment two different compounds are synthesized J and then M from J The first step to form a cobalt II complex from a cobalt II molecule This was done because Cobalt II ligands are much more labile than cobalt III ligands This was then converted from 2 oxidation state to a 3 oxidation state which made the inner sphere ligands much more inert leaving only one ligand still very labile Further in the synthesis a catalyst was used for the process of J A catalyst decreases