These molecules or ions are functioning as ligands (electrophile in organic compounds). They are easily attracted by electrophile (electron deficiency atoms or ions Ligands are species that have at least one lone pair of electrons that are readily donated to a metal or an ion to form a coordinate bond.
According to lewis acid- base theory, all ligands are lewis base as they act as donor. In the contrary, the metal, central atom act as an lewis acid as it receives lone pair electrons from the ligands when forming the complex ions. The properties Of lewis acid is to have high electron deficiency. For transition metals in this experiment, the high charge density, positive charge and their vacant bonding orbitals leads to tendency to attract lone pair electron by filli ng up their vacant orbitals. Metal acetylacetonates, formed by a metal and multiple acetylacetonate anions, are prime examples of coordination complexes.
In this experiment, the metal use is copper (II) ion which is crystal blue in colour when it is copper(ll)nitrate. All metal ions in solution can react well with water. The water molecules can also be weakly bonded or more strongly as a ligand to form a complex ion, and these can also present in solid ‘hydrated’ salts of crystallization. For example, copper (II) nitrate (Cu(N03)203H20) The metal complexes that contain at least one ammonia (NH3) ligand are called metal ammine complexes. Metal acetylacetonates are coordination complexes derived from the acetylacetonate anion(acac) and metal ions.
The coordination number of a omplex ion is the number of coordinate bonds being formed by the metal ions at its central. Apparatus: beaker, glass rod, measuring cylinder, suction filtration set Materials: , ammonia, acetyl acetone, distilled water Methodology: First, 6g of copper(ll) nitrate (Cu(N03)2C]3H20) was dissolved in 60cm3 of water and the solution of Ammonia was added slowly with stirring until the precipitate first formed has just redissolved. The solution was continued to be stirred, then 6cm3 of acetyl acetone was added drop by drop into the solution.
For copper, thee electronic configuration is 1s22s22p63s23p63d104s1. Although the 4s orbital supposed to have lower nergy level than the 3d, but half and complete filled 3d orbital will be much more stable. When the copper(ll)nitrate salt was put into the distilled water, the salt dissolved completely in water to form hexaaquacopper(ll) complex and nitrate ions. The nitrate ions will then later become niric acid. Nitrate ion which a Lewis base will react with water (in this case as acid) to form nitric acid(conjugate acid ) and OH- (conjugate base).
Strong base creates weak conjugate acid; strong acid creates weak conjugate base and vice versa. Nitrate as a strong lewis base the creats a weak acid which is nitric acid. Furthermore all nitrates salts are soluble in water, that is why copper(ll)nitrate dissolve quickly. The formation of the aqua complex is due to high charge density of the copper(ll) which polarize the water molecules that are coordinate to them resulting in formation of Oxo-anions. The complex form in this reaction is blue in colour. The colour depends on the nature of the metal ion, oxidation state and type of ligands.
For copper ion, there are naturally two colours base on their oxidation state. Red precipitate for copper(l) and blue solution for copper(ll). Different ligands produce different colour as well. When ammonia is added into the omplex, two types Of reaction can OCCUr. It could either be a base or a ligand. In this experiment, we added more ammonia in order to undergo the ligand displacement reaction. Why is it reacting as ligand if excess ammonia is added? This is because ammonia itself is a strong base, which produce hydroxides in water. Reaction will then undergo as base and produce will creates white precipitation.
However, when excess ammonia is added, the reaction will move forward until a point where the product is actually a lot more than the reactants, and then reaction turns backwards allowing then ammonia to react as a ligand. In accordance to Le Chateliers principle, when a mixture at equilibrium is subjected to stress, the reaction proceeds in the direction that relieves or partially offsets the impact of the stress. When the ligand reaction exchange occurs, the precipates redissolved to give dark blue solutions in which a ligand exchange reaction has occurred.
There is a slightly unusual case beause only four of the six water molecules get replaced to give the tetraamminediaquacopper(ll) ion, [Cu(NH3)4(H20)6]2+. The diagram below show the tetraamminediaquacopper(ll) ion. The reason for this displacement is due to the more stable form af the mine complex, compare to the aqua complex. It can be justify as complex ions do not have the same stability and undergo ligand displacement reactions. The rate of the displacement depends on the nature of the metal cations and ligands (strength of ligands).
A complex is considered stable if the ligand is not able to be substitute easily. Generally, the stronger the ligand, the more stable the complex and vice versa. Subsequenty, acetyl acetone is added drop by drop into the solution. Another ligand substitution occurs again with the anion of acetyl acetone act as the ligand. In fact that the u bstitution occurs means that the anion of acetyl acetone is a stronger ligand than both ammonia and water. A base must be include in this reaction as the acetyl acetone is currently a weak organic acid realeasing a proton to form an anion.
As a weak acid, the formation of the anion is slow. The base is to function as a deprotonation agent for acetyl aceton. How? Again, Le Chateliers principle is used. In the presence of ammonia base, the proton released by the acetyl acetone will be neutralize. Reduction of the product of the hydrolysis of the acid causes the reaction move forward. Hence, more anions of acetyl acetone is produce. The percentage yield in this experiment is 150%. This is an error due to the factor that too much of water is use to rinse the end product, bis(acetylacetonato)copper(ll).
In the end, it wasn’t able to dry thoroughly, causing it heavier than it supposed to be. Precaution: To avoid reading error, the eye must be perpendicular to the reading on the measuring cylinder. During mixing the ammonia with copper(ll)nitrate, it must be added drop by drop in order to get the exact amount needed to dissolve the first formed precipitate. Conclusion: The reaction between copper (II) nitrate and acetyl acetone produce is(acetylacetonato)copper(ll). Acetyl acetone act as a ligand and form coordinate bond with copper(ll) ion.
The complex is successfully synthesis and with a yield of 150%. It is likely due to unable to fully dry the complex. The colour of bis(acetylacetonato)copper(ll) is dark blue. The strength of ligands in this experiment can be arrange ascending in strength. H20