Title : Preparation of bis (acetylacetonato)copper (II)
Objective : I ) To synthesize the bis (acetylacetonato)copper (II) complex
II) To determine the percentage yield of bis (acetylacetonato)copper (II) complex
Background of study :
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(II)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(NO3)2∙3H2O)
A complex ion has a metal ion at its center with a number of other molecules or ions surrounding it. These can be considered to be attached to the central ion by co-ordinate (dative covalent) bonds. The molecules or ions surrounding the central metal ion are called ligands. Simple ligands include water, ammonia and chloride ions. All ligands are lone pair donors. In other words, all ligands function as Lewis Bases. A base is an electron pair donor and an acid is an electron pair acceptor. Ligands like water, can donate a pair of non-bonding electrons(lone pair) intro a vacant orbital of a central metal ion and so dative covalent(co-ordinate) bonds hold a complex together. The central metal ion with vacant bonding orbitals can act as a Lewis acid. Ligands act as Lewis bases by electron pair donation to form the metal-ligand bond.

Apparatus : filter paper , Buchner funnel, adapter, suction filtration flask, spatula, graduated cylinder, watch glass, glass rod, pipette
Chemicals : water, copper (II) nitrate (Cu(NO3)2∙3H2O), 1:1ammonia solution, acetyl acetone

Procedure : 1. 6g of copper(II) nitrate (Cu(NO3)2∙3H2O) was dissolved in 60cm3 of water, 2. The solution of 1:1 Ammonia was added slowly with stirring until the precipitate first formed has just redissolved. 3. The solution was continuing stirring then 6cm3 of acetyl acetone was added drop by drop into the solution. 4. The crude product was filtered off by using suction filtration. 5. It was washed well with water and it was drained thoroughly. 6. The percentage(%) yield was calculated.

Result : Mass of copper (II) nitrate | 6.0065g | Mass of watch glass | 36.1443g | Mass of filter paper | 0.3288g | Mass of Bis(Acetylacetonato)copper(II) + Mass of watch glass + Mass of filter paper | 38.4764g | Mass of Bis(Acetylacetonato) copper (II) | 2.0033g |
Table 1
Chemical equation :
Equation 1 : (Cu(NO3)2∙3H2O) → Cu(H2O)62+ + 2NO3-
Equation 2 :
Equation 3 : [Cu(NH3)4(H2O)6]2+ + C5H8O2 → C10H16CuO4 + 4NH3 + 4OH-

Calculation :
Molar mass of (Cu(NO3)2∙3H2O) = 241g/mol
Molar mass of C10H16CuO4 = 263.78 g/mol
Number of mole of (Cu(NO3)2∙3H2O) = mass of copper IInitratemolar mass of copperIInitrate = 6.0065g241g/mol = 0.02492mol
According to the equation above from 1 until 3, 1 mol of (Cu(NO3)2∙3H2O) produce 1 mol of C10H16CuO4.
Thus , number of mol of C10H16CuO4 = 0.02492mol
Theoretical yield of C10H16CuO4 = number of mol of C10H16CuO4 x molar mass of C10H16CuO4\ = 0.02492mol x 263.78g/mol = 6.5734g Percentage yield of C10H16CuO4 = actual yield Theoretical yield x 100 % = 2.0033g6.5734g x 100% = 31%

Discussion :
In this experiment, the objective is to synthesize the bis (acetylacetonato)copper (II) complex. The objective was determined and the percentage yield of the product is 31%. The product is in dark blue powder form.
In the first step of the experiment, 6g of copper(II) nitrate (Cu(NO3)2∙3H2O) was dissolved in 60cm3 of water. The purpose of this action is dissolve the blue crystal to get the blue solution which contain of copper(II) hexaaqua complexes which is Cu(H2O)62+.The equation is shown below :
(Cu(NO3)2∙3H2O) → Cu(H2O)62+ + 2NO3- Next, the solution of 1:1 Ammonia was added slowly with stirring until the precipitate first formed has just redissolved. The purpose of this step is to replace the water molecule by ammonia. Ammonia solution can react with hexaaqua metal ions in two quite distinct ways because it can act as a base as well as a ligand. When we added a small amount of ammonia solution, we get milky solution which is precipates of the copper(II) hydroxide – the ammonia is acting as a base. When we added more ammonia to the solution, the precipates redissolved to give dark blue solutions in which a ligand exchange reaction has occurred.
There is a slightly untypical case beause only four of the six water molecules get replaced to give the tetraamminediaquacopper(II) ion, [Cu(NH3)4(H2O)6]2+. The diagram below show the tetraamminediaquacopper(II) ion.

The main equilibrium involved in the ligand exchange reaction is :
Then, acetyl acetone was added drop by drop into the solution. Anion of acetyl acetone act as the ligand. Therefore, a base must add to promote deprotonation of acetyl acetone. Nitrate is not a strong enough base, thus ammonia molecules are sufficiently basic to promote deprotonation of the acetyl acetone. The reaction between tetraamminediaquacopper(II) ion and acetyl acetone is shown below :
[Cu(NH3)4(H2O)6]2+ + C5H8O2 → C10H16CuO4 + 4NH3 + 4OH- The percentage yield of the final product which is bis (acetylacetonato)copper (II) is 31% .Thus , there is loss of 69% of the product . There are several factors that cause the loss of products. First, there is loss of many products during the suction filtration process. Some of the products may trap in the Buchner funnel. Second , our group member used too many water to wash the products which cause the loss of product. Beside that, some of the products may trap inside the beaker which containing the solute. There is some precaution steps needed to be taken in this experiment. First , during the adding of 1:1 ammonia solution into the beaker containing copper(II) nitrate and water, the ammonia of added drop by drop with a fast speed until milky solution is observed. During the suction filtration process, two filter papers were used as the base in the hole of the Buchner funnel so it can withstand the weight of the products efficiently to avoid the losing of product. Next , the products were dried up using the oven to remove the excess water in the products.

Conclusion : The objectives were determined. Bis (acetylacetonato)copper (II) complex was synthesized and its percentage yield is 31%. It was cause by loss of products mostly by suction filtration process. In this experiment, water was used to dissolve copper(II) nitrate and ammonia solution was then used as a base to promote the deprotonation of acetyl acetone. The product which is bis (acetylacetonato)copper (II) complex is in dark blue powder form.

References :

Clark, J. (2003). ligand exchange reaction . Retrieved January 23, 2014, from chemguide: http://www.chemguide.co.uk/inorganic/complexions/ligandexch.html
Clark, J. (2003). Reaction of hexaaqua metal ions with hydroxide ions. Retrieved January 13, 2014, from chemguide: http://www.chemguide.co.uk/inorganic/complexions/aquaoh.html
Kristopher. (2011). synthesis of metal acetyl acetonate compound. Retrieved January 23, 2014, from answer.yahoo: http://au.answers.yahoo.com/question/index?qid=20101016223033AAA8oI3

Question : 1. Draw the structure of the complex

2. Describe the structure by mentioning the ligating atoms of the ligand and its geometry. Discuss the synthesis of the complex.
Ans : Copper(II) ion is in the middle of the complexes while the acetylacetonate anion act as the ligand. The ligand acetylacetonate is often abbreviated acac. Typically both oxygen atoms bind to the metal to form a six membered chelate ring. For the synthesis of the complex, the water was used to dissolve the copper(II) nitrate to get copper(II) hexaaqua complexes which is Cu(H2O)62+ . Then , ammonia solution was added until white precipitate was obtained which is copper(II) hydroxide. After that , the precipitate redissolved when the excess ammonia solution was added to get tetraamminediaquacopper(II) ion, [Cu(NH3)4(H2O)6]2+. Next , acetyl acetone react with tetraamminediaquacopper(II) ion, [Cu(NH3)4(H2O)6]2+ to produce is bis(acetylacetonato)copper (II) which is the complex.