Objective: To synthesize the bis(acetylacetonato) copper(II) complex
Introduction
Complexes consist of a central metal atom surrounded by various other atoms or small molecules called ligands. All ligands are electron pair donor which act as Lewis base. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The number of ligands bound to the transition metal ion is called the coordination number. The natures of ligand are the availability of coordination sites or ligating atoms and the conditions under which these are available for coordination. One of the ways to prepare coordination compounds is through the direct combination of a metal ion and appropriate ligands in solution. Thus, the addition of a sufficiently high concentration of ammonia to an aqueous solution of a nickel2+ salt leads through a series of reactions. Complexes of metal ions in high oxidation states are sometimes more readily formed by adding the ligands to a solution of the metal ion in a lower oxidation state in the presence of an oxidizing agent. Thus, addition of ammonia to an aqueous solution of a cobalt2+ salt in the presence of air or oxygen leads to the formation of cobalt3+-ammine complexes such as hexaamminecobalt3+, [Co(NH3)6]3+, and pentaammineaquacobalt3+, [Co(NH3)5(H2O)]3+, ions.
Apparatus and materials: Copper(II) nitrate, ammonia, acetylacetone, distilled water, glass rod, beaker, suction filtration set, oven, dropper, watch glass, filter paper
Procedures:
1. 6g of copper (II) nitrate (Cu(NO3)2.3H2O) was dissolved in 60 cm3 of water. 2. The solution of 1:1 ammonia was slowly added with stirring until the precipitate fist formed had just redissolved. 3. The solution was continued to stir and then 6 cm3 of acetyl acetone was added dropwise. 4. The crude product was filtered off by using the suction filtration. 5. Then the product was washed it well with water and drained it thoroughly. 6. The percentage yield was calculated.

Results Mass of Cu(NO3)2.3H2O | 6.0288 g | Mass of beaker | 34.0764 g | Mass of beaker + product | 36.6006 g | Mass of product | 2.5242 g |

Equation between copper (II) nitrate and ammonia :
Cu(NO3)2. 3H2O + 4 NH3 → Cu(NH3)4(NO3)2 + 3 H2O
Ionic equation: Cu2+ + 2 NO3+ + 3 H2O + 4 NH3 →Cu(NH3)42+ + 2 NO3+ + 3 H2O
Net ionic equation: Cu2+ + 4 NH3 →Cu(NH3)42+
Equation between tetraamminecopper(II) and acetyl acetone: :
Cu(NH3)42+ + 2 CH3COCH2COCH3 → Cu(CH3COCHCOCH3)2 + 2NH4+
From the equation, 1 mole of Cu(NH3)42+ react with 2 mole of acetyl acetone and produce 1 mole of bis(acetylacetonato)copper(II).
∴ number of mole of copper (II) nitrate dihydrate = number of mole of copper(II) ion produced = mass/ molar mass = 6.0288g/241gmol-1 = 0.025 mole

∴number of mole of copper(II) ion produced = number of mole of bis(acetylacetonato)copper(II) produced = 0.025 mole

∴ Theoretical mass of bis(acetylacetonato)copper(II)= 0.025 mole x 261 gmol-1 = 6.525g

Percentage yield of bis(acetylacetonato)copper(II) = (Crude product / Theoretical mass) x 100% = (2.5242g/6.525g) x 100% = 38.68%
Discussion
In this experiment, copper (II) nitrate, with a chemical formula Cu(NO3)2 ,is used as the starting material. Copper (II) nitrate is a blue crystal with melting point of 256 °C, and boiling point of 170 °C. When it is in hydrated form, it is very soluble in water and ethanol. Bis (acetylacetonato) copper (II), with the chemical formula of (C5H7O2)2 , is the product formed when copper(II) nitrate reacts with ammonia and acetyl acetone. It belongs to the group of metal, acetyl acetonates. It is crystalline powder with slightly soluble in water but soluble in alcohol and blue in colour. The bis (acetylacetonato) copper (II) complex has a coordination number of 2 because there is 2 ligands bonded to the central metal ion which is the copper (II) ion. The ligand in the complex compound is CH3COCHCOCH3 which produced by the acetyl acetone. To synthesis bis(acetylacetonato) copper (II) complex, copper (II) ion and CH3COCHCOCH3 are needed. We used copper (II) nitrate in this experiment to get copper (II) ion by adding ammonia during precipitation process because ammonia, which is NH3, is a base that enables the rearrangement of the structure so that one of the carbonyl groups in copper (II) nitrate was converted to an acidic –OH group and then gave its proton to NH3 and leaves the water-soluble acetylacetonate ion. To generate CH3COCHCOCH3 ion, acetylacetone is used. Acetyl acetone (2,4-pentanedione) is a clear to slightly yellowish liquid. Its melting point is –230C and its boiling point is 1390C. It is also soluble in water and in organic solvents. Acetyl acetone is used in the preparation of metal acetyl acetonates for catalyst application. It ables to act both as chelating agent and solvent, which it is also a competing complex. The ammonia molecule in the Cu (NH3)42+ ion deprotonate the acetyl acetone as ammonia is a good leaving group. With the presence of this competing complex, the process can be done in faster rate as it speeds up the reaction.. Below shows the convertion CH3COCH2COCH3 to CH3COCHCOCH3 : The equation between copper(II) nitrate and ammonia : Cu(NO3)2. 3H2O + 4 NH3 → Cu(NH3)4(NO3)2 + 3 H2O
The equation between Cu (NH3)42+ ion and acetylacetone to form bis(acetylacetonato)copper (II) : Cu(NH3)42+ + 2 CH3COCH2COCH3 → 2NH4+ + Cu(CH3COCHCOCH3)2
From the second equation, 1 mole of Cu (NH3)42+ reacts with 2 mole of CH3COCH2COCH3 to form 1 mole of Cu(CH3COCHCOCH3)2 . The mole of copper (II) nitrate formed is equals to the number of mole of copper (II) produced which is 0.025 mole because copper (II) ion is generated from copper (II) nitrate. The number of mole of bis(acetylacetonato) copper(II) is equals to the number of mole of copper(II) ion which is 0.025 mole. Then, theoretical mass of bis(acetylacetonato) copper(II) is calculated which is 6.525 g. The percentage yield of the product is 38.68% by dividing the actual mass of product with the theoretical mass.
In this experiment, there are few errors which cause low percentage yield of the bis(acetylacetonato)copper (II). First, the ammonia solution added is not enough to form Cu (NH3)42+ ion as this ion is important for the preparation of bis (acetylacetonato) copper (II). Next, the beaker which fills in the precipitate solution and the glass rod which stir it does not rinse cleanly and left some product. So, the product collected is less. Last, some products collected might been blown by the fan or wind in the laboratory. There are some precautionary steps which can be taken during this experiment. First, stir the ammonia and copper (II) nitrate continuously so the reaction take place completely. Next, addition of the ammonia and acetyl acetone should be done in the fume hood because ammonia has pungent smell and acetyl acetone produce toxic gas. Thirdly, make sure the filter paper is in the right size to avoid the precipitate from flowing into the suction filter which causes less product form. Next, the product which placed on the watch glass is heat in the oven for 15 minutes to make sure the product is dry to avoid results been affected. Lastly, switch off the fans to prevent the product been blown off.
Conclusion
Bis(acetylacetonato) copper (II) is prepared by reacting Cu(NH3)42+ ion with acetyl acetone. Cu(NH3)42+ ion is generated from copper (II) nitrate and ammonia. The ammonia molecule in this ion deprotonate the acetyl acetone as ammonia molecule is a good leaving group. The percentage yield of the product is 38.68 % due to some errors.
References
Copper(II) acetylacetone. Available from: <http://www.chemicalland21.com/specialtychem/perchem/COPPER(II)%20ACETYLACETONATE.htm >. [30 January 2013] U.S. Secretary of Commerce on behalf of the United States of America 2011, Copper, bis(2,4-pentanedionato-O,O')-, (SP-4-1)- . Available from : <http://webbook.nist.gov/cgi/cbook.cgi?ID=C13395169&Mask=20> . [ 30 January 2013]
Jim Clark. 2003, An introduction to complex metal ions. Available from :
< http://www.chemguide.co.uk/inorganic/complexions/whatis.html>. [30 January 2013]
George B. Kauffman Jack Halpern n.d. , Synthesis of coordination compounds. Available from: < http://universalium.academic.ru/96956/coordination_compound#sel=.>. [30 January 2013]
Questions
1. Draw the structure of the complex. 2. Describe the structure by mentioning the ligating atoms of the ligand and its geometry.
The copper(II) ion binds with 2 same chelate ligand, the anionic acetylacetone ligands, which is CH3COCHCOCH3 ion. At each side of the ligand, the 2 oxygen atoms form a bonding with the copper ion and form a six-membered chelate ring. The keto form (CH2COCH2COCH3) and enol form (CH3COCH=C(OH)CH3) of acetyl acetone coexist in solution. This enol-keto tautomerism (reversible interconversion of structural isomers) results in the tautomeric migration of a hydrogen atom from an adjacent carbon atom to a carbonyl group of a keto compound to produce the enol form of the compound; the reverse migration of hydrogen atom is also interconvertible, which makes the switch of a single bond and adjacent solid bond. Besides, there are electrons delocalize at the double bond at O-C-C-C-O bond which make the complex more stable. Bis(acetylacetonato)copper(II) is planar transition metal complexes means its geometry is planar.