Experiment 6

Title: Preparation of bis(acetylacetonato)copper(II) complex

Objective: To synthesize the bis(acetyacetonato) copper(II) complex

Theory/Background:

All metal ions in solution are 'associated' 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. E.g Copper(II) nitrate (Cu(NO3) 2.3H2O).

A complex ion has a metal ion at its centre 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,
Reactions of the hexaaqua ions with ammonia solution are complicated by the fact that the ammonia can have two quite different functions. Small amount of ammonaia can act as a base (in the Bronsted-Lowry sense). But it is also a possible ligand which can replace water molecules around the central metal ion if excess of ammonia is added. When it acts as a ligand, it is acting as a Lewis base.

In our experiment, we are using acetyl acetone as the ligand.
The acetylacetonate anion, acac-, forms complexes with many transition metal ions. A general method of synthesis is to react the metal ion with acetylacetone in the presence of a base (B):

Mz + z (acacH) M(acac)z +z BH+

which assists the removal of a proton from acetylacetone and shifts the equilibrium in favour of the complex. Both oxygen atoms bind to the metal to form a six-membered chelate ring. In some cases the chelate effect is so strong that no added base is needed to form the complex. Since the metal complex carries no electrical charge, it is soluble in non-polar organic solvents.

Questions

1) Draw the structure of the complex.

[pic]

2) Describe the structure by mentioning the ligating atoms of the ligand and its geometry. Discuss the synthesis of the complex.

Acetyl acetonate is the ligand. It is a colourless liquid that is a precursor to acetylacetonate (acac), a common bidentate ligand. The acetylacetonate anion,