To synthesize a metal acetylacetonate complex

Aim :

To synthesize a metal acetylacetonate complex .

Theory :-

Acetylacetone (2,4-pentanedione) is an organic compound, a β-diketone, that exists as an equilibrium mixture of tautomeric keto and enol forms.

In basic solution, it is deprotonated to form the acetylacetonate anion (acac).The acac anion can act as a ligand towards metal ions, typically forming a bidentate complex where the metal is bound to the two oxygen atoms, thus forming a 6-membered ring. Metal acac compounds are typically isolated as crystalline solids that are neutral, hence an Mn+ metal forms a complex with n acac ligands .Acetylacetonate forms neutral complexes with most metals.

Preparation Method of Al(acac)3 :-

• To a conical flask, add 3 mL acetylacetone and 40 mL distilled water followed by 8 mL of dilute (5 mol L-1) ammonia solution.
• Dissolve aluminium sulfate [Al(SO4)3.16 H2O] in 30 mL distilled water. To this solution, add the ammoniacal acetylacetone solution gradually with stirring.
• After complete addition of acetyl acetone, check that the solution is neutral.
• If the solution is still acidic, add further small portions of ammonia solution.
• Place the flask in an ice bath until a cream colored precipitate forms. 
• Filter the product using Buchner filtration, wash with small amounts of cold distilled water and dry the product in a desiccator.
• Determine the percentage yield of this dry product.
• Recrystallise a small sample from warm petroleum ether.
• The resulting needles should be filtered using Buchner filtration, rinsed with small portions of cold petroleum ether and dried in a vacuum desiccator.

Preparation Method Of Mn(acac)3 :-

• Dissolve 2.6 g of manganese chloride (MnCl2 •4 H2O) and 6.8 g of sodium acetate in 100 mL of distilled water and add 10 mL acetylacetone.
• Dissolve 0.52 g of potassium permanganate (KMnO4) in 25 mL of distilled water and add to the acetylacetonate solution, with stirring, over a period of about 10 minutes.
• After stirring for 10 minutes, add a solution of sodium acetate (6.3 g) in 25 mL distilled water, with stirring, over a period of about 10 minutes.
• Continue stirring and heat the flask on a hot plate to 60-70°C for 15 minutes, followed by cooling to room temperature and finally placed in an ice bath.
• Using Buchner filtration, filter the dark precipitate using small portions of cold distilled water for washing, followed by drying in a vacuum desiccator.
• Determine the percentage yield of this dry product.
• Recrystallise a small sample from warm petroleum ether.
• The resulting black needles should be filtered using Buchner filtration, rinsed with small portions of cold petroleum ether and dried in a vacuum desiccator.

Al(acac)3 :-

Aluminum is the lightest element to form trivalent ions which have a coordination number of six. Three anionic ketoenolate ligands chelate the ion forming the neutral, water-insoluble, organic solvent soluble complex. 

After forming the complex The IR spectrum of the tris-complex exhibits several signals in the IR region (400 cm-1 - 4000 cm-1) indicating the presence of the organic ligand. The anhydrous nature of the complex is evident from the absence of O-H vibration as no signals are observed beyond 3000 cm-1. The signals observed at 410, 484 cm-1 may be assigned to the bending mode of Al-O vibration.

Mn(acac)3 :-

The band at ~1250-1650cm-1 indicate the acetylacetone ligand. The two bands of the stretching vibration C=C and C-CH3 group have been detected 1253 cm-1. The bending vibration stretch of C=CH is observed at 1185 cm-1 . The bands at 928 cm-1 and 1020 cm-1 show that the Mn(III) is bonded to three acetylacetone ligands. The bending vibration of CH3 is observed at 1350cm-1 & 1388cm-1 and ν(C=C), at 1512cm-1 . 

ν(C-CH3) 928 cm-1 (strong)

ν(C=C), ν(C-CH3) 1253 cm-1 (strong)

ν(C=C), δ(C=CH) 1512 cm-1  (strong)

ν(C=C), δ(C=CH) 1567 cm-1 (strong)

ν(C-H) 2920 cm-1  (weak)