Crystal growing Inorganic Synthesis

[Cu(acac)2] and [Cr(acac)3] complex preparation

Theory: 

Acetylacetone (penta-2,4.dione) is a diketone that can possibly exist in three tautomeric forms. It is a liquid with a boiling point 140 °C at normal pressure and temperature. It contains two acidic hydrogen that can be removed making the molecule a weak acid. For this purpose acetate anion can be used.  An anion formed is known as acetylacetonate and is commonly used as a ligand in coordination chemistry. A charge is evenly distributed between two oxygen atoms from carbonyl group. The ligand binds to a central atom in bidentate manner forming five-membered chelate ring. The stoichiometry of 3d metal complexes is dependent on a charge of a central atom beacuse the complexes formed are strictly neutral. For complexes containg MII square planar arrangement of two acetylacetonate molecules is observed whereas for MIII octahedral coordination is found. The complexes are only slightly soluble in water but soluble in many organic solvents (e.g. chloroform).

Procedure I:

Copper (II) chloride dihydrate (2.0 g, 11.7 mmol) was dissolved in 12.5 mL of distilled water. Under constant stirring acetylacetone (2.5 g, 25 mmol) dissolved in 5 mL of pure ethanol was added over 10 minutes to the solution of copper (II) chloride. A change in color was observed after an addition. To the mixture, sodium acetate (3.4 g, 25 mmol) dissolved in 7.5 mL of distilled water was added. The mixture was heated to 80-90 °C for 15 minutes and cooled down to room temperature. Blue precipitate that formed was filtered off with suction filtration, washed with 50 mL of an ice-cold distilled water and dried at 110 °C. The crude product was recrystalized using chloroform. Yield: 55,9 %.

Cu2+ + 2 CH3COCH2COCH3 -> 2H+ + Cu(CH3COCHCOCH3)2

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Procedure II:

Chromium(III) chloride hexahydrate (0.7 g, 2.6 mmol) was dissolved in 25 mL of distilled water in 100 mL conical flask. To the solution urea (5 g, 83.3 mmol) was added and the mixture was stirred until all reactants has been dissolved. Acetylacetone (1.5 g, 15 mmol) was added dropwise into the solution under constant stirring. The reaction mixture was then heated for 90 minutes at 80-90 °C. The color slowly changes from green to dark violet. After the reaction volume of the mixture was greatly reduced and the residue was rapidly cooled down in an ice bath. The microcrystalline powder was filtered off, washed by water and dried at 110 °C. Yield: 18,2 %.

CO(NH2)2 + H2O -> 2NH3 + CO2

Cr3+ + 3 CH3COCH2COCH3 + 3NH3 -> 3NH4+ + Cr(CH3COCHCOCH3)3


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