Synthesis of metal acetylacetonate complexes
Background. In this experiment you will prepare and characterize complexes of 2 metal ions with the anion of acetylacetone. Acetylacetone (2,4-pentanedione) is a typical α-diketone that can ionize in aqueous solution as a weak acid:
The resulting acetylacetonate anion (abb. acac) can serve as a ligand to metal ions, forming complexes in which the ligand is bonded to the metal through both oxygen atoms to form a six-membered ring.
The six-membered rings (MO2C3) are planar and weakly aromatic because they contain 6 π electrons. In complexes of stoichiometry M(acac)3, the MO6 array is octahedral; in Cu(acac)2, the CuO4 group is square planar; and in VO(acac)2, the VO5 group …exibir mais conteúdo…
If the solution is still acidic, add 5M ammonia dropwise until it is just basic. Let stand for 15 minutes.
Filter the product, wash with 10 mL of distilled water, and dry by suction for 10 minutes. Transfer the product to a watch glass and air dry. Determine the % yield.
Recrystallize a portion of your sample from cyclohexane. Isolate the resulting crystals by suction filtration, wash with a small volume of cold cyclohexane, and suction dry for 15 minutes. Then let dry thoroughly in air.
Place 5 mL distilled water in a 50-mL round bottom flask, and slowly add an equal volume of concentrated H2SO4. Add 12 mL ethanol followed by 2.5 g of vanadium pentoxide, V2O5. Attach a water cooled condenser to the flask and reflux the mixture for about 1.5 hours. Then cool the mixture under the tap, and gravity filter. Discard any solid residue.
To one-sixth of the filtrate, add 1 mL acetylacetone dropwise with swirling. Neutralize the mixture by adding it carefully to a solution of 3.3 g of anhydrous Na2CO3 in 25 mL distilled water contained in a 50 mL Erlenmeyer. Swirl continuously. Cool the resulting mixture in an ice bath for 15 minutes, then suction filter. Wash the product with cold distilled water (2 * 1.5 mL). Suction dry for 15 minutes, then transfer to a watch glass and air dry. Determine % yield.
To recrystallize, dissolve about 0.5 g of the crude, dry product