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Synthesis of Metal Acetylacetonate Complexes

By Alfred Williams,2014-01-06 19:26
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Synthesis of Metal Acetylacetonate Complexes

    Synthesis of Metal Acetylacetonate Complexes

    Synthesis of Metal Acetylacetonate Complexes

    CHHC33

    OOO

    OO

    MTarget MoleculesM

    OO

    OO

    O

    HCCH33

    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 -

    diketone that can ionize in aqueous solution as a weak acid:

    +-CHC(=O)CHC(=O)CHH + [CHC(=O)CHC(=O)CH]32333

    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 (MOC) are planar and weakly aromatic because they contain 6 23

     electrons. In complexes of stoichiometry M(acac), the MO array is octahedral; in 36

    Cu(acac), the CuO group is square planar; and in VO(acac), the VO group is square 2425

    pyramidal. In general the complexes are neutral and may be isolated as crystalline solids having an interesting variety of colors.

    In pure acetylacetone, or solutions of acetylacetone in non-polar organic solvents, the diketo form is in equilibrium with a cyclic enol-like form. This second tautomer may be n+regarded as a complex in which the proton takes the role of the metal ion M.

    Synthesis and Characterization of Metal Acetylacetonates

    Synthetic Procedures

    We would like you to carry out syntheses of two metal acetylacetonate complexes, according to the following plan:

    3+3+a. Al and Cr 33+b. Fe+, Co 3+3+c. Co, and the nitration of the Co

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    Synthesis of Metal Acetylacetonate Complexes

    Characterization of Products

    1. In the case you carry out a.: determine the melting points of your 2 products. Next,

    record the IR spectrum, using the KBr pellet technique. Label and number the

    spectra and assign the "sore thumb" bands. Finally, measure the magnetic

    susceptibility.

    2. In the case you carry out b.: determine the melting points of your 2 products. Next,

    record the IR spectrum, using the KBr pellet technique. Label and number the

    spectra and assign the "sore thumb" bands. Finally, measure the magnetic

    susceptibility.

    3. In the case you carry out c.: determine the melting points of your 2 products. Next,

    record the IR spectrum, using the KBr pellet technique. Label and number the 1H nuclear spectra and assign the "sore thumb" bands. Finally, measure the

    magnetic resonance (NMR), using CDCl as the solvent and TMS as the reference. 3

    Label and number the spectra.

Questions

    Give a reaction mechanism for the formation of the acatylacetone complexes. Explain the magnetic behaviour measured in experiment a and b.

    Try to give an reaction mechanism for the nitration of Co(acac). 3

    In case you carry out experiment c., do you think it is useful to measure the magnetic susceptibility.

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    Synthesis of Metal Acetylacetonate Complexes

    References

    1. R.C. Young, Inorganic Syntheses, 2, 25(1946). Al(acac)3.

    2. R.A. Rowe, M.M. Jones, Inorganic Syntheses, 5, 114(1957). VO(acac)2. 3. W.C. Fernelius, J.E. Blanch, Inorganic Syntheses, 5, 130(1957). Cr(acac)3. 4. R.G. Charles, Inorganic Syntheses, 7, 183(1963). Mn(acac)3. 5. B.E. Bryant, W.C. Fernelius, Inorganic Syntheses, 5, 188(1957). Co(acac)3. 6. J.B. Ellern, R.O. Ragsdale, Inorganic Syntheses, 11, 83(1968). Co(acac)2(H2O)2. 7. C. Glidewell, J.S. McKechnie, J. Chem. Ed., 65, 1015(1988). 8. D.W. Barnum, J. Inorg. Nucl. Chem., 21, 221(1961). Electronic Absorption

    Spectra of metal acac complexes.

    9. K. Nakamoto, P.J. McCarthy, A. Ruby, A.E. Martell, J. Amer. Chem. Soc., 83,

    1066(1961). A discussion of IR spectra of some trivalent metal acac complexes. 10. K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination

    Compounds, 4th ed., Wiley, New York, 1986. An advanced reference with data

    for many metal complexes, including metal acacs.

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    Synthesis of Metal Acetylacetonate Complexes

    Synthetic Procedures for Metal Acetylacetonate

    Complexes

    Tris(acetylacetonate)aluminum

    Weigh 0.33 g acetylacetone into a small Erlenmeyer flask. Add 4 mL distilled water followed by 0.8 mL of 5M NH. 3

    Dissolve 0.3 g of aluminum sulphate, Al(SO).16HO,in 3 mL of distilled water. Add 2432

    the ammoniacal solution of acetylacetone to the aluminum sulfate solution in small portions, with swirling. After complete addition of acetylacetone solution, check the pH using blue litmus paper. 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.

    3++Al3CHCOCHCOCH3HAl(CHCOCHCOCH)++323333

Bis(acetylacetonate)oxovanadium

    Place 5 mL distilled water in a 50-mL round bottom flask, and slowly add an equal volume of concentrated HSO. Add 12 mL ethanol followed by 2.5 g of vanadium 24

    pentoxide, VO. Attach a water cooled condenser to the flask and reflux the mixture for 25

    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 NaCO in 25 mL 23

    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 in 6 mL of dichloromethane, and gravity filter the mixture to remove residue. Add 20 mL of petroleum ether, swirl, and allow to stand for 10 minutes. Isolate the product by suction filtration and wash with cold pet ether. Suction dry.

    +2+VO4H2VO2HO1/2 O+++25222++VO2CHCOCHCOCH2HVO(CHCOCHCH)++323332

    Tris(acetylacetonato)chromium

    Into a 25-mL Erlenmeyer, weigh 0.22 g of chromium(III) chloride hexahydrate and add 8 mL of distilled water. Swirl to dissolve. Add 1.5 g of urea in 3 or 4 portions to the chromium chloride solution, swirling well after each addition. Then add 0.47 g of acetylacetone using a Pasteur pipet. Swirl the mixture, cover it with a watch glass, and

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    Synthesis of Metal Acetylacetonate Complexes

    heat vigorously on a steam bath for 1.5 hour. Cool the reaction mixture and isolate the product by vacuum filtration. Dry the crude product in air.

    In a 25-mL Erlenmeyer, place 0.2 g of crude product and 20 mL of cyclohexane. Cover the flask with a watch glass and heat to boiling on a steam bath. Boil 4-5 minutes with frequent swirling. Remove from the steam bath, allow to settle for 30 seconds, then decant the solution into a clean 100-mL Erlenmeyer, leaving any solid residue behind. Add 2 mL cyclohexane, reheat to boiling, and cool slowly to room temperature, leaving the flask covered with a watch glass. Isolate the product by suction filtration, suction dry, then air dry.

CO(NH)HO2NHCO++22232

    +3+Cr3CHCOCHCOCH3NH3NHCr(CHCOCHCOCH)+++32334333

    Tris(acetylacetonato)manganese

    Dissolve 0.26 g manganese(II) chloride tetrahydrate and 0.68 g of sodium acetate in 10 mL of distilled water. Add 1 g acetylacetone and swirl the mixture. With magnetic stirring, add dropwise a solution of 0.052 g potassium permanganate in 2.5 mL of distilled water over a period of 10-15 minutes. Stir for 10 minutes, then add dropwise a solution of 0.63 g sodium acetate in 2.5 mL distilled water. Heat the resulting mixture on oa hot plate to between 60 and 70C for 15 minutes, with stirring, then cool to room

    temperature. Isolate the product by suction filtration and wash it with 6.0 mL of cold distilled water. Suction dry for 15 minutes, then dry in air. Determine % yield. Recrystallize about 0.2 g of the crude product as follows. Place the product in a 25 mL Erlenmeyer, and add 12 mL of cyclohexane. Place a small glass funnel in the mouth of the flask and boil on a steam bath for 1 minute. Let the mixture settle for 1 minute, then carefully decant the solution from the solid residue into a 100 mL Erlenmeyer. Reheat for 1 minute to redissolve, then add 40 mL of petroleum ether. Swirl, and cool slowly to room temperature, then in an ice bath. Isolate the product by suction filtration and wash with 10 mL of cold pet ether. Dry by suction for 15 minutes, then air dry.

    -2++4MnMnO15CHCOCHCOCH5Mn(CHCOCHCOCH)4HO7H++++43233332

    -+7H7CHO7HCHO+232232

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    Synthesis of Metal Acetylacetonate Complexes

    Tris(acetylacetonato)iron

    Dissolve 0.33 g of finely-ground iron(III) chloride hexahydrate in 2.5 mL of distilled water. Over a period of 15 minutes, add a solution of 0.38 g of acetylacetone in 10 mL methanol, with constant magnetic stirring. To the resulting mixture, add, over a period of 5 minutes, a solution of 0.51 g of sodium acetate dissolved in 1.5 mL of distilled water, omaintaining stirring throughout. Heat the mixture rapidly to about 80C using a hot plate

    and maintain at this temperature for 15 minutes, with rapid stirring. Cool to room temperature, then in an ice bath. Isolate the product by suction filtration and wash with 10 mL of cold distilled water. Suction dry for 15 minutes, then air dry. Determine % yield. Place 0.2 g of the crude product into a 25-mL Erlenmeyer, and add 3 mL of distilled water. Warm on a steambath and add methanol dropwise, maintaining gentle heating, until the crude product just dissolves. Coo