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Metal Acetylacetonate Compounds: Preparation and Characterization

Note: acetylacetone = 2,4-pentanedione

Metal Acetylacetonate Compounds: Preparation and Characterization

Note: acetylacetone = 2,4-pentanedione

Experimental

(VO)2+ complex Place 1.5 mL distilled water in a 25-mL round-bottomed flask and slowly add to it an equal volume of concentrated H2SO4. Then add 4 mL of ethanol followed by 0.75 g vanadium(V) oxide, V 2O5. Attach a water cooled condenser and reflux this mixture for about 1.5 hours using a heating mantle. The solution will turn a dark blue-green color. Cool the mixture and filter using a small plug of glass wool, discarding any solid residue. Add 2 mL of acetylacetone drop wise to the filtrate with stirring. Neutralize the mixture by adding it carefully to a solution of 6 g of anhydrous Na2 CO3 in 45 mL of distilled water, contained in a 150-mL beaker, while stirring the mixture using a magnetic stirrer. The resulting mixture should then be cooled in ice water for 15 minutes before vacuum filtering. Wash the dark green product with cold distilled water (2 x 5 mL). Dry under vacuum for 15 minutes, then dry in a vacuum desiccator over anhydrous CaCl2 . Weigh the dried product and calculate the percent yield (Eq. 6 and 7). V2 O5 + 4H2 6 2(VO)2+ + 2H2O + ½ O2 (VO)2+ + 2CH3 COCH2 COCH3 6 2H+ + VO(CH3COCHCOCH3)2 Determine the melting or decomposition point. (6) (7)

Experimental

Cr3+ complex Weigh directly into a 100-mL erlenmeyer flask 0.7 g of chromium(III) chloride hexahydrate (CrCl3A6H2O) and dissolve it in 25 mL distilled water. Weigh out 3 g urea and add it in 3 or 4 portions to the deep green chromium solution, stirring well after each addition. Then add 1.75 mL of acetylacetone drop-wise, using a pipette. Clamp the flask in a boiling water bath and heat the mixture while stirring for approximately one hour. The solution should initially be very dark and almost black in appearance, but as the reaction proceeds, deep maroon plate-like crystals form as a crust on the surface of the reaction mixture. Cool the reaction mixture and vacuum-filter the product. Do not wash the product with water. Dry it in air. Weigh the dried product and calculate the percent yield (Eq. 8 and 9). CO(NH2 )2 + H2O 6 2NH3 + CO2 (8)

Cr3+ + 3CH 3COCH 2COCH 3 + 3NH 3 6 3NH 4+ + Cr(CH 3COCHCOCH 3)3 (9)

The urea undergoes slow hydrolysis, liberating ammonia, which then controls the pH of the reaction mixture. Determine the melting or decomposition point.

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Metal Acetylacetonate Compounds: Preparation and Characterization

Note: acetylacetone = 2,4-pentanedione

Metal Acetylacetonate Compounds: Preparation and Characterization

Note: acetylacetone = 2,4-pentanedione

Experimental

Mn3+ complex Dissolve 0.52 g of manganese(II) chloride tetrahydrate (MnCl2A4H2O) and 1.4 g of sodium acetate in 20 mL of distilled water in a 100-mL beaker. Stir the mixture using a magnetic stirring hot plate. When dissolution is complete, add 2 mL of acetylacetone. Prepare a solution of 0.11 g of potassium permanganate in 6 mL of distilled water. Stir well and thoroughly as KMnO4 takes a while to dissolve. Add the KMnO4 solution drop-wise over a 10-15 minute period to the reaction mixture. Stir for a further 10 minutes and then add drop-wise a solution of 1.4 g of sodium acetate in 5 mL of distilled water. While continuing to stir, heat the resulting dark mixture in a water bath to between 60E and 70EC for 15 minutes. Monitor the temperature carefully using a thermometer. Then cool to room temperature. Filter off the very dark, almost black product and wash it with ~10 mL of cold distilled water. Vacuum dry for 15 minutes and dry it in a vacuum desiccator over anhydrous CaCl2 . Weigh the dry product and record the yield. Calculate the percent yield. The stoichiometry of this preparation is complicated. First the Mn(II) complex is formed according to Eqn. (10). The manganese(II) then reacts with the manganese(VII) of the permanganate to give manganese(III) (Eqn.11) and, in outline, the overall stoichiometry is in Eqn. (12). In this preparation, the potassium permanganate is the limiting component on which percentage yields should be based, i.e. 1 mol KMnO4 gives 5 mol product. Mn2+ + 2CH2COCH2COCH3 6 2H+ + Mn(CH3COCHCOCH3)2 (10)

Experimental

Mn(VII) + 4Mn(II) 6 5Mn(III) (11)

5Mn2+ + MnO4- + 15CH3 COCH2 COCH3 6 4H2O + 7H+ + 5Mn(CH3COCHCOCH3)3 The purpose of the sodium acetate is to neutralize the acid released, since acetic acid is a weak acid (Eqn.13). 7H+ + 7CH3COO- 6 7CH3COOH Determine the melting or decomposition point.

(12)

(13)

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Metal Acetylacetonate Compounds: Preparation and Characterization

Note: acetylacetone = 2,4-pentanedione

Metal Acetylacetonate Compounds: Preparation and Characterization

Note: acetylacetone = 2,4-pentanedione

Experimental

Fe3+ complex Dissolve 0.7 g of finely-ground iron(III) chloride hexahydrate (FeCl3 A6H2 O) in 5 mL of distilled water in a 100-mL beaker. Add, over a period of 15 minutes, add a solution of 0.8 mL of acetylacetone in 5 mL of methanol. Stir throughout the addition using a large magnetic stirrer. Add to the resulting blood red mixture, over a period of 5 minutes, a solution of 1.1 g of sodium acetate in 3 mL of distilled water, maintaining the stirring throughout. At this point, a red crystalline solid should precipitate. Heat the whole mixture rapidly to about 80EC in a hot water bath. Monitor the temperature carefully with a thermometer and maintain this temperature for 15 minutes while rapidly stirring. Cool to room temperature with a water bath and then cool further in an ice bath. Vacuum-filter the product and wash with 10 mL of cold distilled water. Vacuum dry for 15 minutes. Then dry in a vacuum desiccator over anhydrous CaCl2 . Weigh the dry product and calculate the percent yield (Eqn. 14). Fe3+ + CH3COCH2COCH3 6 3H+ + Fe(CH3COCHCOCH3 )3 (14)

Experimental

Co3+ complex Weigh into a 100-mL beaker 0.38 g of cobalt(II) carbonate and add 3 mL of acetylacetone. Heat the mixture to about 90EC using a hot water bath with continuous stirring. Monitor the temperature carefully with a thermometer. While maintaining the temperature around 90EC, add drop-wise 4.5 mL of a 10% hydrogen peroxide solution using a dropping pipette. Cover the flask with a watch glass between H2O2 additions. The whole addition of the H2 O2 solution should occur over about 15 minutes or when effervescence ceases. Stirring should be maintained throughout the addition and then for a further 15 minutes. Cool in an ice-water bath for 30 minutes. Vacuum-filter the dark green product. Vacuum dry for 15 minutes and then dry in an oven at 110EC. Weigh the dry product and record the percent yield (Eqns. 16, 17 and 18). In this preparation, the Co(II) complex is formed first according to Eqn. (16). This Co(II) complex is then oxidized by the hydrogen peroxide (Eqn. 17) and the overall stoichiometry may be written as in Eqn. (18).

CoCO 3 + 2CH 3COCH 2COCH 3 6 CO 2 + H 2O + Co(CH 3COCHCOCH 3) 2 (1 6)

The sodium acetate is added to neutralize the acid released: acetic acid is a weak acid (Eqn.15). 3H+ + 3CH3COO- 6 3CH3COOH Determine the melting or decomposition point. (15)

2Co2+ + H2 O2 6 2Co3+ + 2OH-

(17)

2CoCO3 + 6CH3COCH2COCH3 + H2O2 6 2Co(CH3COCHCOCH3)3 + 2CO2 + 4H2 O (18) Determine the melting or decomposition point.

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Metal Acetylacetonate Compounds: Preparation and Characterization

Note: acetylacetone = 2,4-pentanedione

In addition to the synthesis of the metal acac compounds, the number of unpaired electrons will be determined with a magnetic susceptibility analysis.

Experimental

Cu2+ complex To a solution of 0.6 g copper(II) chloride dihydrate (CuCl 2 A2H2O) in 4 mL of distilled water in a 50-mL beaker, add dropwise over a period of 20 minutes a solution of 0.75 mL of acetylacetone in 3 mL of methanol, while maintaining constant stirring. Add to the resulting mixture 1.0 g of sodium acetate in 3 mL of distilled water over a period of 5 minutes. Heat the mixture to ca. 80EC in a hot water bath for 15 minutes, still maintaining rapid stirring. Monitor the temperature carefully with a thermometer. Cool to room temperature and then place in an ice water bath. Filter off the blue-gray product and wash with ~8 mL of cold distilled water and vacuum dry for 15 minutes before drying in an oven at 110EC. Weight the dry product and record the percent yield (Eqn. 19). Cu2+ + 2CH3COCH2COCH3 6 2H+ + Cu(CH3COCHCOCH3)2 (19)

Magnet susceptibility calculations

Mass susceptibility: Cbal = balance constant l = sample height (cm) R = sample reading R0 = empty tube reading m = sample mass (g) Molar susceptibility: M = molar mass (g/mol) Corrected molar susceptibility:

Effective magnetic moment:

The sodium acetate is added to neutralize the H+ liberated: acetic acid is a weak acid (Eqn. 20). H+ CH3 COO- 6 CH3COOH Determine the melting or decomposition point. (20)

T = absolute temperature (K) Number of unpaired electrons, n:

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