experiment 22B

Name: Jiani He ID: 26380107 Performance date: 10/24/2023 Lab partner: Tran Ahn Tuan Nguyen Reports due date: 11/07/2023 Experiment 22B: Synthesis of Metal Acetylacetonates

Abstract: The goal of this experiment is to synthesize two metal complex which are Mn(acac) 3 and VO(acac) 2 . The acetyl acetone (also known as acac as ligand). And their characterization was determined by using infrared spectroscopy. Once the coordination occurs, shifting of peaks was observed on the infrared spectrum. Since the weakening of bonds involving the donor atom and strengthening of the bonds are adjacent to the donor atom. The geometry of products are octahedral and square pyramidal for Mn(acac)3 and VO(acac)2 respectively. And the corresponding mass and percentage yield are 29 mg with 14% and 0.65 with 42.5%.

Experimental: Synthesis of Mn(acac)3: 100 mg of manganese (II) chloride tetrahydrate and 260 mg of anhydrous sodium acetate were added into a 10-mL Erlenmeyer flask with a stir bar followed by 4 mL of water. If the solid was dissolved completely, 400 μ L of acetylacetone was added. 20 mg of aqueous potassium permanganate solution was added to the mixture by dropwise. Another portion of 260 mg of anhydrous sodium acetate in 1 mL of water was added dropwise after the original mixture stirring for five minutes. Once the mixture boiled, cooled it to room temperature, and collected the solid by suction filtration, and washed with water. The mass of the product was determined, and its infrared spectrum was obtained. Synthesis of VO(acac)2: 1 g vanadyl sulfate (VOSO 4 ·2H 2 O) was dissolver in approximately 15 ml of water. Then, add 1.025ml of 2,4-pentanedione. Then approximate 6ml saturated sodium carbonate solution was added in to the solution until effervescence stops. Stir the reaction for approximately 10 minutes. Then collect your product by vacuum filtration using a Buchner funnel, wash the product with 5ml of water 3 times, dry the product in oven under 100 degrees for 15 minutes, then cool into the desiccator. The mass of product was recorded and its infrared spectrum was obtained. Data: Table 1. Amount of Reagents of Mn(acac)3 Chemical Mass (mg) Moles (mmol) MnCl 2 4H ∙ 2 O 121.5 0.617 NaCH 3 CO 2 266.2 1.96 KMnO 4 19.8 0.125 NaCH 3 CO 2 262.6 1.93

Based on the reaction equation MnCl 2 4H ∙ 2 O + 3 acacH NaOAc , KMnO 4 H 2 O ,∆ → Mn(acac) 3 , the limiting reagent is MnCl 2 4H ∙ 2 O, and the stoichiometric ratio of reagent and product is 1: 1. Therefore, the theoretical yield is calculated as m=0.617 mmol × 355.28 mg/mmol=206.06 mg. The percentage yield can be calculated as experimental yield theoretical yield × 100% = 29 mg 206.06 mg × 100% = 14.07% Table 2. Yield of Mn(acac) 3 Theoretical Yield (mg) Experimental Yield (mg) Percentage yield 206.06 29 14.07% Table 3. Amount of Reagents of VO(acac)2 Chemical Mass (g) Moles (mmol) VOSO 4 ·2H 2 O 1.0526 5.26 H2O 15 -- 2,4-pentanedione 1 9.98 Na2CO3 -- 11.7 Based on the reaction equation VOSO 4 ·2H 2 O + 2acac Na 2 CO 3 H 2 O VO(acac)2, the limiting reagent is VOSO 4 ·2H 2 O, and the stoichiometric ratio of reagent and product is 1: 1. Therefore, the theoretical yield is calculated as m=0.617 mmol × 355.28 mg/mmol=1.395g. The percentage yield can be calculated as experimental yield theoretical yield × 100% = 0.63 g 1.395 g × 100% = 45.2% Table 2. Yield of Mn(acac) 3 Theoretical Yield (g) Experimental Yield (g) Percentage yield 1.395 0.63 45.2% Table 3. Analysis of Infrared Spectrum of VO(acac)2

Results: For Mn(acac)3, the mass of dark brown powder product was 29 mg, with a percentage yield of 14%, and its IR spectrum indicates the bands agree with the bands of the literature spectrum [2] . The literature wavenumber of C=O vibration of the ligand in acacH is 1622 cm -1[3] , and the experimental wavenumber is 1567.3 cm -1 . As a result, the deprotonation and coordination are weakened with a smaller wavenumber. The literature wavenumber of C=C vibration of the ligand in acacH is 1422 cm -1[3] , and the experimental wavenumber is 1500.3 cm -1 . Therefore, C=C vibration is strengthened with a larger wavenumber. The melting point was not obtained at this time. For VO(acac)2, the mass of light blue powder was obtained as 0.63g, which gives 45% of yield. And the IR spectrum indicates that the bands agree with the bands of the literature spectrum, which shows the wavenumber of V=O at 991.5 cm -1 and wavenumber of C=O at 1517.0 cm -1 . The value of V=O stretch is quite close to the literature value 997 cm -1 , which indicated VO(acac)2 was formed successfully. but the position of C=O was shifted to lower wavenumber at 1517 cm -1 . Discussion: Acetylacetone (acacH) with a 8.99 as pKa value, which acts as a bidentate ligand once the deprotonation of the acidic α hydrogen through its two oxygen atoms [9] . Acetate is the conjugate base of acetic acid with the pKa of 4.75 [10] . In general, acid-base reactions favor the side of weaker acid and base. At this time, acacH and acetate as the labile proton of acacH has a higher pKa value. For some acac, once the deprotonation finished, it will coordinate to manganese and VO 2+ by displacing two of its existing ligands, and then forming a stable six-membered chelate ring. The reaction mechanism is shown in Figure 1 below. Figure 1. Acid-Base Reaction Mechanism

To substituent the ligand, Figure 2 shows the reaction equation. Figure 2. Ligand Substitution Equation To form the Mn(acac) 3 and VO(acac) 2 with a stable six-membered chelate ring, the full redox reactions are shown as [MnCl 2 (H 2 O) 4 ]+2H 2 O → [Mn(H 2 O) 6 ] 2+ +2Cl - and [Mn(H 2 O) 6 ] 2+ +3acac → Mn(acac) 3 + 6H 2 O. VOSO 4 ·2H 2 O + 2acac Na 2 CO 3 H 2 O VO(acac)2 + 2H 2 O respectively. Furthermore, there are two possible isomers for the product [Mn(acac) 3 ], and only one structure for VO(acac) 2 their structures are shown in Figure 3. Figure 3. Isomers of Product Mn(acac) 3 [11] Structure of VO(acac) 2 From the infrared spectrum in acacH, the stretch of C=O bond appears at 1600.9 cm -1 and C=C bond appears at 1414.5 cm -1 . For the [Mn(acac) 3 ] product, the stretch of C=O bond appears at 1567.3 cm -1 and C=C bond appears at 1500.3 cm -1 . The wavenumber of C=O becomes larger, while wavenumber of C=C decreases. Since the deprotonation occurs, C=O double bond becomes C-O single bond and a lone pair.

Conclusion: Two complex with bidentate ligands Mn(acac) 3 and VO(acac)2 were prepared and characterized as well. The wavenumber changes of C=O and C=C bonds were compared between acacH and the product. With the single bond character increases, the wavenumber decreases since single bond is weaker than double bond. For the double bond character increases, the same story. Then for VO(acac)2, the V=O stretch was obtained and illustrate at 991 cm -1 in IR spectrum. The mass of the product 29 mg and 0.635g with a percentage yield of only 14% and 43.5% for Mn(acac)3 and VO(acac)2 respectively. However, the infrared spectrum analysis was successful. Therefore, the product was in a high purity. 1. Write and balance the half-reactions by any redox reactions in this experiment MnO 4 - +8H + +4e - → Mn 3+ +4H 2 O (1) 4Mn 2+ → 4Mn 3+ +4e - (2) (1)+(2): MnO 4 - +8H + +4Mn 2+ → 5Mn 3+ +4H 2 O 2. In acetone, the alkyl hydrogen atoms are quite difficult to remove in the presence of base. In acetylacetone, however, a proton is readily lost, forming the acac ion. Why is there a difference between these two similar compounds? In acetone, α hydrogen to a carbonyl group is slightly acidic. Deprotonation of the action results in a carbanion, and the process is unfavorable. Then, the electron lone pair on the carbanion will move to form a double bond and the negative charge then will be delocalized onto the oxygen atom and an enolate will form. Therefore, the electron density is mainly on oxygen, and it will be more capable of stabilizing the charge on oxygen than carbon. For acetylacetone, the α hydrogen is adjacent to two carbonyl groups. The deprotonation results in a negative charge will be more delocalized, which makes the structure more stable. Therefore, the α hydrogen is more readily lost for a dicarbonyl compound acetylacetone. 3. Manganese (II) (d 5 ) is nearly colorless, whereas Mn (VII) (d 0 ) is dark violet. Explain. Electronic transitions relate to colors of complex, and the transitions can be considered as d-d transitions which arising from transitions between d-orbitals [4] . In Mn (VII) in d 0 configuration, there is no d-electron available for d-d transitions. Therefore, a large absorption will be at a short wavelength, and no d-d transition occurs to change the color. Hence, Mn (VII) is in dark violet. No Manganese (II) compound was synthesis during the experiment.

4. Explain why Mn (II) and Mn (VII) are used in a roughly 4:1 ratio in this experiment. Based on the reaction equation MnO 4 - +8H + +4Mn 2+ → 5Mn 3+ +4H 2 O, the stoichiometric ratio between Mn (II) and Mn (VII) should be 4:1. Mn (VII) requires 4 electrons to be reduced to Mn (III). Therefore, the electrons are provided by 4 equivalents of Mn (II). 5. Would either the Cr(acac) 3 or Mn(acac) 3 species exhibit the Jahn-Teller effect? Explain. Jahn-Teller effect indicates molecules distort in order to remove degeneracy from the unequal occupation of degenerate orbitals and obtain overall low energy state [5] . Cr (III) has d 3 configuration, the t 2g orbitals are equally distributed with one electron each, and there will be no degeneracy. Therefore, no Jahn-Teller effect will occur. Mn (III) has d 4 configuration and leading to a strong Jahn-Teller effect, because Mn(acac) 3 is a high spin complex, which will populate the anti-bonding e g orbitals. Reference: 1. Szafran, Zvi, et al. Microscale Inorganic Chemistry: A Comprehensive Laboratory Experience . John Wiley & Sons, 1991. 2. Spectral Database for Organic Compounds, SDBS. No. 4168 (n.d.). Retrieved November 21, 2020, from https://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi. 3. Spectral Database for Organic Compounds, SDBS. No. 1030 (n.d.). Retrieved November 21, 2020, from https://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi 4. Miessler, Gary L., et al. Inorganic Chemistry . Pearson Education South Asia Pte Ltd, 2018. 5. Libretexts. (2020, August 15). Jahn-Teller Distortions. Retrieved November 29, 2020, from https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Modules_and_Websites_(Inorganic_ Chemistry)/Coordination_Chemistry/Structure_and_Nomenclature_of_Coordination_Compounds/ Coordination_Numbers_and_Geometry/Jahn-Teller_Distortions. 6. Acetylacetone. (n.d.). Retrieved December 06, 2020, from https://www.chemicalbook.com/ChemicalProductProperty_EN_CB2179401.htm.