exp.28

Name: Jiani He ID: 26380107 Performance date: 11/07/2023 Lab partner: Tran Ahn Tuan Nguyen Reports due date: 11/21/2023 Experiment 28: oxidation state of Vanadium and UV-vis analysis of V complex

Abstract Complexes of transition metals present various colors due to their different electronic configuration. In this experiment, 5 different vanadium complex solutions were prepared into four different ion species in different oxidation states. And the oxidation of ions were characterized by UV-vis spectrophotometry. These ions were in yellow, blue, green and purple colors. For the yellow species, the given UV-Vis spectra did not show the wavelength at maximum absorbance. For the blue species, the given wavelength at maximum absorbance was at 768 nm. Other wavelengths of interest are summarized in Table 2 in the following report. From the analysis of Tanabe-Sugano diagram of d 2 and d 3 ions, corresponding the oxidation states of +3 and +2, the Racah parameters were calculated as 724 and 716 cm -1 , respectively. Introduction One of the characteristic properties of transition metal complexes is the colors of them. It is possible for the same metal to exhibit different colors depending their oxidation states, since they have different d n configurations. Colors come from electron transitions between different energy levels in UV-Vis spectrum, which are related to photon absorption or its emission. In this experiment, absorption of a wavelength was obtained from the UV-Vis spectra, and the interest metal was vanadium. Five vanadium species in four different oxidation states were prepared from ammonium metavanadate solution. Then different charge of vanadium was made by VOSO4 as stock solution, then reacted with Zn-Hg amalgam to obtain V2+ solution under N2 condition to avoid be oxidized. Experimental [VO2(H2O)4] + (yellow): Using a graduated cylinder, take 10 mL of the prepared NH4VO3 solution and place it in a 50 mL beaker. Add 2 mL of 3 M H2SO4, mix well, transfer into a cuvette and analyze by UV- Vis. [VO(H2O)5] 2+ stock solution (blue) Weigh 0.3403 g of VOSO4.xH2O and place it in a 50 mL beaker. Add about 25 mL of distilled water and a stir bar to the beaker and stir well until all the VOSO4.xH2O is dissolved. Transfer into a 50 mL volumetric flask and dilute up to the 50 mL mark with distilled water and mix well. Transfer some of this stock solution into a cuvette and analyze by UV-Vis. [V(H2O)6] 2+ (violet) Weigh about 20 g of the prepared Zn/Hg amalgam into a filter flask. Rinse the Zn/Hg amalgam very well with distilled water and drain the water until only trace amounts of water is left. Connect the flask to nitrogen and purge the flask for about 5 minutes. Add 25 mL of the [VO(H2O)5] 2+ stock solution and 2.0 mL of 3M H2SO4 into the flask while still under nitrogen and stir very well until a violet color of the solution is observed. Keep the solution under nitrogen and using a syringe take some

For the V 2+ d 3 purple species: λ 1 = 560 nm , v 1 =10 7 cm -1 ÷ 560nm =17857 cm -1 λ 2 = 375 nm , v 1 =10 7 cm -1 ÷ 375nm =26666 cm -1 v 2 v 1 = 26666 17857 = 1.4 93 , which is corresponding to a ∆ 0 /B value of 27.2025 from the Tanabe-Sugano diagram. E 1 B' =25.533, then B’=17857 cm -1 ÷ 25.553= 698.82 cm -1 E 2 B' =35.5119, then B’=26666 cm -1 ÷ 35.512= 750.90cm -1 Racah’s parameter: (698.82 +750.90)/2= 724.86 cm -1 For V 3+ d 2 green species: λ 1 = 604 nm , v 1 =10 7 cm -1 ÷ 604nm =16556 cm -1 λ 2 = 400 nm , v 1 =10 7 cm -1 ÷ 400nm =25000 cm -1 v 2 v 1 = 25000 16556 = 1.51 0 E 1 B' =21,758 then B’=16556 cm -1 ÷ 21.758= 760.91 cm -1 E 2 B' =32.619, then B’=25641 cm -1 ÷ 32.619= 786.08cm -1 Racah’s parameter: (760.91 +786.08)/2=773.5 cm -1 Table 4. Electronic Transitions in Each Species Species Transition VO 2 + LMCT

VO 2+ 2 E ← 2 T 2 V 3+ 3 T 2g (F) ← 3 T 1g (F) 3 T 1g (P) ← 3 T 1g (F) 3 A 2g (F) ← 3 T 1g (F) V 2+ 4 T 2g (F) ← 4 A 2g (F) 4 T 1g (F) ← 4 A 2g (F) 4 T 1g (P) ← 4 A 2g (F) Discussion In the present study, vanadium was the target transition metal, whose different oxidation states species were studied. Those different were prepared from the redox reactions from ammonium metavanadate. At first, ammonium metavanadate was reacted with sulfuric and VO 2+ ion formed, with the reaction equation of 2NH 4 + +6VO 3 - +16H + → N 2 +6VO 2 + +12H 2 O. Then the VO 2 + species would be reduced into V 3+ and V 2+ by Zn-Hg amalgam with the following reaction equations Zn+2 VO 2 + +4 H + → Zn 2+ +2V 3+ +2H 2 O and Zn+2V 3+ → Zn 2+ +2V 2+ . And by adding 10.25ml of [V(H2O)] 2+ to [VO(H2O) 5 ] 2+ stock solution, V 3+ ion was obtained as green solution. UV-Vis spectrophotometry of each species was characterized with their wavelength in maximum absorbance, and the results were summarized in Table 2. The wavelength of maximum absorption of VO 2 + is unknown, and this species appeared to yellow color. This transition belongs to ligand to metal charge transfer (LMCT). V (V) species with d 0 configuration does not have d-electron for d-d transitions, since the ion [V(O) 2 (H 2 O) 4 ] + is in an octahedral geometry with distortion in aqueous solution. Therefore, the transitions have to be from the ligand orbitals to the metal d-orbital. For the oxidation of +5 species, the vanadium will be very polarizing, which has a high charge density. For blue VO 2+ species, shows a maximum absorbance at 767 nm, corresponding the blue region on the electromagnetic spectrum, and the ion [V(O) 2 (H 2 O) 5 ] + is also in an octahedral geometry with slightly distortion. The transition is in a d-d transition with a d 1 configuration. There is only one such a transition from t 2g to e g , with the term symbol 2 E ← 2 T 2 . V 3+ is a Jahn-Teller distorted octahedral hexaaquavanadium (III) in aqueous solution since two electrons are in the t 2g orbitals, whose wavelength at maximum absorbance at 390 and 567 nm. The color of this

3VO 2+ +3H 2 O → 3VO 2 + +6H + +3e - (1) MnO 4 - +4H + +3e - → MnO 2 +2H 2 O (2) (1)+(2): 3VO 2+ +H 2 O+ MnO 4 - → 3VO 2 + +2H + Other redox reactions: 2NH 4 + +6VO 3 - +16H + → N 2 +6VO 2+ +12 H 2 O 2V 2+ +2H + → 2V 3+ +H 2 3. What is an amalgam? Give an everyday example of the use of an amalgam. An amalgam is a kind of a metal alloy containing mercury, which is prepared by dissolving metal in mercury, and metallic solution forms [4] . An amalgam can be used in dental filling materials. Reference: 1. Szafran, Zvi, et al. Microscale Inorganic Chemistry: A Comprehensive Laboratory Experience . John Wiley & Sons, 1991. 2. Miessler, Gary L., et al. Inorganic Chemistry . Pearson Education South Asia Pte Ltd, 2018. 3. 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 4. Berg, J. M.; Tymoczko, J. L.; Gatto, G. J.; Stryer, L. Biochemistry , 8 th ed.; W. H. Freeman and Company: New York, N. Y., 2015. 5. Krakowiak, J.; Lundberg, D.; Persson, I. Inorganic Chemistry . 2012 , 51, 9598. 6. Rossi, A. R. The Intersection of Computational Chemistry and Experiment: UV-Visible Spectra of Aquavanadium Complexes. University of Connecticut, Storrs, CT, 2017. 7. Acetylacetone. (n.d.). Retrieved November 18, 2023, from https://www.chemicalbook.com/ChemicalProductProperty_EN_CB2179401.htm