CH 431 lab 2Thermochromism PDF

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CH 431 – Inorganic Chemistry Experiment 2: Thermochromism lab Choi, Youngjung (yc25744) * Song, Munsoo Abstract Thermochromism is the reversible change in the color of a compound when it is cooled or heated. In this experiment, the polynuclear Cu 4I4X4 complex has been synthesized and successfully demonstrate phenomenon of luminescence thermochromism. The luminescence thermochromic of copper (I)-iodide complex, Cu 4I4Py4, shows bright yellow luminescence at room temperature and an intense violet luminescence when cooled in liquid nitrogen. For luminescence thermochromic of Cu4I4L4, illustrated bright pink luminescence at room temperature and neon blue when cooled in liquid nitrogen. The color changes are due to subtle changes in crystal structure. This experiment demonstrated excellent results of luminescence thermochromism. Introduction The experimental and concept of luminescence thermochromism refers to the effect of temperature on the changing colors of a particular substance. This demonstration in particular stems from the work of H.D. Hardt, who developed the tetranuclear cluster. In this experiment, Hardt’s sysnthesis of the complex was extended to a few substituted pyridines and lutidine. From his general theory, there are two distinct types: continuous and discrete. For continuous luminescent thermochromoism, function of temperature depends on frequency of the emission band. However, discrete luminescent thermochromism’s frequency of the emission band is not related on temperature. This experiment synthesize a copper polynuclear cluster from common reagents. 2CuSO4*5H2O + 2KI + 2Na2SO3 2CuI + 10H2O + SO2 + K2SO4 + 2Na2SO4

CH 431 – Inorganic Chemistry Experiment 2: Thermochromism lab Choi, Youngjung (yc25744) * Song, Munsoo The configuration of Cu(I) complexes in solution are very labile to ligand substitution. Therefore, the species present are defined by thermodynamic rather than kinetic control. When CuI is mixed with “X” ligands, it creates each Cu4I4X4 clusters. 4 CuI + 4 X  Cu4I4X4 The most important luminescence thermochromic copper (I)-iodide complex, Cu4I4Py4 shows bright yellow luminescence at room temperature and violet luminescence when cooled in liquid nitrogen. The color change is controlled by the intensity of the low energy (LE) and high (HE) energy bands. The HE is rarely detectable at room temperature, but it is visible at extremely low temperature because it overcomes the LE bands. Due to CuI’s partial ionic bonding character, it is very flexible. It causes the compound to favor one of its excited state geometric whether at HE or LE.

The variation in the size of the inner copper core can

dominance one band over the other which is caused by the close packing of the “X” ligands.

Experimental Method, Calculations, and Yield There were multiple steps for this experiment to successfully synthesize Cu 4I4X4. This experiment was performed with the starting reagents of Copper (II) sulfate pentahydrate, potassium iodide, sodium sulfite, sulfuric acid and acetone to produce copper (I) iodide, CuI. When Na2SO3 was dissolved with sulfuric acid, a small amount of toxic SO 2 was produced. Therefore, performing in a fume hood was required. Since copper salts are harmful and dangerous for the environment, all of the waste solids and solution were thrown away in the waste containers.

CH 431 – Inorganic Chemistry Experiment 2: Thermochromism lab Choi, Youngjung (yc25744) * Song, Munsoo The experiment began with dissolving1.62 g (6.5mmol) of CuSO 4•5H2O in 15 mL of water. In a separate beaker with a stir bar, 0.42 g (4.0mmol) of Na 2SO3 was dissolved in 30 mL in water. When all of Na 2SO3 dissolved, 0.21 mL (4.0mmol) of concentrated sulfuric acid was added. To this solution, the CuSO4 was added with 1.07g (6.5mmol) of KI which was dissolved in 10 mL of water. The solution immediately changed color from cobalt blue to greyish brown. This copper (I) iodide product was collected by vacuum filtration and washed with 100 mL of water twice and 20 mL of cold acetone. The final product weight of CuI was 1.165 g 2CuSO4*5H2O + 2KI + 2Na2SO3 2CuI + 10H2O + SO2 + K2SO4 + 2Na2SO4 The percent yield for this reaction was calculated by:

(

1mol CuSO •5 H O

)(

2 mol CuI

)( 190.45 g )

4 2 ( 1.62 g CuSO 4 •5 H 2 O) 249.677 g CuSO • 5 H O 2 mol CuSO • 5 H O 1 mol CuI =1.24 g 4 2 4 2

Actual yield = 1.165g Percent yield =

1.165 g ∗100 %=94 % 1.24 g

In order to produce Cu 4I4X4 clusters, duplicated 0.5 g of CuI was used for next step because two ligands: pyridine and 3,4-lutidine need to be produced. Therefore, each 0.5 g of CuI was mixed with 0.0092 g of ascorbic acid and 0.323 g of potassium iodide were added to the 15 mL of acetonitrile. For pyridine cluster, 0.21 mL was dissolved with 5 mL of acetonitrile and added to the CuI solution. The lutidine cluster needed 0.295 mL of 3,4-lutidine and added to the yellow CuI solution. After 25 mL of water were added to each solution, Cu4I4X4 clusters started to precipitate. The solid was gathered via vacuum filtration and washed twice with 50 mL of water and ethanol. The final weight of Cu4I4Py4 clusters was 0.643 g and final weight of Cu4I4L4

CH 431 – Inorganic Chemistry Experiment 2: Thermochromism lab Choi, Youngjung (yc25744) * Song, Munsoo clusters was 0.88g. The lutidine cluster had color of greyish green because some of the CuI was remained on the product.

*figure 1 Synthesis of Cu4I4X4 clusters The percent yield for Cu4I4Py4 reaction was calculated by:

( 0.5 gCuI )

1 mol CuI ( 190.45 g CuI ) (

1 mol Cu 4 I 4 Py4 4 mol CuI

g =.707 g )( 1mol1078.18 Cu I Py ) 4 4

4

Actual Yield =0.643 g

Percent Yield=

0.643 g ∗100 % =90.86 % 0.707 g

The percent yield for Cu4I4L4 reaction was calculated by:

( 0.5 gCuI )

(

)(

)(

)

1 mol Cu4 I 4 L4 1 mol CuI 1190.4 g =.78 g 4 mol CuI 190.45 g CuI 1 mol Cu4 I 4 L 4 Actual Yield =0.68 g Percent Yield=

0.68 g ∗100 % =87.17 % 0.78 g

CH 431 – Inorganic Chemistry Experiment 2: Thermochromism lab Choi, Youngjung (yc25744) * Song, Munsoo The last part of the experiment was to demonstrate luminescent thermochromism of Cu4I4Py4 and Cu4I4L4 clusters. A spatula tip full of the cluster was added to a beaker followed by a few drop of water in order to create a suspension. Each of the clusters was exposed to long-wave UV light (365nm) and observations were recorded. Then each beaker was submerged into liquid nitrogen and exposed to the UV light to get results.

Room temperature Low temperature

Pyridine Yellow Violet

3,4 lutidine Pink Neon Blue(violet blue)

(liquid nitrogen) Back to Room temperature

Violet->orange->yellow

Pink color (slowly)

(rapidly) Results and Discussion From the first part of the experiment, the weight of the CuI was 1.165 g and percent yield was 94 % which was very successful. This product was obtained mainly throught the reaction of the CuSO4.5H2O with the sodium sulfite, sulfuric acid and potassium hydroxide to produce grey precipitate of CuI. This CuI product was then divided in two, each with a mass of 0.5 g and reacted with the MeCN, KI, ascorbic acid and the unique ligands. The percent yields of the Cu4I4Py4 and Cu4I4L4 were 90.86% and 87.17%. For the Cu4I4Py4 cluster at room temperature, a yellow luminescence under UV light. After being submerged in liquid nitrogen for 15 seconds, exposure of UV light gave a violet color. When it comes back to room temperature, it changed color from violet to orange and back to yellow rapidly. For the

Cu 4I4L4 cluster at room

temperature, a neon blue luminescence under UV light. After being submerged in liquid nitrogen for 15 seconds, exposure of UV light gave a pink color. When it comes back to room

CH 431 – Inorganic Chemistry Experiment 2: Thermochromism lab Choi, Youngjung (yc25744) * Song, Munsoo temperature, it changed color from neon blue to pink color very slowly. The oxidation state of CuSO4.5H2O and CuI are +2 and +1. The reductant used in the synthesis of CuI was the sodium sulfite solution. In the synthesis of the Cu 4I4X4 clusters, ascorbic acid was added to prevent the oxidation of Cu (I) to Cu (II). From this experiment, the luminescent thermochromism is continuous because of the gradual color changes. It contains a range of various colors going back to the room temperature. The luminescent thermochromism can caused by the difference in the sizes of the interior Cu4 core. This change is dependent on selective reflection of wavelengths by the closer crystal packing of the X (pyridine and 3,4 lutidine) ligands. The inner CuI core can deform according to the positive or negative pressure exerted by the ligand packing at different temperature. It causes increased favorability for one or the other excited states geometries. Conclusion This lab procedures and results were very straightforward. Overall calculated percent yields were very high which means it can be explained as very successful lab. The CuI product was successfully prepared and converted to its products which are Cu4I4Py4 and Cu4I4L4. The color of the Cu4I4Py4 and Cu4I4L4 were presented as expected. In order to improve this lab, ensure that all of the equipment is properly calibrated, clean and functioning ready to use. Also, take each measurement multiple times to reduce and human error. In addition, calculating correct amount of reagents or substances is very essential. Reference 1. Hardt, H.D.; Pierre, A.Z. Anorg. Allg. Chem.1973,402, 107-112. 2. 3. Ford, P.C.; Cariati, E.; Bourassa, J.Chem. Rev.1999,99, 3625-3647. 4.

CH 431 – Inorganic Chemistry Experiment 2: Thermochromism lab Choi, Youngjung (yc25744) * Song, Munsoo 5. Feng, J.; Tian, K.; Hu, D.; Wang, S.; Li, S.; Zeng, Y.; Li, Y.; Yang, G.Angew. Chem. Int.Ed.2011,50, 8072-8076. 6. 7. Parmeggiani, F.; Sacchetti, A.J. Chem. Ed.2012,89, 946-949....