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2008 级无机化学研究性实验 Synthesis and Spectral Study of Copper (II) Complexes Zhong Aoshu College of chemistry and molecular sciences Wuhan University Abstract. Cu2+ forms different compounds with different ligands. Some of the compounds are prepared. The spectra and the color of them are measured and observed .Then crystal field theory and MO are used to explain the results, including the color, Amax and εmax. Key words. Copper complexes Spectrochemical series Crystal field theory 1. Introduction Crystal field theory predicts for transition metal octahedral complexes that the d orbitals are split into two groups. The original assumption of this theory that the d electrons have a columbic interaction with the ligands considered as point charges is certainly not correct and a priori calculation of the crystal field splitting parameter 10 Dq, based on this model are generally in poor agreement with experimental values. However because of the octahedral symmetry it is true that the splitting of the d levels predicted by crystal field theory is qualitatively correct. That is, whatever the nature of the ligand-metal interaction, the dxy, dyz,and dxz orbitals will form a three-hold equivative (t2g set) and the dx2-y2 and dz2 orbitals will form a two-fold equivalent (eg set) in the complex. Thus, 10 Dq the energy difference between these two sets, may be determined by experiment, even though its accurate theoretical calculations are difficult. Because the values of 10 Dq are is different when different ligands are present, they absorb different light. Thus they give different colors. The interpretation of spectra in terms of the spectrochemical series is in principle easily done in the case of octahedral complexes of metal ion with d9 configurations. In this cases there is no interaction with d electrons and since the d orbitals interact uniformly with the core of nonvalance metal electrons the only d lever splitting is due to the interaction of the d orbitals with the ligands, thus, a single spectral transitions of energies, 10 Dq, is predicted. 2. Experiment 1 2008 级无机化学研究性实验 2.1. Materials and instruments Copper (II) sulfate pentahydrate, hydrochloric acid, glycine, sodium hydrogen carbonate, ethanol, ice, acetylacetone, ethylenediammine sodium hydroxide, oxalate monohydrate, chloroform. Spectrophotometer. 2.2. Preparation of cis-Bis(glycinato) copper(II) Monohydrate (1),(2) A 3.00 g sample (12.0 mmole) of copper (II) sulfate pentahydrate is dissolved in 17.0 mL of 1.0 M hydrochloric acid. To this solution 1.50g (20.0 mmole) of glycine is added and then warmed in hot water bath for about 1hour in 50℃. Sodium hydrogen carbonate is added until precipitation is complete (avoid a large excess). Add about 40 mL of ethanol and cool in ice bath for 30 minutes. The precipitate is suction filtered, and dried in an oven for 30 minutes in 50℃.After the precipitate is cooled, weight it . 2.3. Preparation of Bis(acetylacetanato)copper(II) (1) Etylacetone is prepared by adding 2.50 g (25.0 mmole) of acetylacetone to 100 mL of 0.25 M NaOH solution (25.0 mmole). This solution is added to a solution of 3.10 g (12.5 mmole) of copper(II) sulfate pentahydrate in 100.0 mL of water. The precipitates are suction filtered, then add 40.0 mL of ethanol to it and cool in ice bath for 30 minutes and air dried. Weigh it. 2.4. Preparation of potassium bioxalatocuprate(II) (3) A 6.25g sample (0.025mmole) of copper(II) sulfate pentahydrate is dissolved in 12.5mL of water. Heat the solution to 90℃ , stir the solution violently and add 18.40 g of oxalate monohydrate to the solution quickly. Cool the solution to 10℃ in ice bath. The precipitates are suction filtered, and use 25.0 mL of cool water to wash the precipitate and air dried. Weigh it. 2.5. Spectral study. (4) Group one: In water solution the complex ion Cu(H2O)62+ is formed. Weigh 0.60 g Cu(NO3)2·3H2O and 40 g NH3NO3 to prepare 250 mL of 0.01 M Cu(NO3)2 and 2 M NH4NO3 solution. Group two: Add 2.5 mL of 0.1 M NH3·H2O and 22.5 mL of water to 25.0 mL of the solution prepared, thus we get Cu(NH3)(H2O)52+.Group three: Add 5.0 mL of 0.1 M NH3·H2O to 25 mL of the solution prepared, thus we get Cu(NH3)2(H2O)42+.Group four: Add 7.5 ml of 0.1 M 2 2008 级无机化学研究性实验 NH3·H2O and 17.5 mL of water to 25.0 mL of the solution prepared, thus we get Cu(NH3)3(H2O)32+. Group five: Add 10.0mL of 0.1 M NH3·H2O and 15.0 mL of water to 25 mL of the solution prepared, thus we get Cu(NH3)4(H2O)22+.Weigh 0.60 g of Cu(NO3)2·3H2O and 25.25g of KNO3 to prepare 250 ml of 0.01 M Cu(NO)3 and 1 M KNO3 solution. Weigh 0.60g ethylenediammine to prepare 100 mL of 0.1 M en solution. Group six: Add 2.5 mL of en solution and 22.5 mL of water to 25 mL of the solution prepared, thus we get Cu(en)(H2O)42+ .Group seven: Add 2.5 mL of en solution and 22.5 mL of water to 25.0 mL of the solution prepared, thus we get Cu (en)2(H2O)22+ .Group eight: Weigh 0.12 g of cis-Bis(glycinato)copper(II) monohydrate to prepare 50 mL of 0.01 M Cu(gly)2(H2O)2 solution. Group nine: Weigh 0.11 g of Bis(acetylacetanato)copper and chroform to prepare 50 mL of 0.01 M Cu(acac)2 solution. Group ten: Weigh 0.18 g of potassium bioxalatocuprate ( II ) to prepare 50 mL of 0.01 M Cu(C2O4)2(H2O)22- solution. Clean two quartz-cells with distilled water and then put the solution to the tubes, make initial adjustment to the spectrophotometer before measurement. Except group nine, pure water is the reference solvent. Chroform is the reference solvent for group nine. Using the spectrophotometer to measure the absorption with one nm per point and get a list of absorption data. Use Microsoft office to get the figure below from the date. 0.14 0.25 Absorption/Abs Absorption/Abs 0.12 0.1 0.08 Group one 0.06 0.04 0.2 Group Group Group Group 0.15 0.1 0.05 0.02 0 0 400 500 600 700 800 900 400 500 λ/nm Figure 1 600 λ/nm 700 800 Figure 2 0.35 0.4 0.3 0.35 0.25 0.3 0.2 Absorption/Abs Absorption/Abs two three four five Group six Group seven 0.15 0.1 0.05 2.5 2 0.25 1.5 0.2 1 0.15 0.1 0.5 0.05 0 400 500 600 λ/nm 700 0 400 800 Figure 3 0 500 600 λ/nm Figure 4 3 700 800 Group ten Group eight Group nine 2008 级无机化学研究性实验 3. Results and discussion. Table 1. Color, λmax, Amax and concentration for complexes studied Group Complex Color number λmax λmax (literature) nm Amax Abs nm C mol/L One Cu(H2O)62+ no 811 794 0.13204 0.001 Two Cu(NH3)(H2O)52+ Light blue 766 745 0.0869 0.005 There Cu(NH3)2(H2O)42+ Blue 719 680 0.1922 0.008 Four Cu(NH3)3(H2O)32+ Blue 660 645 0.1024 0.005 Five Cu(NH3)4(H2O)22+ Dark blue 639 591 0.1157 0.005 Six Cu(en)(H2O)42+ Light blue 660 658 0.1520 0.005 Seven Cu(en)2(H2O)22+ Purple 547 549 0.2939 0.005 Eight Cu(gly)2(H2O)2 Dark blue 628 630 0.3623 0.01 Nine Cu(acac)2 Dark green 656 650 0.3672 0.01 Ten Cu(C2O4)2(H2O)22- Light blue 713 --- 0.3266 0.01 Half of the absorption max is a little different from the literature data, the spectrometer itself may have some deviations. But the date is not very good when water and ammonia serve as ligands. We assume that the concentration of aqueous ammonia may not be true because ammonia is highly volatilizable. What’s more, there may exist other species in the solution, so we can not get very exalt date. Table 2. Yields of the complexes prepared. Complex Mass g Yield Yield(literature) Cu(gly)2·H2O 2.15 92.7% >90% Cu(acac)2 2.53 76.7% --- K2[Cu(C2O4)2]·2H2O 8.07 91.2% 97% The yields are very good because the experiment is done carefully. In Cu2+ and ammonia solution,NH4NO3 acts as a buffer, so there are not participants in the solution. 4 2008 级无机化学研究性实验 4. Conclusion Because the absorption max for Cu(H2O)62+ does not lie in the visual area, it does not have color. Cu(en)2(H2O)22+ appears purple in aqueous solution. Hydrated Cu2+ is a d9 ion. Because the absorption max for it is 547 nm, the energy difference between t2g and eg orbitals in this is correspond to the energy of photos spanning the green and yellow range, when white light shine on the solution, these colors of light are absorbed, transmitted, so the solution appears purple. The color of others can be explained in the similar way as that of Cu(en)2(H2O)22+. When more NH3 are added to Cu2+, λmax becomes smaller. That is to say, light of higher energy is absorbed and the energy difference between t2g and eg orbitals is greater. That indicates that NH3 is a stronger ligand than water. The λmax of Cu2+ and ammonia solution is bigger than that of Cu2+ and en solution. What’s more, en is a chelate, they both use N atom as donor atom, so en is a stronger ligand then NH3. The λmax of Cu(gly)2(H2O)2 is bigger than Cu(acac)2, so gly is a stronger ligand than acac. The λmax of Cu(ox)2(H2O)22- is smaller than that of Cu(H2O)62+ and bigger than that of Cu(acac)2, so ox2- is a stronger ligand than water and weaker ligand than acac.We get the spectrochemical series. H20<ox2-<acac< (gly NH3) <en As the date is not very well, the strength of gly and NH3 can not be compared. For group nine, it appears to have only one absorption max. The reason that the second crystal field transition is not readily detected is that it is obscured by the intense absorption of light associated with electronic transitions between orbitals that are primarily ligand-like in nature. Such transition are called charge transfer transitions and commonly are associated with much stronger absorption of light than are crystal filed transitions. εmax indicates how intense the absorption is. εmax for group one to five are relatively small compared to those from group six to ten. This qualitatively explained by the lower symmetry of the chelate complexes. Specifically the chelates 5 2008 级无机化学研究性实验 lack a center of symmetry whereas the complexes from group one to five have a center of symmetry. Since the absorption of light should be completely forbidden. By the electron dipole mechanism, we may anticipate that a centrosymmetric would show weaker transitions even though vibrations always cause small instantaneous from the centrosymmetric arrangements. Using MO, Orgel diagram can be used to explain the phenomenon. Only one kind of transfer is possible according to the diagram. (5)The transitions are all d-d transition .They are all spin-allowed and Larport-forbidden, so the absorptions are all not strong. Figure five 5. Acknowledgement. We thank all the teachers in Wuhan University that helped us during the experiment. They give us help and sound instructions when we need. 6. Literature cited. (1)Potts Richard. Synthesis and spectral Study of Copper (II) Complexes. Journal of chemical education, 51 (1974): 539. (2)Du Xiangge. Preparation and Characterization of the chelate of glycine with Copper. Journal of Anhui Agri .Sci .2009, 37(5):1897 – 1898. (3)Muttertiles Earl. Inorganic synthesis (Vol ten). McGraw-Hill Book Company, Inc.New York, London, 1967. (4)Trapp chrles, Johnson Richard. Crystal field spectra of transition metal ions. Journal of chemical education, 44 (1967): 527-530. (5)Housecroft Catherine, Sharpe Alan. Inorganic chemisty.Second edition. Prentice Hall, 2005. 6