Synthesis of Metal Acetylacetonate Complexes
Background. In this experiment you will prepare and characterize complexes of 2 metal ions with the anion of acetylacetone. Acetylacetone (2,4-pentanedione) is a typical α-diketone that can ionize in aqueous solution as a weak acid:
The resulting acetylacetonate anion (abb. acac) can serve as a ligand to metal ions, formingcomplexes in which the ligand is bonded to the metal through both oxygen atoms to form a six-membered ring.
The six-membered rings (MO2C3) are planar and weakly aromatic because they contain 6 π electrons. In complexes of stoichiometry M(acac)3, the MO6 array is octahedral; in Cu(acac)2, the CuO4 group is square planar; and in VO(acac)2, the VO5 group is square pyramidal. In general the complexes areneutral and may be isolated as crystalline solids having an interesting variety of colors.
In pure acetylacetone, or solutions of acetylacetone in non-polar organic solvents, the diketo form is in equilibrium with a cyclic enol-like form. This second tautomer may be regarded as a complex in which the proton takes the role of the metal ion Mn+.
Synthesis and Characterization of MetalAcetylacetonates
We would like you to carry out syntheses of two metal acetylacetonate complexes, according to the following plan:
a. Al3+ and Cr3+
b. Fe3+, Co3+
c. Co3+, and the nitration of the Co3+
Characterization of Products
1. In the case you carry out a.: determine the melting points of your 2 products. Next, record the IR spectrum, using the KBr pellettechnique. Label and number the spectra and assign the "sore thumb" bands. Finally, measure the magnetic susceptibility.
2. In the case you carry out b.: determine the melting points of your 2 products. Next, record the IR spectrum, using the KBr pellet technique. Label and number the spectra and assign the "sore thumb" bands. Finally, measure the magnetic susceptibility.
3. In the caseyou carry out c.: determine the melting points of your 2 products. Next, record the IR spectrum, using the KBr pellet technique. Label and number the spectra and assign the "sore thumb" bands. Finally, measure the 1H nuclear magnetic resonance (NMR), using CDCl3 as the solvent and TMS as the reference. Label and number the spectra.
Give a reaction mechanism for the formation of theacatylacetone complexes. Explain the magnetic behaviour measured in experiment a and b.
Try to give an reaction mechanism for the nitration of Co(acac)3.
In case you carry out experiment c., do you think it is useful to measure the magnetic susceptibility.
1. R.C. Young, Inorganic Syntheses, 2, 25(1946). Al(acac)3.
2. R.A. Rowe, M.M. Jones, Inorganic Syntheses, 5,114(1957). VO(acac)2.
3. W.C. Fernelius, J.E. Blanch, Inorganic Syntheses, 5, 130(1957). Cr(acac)3.
4. R.G. Charles, Inorganic Syntheses, 7, 183(1963). Mn(acac)3.
5. B.E. Bryant, W.C. Fernelius, Inorganic Syntheses, 5, 188(1957). Co(acac)3.
6. J.B. Ellern, R.O. Ragsdale, Inorganic Syntheses, 11, 83(1968). Co(acac)2(H2O)2.
7. C. Glidewell, J.S. McKechnie, J. Chem. Ed., 65, 1015(1988).8. D.W. Barnum, J. Inorg. Nucl. Chem., 21, 221(1961). Electronic Absorption Spectra of metal acac complexes.
9. K. Nakamoto, P.J. McCarthy, A. Ruby, A.E. Martell, J. Amer. Chem. Soc., 83, 1066(1961). A discussion of IR spectra of some trivalent metal acac complexes.
10. K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, 4th ed., Wiley, New York, 1986. Anadvanced reference with data for many metal complexes, including metal acacs.
Synthetic Procedures for Metal Acetylacetonate Complexes
Weigh 0.33 g acetylacetone into a small Erlenmeyer flask. Add 4 mL distilled water followed by 0.8 mL of 5M NH3.
Dissolve 0.3 g of aluminum sulphate, Al2(SO4)3.16H2O,in 3 mL of distilled water. Add the ammoniacal solution...
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