American Chemical Society
cm020902u_si_008.cif (18.45 kB)

A Novel Family of Structurally Characterized Lithium Cobalt Double Aryloxides and the Nanoparticles and Thin Films Generated Therefrom

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posted on 2003-09-05, 00:00 authored by Timothy J. Boyle, Mark A. Rodriguez, David Ingersoll, Thomas J. Headley, Scott D. Bunge, Dawn M. Pedrotty, Sacha M. De'Angeli, Sara C. Vick, Hongyou Fan
The reaction between LiN(SiMe3)2 and Co(N(SiMe3)2)2 in THF followed by the addition of an aryl alcohol (HOAr) yielded:  [Co[(μ-OAr)2Li(THF)x]2 [where x = 2:  OAr =:  OC6H4Me-2 (oMP, 1), OC6H4(OCHMe2)-2 (oPP, 2), OC6H3(Me)2-2,6 (DMP, 3); where x = 1:  OAr = OC6H3(OCHMe2)2-2,6 (DIP, 4)]. Undertaking the same synthesis in pyridine (py) led to the same general structure with py molecules substituted for the THF solvent molecules:  [Co[(μ-OAr)2Li(py)2]2 (OAr = oMP (5), oPP (6)]. For 16, the tetrahedrally (Td) bound Co atom bridges two OAr ligands to each of the Li atoms. The Li atom adopts a Td or trigonal bipyramidal (TBP) geometry, as determined by the number of bound solvent molecules. For the more sterically demanding ligands with py as the solvent, the mononuclear monometallic species [Co[(μ-OAr)2(py)x]2 (OAr = DMP (7), x = 2; DIP (8), x = 3) were observed adopting a Td or TBP geometry, respectively, based on the number of bound solvent molecules. Increasing the steric bulk of the OAr to OC6H3But2-2,6 (DBP) in either THF or py led to the isolation of the previously characterized [Li(DBP)(solv)]2. Calculated XRD powder patterns were generated from the single-crystal structure of 18 and used to verify the identity of the bulk powder. Attempts to use these compounds for MOCVD applications were not successful due to low volatility of these compounds. Attempts to generate nanoparticles of the spinel phase of LiCoO2 by injecting a py solution of 5 or 6 into boiling methyl-imidazole (MeIm)/H2O 95:5) led to nanoparticles of Co(OH)2 only, as characterized by XRD and TEM. Thin films of the spinel phase of LiCoO2 were formed by spin-cast deposition methods using 5 or 6 dissolved in a py/toluene mixture onto platinized silicon wafers followed by firing at 700 °C. Cyclic voltammetry revealed two irreversible oxidation processes followed by one reversible process, the latter of which is found to occur at about 4.2 V. XRD analysis of the thin film, both before and after electrochemical cycling, revealed only minimal variations in the crystal structure of the film after cycling. This family of compounds, even though stoichiometrically incorrect, have been shown to be useful for single-source applications in the solid and liquid techniques.