Cerium acetylacetonates -: new aspects, including the lamellar clathrate [Ce(acac)4] • 10H2O

Reactions of CeCl3 .7H(2)O and Ce(NO3)(3) . 6H(2)O with Naacac or NH(4)acac in aqueous solution at 21 and 45 degreesC yielded the trihydrate [Ce(acac)(3)(H2O)(2)].H2O and the dihydrate [Ce(acac)(3)(H2O)(2)], respectively, whereas similar treatment of (NH4)(2)[Ce(NO3)(6)] gave the trihydrate at both temperatures. Desiccation of the hydrates over silica gel left the dihydrate unchanged. whereas the trihydrate underwent decomposition rather than dehydration. Aerial oxidation of [Ce(acac)(3)(H2O)(2)] ill CH2Cl2 and toluene yielded alpha-[Ce(acac)(4)] and beta-[Ce(acac)(4)], respectively, the structure of the former being re-determined with improved precision. Careful treatment of aqueous (NH4)(4)[Ce(SO4)(4)] and Hacac (initially pH 1-2) with aqueous ammonia to pH 5 precipitated hydrated [Ce(acac)(4)], from which [Ce(acac)(4)] . 10H(2)O was isolated as unstable, light-sensitive single crystals, and the structure was determined. The complex is a laminar clathrate containing layers of Ce(acac)(4) molecules sandwiched between extensive hydrogen-bonded layers of water molecules which do not interact with the metal. Electrochemical experiments confirmed the unstable nature of hydrated Ce-III (acac)(3), while the reduction of [Ce(acac)(4)] yielded well-defined cyclic voltammograms in acetonitrile and acetone, corresponding to a quasi-reversible process. For the [Ce-IV(acac)(4)]/[Ce-III(acac)(4)](-) redox couple, a calculated reversible potential of 0.22 +/- 0.02 V versus SHE was obtained in acetone or acetonitrile (0.1 M Bu4NPF6) at both gold and glassy carbon electrodes. This potential is consistent with the ease of both oxidation and reduction of cerium acetylacetonate complexes as found in the synthetic studies. (C) 2003 Elsevier Science B.V. All rights reserved.