Substituent Effects on the Volatility of Metal b-diketonates

Volatile trends are established for a series of M(b-diketonate)n complexes, where M = Cu (n = 2); Al, Sc, Cr, Fe, Co, Ga (n = 3); Zr (n = 4) and b-diketonate = acetylacetonate (acac), trifluoroacetylacetonate (tfac), hexafluoroacetylacetonate (hfac) and 2,2,6,6-tetramethyl-3,5-heptanedionate (tmhd). Sublimation enthalpies (DHsub) were calculated from thermogravimetric analysis (TGA) data, which show that the dependence of DHsub on the number and type of intermolecular interactions appears to be more substantial than molecular mass effects. Irrespective of the metal, the DHsub values for the M(tmhd)3 derivative have a DHsub value of between 93 and 99% of that of the M(acac)3 derivative. In contrast, the M(tfac)3 and M(hfac)3 derivatives have DHsub values of ca. 82% and 54% of the values for the corresponding M(acac)3. Similar trends are observed for M(b-diketonate)2 and M(b-diketonate)4 derivatives. The relationship between the DHsub and (Tsub) of the substituted b-diketonate derivatives as compared with the values for parent M(acac)n may be used to predict either quantity for a range of M(b-diketonate)n complexes where the values for M(acac)n are known. Using the TGA sublimation data, vapour pressures have been calculated for each of the M(b-diketonate)n complexes. Copyright 2000 John Wiley & Sons, Ltd.