CHARACTERIZATION OF SUPPORTED AND UNSUPPORTED TRANSITION-METAL COMPOUNDS BY LIQUID SECONDARY-ION MASS-SPECTROMETRY

The positive ion liquid secondary ion mass spectra (LSIMS) of metal ac etylacetonates (acacs) contain cluster ions that involve multiple meta l centers. Several metal acacs form adduct ions with m-nitrobenzyl (m- NBA) alcohol used as the LSIMS support matrix. In these adduct ions, d eprotonated m-NBA molecules act as bridges between metal centers. The LSIMS of a series of dirhodium carboxylates show that the electron-wit hdrawing strength of the carboxylate group controls whether the base p eak in the mass spectrum is the molecular ion or an adduct ion formed between the molecule and a matrix molecule of sulfolane. However, no c luster ions are formed for these dirhodium compounds. Similarly, highl y charged cationic compounds do not form cluster ions, nor do they for m adduct ions with the LSIMS solvent. Instead, the counter ion is reta ined to maintain a single positive charge in the ion. LSIMS spectra of neutral and charged metallocene compounds are compared. Contrary to t he assertions that these compounds cluster extensively in the gas phas e, the LSIMS provide no evidence for this process. To support studies of surfaces prepared for catalytic studies, silica- and clay-supported transition metal acacs were characterized by LSIMS. Release of the su pported transition metal compounds from the surface occurs during ion exchange.