CF-252-PLASMA DESORPTION MASS-SPECTROMETRY OF GOLD CLUSTERS - FRAGMENTATION PATTERNS IN SMALL CLUSTERS AND DIFFERENCES IN SAMPLE COMPOSITION IN LARGE CLUSTERS

A series of small gold phosphine clusters, including [Au6(PPh3)6](NO3)2(1), [Au6(PPh3)8](NO3)2 (2), [Au9(PPh3)8]-(NO3)3 (3), [Au11(PPh3)8Cl2]Cl (4), [Au13(PPh2Me)8I4]I (5), and [CAu6(PPh3)6](BF4)2 (6), have been studied using 252-Cf-plasma desorption mass spectrometry (Cf-252-PDMS). This series of well-characterized clusters was studied to develop an understanding of Cf-252-PDMS as applied to gold clusters and, hence, use Cf-252-PDMS to study much larger gold clusters. The study of small gold clusters indicates that extensive fragmentation occurs. Oligomerization of these clusters, or cluster fragments, is uncommon, and even when it occurs it is limited. These results allow us to estimate the molecular mass of much larger clusters, on the basis of the highest observed fragment ion, and not the centroid of peak distributions as suggested previously. The study of the large clusters, moderated by our knowledge of the spectra of small clusters, indicates that a large gold cluster, formulated by Schmid as Au55(PPh3)12Cl6, gives spectra that indicate that sample composition varies dependent on a number of factors. These factors include the source of the sample, the age of the sample, and the temperature at which the sample is stored. It is also possible that the sample is inhomogenous as prepared; it is probable that aged samples are inhomogeneous and contain at least three clusters of molecular weight ca. 9500,14 000, and 20 000 mu (mass units).