Natural rhenium sulfide clusters formed under conditions of laser desorption-ionization

Cluster forms of rhenium sulfides have important practical applications as catalysts in oil refining and thus present high interest. However, only a limited number of rhenium sulfide clusters have been described previously. It is known that cluster formation actively occurs under conditions of laser desorption-ionization; nevertheless, detailed studies of rhenium sulfides under such conditions were apparently not conducted previously.

A sample of natural rhenium sulfide, collected from the fumarolic field of Kudriavy volcano (Iturup island, Russia) in 2002, was investigated using the laser desorption-ionization mass spectrometry method. The formed rhenium sulfide clusters were registered by a time-of-flight detector and identified programmatically using the software developed in IPCE RAS. The identification involved a comparison of the distribution of isotopic peak intensities, observed in the resulting mass spectra, with the theoretical probabilities of occurrence of various isotopologues for hypothetical rhenium sulfide species.

Over 60 rhenium sulfide clusters of Re_xS_y ⁺ and Re_xS_yO_z ^- types containing up to 10 rhenium atoms were formed when a sample of natural rhenium sulfide was exposed to laser desorption-ionization conditions. Several isolated heterometallic Re_XMoS_Y ⁺ and Re_XMoS_YO_Z ^- clusters containing up to eight rhenium atoms were additionally observed in the resulting mass spectra. The species with compositions, for which the electrically neutral analogs are known, apparently were the most stable rhenium sulfide clusters among the detected ones.

The obtained data allowed summarizing the patterns of formation of rhenium sulfide clusters under conditions of laser desorption-ionization. The ability of rhenium and sulfur to form cluster species containing from 7 to 10 atoms of rhenium was likely discovered for the first time. The majority of the rhenium sulfide clusters described in this study, notably Re_xS_y ⁺ ions containing over seven atoms of rhenium, were apparently not observed previously.