Exact mass analysis of sulfur clusters upon encapsulation by a polyaromatic capsular matrix.

Abstract

Structural determination of inorganic clusters relies heavily on mass spectrometry because of, in most cases, their poor responsivities toward nuclear magnetic resonance, ultraviolet/visible, and infrared analyses. Nevertheless, mass spectrometry analysis of oligosulfurs (S _n ), which are unique clusters with copious allotropic forms, usually displays their fragment peaks. Here we report that a polyaromatic capsule acts as a supramolecular matrix for the mass determination of the neutral sulfur clusters. Upon encapsulation, molecular ion peaks derived from the host-guest complexes including cyclic S₆ and S₈ clusters are exclusively detected by common electrospray ionization time-of-flight mass spectrometry analysis. Furthermore, mass spectrometry analysis of a cyclic S₁₂ cluster, which is in situ prepared from two S₆ clusters within the matrix upon light irradiation, is achieved by the same way. The present matrix can remarkably stabilize the otherwise labile S₆ and S₁₂ clusters in the polyaromatic shell not only under mass spectrometry conditions but also in an ambient solution state.The structures of inorganic clusters are commonly characterized by mass spectrometry (MS), but neutral sulfur clusters heavily fragment under MS conditions, preventing their exact mass determination. Here, the authors successfully perform MS on labile cyclic sulfur clusters by stabilizing them within ionic supramolecular capsules.