Unexpected Minor Products from the Thermal Auto-Fusion of Arachno-Sb8h12: Luminescent 4-(Hs)-syn-b18h21 and 3-(Hs)-syn-b18h21

The oxidative or thermal fusion of nonaborane and nonaheteroborane species to form bicluster assemblies, in which two conjoined subclusters share a common edge or triangular face, remains the most common route to such macropolyhedral compounds. One known example is the thermal auto-fusion of nonathiaborane arachno- SB8H12, which gives as its main products 18-vertex macropolyhedral isomers n-S2B16H16 and i-S2B16H16. Here we report new and unexpected minor products from the same reaction, isomers 4-(HS)-syn-B18H21 (1) and 3-(HS)-syn-B18H21 (2), in which the sulphur atoms are not a constituent of the cluster, but instead are extruded as thiol substituents to an otherwise classical {syn-B18}-octadecaborane cluster architecture. Both compounds 1 and 2 are structurally characterised by single-crystal X-ray diffraction (SCXRD) studies and, in the case for the former, by NMR spectroscopy, GC-MS and computational analysis. Additionally, it was observed that 1 and 2 are brightly luminescent under UV irradiation, making these compounds rare examples of a derivative of syn-B18H22 to be luminescent.