Trithiatetrazocine cations, [RCN4S3]+; planar sulfur-nitrogen 10pi aromatics

The reaction of bicyclic sulfur-nitrogen heterocyles RCN 5S 3 (R = F 3C, Ph, Me 2N, 2-FC 6H 4, 2,6-F 2C 6H 3) with [Hg(SO 2) 2][AsF 6] 2 in liquid SO 2 yielded the corresponding trithiatetrazocinium-hexafluoroarsenates [RCN 4S 3][AsF 6] as yellow solids and a red-brown insoluble byproduct with the approximate composition Hg 3N 2. Single crystal structure determinations of the salts and theoretical calculations on the trithiatetrazocine cations [RCN 4S 3] (+) revealed the cations to be planar eight-membered heterocycles. The [RCN 4S 3] (+) cations are the missing link in the series of known valence isoelectronic eight-membered 10pi azocines, that is, [S 4N 4] (2+) and RC(NSN) 2CR. In contrast to neutral trithiatetrazocines and dithiatetrazocines RC(NSN) 2CR carrying donor substituents, which have a folded butterfly structure with a transannular S-S bond, the positive charge on the [RCN 4S 3] (+) cations always stabilizes the planar structure independent of the nature of the substituent. Experimentally obtained structures and theoretical calculations (geometries, frequencies, charges, nucleus-independent chemical shifts (NICS)) are in agreement with the description of [RCN 4S 3] (+) as planar eight-membered 10pi Huckel aromatic. The single crystal structure determinations of some 3,5-R-1,2,4,6-thiatriazinyl hexafluoroarsenates (R = Ph, 2-FC 6H 4, 4-FC 6H 4), which were isolated from the above reaction as well, are also included.