REDOX CHEMISTRY OF 1,2,4,6-THIATRIAZINYLS - PREPARATION AND CRYSTAL-STRUCTURES OF "3,5-DIPHENYL-1,2,4,6-THIATRIAZINIUM HEXAFLUOROPHOSPHATE, PH2C2N3S + PF6 -, AND 3,5-DIPHENYL-4-HYDRO-1,2,4,6-THIATRIAZINE, PH2C2N3SH