STEREOCHEMISTRY OF OXIDATION OF 1,5,2,4,6,8-DITHIATETRAZOCINES - PREPARATION AND CRYSTAL-STRUCTURES OF (ME2N)2C2N4S2C1 +PFG-, (ME2N)2C2N4S2CL +CL3- AND (ME2N)2C2N4S2(O)2 N(CF3)2 2