SYNTHESIS AND CHARACTERIZATION OF OXOTECHNETIUM(V) MIXED-LIGAND COMPLEXES CONTAINING A TRIDENTATE N-SUBSTITUTED BIS(2-MERCAPTOETHYL)AMINE AND A MONODENTATE THIOL

A series of 22 mixed-ligand complexes of the general formula TcOL(1)L( 2), where L(1)H(2) are N-substituted bis(2-mercaptoethyl)amine ligands , [SN(R)S], and L(2)H are monodentate thiols as coligand, is reported. The complexes were prepared by the ligand exchange method using Tc-gl uconate as precursor and equimolar quantities of the two ligands. In a ll cases the syn stereoisomer was formed in high yield and isolated as a crystalline product. In four cases HPLC analysis demonstrated the p resence of the anti stereoisomer in the reaction mixture. Although the yield was less than 1%, one anti isomer, 4a, was successfully isolate d as brown crystals. The isolated complexes were characterized by spec troscopic methods and elemental analysis. The formation of the two dia stereomers, syn and anti, was expected due to the configuration of the nitrogen substituent (R) with respect to the central TcO core. The X- ray crystallography showed that the coordination geometry of the syn i somers 9, 11, and 18 is trigonal bipyramidal while for the anti isomer 4a it is distorted square pyramidal. This is the first documentation of synlanti isomerism in N-substituted TcO[SN(R)S][S] mixed-ligand com plexes.