The design and synthesis of mixed oxotechnetium(V)-99 complexes with a novel series of aza-substituted 2,6-dimethyl-4-azaheptane-2,6-dithiol ligands of the general type NS2 and benzyl mercaptan as coligand are reported. Ligands (general formula R-CH2CH2N[CH2C(CH3)(2)SH](2) with R = N(C2H5)(2), piperidin-1-yl, pyrrolidin-1-yl, and morpholin-4-yl) were synthesized through the reduction of aza-substituted heterocyclic aza disulfides which result from the reductive cyclization of 2.2’-dithiobis(2-methylpropanal) with the appropriate primary amine. The Tc-99 complexes 5 (general formula TcO{[SC(CH3)(2)CH2](2)NCH(2)CH(2)R}X where X = benzyl mercaptan) were prepared in high yield by the reaction of Tc-99(V) gluconate with a 1:1 mixture of the appropriate tris-chelating ligand and the monodentate benzyl mercaptan. The resulting complexes were purified through flash column chromatography. Crystals were formed by dissolving complexes in a mixture of MeOH/water and slowly evaporating the solvents. Complexes were characterized by elemental analyses and spectroscopic methods. Complete assignments of H-1 and C-13 NMR resonances were made for all complexes. X-ray crystallographic analysis of 5d (C21H35N2S3O2TC, R = morpholin-4-yl) showed that the complex crystallizes in the monoclinic space group P2(1)/c with a 17.166(2) Angstrom, b = 8.9282(7) Angstrom, c = 17.738(2) Angstrom, beta = 116.031(3)degrees, V = 2442.7(4) Angstrom(3), and Z = 4. Complex 5d has trigonally distorted square pyramidal coordination geometry around technetium with the side chain on nitrogen directed toward the oxygen of the Tc=O core (syn configuration). The nOe data confirm that in all cases the major isolated product of the synthesis has the syn configuration of the side chain.