A new approach to the "3 + 1" mixed ligand oxotechnetium complexes of the general formula TcOL1L2, with ligands (L1H(2)) containing the SNN donor set and various monodentate thiols as coligands (L2H) is reported. The ligands L1H(2) (1-3, general formula R(1)CH(2)CH(2)NHCH(2)C(R(2))(2)SH where R(1) = N(CH3)(2) and R(2) = H in 1, R(1) = pyrrolidin-1-yl and R(2) = H in 2, and R(1) = piperidin-1-yl and R(2) = CH3 in 3) act as tridentate SNN chelates to the TcO3+ core, leaving open one coordination site cis to the oxo group. In the presence of a monodentate thiol (L2H) and using Tc-99(V)-gluconate as precursor, the vacancy is filled by the thiol which acts as the coligand. With this approach four neutral oxotechnetium complexes (4-7, general formula TcO[R(1)CH(2)CH(2)NCH(2)C(R(2))(2)S][SR] where RSH = p-methoxybenzenethiol, or p-methylbenzenethiol or benzyl mercaptan) were prepared in high yield by reacting L1H(2) and L2H with Tc(V)-gluconate in a ratio 1:1:1. The complexes were characterized by elemental analysis and spectroscopic methods. Complete assignments of H-1 and C-13 NMR resonances were made for all complexes. X-ray crystallographic studies of 5 (R(1) = pyrrolidin-1-yl, R(2) = H, RSH = p-methylbenzenethiol) and 7 (R(1) = piperidin-1-yl, R(2) = CH3, RSH = benzyl mercaptan) showed that the complexes crystallize in the monoclinic space group P2(1)/n (a = 10.223(1) Angstrom, b = 9.283(1) Angstrom, c = 18.337(2) Angstrom, beta = 97.262(2)degrees, V = 1726.3(4) Angstrom(3), Z = 4; a = 11.876(2) Angstrom, b = 10.470(2) Angstrom, c = 17.098(3) Angstrom, beta = 105.990(4)degrees, V = 2043.8(6) Angstrom(3), Z = 4, for 5 and 7, respectively). Complexes 5 and 7 have distorted square pyramidal coordination geometry with the oxo ligand in the axial position. The steric requirements of the oxo group cause the Tc atom to be displaced 0.68 Angstrom out of the mean equatorial plane of the NNSS donor atoms in both complexes.