The air-stable technetium(II) complex trans-(Tc(DPPE)/sub 2/(NCS)/sub 2/)/sup 0/, where DPPE represents 1,2-bis(diphenylphosphino)ethane, has been characterized by single-crystal x-ray structural analysis refined to a conventional R factor of 0.069. Rose-colored crystals of this material, fw 1012.01, crystallize in the triclinic space group P1 with a = 21.384 (6) A, b = 12.878 (5) A, c = 9.549 (4) A, ..cap alpha.. = 71.51 (3)/sup 0/, ..beta.. = 81.94 (4)/sup 0/, and Z = 2. In this complex the technetium(II) center is approximately octahedrally coordinated with four equatorial P atoms at an average distance of 2.44 (1) A and two trans axial N-bonded NCS/sup -/ ligands at 2.04 (2) A. Spectroelectrochemical investigation of this complex shows that it undergoes reversible 1-equiv reduction to the Tc(I) anion and reversible 1-equiv oxidation to the Tc(III) cation, all three species being stable on the time scale of hours. The E/sup 0/' values (0.50 M tetraethylammonium perchlorate in N,N-dimethylformamide) for the Tc(III)/Tc(II) and Tc(II)/Tc(I) couples are 0.392 and -0.601 V vs. Ag/AgCl, respectively. Relative to chloro or bromo ligands, in the analogous trans-(Tc(DPPE)/sub 2/X/sub 2/)/sub /+/0/-/ (X = Cl, Br) complexes, the N-bonded NCS/sup -/ ligand markedly stabilizes the lower oxidation states. This effect and themore » dependence of the Tc-P bond length on the technetium oxidation state are discussed in terms of ..pi.. back-bonding. 25 references, 3 figures, 2 tables.« less