The substitution chemistry of TcCl3(PPh(3))(2)(CH3CN) is rather facile relative to the analogous rhenium complex, since both the chloride and phosphine ligands are easily substituted for various pyridine ligands. Consequently a series of Tc-III complexes with amine, pyridine, and polypyridyl ligands were prepared and characterized by H-1 NMR and cyclic voltammetry. In addition, the zinc reduction of TcCl4(py)(2) in the presence of pyridine results in TcCl2(py)(4). Structural and spectroscopic data indicate that this Tc-II complex exhibits strong metal-pyridine interactions characteristic of low-valent amine complexes of Re-II and Os-II. For example, a decrease of 0.04 and 0.06 Angstrom is observed for the trans-Tc-N bond length in TcCl2(py)(4) relative to mer-TcCl3(py)(3) and [TcCl2(py)(3)(PPh(3))](+), respectively. This ability of pyridine to function both as a strong a-donor and moderate Jc-acid ligand has resulted in the isolation of technetium complexes in various oxidation states with similar ligand environments. As a result, a structural comparison of [TcCl2(py)(3)(PPh(3))(3)](+), TcCl2(py)(4), TcCl(tpy)(py)(2), and other known Tc-III and Tc-II pyridine complexes is presented. Crystals of [TcCl2(py)(3)(PPh(3))]PF6 are triclinic, with space group , Z = 2, and lattice parameters a = 12.677(4) Angstrom, b = 13.064(4) Angstrom, c = 13.103(5) Angstrom, alpha = 110.14(3)degrees, alpha = 101.12(3)degrees, gamma = 96.61 degrees, V = 1959 Angstrom(3), and R = 0.0615 (R(w) = 0.1148). Crystals of TcCl2(py)(4) are tetragonal, with space group I4(1)/acd, Z = 8, and lattice parameters a = 15.641(4) Angstrom, c = 16.845(6) Angstrom, V = 4121 Angstrom(3), and R = 0.0373 (R(w) = 0.0290). Crystals of TcCl(tpy)(py)(2) are orthorhombic, with space group C222(1), Z = 4, and lattice parameters a = 9.359(3) Angstrom, b = 16.088(6) Angstrom, c = 18.367(4) Angstrom, V = 2765 Angstrom(3), and R = 0.0499 (R(w) = 0.0599).