TECHNETIUM COMPLEXES OF PYRIDINES AND IMIDAZOLES

The synthesis and spectra of a series of trans-dioxotechnetium(V) complexes with pyridine and imidazole ligands are reported. Crystal structures are presented for trans-{lcub}TcO(,2)(imidazole)(,4){rcub}Cl(.)2H(,2)O and trans-{lcub}TcO(,2)(1-methylimidazole)(,4)Cl(.)3H(,2)O. The compounds are all diamagnetic at room temperature (14,500 G). Infrared absorbances assigned to the asymmetric O=Tc=O stretch occur in the range 810-830 cm('-1). Proton NMR resonances are deshielded slightly relative to the free ligands. All complexes are unstable in aqueous solution unless additional free ligand is also present.; The synthesis and spectra of a series of compounds of the type {lcub}TcO(OR)X(,2)L(,2){rcub}, where X = Cl or Br, L = 4-cyanopyridine or 4-nitropyridine, and R = CH(,3)- and CH(,3)CH(,2)-, are reported. A complete crystal and molecular structure determination is presented on {lcub}TcO(OCH(,2)CH(,3))Br(,2)(4-nitropyridine)(,2){rcub}. The geometry of the molecule exhibits trans halides, trans pyridines, and trans oxo and alkoxo moieties. Infrared and proton NMR spectra are reported with Tc-Cl and Tc-N stretching frequencies occurring at 309-344 cm('-1) and 220-270 cm('-1), respectively, and ring proton resonances being shifted somewhat downfield. All but the oxo ligands appear to be easily substituted in a variety of solvents.; A series of complexes of the type {lcub}XL(,4)Tc-O-TcX(,4)L{rcub}, where X = Cl or Br, and L = pyridine, 4-picoline, or 3,5-lutidine, have been synthesized and characterized. The structure of this class of compounds has been determined by a crystallographic study of {lcub}Cl(picoline)(,4)Tc-O-TcCl(,4)(picoline){rcub}(.)H(,2)O. The structure was determined to involve two octahedrally coordinated technetium atoms bridged by a single oxygen atom with the Tc-O-Tc group being nearly linear. Consistent with their solid state structure, fresh solutions of these compounds are essentially nonionic. In the solid state these compounds exhibit a small magnetic moment ((mu)(,eff) (TURNEQ) 1.0 (beta)) and show a broad EPR signal at low temperature. Frozen solutions reveal complex EPR spectra consistent with an axial binuclear species (splitting by two I = 9/2 nuclei). Infrared Tc-O stretching frequencies are in the range 694-701 cm('-1), while Tc-Cl bands appear in the range 305-317 cm('-1) and Tc-Br at 235-266 cm('-1). Cyclic voltammetry typically revealed two separate and nearly reversible single-electron redox processes, which were sensitive to the ligands present. UV-visible spectra exhibited broad intense bands.