Synthesis and characterization of technetium(V) and (VII) complexes with bidentate nitrogen donor ligands. X-ray molecular structures of tetrabutylammonium bis(1,2-diimidobenzene)oxotechnetium(V) and tris(1,2-diimidobenzene)technetium(VII) pertechnetate

The reaction of pertechnetate with 1,2-diaminobenzene (H2pda) in the presence of the reducing agent sodium dithionite in alkaline aqueous solution led to the formation and isolation of (n-Bu4N)[TcO(pda)2] (1). If the reaction is performed without reducing agent in methanol, the green compound [Tc(pda)3](TcO4) (2) is formed. Both complexes are diamagnetic, and a single N-H stretching frequency in both indicates that each pda ligand contains one hydrogen per nitrogen, and is dianionic. X-ray crystal structures of both compounds are also reported. Crystal data for complex 1, C28H48N5OTc: orthorhombic, space group P2(1)2(1)2(1), a = 11.644(3), b = 15.303(4), c = 16.950(5) angstrom and U = 3020.3(1.5) angstrom3 to give Z = 4 for D(calc) = 1.25 g cm-3. Crystal data for 2, C18H18N6O4Tc2: orthorhombic, Pna2(1), a = 13.869(4), b = 12.799(5), c = 10.851(3) angstrom and U = 1926.2(1.1) angstrom3 to give Z = 4 for D(calc) = 1.99 g CM-3. The structures have been solved by Patterson and Fourier methods and refined by least-squares methods to R = 0.058 for 1 and 0.090 for 2. Complex 2 represents the first tris-bidentate cationic complex of technetium to be structurally characterized. Complex 1, with an unexpectedly low v(Tc=O) of 891 cm-1, has a Tc=O bond distance of 1.668(7) angstrom, that is typical for monooxotechnetium(V) square-pyramidal complexes.