STRUCTURAL AND CONFORMATIONAL-ANALYSIS OF TC-V AND RE-V DIOXO COMPLEXES - X-RAY CRYSTAL-STRUCTURE OF [TCO2(TN)(2)]I-CENTER-DOT-H2O

[(TcO2)-O-V(tn)(2)]I (tn = trimethylenediamine) was prepared from dire ct reduction of TcO4- with dithionite in presence of the ligand. The c rystal structure of [TcO2(tn)(2)]I . H2O was determined from X-ray dat a. It consists on a squashed octahedron with Tc-O bond lengths of 1.78 4 and 1.754 Angstrom conforming a TcO2+ core. The amines lie in the eq uatorial plane, almost perpendicular to the core. Conformational analy ses of several analogous trans-M-V dioxo complexes (M =Tc, Re) was per formed by molecular mechanics and semiempirical calculations. Energy d ifferences between possible conformers are low. Therefore, a mixture o f different conformers is expected to be found in solution. (C) 1997 E lsevier Science Ltd.