Synthesis, characterization and electrochemical studies on technetium(V) and rhenium(V) oxo-complexes with N,N′-2-hydroxypropane-1,3-bis(salicylideneimine)

Ligand-exchange reactions of potential quinquedentate Schiff base ligands derived from salicylaldehyde and 1,3-diamino-2-hydroxypropane (H3L) with [MOCl4]− (M = Tc and Re) have been investigated. The complexes [MOCl2(R-OH)(H2L·HCl)] (I) (R = Me, Et), [ReOCl(HL)] (II) and μ-O[MO(HL)]2 (III) were synthesized and characterized by the usual physicochemical measurements. Cyclic voltammetries for both III complexes reveal two separate and single-electron redox processes. The crystal structure of μ-O[TcO(HL)]2 was determined by single-crystal X-ray diffraction methods. Crystals are monoclinic, space group P21/c, with a = 9.423(6), b = 19.666(9), c = 22.785(11) Å, β = 99.41(4)° and Z = 4. X-ray diffraction provides 2842 observed reflections (up to θ = 40°) and the structure has been refined by full-matrix least-squares methods to R = 0.10. The ‘dimeric’ structure of μ-O[TcO(HL)]2 consists of two distorted octahedral TcO(HL) moieties bridged by an oxygen atom which occupies the sixth coordination site of each moiety with the Tc-O-Tc angle nearly linear (173°).