ReO2+ chelates with aliphatic diamines. Structural and proton transfer properties

The structure and protonation of the complexes trans-[ReVO2L2]+ (L = tmen (N,N,N0,N0-tetramethylethylenediamine), deten (N,N-diethylethylenediamine) and dieten (N,N0-diethylethylenediamine)) were studied. The structure of [ReO2(dieten)2]I . 2H2O shows a trans-dioxo geometry (Re–O average distance 1.766(5) A ˚ ) and an equatorial plane defined by four N atoms belonging to two bidentate amines (Re–N average distance 2.190(7) A ˚ ). The Re atom lies on an inversion centre. These complexes can be protonated in aqueous solution and the protonation constants have been determined at 25 1C and I = 0.5 M KCl. The protonated species [ReO(OH)(deten)2](ClO4)2 was isolated and characterized by X-ray diffraction. The squashed octahedral geometry is maintained around the Re(V) atom (which also lies on an inversion centre) with larger Re–O distances (average 1.780(6) A ˚ ). By the use of N-alkylated diamines as equatorial ligands, complex protonation is confined to a low pH range (pH < 3) and one oxo group is preserved even in very acidic media.