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

Abstract

The structure and protonation of the complexes trans-[Re^VO₂L₂]⁺ (L = tmen (N,N,N′,N′-tetramethylethylenediamine), deten (N,N-diethylethylenediamine) and dieten (N,N′-diethylethylenediamine)) were studied. The structure of [ReO₂(dieten)₂]I·2H₂O shows a trans-dioxo geometry (Re–O average distance 1.766(5) Å) and an equatorial plane defined by four N atoms belonging to two bidentate amines (Re–N average distance 2.190(7) Å). 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 °C 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) Å). 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.