The first structural and spectroscopic study of a paramagnetic 5f DO3A complex.

A 5f(2) uranium(IV) complex of the macrocycle DO3A (DO3A = [4,7,10-tris-carboxymethyl-,1,4,7,10-tetraaza-cyclododec-1-yl]-acetic acid) has been prepared and characterised in the solid state and in solution. The DO3A scaffold containing no strongly absorbing chromophores enables the facile detection of relatively long-lived (8-13 ns) UV-visible emission that possesses significant charge transfer character tentatively assigned to deactivation of the excited (3)F(2) 5f(1) 6d(1) electronic configuration. This study demonstrates, for the first time, that luminescence of simple U(iv) chelates is detectable in the absence of an antenna, potentially serving as a diagnostic tract for environmental U(IV) species.