Oligomers Intermediates in Between Two New Distinct Homonuclear Uranium(IV) DOTP Complexes*.

Two new aqueous U complexes were synthesized by the interaction between the tetravalent uranium cation and the (1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetra(methylene phosphonic acid) (DOTP) macrocyclic ligand. Two distinct homonuclear complexes were identified; the first was characterized by X-ray crystallography as a unique "out-of-cage", [U(DOTPH ) ] complex, in which the U cation is octa-coordinated to 4 phosphonic arms from each ligand in a square anti-prism geometry, with a C symmetry. The second is the "in-cage" [U(DOTPH )] complex, in which the tetravalent cation is located between the macrocycle O and N planes. With the help of UV-Vis absorption, H/ P NMR, ATR-IR, and MALDI-TOFMS analytical techniques, the chemical interchange between both species is presented. It is shown that the one-way transition is governed by the formation of a multiple number of soluble oligomeric species consisting of varied stoichiometric ratios of both characterized homonuclear complexes.