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

Two novel aqueous U IV 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 6 ) 2 ] complex, in which the U IV cation is octa-coordinated to 4 phosphonic arms from each ligand in a square anti-prism geometry, with a C 4 symmetry. The second is the "in-cage" [U(DOTPH 4 )] complex where the tetravalent cation is located between the macrocycle O 4 and N 4 planes. With the help of UV-vis absorption, 1 H/ 31 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 a varied stoichiometric ratios of both characterized homonuclear complexes.