Uranyl(VI) complexes with [1+1] asymmetric compartmental ligands containing a Schiff base and a crown ether-like chamber

The [1+1] asymmetric compartmental ligands H2LA and H2LB, containing a N3O2 Schiff base coordination chamber and an adjacent O2On (n=3, 4) crown-like coordination chamber, have been prepared by reaction of equimolar amount of 3,3′-(3-oxapentane-1,5-diyldioxy)bis(2-hydroxybenzaldehyde (H2LI) or 3,3′-(3,6-dioxaoctane-1,8-diyldioxy)bis(2-hydroxybenzaldehyde) (H2LII) and 1,5-diamino-3-azamethylpentane. These macrocycles react with UO2 2+ to form the mononuclear complexes [UO2(LA)] and [UO2(LB)]; the same complexes have been obtained by condensation of the above formyl- and amine-precursors in the presence of UO2 2+ as templating agent. The uranyl(VI) ion invariantly prefers the N3O2 site as evidenced by IR and NMR spectroscopy and confirmed by an X-ray diffractometric investigation for the complex [UO2(LA)]. [UO2(LA)] crystallizes in the monoclinic space group P21/c with four formula units in a cell of dimensions a=10.412(2), b=12.973(3), c=19.743(4) Å and β=100.22(3)°. The structure was solved by standard methods and refined by full-matrix least-squares to the conventional R index of 6.9%. The uranyl(VI) atom presents a classic pentagonal bipyramidal coordination polyhedron with the base formed by three nitrogen and two phenolic oxygen atoms of the cyclic ligand. A detailed 1H and 13C NMR study was carried out in order to compare the structure in solution with that found in the solid state.