Polynuclear uranium(IV) compounds with (μ3-oxo)U3 or (μ4-oxo)U4 cores and compartmental Schiff base ligands

Two uranium(IV) complexes with hexadentate Schiff base ligands have been isolated and their crystal structures were determined. The first is a trianionic [U3L1Cl9O]3− trinuclear complex [H4L1 = N,N′-bis(3-hydroxysalicylidene)-2-methyl-1,2-propanediamine] which contains a nearly equilateral triangle of U4+ ions with a central trigonal μ3-oxo ion. The nearly planar Schiff base is bound to the three seven-coordinate uranium atoms, whose coordination sphere is completed by terminal and bridging chlorine atoms to give pentagonal bipyramidal environments. The second is a dicationic [U4(L2)2(H2L2)2(py)2O]2+ tetranuclear complex [H4L2 = N,N′-bis(3-hydroxysalicylidene)-2,2-dimethyl-1,3-propanediamine] which contains a U4 tetrahedron held by a central, μ4-oxo ion and eight bridging oxygen atoms from the Schiff bases. The two ligands in the asymmetric unit display different conformations, either slightly curved with an uranium atom in the inner N2O2 site or very strongly folded with a uranium atom bound to the outer O4 site, with further bridging in both cases. The uranium(IV) environment is either dodecahedral or capped square antiprismatic.

Polynuclear complexes of uranium(IV) with the Schiff bases N,N′-bis(3-hydroxysalicylidene)-2-methyl-1,2-propanediamine (H4L1) and N,N′-bis(3-hydroxysalicylidene)-2,2-dimethyl-l,3-propanediamine (H4L2) contain U3 or U4 cores held by central μ3- or μ4-oxo atoms, respectively. Different Schiff base conformations and uranium environments are present in these trianionic [U3L1Cl9O]3− and dicationic [U4(L2)2(H2L2)2(py)2O]2+ species.Figure optionsDownload as PowerPoint slide