Polynuclear uranium(IV) compounds with (μ 3-oxo)U 3 or (μ 4-oxo)U 4 cores and compartmental Schiff base ligands

Abstract

Two uranium(IV) complexes with hexadentate Schiff base ligands have been isolated and their crystal structures were determined. The first is a trianionic [U 3L 1Cl 9O] 3− trinuclear complex [H 4L 1 = N, N′-bis(3-hydroxysalicylidene)-2-methyl-1,2-propanediamine] which contains a nearly equilateral triangle of U 4+ ions with a central trigonal μ 3-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 [U 4(L 2) 2(H 2L 2) 2(py) 2O] 2+ tetranuclear complex [H 4L 2 = N, N′-bis(3-hydroxysalicylidene)-2,2-dimethyl-1,3-propanediamine] which contains a U 4 tetrahedron held by a central, μ 4-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 N 2O 2 site or very strongly folded with a uranium atom bound to the outer O 4 site, with further bridging in both cases. The uranium(IV) environment is either dodecahedral or capped square antiprismatic.