Synthesis and Characterization of Uranyl Compounds with Iminodiacetate and Oxydiacetate Displaying Variable Denticity

Eight uranyl compounds containing the dicarboxylate ligands iminodiacetate (IDA) or oxydiacetate (ODA) have
been characterized in the solid state. The published polymeric structures for [UO2(C4H6NO4)2] and [UO2(C4H4O5)]n
have been confirmed, while Ba[UO2(C4H5NO4)2]·3H2O, [(CH3)2NH(CH2)2NH(CH3)2][UO2(C4H4O5)2] [orthorhombic space
group Pnma, a = 10.996(5) Å, b = 21.42(1) Å, c = 8.700(3) Å, Z = 4], and [C2H5NH2(CH2)2NH2C2H5][UO2(C4H4O5)2] [monoclinic space group P21/n, a = 6.857(3) Å, b = 9.209(5) Å, c = 16.410(7) Å, β = 91.69(3), Z =
2] contain monomeric anions. The distance from the uranium atom to the central heteroatom (O or N) in the ligand
varies. Crystallographic study shows that U−heteroatom (O/N) distances fall into two groups, one 2.6−2.7 Å in
length and one 3.1−3.2 Å, the latter implying no bonding interaction. By contrast, EXAFS analysis of bulk samples
suggests that either a long U−heteroatom (O/N) distance (2.9 Å) or a range of distances may be present. Three
possible structural types, two symmetric and one asymmetric, are identified on the basis of these results and on
solid-state 13C NMR spectroscopy. The two ligands in the complex can be 1,4,7-tridentate, giving five-membered
rings, or 1,7-bidentate, to form an eight-membered ring. (C4H12N2)[(UO2)2(C4H5NO4)2(OH)2]·8H2O [monoclinic
space group P21/a, a = 7.955(9) Å, b = 24.050(8) Å, c = 8.223(6) Å, β = 112.24(6), Z = 2], (C2H10N2)[(UO2)2(C4H5NO4)2(OH)2]·4H2O, and (C6H13N4)2[(UO2)2(C4H4O5)2(OH)2]·2H2O [monoclinic space group C2/m, a = 19.024(9) Å, b = 7.462(4) Å, c = 2.467(6) Å, β = 107.75(4), Z = 4] have a dimeric structure with two capping tridentate
ligands and two μ2-hydroxo bridges, giving edge-sharing pentagonal bipyramids.