Synthesis, properties, and crystal structures of new mono- and homo-binuclear uranyl(VI) complexes with compartmental Schiff bases

Mono-and homo-binuclear uranyl(VI) complexes of the type [UO2(H2L1)]·solv, [(UO2)2(L1)(solv)], [UO2(H2L2)]·solv, and [(UO2)2(L2)(solv)], where solv is a co-ordinating solvent [H2O, dimethylformamide (dmf), or dimethyl sulphoxide (dmso)] and H4L1 and H4L2 are the potentially heptadentate dinucleating ligands derived by the condensation of 2,3-dihydroxybenzaldehyde with 1,5-diamino-3-azapentane or 1,5-diamino-3-thiapentane, have been prepared by a template procedure or by reaction of the preformed ligands with [UO2(CH3CO2)2]·2H 2O and characterized by i.r., 1H and 13C n.m.r. spectroscopic and X-ray diffraction techniques. The crystal structures of [UO2(H2L1)]·dmf, [(UO2)2(L1)(dmso)], and [(UO2)2(L1)(dmf)] have been determined by X-ray crystallography and refined to conventional R values of 0.044, 0.054, and 0.039 respectively: [UO2(H2L1)]·dmf is monoclinic, space group P21/n, with a = 21.155(5), b = 11.833(8), c = 9.679(8) Å, ? = 102.34(3)°, Z = 4; [(UO2)2(L1)(dmso)] is monoclinic, space group P21/c, with a = 14.985(5), b = 16.536(5), c = 19.956(5) Å, ? = 90.13(3)°, Z = 8; [(UO2)2(L1)(dmf)] is monoclinic, space group P21/c, with a = 9.285(6), b = 16.187(5), c = 17.544(5)Å, ? = 104.56(3)°, and Z = 4. In [UO2(H2L1)]·dmf the ligand behaves as a quinquedentate dianionic and, using the inner co-ordination chamber, binds equatorially to UO22+ leading to seven-co-ordinated uranium in a distorted bipyramidal co-ordination geometry. A dmf molecule is hydrogen bonded to the phenolic oxygens of the ligand. Selected bond distances for this compound are U-O(uranyl) 1.79 (mean), U-O(ligand) 2.235 (mean), and U-N (mean) 2.59 Å. In [(UO2)2(L1)(dmso)] and [(UO2)2(L1)(dmf)] the tetra-anionic chelating ligand co-ordinates the inner UO22+ as in [UO2(H2L1)]·dmf, while the outer UO22+ is co-ordinated by four oxygen atoms of the dinucleating ligand and by the oxygen atom of the solvent molecule. Structural details of the binuclear complexes are comparable. Comparison of the structures in the solid and in solution revealed some conformational differences.