Effect of solvents in mixed-ligand supramolecular self-assembly architectures

Abstract

Seven new uranyl isothiosemicarbazone complexes with the general formula UO2L(hmb)X (X; 1: ethanol, 2: 1-propanol 3: 1-butanol, 4: 1-pentanol, 5: ethylene glycol, 6: propane-1,2-diol, 7: DMSO) were synthesized by the template reaction of allyl N′-2-hydroxy-3-methoxybenzylidenecarbamohydrazonothioate.hydrobromide (H2L·HBr), 2-hydroxy-4-methoxybenzaldehyde (hmb), a U(VI) salt and the appropriate solvent or by recrystallization of 1 from the aforementioned solvents. These compounds were characterized by FT-IR, 1H and 13C NMR, mass spectrometry, elemental and TGA analyses. Single-crystal X-ray diffraction analyses of the complexes reveal distorted pentagonal bipyramidal geometries in which the N2O2 compartment and the oxygen atom of the coordinated solvent form the equatorial plane and the two uranyl oxygen atoms occupy the apical positions. Compounds 1–6 form dimers through pairwise bifurcated hydrogen bonds between solvent molecules and phenoxy oxygen atoms. Moreover, the self-assembly along the c axis with C–H⋯O and C–H⋯πring interactions generates a one-dimensional topology. The aromatic rings play the most important role in constructing the second dimension while different interactions are responsible for the formation of the third dimension in each of compounds 1–6. Classical and non-classical van der Waals interactions in compound 7 generate a one-dimensional expansion of two woven ribbons along the c direction and these woven chains join together to complete the supramolecular architecture, which resembles a set of bricks. The thermal decomposition of all the complexes occurs in three steps, starting with the removal of the coordinated solvent, followed by loss of the S-allyl group and finally the residual ligand fragment. U3O8 is obtained as the final residue.