Reactions of the Uranyl Ion and a Bulky Tetradentate, “Salen-Type” Schiff Base: Synthesis and Study of Two Mononuclear Complexes

The reactions of UO2(NO3)2·6H2O or UO2(O2CMe)2·2H2O and 2,2′-{(1,2-ethanediyl)bis[nitrilo(phenyl)methylidene]}bisphenol (H2L) in MeOH and DMF have provided access to complexes [UO2(L)(MeOH)] (1) and [UO2(L)(DMF)]·DMF (2·DMF), respectively. The molecular structures of the complexes are similar. The central UVI atom is surrounded by five oxygen and two nitrogen atoms in a distorted pentagonal bipyramidal geometry; the two uranyl oxygen atoms are at the axial positions. Two phenolato oxygen and two imino nitrogen atoms from the tetradentate chelating (1.1111 using Harris notation) L2− ligand are located at the equatorial plane, which is completed by the oxygen atom of a terminally ligated solvent (MeOH, DMF) molecule. Interestingly, the L2− ligand adopts a chair (or stepped) conformation in 1 and a boat conformation in 2·DMF. The supramolecular features of 1 and 2·DMF are distinctly different due to the different H-bonding abilities of coordinated MeOH and DMF, and the presence of an extra-lattice solvent molecule in the latter. The solid complexes were studied by IR, Raman, electronic (UV/Vis), and emission spectroscopic techniques. Complex 1 decomposes in CHCl3 and DMSO, whereas the molecular structure of 2 is retained in these solvents. A new polymorph of the free ligand, H2L(B), has also been discovered and its crystal structure is described.