Inorganic Chemistry, Vol.49, No.14, 6755-6765, 2010
Influence of Linker Geometry on Uranyl Complexation by Rigidly Linked Bis(3-hydroxy-N-methyl-pyridin-2-one)
A series of bis(3-hydroxy-N-methyl-pyridin-2-one) ligands was synthesized, and their respective uranyl complexes were characterized by single crystal X-ray diffraction analyses. These structures were inspected for high-energy conformations and evaluated using a series of metrics to measure co-planarity of chelating moieties with each other and the uranyl coordination plane, as well as to measure coordinative crowding about the uranyl dication. Both very short (ethyl, 3,4thiophene and o-phenylene) and very long (alpha,alpha'-m-xylene and 1,8-fluorene) linkers provide optimal ligand geometries about the uranyl cation, resulting in planar, unstrained molecular arrangements. The planarity of the rigid linkers also suggests there is a degree of pre-organization for a planar coordination mode that is ideal for uranyl-selective ligand design. Comparison of intramolecular N-amide-O-phenolate distances and H-1 NMR chemical shifts of amide protons supports eadier results that short linkers provide the optimal geometry for intramolecular hydrogen bonding.