Macro-Acyclic Pyrrophen Ligands for Hexadentate Coordination of Uranyl (UO22+)

Pyrrophen ligands are acyclic hexadentate ligands containing salen-type N donors: two phenolic O donors, two pyrrolic N-type donors, and two oxo-carbonyl coordinating units. Uranyl complex derivatives of pyrrophen UO₂L_1–2a-c (L1=H); (L2=CH₃); (L=2-pyridinemethanol (a), N-(2-pyridinylmethyl) (b), N-benzyl (c), were synthesized and characterized by x-ray diffraction (XRD), nuclear magnetic resonance (NMR), and UV-vis. Each uranyl-containing structure was found to crystalize in a hexagonal bipyramidal coordination environment. We observed solid-state coordination deviations caused by the amide/ester substituent. The inductive effects and structural features were examined, and the effects on the bond lengths of the uranyl coordination and deviations in the -yl oxygen bond lengths and angles were studied.