Dioxouranium Complexes with Acetylpyridine Benzoylhydrazones and Related Ligands

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AbstractAcetylpyridine benzoylhydrazone and related ligands react with common dioxouranium(VI) compounds such as uranyl nitrate or [NBu4]2[UO2Cl4] to form air‐stable complexes. Reactions with 2, 6‐diacetylpyridinebis(benzoylhydrazone) (H2L1a) or 2, 6‐diacetylpyridinebis(salicylhydrazone) (H2L1b) give yellow products of the composition [UO2(L1)]. The neutral compounds contain doubly deprotonated ligands and possess a distorted pentagonal‐bipyramidal structure. The hydroxo groups of the salicylhydrazonato ligand do not contribute to the complexation of the metal. The equatorial coordination spheres of the complexes can be extended by the addition of a monodentate ligand such as pyridine or DMSO. The uranium atoms in the resulting deep‐red complexes have hexagonal‐bipyramidal coordination environments with the oxo ligands in axial positions.The sterical strains inside the hexagonal plane can be reduced when two tridentate benzoylhydrazonato ligands are used instead of the pentadentate 2, 6‐diacetylpyridine derivatives. Acetylpyridine benzoylhydrazone (HL2) and bis(2‐pyridyl)ketone benzoylhydrazone (HL3) deprotonate and form neutral, red [UO2(L)2] complexes. The equatorial coordination spheres of these complexes are puckered hexagons.X‐ray diffraction studies on [UO2(L1a)(pyridine)], [UO2(L1b)(DMSO)], [UO2(L2)2] and [UO2(L3)2] show relatively short U—O bonds to the benzoylic oxygen atoms between 2.328(6) and 2.389(8) Å. This suggests a preference of these donor sites of the ligands over their imino and amine functionalities (U—N bond lengths: 2.588(7)—2.701(6) Å ).