| Abstract
| - A series of uranyl aryloxide complexes has been prepared via metathesis reactions between [UO2Cl2(THF)2]2 anddi-ortho-substituted phenoxides. Reaction of 4 equiv of KO-2,6-tBu2C6H3 with [UO2Cl2(THF)2]2 in THF produces thedark red uranyl compound, UO2(O-2,6-tBu2C6H3)2(THF)2·THF, 1. Single-crystal X-ray diffraction analysis of 1 revealsa monomer in which the uranium is coordinated in a pseudooctahedral fashion by two apical oxo groups, twocis-aryloxides, and two THF ligands. A similar product is prepared by reaction of KO-2,6-Ph2C6H3 with [UO2Cl2(THF)2]2 in THF. Single-crystal X-ray diffraction analysis of this compound reveals it to be the trans-monomerUO2(O-2,6-Ph2C6H3)2(THF)2, 2. Dimeric structures result from the reactions of [UO2Cl2(THF)2]2 with less stericallyimposing aryloxide salts, KO-2,6-Cl2C6H3 or KO-2,6-Me2C6H3. Single-crystal X-ray diffraction analyses of [UO2(O-2,6-Cl2C6H3)2(THF)2]2, 3, and [UO2Cl(O-2,6-Me2C6H3)(THF)2]2, 4, reveal similar structures in which each U atom iscoordinated by seven ligands in a pseudopentagonal bipyramidal fashion. Coordinated to each uranium are twoapical oxo groups and five equatorial ligands (3, one terminal phenoxide, two bridging phenoxides, and twononadjacent terminal THF ligands; 4, one terminal chloride, two bridging phenoxides, and two nonadjacent terminalTHF ligands). Apparently, the phenoxide ligand steric features exert a greater influence on the solid-state structuresthan the electronic properties of the substituents. Emission spectroscopy has been utilized to investigate themolecularity and electronic structure of these compounds. For example, luminescence spectra taken at liquid nitrogentemperature allow for a determination of the dependence of the molecular aggregation of 3 on the molecularconcentration. Electronic and vibrational spectroscopic measurements have been analyzed to examine trends inemission energies and stretching frequencies. However, comparison of the data for compounds 1−4 reveals thatthe innate electron-donating capacity of phenoxide ligands is only subtly manifest in either the electronic or vibrationalenergy distributions within these molecules.
- A series of uranyl aryloxide complexes containing substituted phenoxide ligands has been prepared via metathesis reactions between [UO2Cl2(THF)2]2 and KO-2,6-R2C6H3 (R = tert-butyl, phenyl, chloro, and methyl). Steric control of the aryloxide ligand, rather than the electronic properties, exerts a greater influence on the molecular structures formed. Single-crystal X-ray diffraction analysis of these products shows that monomeric compounds are produced if the ortho-substituent is sterically bulky (UO2(O-2,6-tBuC6H3)2(THF)2·THF, 1, and UO2(O-2,6-Ph2C6H3)2(THF)2, 2). In contrast, dimeric products are formed in the presence of less sterically imposing ligands ([UO2(O-2,6-Cl2C6H3)2(THF)2]2, 3, and [UO2Cl(O-2,6-Me2C6H3)(THF)2]2, 4). Furthermore, the innate electron-donating capability of these phenoxide ligands is only subtly manifest in the electronic or vibrational spectroscopic data for these molecules.
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