Steric Control of Substituted Phenoxide Ligands on Product Structures of Uranyl Aryloxide Complexes

Abstract

A series of uranyl aryloxide complexes has been prepared via metathesis reactions between [UO(2)Cl(2)(THF)(2)](2) and di-ortho-substituted phenoxides. Reaction of 4 equiv of KO-2,6-(t)()Bu(2)C(6)H(3) with [UO(2)Cl(2)(THF)(2)](2) in THF produces the dark red uranyl compound, UO(2)(O-2,6-(t)()Bu(2)C(6)H(3))(2)(THF)(2).THF, 1. Single-crystal X-ray diffraction analysis of 1 reveals a monomer in which the uranium is coordinated in a pseudooctahedral fashion by two apical oxo groups, two cis-aryloxides, and two THF ligands. A similar product is prepared by reaction of KO-2,6-Ph(2)C(6)H(3) with [UO(2)Cl(2)(THF)(2)](2) in THF. Single-crystal X-ray diffraction analysis of this compound reveals it to be the trans-monomer UO(2)(O-2,6-Ph(2)C(6)H(3))(2)(THF)(2), 2. Dimeric structures result from the reactions of [UO(2)Cl(2)(THF)(2)](2) with less sterically imposing aryloxide salts, KO-2,6-Cl(2)C(6)H(3) or KO-2,6-Me(2)C(6)H(3). Single-crystal X-ray diffraction analyses of [UO(2)(O-2,6-Cl(2)C(6)H(3))(2)(THF)(2)](2), 3, and [UO(2)Cl(O-2,6-Me(2)C(6)H(3))(THF)(2)](2), 4, reveal similar structures in which each U atom is coordinated by seven ligands in a pseudopentagonal bipyramidal fashion. Coordinated to each uranium are two apical oxo groups and five equatorial ligands (3, one terminal phenoxide, two bridging phenoxides, and two nonadjacent terminal THF ligands; 4, one terminal chloride, two bridging phenoxides, and two nonadjacent terminal THF ligands). Apparently, the phenoxide ligand steric features exert a greater influence on the solid-state structures than the electronic properties of the substituents. Emission spectroscopy has been utilized to investigate the molecularity and electronic structure of these compounds. For example, luminescence spectra taken at liquid nitrogen temperature allow for a determination of the dependence of the molecular aggregation of 3 on the molecular concentration. Electronic and vibrational spectroscopic measurements have been analyzed to examine trends in emission energies and stretching frequencies. However, comparison of the data for compounds 1-4 reveals that the innate electron-donating capacity of phenoxide ligands is only subtly manifest in either the electronic or vibrational energy distributions within these molecules.

Syntheses, structures, and electrochemistry of a dinuclear compound and a mononuclear–mononuclear cocrystalline compound of uranyl(VI)

“…The analysis showed that the compound is a dialkoxo-bridged diuranyl(VI) compound containing two deprotonated Schiff base ligands, [L] (7) Å) as expected due to π-back bonding. All the bond distances are in the usual ranges observed in the related compounds [13,18,19,[29][30][31].…”

“…The metal-ligand bond distances lie in three distinct ranges with the decreasing order U-O(water/imine) (2.491(7)-2.563(7) Å) > U-O(phenoxo) (2.240(6)-2.280(6) Å) > U-O(uranyl) (1.777(6)-1.792(6) Å). All the bond distances are in the usual ranges [13,18,19,[29][30][31]. The transoid angle (178.9(3)° for unit 1 and 177.6(3)° for unit 2) involving the axial uranyl oxygens and the cisoid angles (85.5(3)°-93.5(3)° for unit 1 and 84.5(3)°-93.4(3)° for unit 2) involving the axial oxygens and five donor atoms in the basal plane show slight deviation from ideal values.…”

Separation of actinides and lanthanides: Synthesis and molecular structure of a new di-μ-phenoxo-bridged dinuclear bis(dioxouranium(VI)) complex

“…The uranium ions are bridged by two phenoxo ligands. Two tetrahydrofuran ligands are coordinated to each uranium in a non-adjacent trans fashion [21]. The coordination is completed by an imine nitrogen and a terminal phenoxide (not bridging).…”

“…The coordination is completed by an imine nitrogen and a terminal phenoxide (not bridging). The oxo groups of the uranyl moiety lie trans to one another with a near linear O@U@O bond angles of 177.33 (18) [21].…”

Dimethylsuphoxide and its roles in the coordination chemistry of the uranyl ion

“…This is perhaps a factor favouring both O-coordination to U and the binding of DMSO in preference to the anions. There is evidence in very different contexts [23,24] for the unrecognised importance of uranyl-O basicity in determining the properties of U(VI) compounds and it may be noted also that uranyl-O in [UO 2 (OH 2 ) 5 ] 2+ lie within H-bonding distances of the water ligands. In this particular case, however, it has recently been shown [13] that the presence or absence of perchlorate in the primary coordination sphere of U(VI) in various hydrated uranyl perchlorates seems to depend largely on the composition of the solution from which the crystals deposit, so that if there is no marked preference for water over what is conventionally regarded as a very weak ligand [17], a special interaction with uranyl-O cannot be considered dominant and perhaps angular factors minimise any H-bonding interaction of coordinated water and uranyl-O.…”