title: Synthesis, Structures, and Proton Self-Exchange Reaction of μ3-Oxido/Hydroxido Bridged Trinuclear Uranyl(VI) Complexes with Tridentate Schiff-Base Ligands.
abstract: New μ3-hydroxido/oxido bridged trinuclear uranyl(VI) complexes with 3,5-di-t-butyl-N-salicylidene-2-aminophenolato (dbusap2-) ligands, Et3NH[(UO2)3(μ3-OH)(dbusap)3] (Et3NH[1]) and (Et3NH)2[(UO2)3(μ3-O)(dbusap)3] ((Et3NH)2[2]) were synthesized and characterized. Single-crystal X-ray structures of both complexes were determined. The oxygen atom on μ3-hydroxido center in [1]-is sp3hybridized with an average U-(μ3-O)-U bond angle of 109.7(5)°; the μ3-oxido atom in [2]2-is sp2hybridized with an average U-(μ3-O)-U bond angle of 118.0(10)°. U-(μ3-O) distances in [1]-are long (average of 2.43(1) Å) compared with those in [2]2-(average of 2.23(2) Å). The optimized geometries of the [(UO2)3(μ3-OH)]5+core in [(UO2)3(μ3-OH)(sap)3]-and the [(UO2)3(μ3-O)]4+core in [(UO2)3(μ3-O)(sap)3]2-(where sap = N-salicylidene-2-aminophenolato) from density functional theory (DFT) calculations resemble those in [1]-and [2]2-, respectively. The U-(μ3-O) bond in [2]2-is significantly shorter than that in [1]-, because of the greater negative charge on the central μ3-oxido. A reversible structural conversion between [2]2-and [1]-was conducted by protonation and deprotonation of the μ3-oxido/hydroxido group. The activation enthalpy and entropy of the proton self-exchange reaction between [1]-and [2]2-determined from the temperature dependence of1H NMR coalescence are ΔH⧧= 23 ± 2 kJ mol-1and ΔS⧧= -77 ± 5 J K-1mol-1.
authors.affiliation: Radioisotope Research Center, Osaka University , Suita 565-0871, Japan.
authors.forename: Takashi
authors.identifier: http://orcid.org/0000-0002-9216-9043
authors.initials: T
authors.lastname: Yoshimura
authors.affiliation: Department of Chemistry, Graduate School of Science, Osaka University , Toyonaka 560-0043, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Nakaguchi
authors.affiliation: Department of Chemistry, Graduate School of Science, Osaka University , Toyonaka 560-0043, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Morimoto