MONOMERIC URANYL ALKOXIDE AND AMIDE COMPLEXES

Reaction of UO2Cl2(Ph3PO)2 with 2 equiv of KO-t-Bu or NaN(SiMe3)2 in THF results in the formation of UO2(O-t-Bu)2(Ph3PO)2 (1) or UO2[N(SiMe3)2]2(Ph3PO)2 (2); the yields are 84 (1) and 77% (2). The infrared spectra of these compounds exhibit strong U-O stretching bands at 861 (1) and 901 (2) cm-1; these features shift to 822 and 854 cm-1, respectively, upon O-18 substitution. The solid-state structure of 1 reveals that the alkoxide and phosphine oxide ligands are arranged in a cis geometry in the equatorial plane of the uranyl ion (U-O(1)(oxo) = 1.789 (5) angstrom, U-O(2)(oxo) = 1.795 (6) angstrom, O(1)-U-O(2) = 174.8 (2)-degrees). NMR spectroscopy shows that both cis and trans isomers exist for 1 and 2. Exchange with free phosphine and equilibration of the isomers occur at 80-degrees-C for 1 and 55-degrees-C for 2. 1 and 2 luminesce (1, lambda(max) 571 nm; 2, lambda(max) 555 nm); the 77 K excitation and emission spectra of 1 are highly structured, with the dominant vibronic progression assigned to the symmetric O-U-O stretch (excitation, 643 +/- 16 cm-1, with O-18 substitution 606 +/- 10 cm-1; emission, 770 +/-20 cm-1, with O-18 substitution 737 +/- 7 cm-1).