Uranyl-tri-bis(silyl)amide Alkali Metal Contact and Separated Ion Pair Complexes

Abstract

We report the preparation of a range of alkali metal uranyl(VI) tri- bis(silyl)amide complexes [{M(THF) }{(μ-O)U(O)(N″)}] (1M) (N″ = {N(SiMe)}, M = Li, Na, x = 2; M = K, x = 3; M = K, Rb, Cs, x = 0) containing electrostatic alkali metal uranyl-oxo interactions. Reaction of 1M with 2,2,2-cryptand or 2 equiv of the appropriate crown ether resulted in the isolation of the separated ion pair species [U(O)(N″)][M(2,2,2-cryptand)] (3M, M = Li-Cs) and [U(O)(N″)][M(crown)] (4M, M = Li, crown = 12-crown-4 ether; M = Na-Cs, crown = 15-crown-5 ether). A combination of crystallographic studies and IR, Raman and UV-vis spectroscopies has revealed that the 1M series adopts contact ion pair motifs in the solid state where the alkali metal caps one of the uranyl-oxo groups. Upon dissolution in THF solution, this contact is lost, and instead, separated ion pair motifs are observed, which is confirmed by the isolation of [U(O)(N″)][M(THF) ] (2M) (M = Li, n = 4; M = Na, K, n = 6). The compounds have been characterized by single crystal X-ray diffraction, multinuclear NMR spectroscopy, IR, Raman, and UV-vis spectroscopies, and elemental analyses.

Single metal four-electron reduction by U(ii) and masked “U(ii)” compounds

“…5 i ,12 b ,20 In addition, the mean U–N amide bond length of 2.34(2) Å is close to the one reported for the analogous uranyl complex, [K(2.2.2-cryptand)][U(O) 2 {N(SiMe 3 ) 2 } 3 ] (2.323(2) Å). 21 The U N-Ph angles (162.5(6) and 165.0(6)°) deviate significantly from linearity as found in other bis(imido) U( vi ) complexes 12 b ,22 and suggest partial localization of the pi lone pair on the imido nitrogen (supported by the bonding analysis in ESI † ). Trans bis(imido) U( vi ) complexes have attracted considerable interest in uranium chemistry because of their fundamental insight in the study of U–L multiple bonds, their isoelectronic structure with the ubiquitous uranyl( vi ) cation and their potential application in small molecule activation and catalysis.…”

Nature of the Arsonium‐Ylide Ph3As=CH2 and a Uranium(IV) Arsonium–Carbene Complex

“…For comparison, analytical frequencies calculations on phosphino-silyl-stabilised U=C double bonds returned values of 595 and 650 cm À1 , [3c] respectively, and, for wider reference, the lower end of uranyl n 1 U = O stretches is % 790 cm À1 . [23] Thus, in terms of how well-developed their U À C bonds are, from these vibrational data the UÀC units can be qualitatively ordered as UCHAsPh 3 > UC(PPh 2 )(SiMe 3 ) > UCHPPh 3 .…”

Photoluminescence of Pentavalent Uranyl Amide Complexes

“…[49][50][51] The identity of these complexes was established through single-crystal X-ray diffraction (SC-XRD) experiments, which demonstrated the formulation of the anionic [UO2N′′3] 2− fragment with two cationic [K(L)] + counterions to balance the overall charge in 3-crypt and 3-18C6 and a trigonal bipyramid geometry around the metal center, close to that observed for precursors 1 48 and 2 (Figure 1 and S37-39). 48 S3-4). 21,25 The [U V O2] + fragment is perfectly linear in all polymorphs, together with a near perfect trigonal planar arrangement around the equatorial coordination plane.…”

“…This approach has proven successful in enabling the identification and characterization of the optical properties of U 4+ , [Np V O2] + , and [Np VI O2] 2+ . 47 The monomeric, [ 48 and 4, (Scheme 1, and Fig. S40) with KC8.…”

“…This effect can also be quantified by calculating the relative stretching and interaction force constants (k1 and k12). 48,65,66 The uranyl(VI) precursors 2-18C6 and 2-crypt have stretching force constants of 6.85 and 6.94 mdyn Å -1 respectively. As expected, the force constants decrease for 3-18C6 and 3-crypt and are measured at 5.66 and 5.53 mdyn Å -1 , respectively.…”