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.

The synthesis of a range of rhodium(iii) and iridium(iii) half sandwich complexes with aryl dithiolato ligands of varying geometry and flexibility are reported. These include dinuclear [Cp*M(S-R-S)]2 complexes 3b and 4b, M = Rh, Ir; S-R-S = naphthalene-1,8-dithiolate (b) and four dinuclear complexes bearing bridging dithiolate ligands [(Cp*M)2(μ2-Cl)(μ2-S-R-S)]Cl 3c, 4c, 5b, 6b, M = Rh, Ir; S-R-S = naphthalene-1,8-dithiolate (b) or acenaphthene-5,6-dithiolate (c). The introduction of a less rigid biphenyl dithiolate backbone resulted in the tetranuclear dicationic complex [(Cp*Rh)4(S-R-S)3]Cl2 (3d), S-R-S = biphenyl-2,2'-dithiolate (d) with dithiolate ligands in two different bridging modes. All new complexes were fully characterised by multinuclear NMR, IR, Raman and MS spectroscopy and single crystal X-ray diffraction.

Pentavalent uranyl species are crucial intermediates in transformations that play a key role for the nuclear industry and have recently been demonstrated to persist in reducing biotic and abiotic aqueous environments. However, due to the inherent instability of pentavalent uranyl, little is known about its electronic structure. Herein, we report the synthesis and characterization of a series of monomeric and dimeric, pentavalent uranyl amide complexes. These synthetic efforts enable the acquisition of emission spectra of well-defined pentavalent uranyl complexes using photoluminescence techniques, which establish a unique signature to characterize its electronic structure and, potentially, its role in biological and engineered environments via emission spectroscopy.

We report the synthesis and characterization of a new family of pentavalent uranyl amide complexes, supported also by photoluminescence and theoretical investigations. These studies reveal for the first time that the UV-visible emission of uranyl(V) is an admixture of charge transfer transitions accompanied by vibronic coupling of the quartet excited state with uranyl oxo and amide vibrations, thereby offering new insights into the electronic structure of the reactive uranyl(V)