Synthesis and crystal structure of pentavalent uranyl complexes. The remarkable stability of UO2X (X = I, SO3CF3) in non-aqueous solutions

The reaction of [UO2I2(THF)(3)] with KC5R5 (R = H, Me) or K2C8H8 in pyridine gave crystals of [{UO2(py)(5)}{KI2(py)(2)}](infinity) (1), which were desolvated under vacuum into pulverulent [UO2(py)(2.2)KI2] (2). Similar reactions with [UO2(OTf)(2)] afforded [UO2(py)(2.3)K(OTf)(2)] (3) as a powder and crystals of [{UO2(py)(5)}(2){K-3(OTf)(5)}center dot py](infinity) (4 center dot py), which were also obtained together with crystals of [{UO2(py)(5)}(2){K(OTf)(2)(py)(2)}][OTf]center dot py (5 center dot py) by treating [UO2(OTf)(2)] with KC4Me4P. Crystals of 6 center dot py, the thallium analogue of 5 center dot py, were isolated from the reaction of [UO2(OTf)(2)] and TlC5H5. Treatment of [UO2I2(THF)(3)] with LiCH2SiMe3 in pyridine afforded crystals of [{UO2(py)(5)}{Lil(py)(2)}][I] (7) while [UO2(OTf)(2)] reacted with the alkyllithium reagent in acetonitrile to give crystals of [{UO2(py)(5)}{Li-2(OTf)(3)}](infinity) (8) in pyridine. The crystal structures of 1, 4 center dot py, 5 center dot py, 6 center dot py, 7 and 8 revealed the presence of U=O -> M interactions (M = Li, K, Tl), and the rich diversity of these structures, from dinuclear (7) to 3D polymeric (4), is related to the distinct coordination numbers of the M+ ion and ligation modes of the bridging iodide and triflate ligands as well as the presence of U=O -> M interactions. The mononuclear complexes [UO2(OTf)(THF)(n)] (9) and [UO2(OTf)(Et2O)(0.5)] (10) were respectively obtained by reaction of [UO2(OTf)(2)] with KC5R5 in THF or LiCH2SiMe3 in Et2O, and were transformed into [UO2(OTf)(py)(2)] (11) in pyridine. Treatment of [UO2I2(THF)(3)] with TlC5H5 in pyridine afforded crystals of [UO2(py)(5)][I]center dot py (12 center dot py) which were desolvated under vacuum into the powder of [UO2I(py)(2.5)] (14). The same reaction in THF gave [UO2I(THF)(2.7)] (13) in powder form. Crystals of [UO2(CyMe4BTBP)(py)][OTf]center dot 1.5py (15.1.5py) and the powder of [UO2I(CyMe4BTBP)] (16) were obtained by treating [UO2(CyMeBTBP)X-2] (X = OTf, I) with KC5Me5 or TlC5H5, respectively The uranyl(v) chloride and nitrate compounds [UO2Cl(py)(3)] (17) and [UO2(NO3)(py)(3)] (18) were prepared by reaction of the uranyl(vi) precursors with TlC5H5 in pyridine; complex 18 was also obtained by treating 13 with TlNO3. Crystals of the neutral mononuclear complex [UO2(OTf(py)(4)] (19) were isolated from reaction of [UO2(OTf)(2)] with Me3SiC3H5 in acetonitrile. Similar reaction with [UO2Cl2(THF)(2)](2) in pyridine gave crystals of [UO2Cl2(py)(3)]. The crystal structures of 12 center dot py, 15.1.5py and 19 were determined; the structure of 15 was compared with that of the uranyl(vi) counterpart. All the uranyl(v) compounds are remarkably stable in pyridine solution; the IR absorption at 816 cm(-1) is attributed to the nu(asym) (U=O) of the ubiquitous [UO2(py)(5)](+) species.