New Efficient Synthesis of [UI₄(MeCN)₄]. X-ray Crystal Structures of [UI₂(MeCN)₇][UI₆], [UI₄(py)₃], and [U(dmf)₉]I₄

Reaction of UCl4 and excess Me3SiI in acetonitrile provides a convenient route to [UI4(MeCN)4] (1), which was isolated in excellent yield and crystallized in acetonitrile as the ion pair complex [UI2(MeCN)7][UI6] (2). Compound 1 was transformed in pyridine (py) and dimethylformamide (dmf) into the Lewis base adducts [UI4(py)3] (3) and [UI4(dmf)6] (4). Crystals of 3 and [U(dmf)9]I4 (5) were obtained by slow diffusion of diethyl ether into pyridine or dmf solutions of 1; compound 5 is the first tetracationic {U4+} entity to have been crystallographically characterized.