Auto-ionization in Lutetium Iodide Complexes: Effect of the Ionic Radius on Lanthanide−Iodide Binding

Reaction of lutetium metal with 1.5 equiv of elemental iodine in 2-propanol leads to the isolation of LuI3(HOiPr)4 (1).
An X-ray crystal structure reveals an ionic structure with well-separated [LuI2(HOiPr)4] cations and [I] anions. Dissolution
of 1 in pyridine generates the unusual alkoxide species [LuI(OiPr)(py)5][I] (2) with the elimination of HI. An X-ray
crystal structure of 2 confirmed the ionic nature of the compound, with the cationic portion of the complex exhibiting
a seven-coordinated lutetium center with trans-disposed iodo and alkoxide ligands and five pyridine molecules
equally displaced within the equatorial plane. Exposure of 2 to iodotrimethylsilane yields the expected triiodide
species [LuI2(py)5][I] (3), which may also be prepared by refluxing commercially available LuI3 in THF, followed by
crystallization from a THF/pyridine mixture. The solid-state structure of 3 is similar to that of 2, with the alkoxide
ligand having been replaced by an iodide. The formation of ionic structures 1−3 as opposed to the higher-coordinated
neutral species may be traced to the small lutetium center and the presence of relatively strong Lewis bases within
the coordination sphere of the metal.

金属镥(lutetium)与1.5当量单质碘在异丙醇(2-propanol)中反应，可分离得到配合物LuI₃(HOiPr)₄（化合物1）。X射线晶体结构(X-ray crystal structure)表征显示该配合物为离子型结构，存在相互分离的[LuI₂(HOiPr)₄]阳离子与[I]阴离子。将化合物1溶解于吡啶(pyridine)中，可消除碘化氢并生成罕见的醇盐类配合物[LuI(OiPr)(py)₅][I]（化合物2）。对化合物2的X射线晶体结构表征证实了其离子属性：配合物的阳离子部分呈现七配位镥中心，该中心带有反式排布的碘配体与醇盐配体，另有五个吡啶分子均匀排布于赤道平面。将化合物2与三甲基碘硅烷(iodotrimethylsilane)反应，可得到预期的三碘化物配合物[LuI₂(py)₅][I]（化合物3）；该配合物也可通过将市售LuI₃在四氢呋喃(THF)中回流，随后从THF/吡啶混合溶剂中结晶制备得到。化合物3的固态结构与化合物2相似，仅其醇盐配体被碘配体取代。相较于高配位数的中性配合物，离子型结构的配合物1~3能够稳定存在，这可归因于镥中心的离子半径较小，且金属配位球内存在较强的路易斯碱(Lewis base)。