Molecular Structure of Te(OMe)₄·ClTe(OMe)₃, a Model for Ligand Exchange between Te(IV) Centers

ClTe(OⁱPr)₃ could be prepared from stoichiometric amounts of TeCl₄ and Te(OⁱPr)₄, a reaction that requires the exchange of ligands between different Te centers. Ligand redistribution between telluranes was studied, and rapid exchange of −Cl and −OR (R = Me, ⁱPr) ligands in solutions of several binary mixtures of Te(OMe)₄, Te(OⁱPr)₄, ClTe(OMe)₃, and ClTe(OⁱPr)₃ was established by multinuclear NMR spectroscopy. The solid-state structure of Te(OMe)₄·ClTe(OMe)₃, the first structurally characterized adduct between different telluranes, was investigated by single-crystal X-ray diffraction. It exhibits a very short Te−O···Te bridge between the two Te centers and additional Te···O and Te···Cl contacts between different adduct molecules. Selected structural parameters of Te(OMe)₄·ClTe(OMe)₃ are Te1−Cl1 274.6(3), Te1−O13 191.0(5), Te1−O12 194.9(6), Te1−O11 200.9(7), Te1···O24 226.8(5), Te1···O11a 314.2(8), Te2−O21 191.6(5), Te2−O22 198.7(5), Te2−O23 190.1(5), Te2−O24 225.3(5), Te2···O13 307.8(6), and Te2···O22b 269.2(6) pm and Te2−O24···Te1 126.1(2)°. Ab initio (MP2/LANL2DZP) geometry optimization of the model compound Te(OH)₄·ClTe(OH)₃ revealed that the central Te−O···Te bridge is less symmetric and hence weaker in the isolated adduct molecule than in the solid state. The stability of Te(OMe)₄·ClTe(OMe)₃ toward decomposition in Te(OMe)₄ and ClTe(OMe)₃ is attributed to the strengths of the short Te−O···Te bridge between Te(OMe)₄ and ClTe(OMe)₃. On the basis of the molecular structures of Te(OH)₄·ClTe(OH)₃ and Te(OMe)₄·ClTe(OMe)₃, a mechanism for the exchange of −OR groups between Te(IV) centers is proposed.