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(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) degrees. 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.