The structures of tellurium(iv) halides in the gas phase and as solvated molecules

Abstract

The structures of molecular tellurium tetrafluoride and tellurium tetrachloride were determined by a combination of gas-phase electron diffraction, mass spectrometry and quantum chemical calculations. The combined GED/MS experiments showed no evidence of decomposition of TeF₄ and TeCl₄. No ions of oligomeric (dimeric, trimeric, etc.) or any other composition were found in the mass spectra. The monomeric molecules possess a pseudo trigonal bipyramidal structure (C_2v symmetry) with the equatorial Te–X distances being shorter than the axial ones. The fluorine atoms are bent away from the lone pair resulting in X_eq–Te–X_eq and X_eq–Te–X_ax bond angles smaller than 120 and 90°, respectively. The structure of solvates TeF₄ (THF)₂, TeF₄ (dioxane) TeF₄ (DME)₂, TeF₄(Et₂O) TeF₄(toluene), TeCl₄(CH₃CN)₂, TeCl₄(DME)₂ and TeCl₄(dioxane) were determined by X-ray diffraction. The structures of tellurium tetrafluoride solvates are strongly influenced by the choice of the solvent molecules. Monomeric TeF₄ units were obtained with THF, DME and dioxane whereas fluoride bridged coordination polymers were formed using diethyl ether or toluene. All tellurium tetrachloride solvates studied contain monomeric TeCl₄ units with coordinated solvent molecules. Coordination numbers range from four in the gas phase to eight in the TeF₄ dimethoxyethane solvate. Geometric parameters of the TeX₄ molecules in the crystal, solvates and gas phase were compared. DFT, MP2, CCSD, CCSD(T) methods were applied for calculation of geometric and vibrational characteristics of free TeX₄ molecules (X = F, Cl). The pseudorotation barriers were estimated and an NBO analysis was performed. It was shown that both, GED and theoretical, quantitative results are in agreement with the qualitative results of the VSEPR model.