ON THE REACTION OF TELLURIUM WITH TUNGSTEN HALIDES - SYNTHESIS AND CRYSTAL-STRUCTURE OF TE7WOCL5, A COMPOUND WITH A POLYMER TELLURIUM CATION

The reaction of tellurium with WOCl4 in the presence of a large excess of WCl6 in a sealed evacuated glass ampoule at 150-degrees-C yields beside the main product Te8(WCl6)2 a small amount of Te7WOCl5. The crystal structure determination (orthorhombic space group Pcca, lattice parameters at 173 K: a = 2 596.5(9) pm, b = 810.0(3) pm, c = 775.7(2) pm) shows that Te7WOCl5 is built of one-dimensional band shaped polymeric tellurium cations, one-dimensional associated pyramidal WOCl4- anions and of isolated Cl- anions. Te7WOCl5 can thus be formulated as [Te7(2+)]n [WOCl4-]n (Cl-). The structure is closely related but not isotypic to the bromine containing analogue Te7WOBr5. The difference between the two structures lies in different directions of the polar [WOX4-]n chains (X = Cl, Br). The strongly elongated thermal ellipsoid of one tellurium atom is shown to be caused by thermal vibration by determing the crystal structure of Te7WOCl5 at three different temperatures (223, 173 and 123 K). All displacement parameters of all atoms can be extrapolated to zero for OK.