Determination of the Correct Composition of “Hydrous Lead(II) Oxotellurate(IV)” as PbTeO 3 , Crystallizing as a New Polymorph

摘要

In previous studies, it has been reported that the crystalline product precipitated from the reaction of aqueous solutions of lead(II) salts with sodium oxotellurate(IV) is hydrous lead(II) oxotellurate(IV); however, there have been conflicting specifications of the water content, and the crystal structure of the product is yet undetermined. During the present study, it was shown that the precipitated material does not contain any structural water and in fact represents the third modification (denoted as γ -) of PbTeO 3 , as revealed by thermal analysis, vibrational spectroscopy, single crystal and powder X-ray diffraction. This modification crystallizes in the space group P 1 ˉ with five formula units in the asymmetric unit, comprising off-centred coordination polyhedra around the Pb II cations (coordination numbers: 5–7 with Pb-O distances ranging from 2.3–3.0 ?), and trigonal-pyramidal TeO 3 2? units. The thermal behaviour and structural phase transitions of PbTeO 3 were investigated by means of temperature-dependent X-ray powder diffraction and complementary thermal analysis measurements. In addition, the crystal structure of β -PbTeO 3 was redetermined, and a comparison was made between the three known polymorphs of PbTeO 3 .