Re-examination of “Pb3TeO6”: Determination of its correct composition as Pb5TeO8

Hydrothermal synthesis, crystal structures, and X-ray photoelectron spectroscopy of lead tellurium(IV) and tellurium(VI) oxycompounds: Ba3PbTe6O16 and Na2Pb9(μ6-O)2(Te2O10)2

An exploratory study of the lead-tellurium-oxygen phase space led to two new compounds, Ba3PbTe6O16 (BPTO) and Na2Pb9(μ6-O)2(Te2O10)2 (NPTO), which were synthesized under hydrothermal conditions at 550 °C and 210 °C, respectively, and characterized by single-crystal X-ray diffraction, infrared and X-ray photoelectron spectroscopy. BPTO adopts a layer structure. The Te4+ cation in BPTO is bonded to four oxygen atoms at about 2.0 Å with two more oxygens at about 3.0 Å. The seesaw-shaped TeO4 units share corners to form 2D layers containing six-membered rings and the Ba2+ and Pb2+ cations are situated in the interlayer region. The structure of NPTO contains dimers of edge-sharing Te6+O6 octahedra, which are connected through five-coordinate Pb2+ cations. A unique six-coordinate O atom is at the center of the octahedron formed by five Pb2+ and one Na+ cations. BPTO is one of the few metal tellurites which were synthesized under supercritical hydrothermal reaction conditions. The Pb2+ cation in NPTO shows pronounced stereochemical effects of the lone electron pair. In contrast, BPTO shows no stereochemical evidence of the inert pair.

On tungstates of divalent cations (III) – Pb5O2[WO6]

Pb 5 O 2 [ WO 6 ] ${\text{Pb}}_{5}{\text{O}}_{2}\left[{\text{WO}}_{6}\right]$ was discovered as a frequently observed side phase during our investigation on lead tungstates. Its crystal structure was solved by single-crystal X-ray diffraction ( P 2 1 / n $P{2}_{1}/n$ , a = 7.4379 ( 2 ) $a=7.4379\left(2\right)$ Å, b = 12.1115 ( 4 ) $b=12.1115\left(4\right)$ Å, c = 10.6171 ( 3 ) $c=10.6171\left(3\right)$ Å, β = 90.6847 ( 8 ) $\beta =90.6847\left(8\right)$ °, Z = 4 $Z=4$ , R int = 0.038 ${R}_{\text{int}}=0.038$ , R 1 = 0.020 ${R}_{1}=0.020$ , ω R 2 = 0.029 $\omega {R}_{2}=0.029$ , 4188 data, 128 param.) and is isotypic with Pb 5 O 2 [ Te 6 ] ${\text{Pb}}_{5}{\text{O}}_{2}\left[{\text{Te}}_{6}\right]$ . Pb 5 O 2 [ WO 6 ] ${\text{Pb}}_{5}{\text{O}}_{2}\left[{\text{WO}}_{6}\right]$ comprises a layered structure built up by non-condensed [WO6] 6 − ${}^{6-}$ octahedra and [ O 4 Pb 10 ] 12 + ${\left[{\text{O}}_{4}{\text{Pb}}_{10}\right]}^{12+}$ oligomers. The compound was characterised by spectroscopic measurements (Infrared (IR), Raman and Ultraviolet–visible (UV/Vis) spectra) as well as quantum chemical and electrostatic calculations (density functional theory (DFT), MAPLE) yielding a band gap of 2.9 eV fitting well with the optical one of 2.8 eV. An estimation of the refractive index based on the Gladstone-Dale relationship yielded n ≈ 2.31 $n\approx 2.31$ . Furthermore first results of the thermal analysis are presented.