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

Abstract

Abstract 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.