Sarah Wittmann, M. Mangir Murshed, Thorsten M. Gesing
Z. Anorg. Allg. Chem. 2022, 648, e20220031
Polycrystalline red tin(II)oxide (RSO) has been synthesized by a fast reflux method. X-ray powder diffraction (XRPD) data Rietveld refinement confirms the orthorhombic space group Cmc21 (Z=8). The presence of 5 s2 lone electron pair (LEP) of the Sn2+ cation results in layers of highly distorted SnO4 tetrahedra with an averaged Wang-Liebau eccentricity (WLE) parameter of 4.3(1) x10−5 as a measure of the stereochemical activity. The significantly different Sn−O bond distances demonstrate the under-bonding nature of both the tin and the oxygen atoms in the SnO4 coordination. The band gap of red tin(II)oxide is found to be 1.75(1) eV which is compared with those of blue-black tin(II) (BSO) and white tin(IV) oxide (WSO) based on the UV-Vis diffuse reflectance spectral data. Temperature-dependent XRPD reveals the phase transitions, which is complemented by thermogravimetric and differential scanning calorimetry (TG/DSC) investigations. Moreover, in-situ Raman spectroscopy additionally hints to an intermediate phase either of Sn2O3 or Sn3O4 appears within a short temperature range before the RSO to BSO transition occurs. Due to axial negative thermal expansion for the b-lattice parameter RSO exhibits nearly a zero thermal expansion coefficient for a given temperature range above room temperature.