THE STRUCTURES OF TWO NOVEL SN2+ OXYSALTS FOUND WITH ROMARCHITE AND HYDROROMARCHITE AS CORROSION PRODUCTS OF PEWTER ARTIFACTS

Abstract

The crystal structures of an anthropogenic Sn2+ silicate, Sn6O4(SiO4), hexagonal, space group P63mc, a 7.3742(4), c 11 9598(10) Å, V 563.23(6) Å3, Z = 2, Dcalc 5.12 g/cm3, and an anthropogenic Sn2+ sulfate, Sn6O4(SO4)(OH)2, orthorhombic, space group Pbca, a 14.0071(8), b 12.5016(7), c 14.5030(9) Å, V 2539.6(3) Å3, Z = 8, Dcalc 4.74 g/cm3, were refined by fullmatrix least-squares techniques on the basis of F2 to agreement indices R1 (Sn2+ silicate and Sn2+ sulfate) of 3.0 and 4.2%, calculated for 704 anal 3281 unique observed reflections ( Fo ≥4σ F), and wR2 of 5.5 and 11.0% for all data, respectively. Intensity data were collected at room temperature using MoKα radiation anda CCD-based area detector. Both structures contain the [Sn6φ8] cluster [φ: O2- or (OH)-], which has been found in several stannous compounds, and which can be derived from the structure of fiuorite. These two compounds occur with romarchite, SnO, and hydroromarchite, Sn3O2(OH)2, on pewter bowls that had become corroded in cold freshwater for approximately 160 years.