THE STRUCTURES OF TWO NOVEL Sn2+ OXYSALTS FOUND WITH ROMARCHITE AND HYDROROMARCHITE AS CORROSION PRODUCTS OF PEWTER ARTIFACTS

The crystal structures of an anthropogenic Sn 2+ silicate, Sn 6 O 4 (SiO 4 ), hexagonal, space group P6 3 mc, a 7.3742(4), c 11.9598(10) Å, V 563.23(6)Å 3 , Z = 2, D calc 5.12 g/cm 3 , and an anthropogenic Sn 2+ sulfate, Sn 6 O 4 (SO 4 )(OH) 2 , orthorhombic, space group Pbca, a 14.0071( 8), b 12.5016(7), c 14.5030(9) Å, V 2539.6(3)Å 3 , Z = 8, D calc 4.74 g/cm 3 , were refi ned by fullmatrix least-squares techniques on the basis of F 2 to agreement indices R1 (Sn 2+ silicate and Sn 2+ sulfate) of 3.0 and 4.2%, calculated for 704 and 3281 unique observed refl ections (|F o | ≥ 4 F ), and wR 2 of 5.5 and 11.0% for all data, respectively.Intensity data were collected at room temperature using MoK␣ radiation and a CCD-based area detector.Both structures contain the [Sn 6 8 ] cluster [: O 2-or (OH) -], which has been found in several stannous compounds, and which can be derived from the structure of fl uorite.These two compounds occur with romarchite, SnO, and hydroromarchite, Sn 3 O 2 (OH) 2 , on pewter bowls that had become corroded in cold freshwater for approximately 160 years.