Synthesis and Structures of Pb₃O₂(CH₃COO)₂·0.5H₂O and Pb₂O(HCOO)₂: Two Corrosion Products Revisited

Abstract

Reactions of carboxylic acids with lead play an important role in the atmospheric corrosion of lead and lead-tin alloys. This is of particular concern for the preservation of lead-based cultural objects, including historic lead-tin alloy organ pipes. Two initial corrosion products, Pb(3)O(2)(CH(3)COO)(2)·0.5H(2)O (1) and Pb(2)O(HCOO)(2) (2), had been identified through powder diffraction fingerprints in the Powder Diffraction File, but their structures had never been determined. We have crystallized both compounds using hydrothermal solution conditions, and structures were determined using laboratory and synchrotron single-crystal X-ray diffraction data. Compound 1 crystallizes in P1, and 2 in Cccm. These compounds may be viewed as inorganic-organic networks containing single and double chains of edge-sharing Pb(4)O tetrahedra and have structural similarities to inorganic basic lead compounds. Bond valence sum analysis has been applied to the hemidirected lead coordination environments in each compound. Atmospheric exposure experiments contribute to understanding of the potential for conversion of these short-term corrosion products to hydrocerussite, Pb(3)(CO(3))(2)(OH)(2), previously identified as a long-term corrosion product on lead-rich objects. Each compound was also characterized by elemental analysis, thermogravimetric analysis and differential scanning calorimetry (TGA-DSC), and Raman spectroscopy.