Synthesis, open-framework structure and thermal behaviour of ammonium tin oxalate, Sn2(NH4)2(C2O4) 3.3H2O

Nathalie Audebrand, Marie Laure Vaillant, Jean Paul Auffrédic, Daniel Louër

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20 Citations (Scopus)


A new mixed ammonium tin oxalate trihydrate, Sn2(NH4)2(C2O4) 3.3H2O, has been prepared from evaporation of a solution of tin and ammonium oxalates. Its crystal structure has been solved from single-crystal diffraction data. The symmetry is orthorhombic, space group Pnma (No. 62), cell dimensions a = 15.1821(5) Å, b = 11.7506(2) Å, c = 10.8342(3) Å, and Z = 4. The structure consists of macroanionic layers built from [Sn(C2O4)3]2- groups. The SnO6 polyhedron can be described as a pseudo pentagonal bipyramid, with the lone pair of electrons presumably occupying one apex. The resulting framework displays holes in which the water molecules and ammonium groups are located. The thermal behaviour of the mixed ammonium tin oxalate has been investigated with temperature-dependent X-ray powder diffraction and conventional thermal analysis. The degradation process has been completely explained, as well as that of oxammite, a phase always obtained in the preparations. The thermal decomposition of oxammite leads to (NH4)2C2O4 and a new acid salt, NH4HC2O4. The mixed ammonium tin oxalate decomposes successively into the amorphous compounds, Sn2(NH4)2(C2O4) 3.H2O and Sn2(NH4)2(C2O4) 3, SnC2O4and, finally, cassiterite SnO2.

Original languageEnglish
Pages (from-to)483-494
Number of pages12
JournalSolid State Sciences
Issue number4
Publication statusPublished - 2001
Externally publishedYes


  • Ammonium tin oxalate
  • Crystal structure
  • Oxammite decomposition
  • Synthesis
  • Thermal behaviour


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