The crystal structure of the mineral strontiodresserite, (Sr,Ca)Al2(CO3)2(OH)4⋅H2O, from the Francon Quarry, Montreal, Quebec, Canada, has been solved from laboratory powder diffraction data using a combination of charge-flipping and simulated annealing methods. The structure is orthorhombic in space group Pnma with a=16.0990(7), b=5.6133(3), and c=9.1804(4) Å (Z=4) and the framework of the mineral is isostructural with that of dundasite. The strontium has a coordination number of 9 and the carbonate anions form a bridge between the SrO9 polyhedra and AlO6 octahedra. The water molecule lies in a channel that runs parallel to the b axis. An ordered network of hydrogen atoms could be uniquely determined from crystal-chemical principles in the channels of strontiodresserite. Ab initio density functional theory (DFT) energy minimization of the whole structure gave results in full agreement with X-ray refinement results for nonhydrogen atoms. The stability of this model (as well as that of the corresponding model of dundasite) in the proposed Pnma space group was tested by DFT optimization in space group P1 of random small distortions of this structure. This test confirms that both minerals are isostructural, including their hydrogen-bond networks.

The crystal structure of Sb(C2O4)OH has been solved by charge flipping in combination with difference Fourier techniques using laboratory X-ray powder data exhibiting significant preferred orientation and refined by the Rietveld method. The compound crystallizes in Pnma with a=5.827 13(3), b=11.294 48 (10), c=6.313 77(3) Å, V=415.537(5) Å3, and Z=4. The crystal structure contains pentagonal pyramidal Sb3+ cations, which are bridged by hydroxyl groups to form zigzag chains along the a axis. Each oxalate anion chelates to two Sb in approximately the ab plane, linking the chains into a three-dimensional framework. The H of the hydroxyl group is probably disordered in order to form stronger more-linear hydrogen bonds. The highest energy occupied molecular orbitals are the Sb3+ lone pairs. The structure is chemically reasonable compared to other antimony oxalates and to Bi(C2O4)OH.