Small molecule crystallography
 
 
RAPID II Application Byte

 

A new mineral type

A new naturally occurring mineral, discovered by an amateur geologist, who passed his sample onto the Natural History Museum, is under investigation. Chemical analysis of the compound had suggested an approximate empirical molecular formula of CaCe2Cu6(SO4,CO3)6(OH)8. Although it had been possible to collect powder data on this compound, the data were not easily indexed. The sample contained very small blue single crystals, and a data collection was attempted on one of these.

This data collection pushes the boundaries of what is possible with any standard laboratory diffractometer. The crystal is circled in yellow in the figure below (left). The crystal is estimated at being at most about 0.01 mm thick in its thinnest dimension, and no more than 0.02 mm wide in its second dimension; it is barely visible behind the piece of glass wool on which it is mounted.

440-minute exposures (per image) were collected on the RAPID II for this structure, one of which is shown (below, right); despite the high background it is possible to see some single crystal diffraction peaks. Exposures of this duration (greater than seven hours) would be virtually impossible with a CCD detector.

 

The data collected is sufficient to index the cell as C-centered monoclinic, with cell dimensions a = 24.4 Å, b = 6.4 Å, c = 11.2 Å, β = 114.9°. This matches the powder pattern and is enough to confirm this as a totally new mineral type.

 

Tags:  hydrogen bonding, variable temperature studies, disorder