Polycationic disorder in [Bi6O4(OH)4](NO3)6: Structure determination using synchrotron radiation and microcrystal X-ray diffraction

The bismuth basic nitrate [Bi6O4(OH)4](NO3)6 crystallizes in a rhombohedral hexagonal unit cell with parameters image, image, image, image, space group R-3. The synthesis, formula determination, thermogravimetric analysis and nitrate assay, and finally, its crystal structure refinement determined at 150(2) K by synchrotron X-ray microcrystal diffraction are reported. Its structure is built from [Bi6O4(OH)4]6+ polycations, six per unit cell, disordered over two positions. Two oxygen atoms are common to the two antagonist polycations (full occupancy) while the remaining six are partially occupied. The [Bi6O4(OH)4]6+ hexanuclear clusters form columns along the c-axis. The cohesion between polycationic entities is effected by nitrate anions through either OH–ONO2 hydrogen bonds or Bi–ONO2 bonds. One of the two independent [NO3]− groups is also disordered over two positions. Only a local order in the columns is obtained by formation of pairs of ordered [Bi6O4(OH)4]6+ polycations.