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 a = 15.1332(6) angstrom, c = 15.7909(9) angstrom, V = 3131.8(3) angstrom(3), Z = 6, 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. (c) 2006 Elsevier Inc. All rights reserved.