[Bi6O4.5(OH)3.5]2(NO3)11:: a new anhydrous bismuth basic nitrate.: Synthesis and structure determination from twinned crystals

The bismuth basic nitrate [Bi6O4.5(OH)(3.5)](2)(NO3)(11) crystallizes in the monoclinic space group P2(1) with a = 15.850(3) Angstrom b. = 14.986(3) Angstrom, c = 18.230(4) Angstrom, beta = 107.329(17)degrees and V = 4133.7(14) Angstrom(3) (Z = 4). Its structure has been determined from 120 K, twinned crystal X-ray data (16 781 reflections, 683 parameters, R = 0.0703). It is built upon [Bi6Ox(OH)(8-x)]((10-x)+), x = 4 and x = 5 hexanuclear complexes and nitrate groups. The polycationic entities are linked to the nitrate anions either by hydrogen bonds or through bismuth-oxygen coordination. Even at 120 K, the [Bi6O4(OH)(4)](6+) and [Bi6O5(OH)(3)](5+) polycations could not be observed as such, the crystal structure refinement only detecting an average [Bi6O4.5(OH)(3.5)](5.5+) polycation. To prove the presence of both hexanuclear complexes in the structure, we report the existence of a correlation between the bismuth-linked oxygen bond-valence parameters and the presence, or not, of hydroxyl groups. Moreover, the Raman spectrum of the new anhydrous bismuth basic nitrate is compared to those of [Bi6O5(OH)(3)](NO3)(5).3H(2)O, [Bi6O4(OH)(4)](NO3)(6).4H(2)O, and two yet uncharacterized bismuth nitrates. (C) 2003 Elsevier Inc. All rights reserved.