Powder neutron-diffraction profile analysis of zero-dimensional H-bonded crystal HCrO2

Powder neutron-diffraction profile analysis of alpha-HCrO2 has been done at five temperatures, 295, 210, 140, 70 and 10 K, to confirm the space group and the hydrogen-bond distance. The data were analyzed for three models: (1 ) space group R(3) over bar m with off-centered disordered hydrogen; (2) R( 3) over bar m with centered hydrogen; and (3) R3m. The space group R(3) ove r bar m with off-centered disordered hydrogen gave the most reasonable resu lts in the range of 70-295 K, consistent with earlier results. The hydrogen bond distance 2.471(3) Angstrom at 295 K agrees with one of the earlier st udies. The space group at 10 K is less conclusive. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.