Powder-neutron diffraction studies of geometric isotope and hydrogen-bonding effects in β-CrOOH

Powder-neutron diffraction studies have been done on beta -CrOOH and beta -CrOOD to confirm whether or not the reported exceptionally large geometric isotope effect is real, and also to study hydrogen-bonding effects in beta -CrOOH compared to the prototype CrO2. The R(O . . .O) distance in the H-compound at room temperature is confirmed to be 2.472(3) Angstrom, but in the D-compound it is significantly shorter, 2.518(3) Angstrom, than in the earlier work. The resulting magnitude of the geometric isotope effect, 0.046(4) Angstrom, is thus not as exceptionally large as earlier reported, but is still within the maximum range. Structural comparison with CrO2 clarified the hydrogen-bonding effect in beta -CrOOH: the formation of hydrogen bonds brings CrO6 Closer to a regular octahedron. (C) 2001 Elsevier Science Ltd. All rights reserved.