Cobaltic acid, HCoO2, and deuterated cobaltic acid, DCoO2, have been prepared and studied by x-ray and neutron-diffraction techniques, and by infrared spectroscopy and cold-neutron scattering. The materials crystallize in apparent space group D3d5–R<3¯m of the trigonal system with three molecules in a hexagonal cell of dimensions: HCoO2, a = 2.851(1), c = 13.150(5) Å; DCoO2, a = 2.854(1), c = 13.354(5) Å. The O–O distance, as determined by neutron-powder studies, of HCoCO2 is 2.50(2) Å. On this basis and the fact that there are three O–H–O bonds along the c direction, the O–D–O distance is 2.57(2) Å. Hence, the isotope effect here is as large as in the system HCrO2–DCrO2. Infrared studies at room temperature and at − 195°C over the region 70–4000 cm−1 may be interpreted in terms of an effectively symmetric O–H–O bond and an effectively asymmetric O–D–O bond. Although the neutron inelastic scattering measurements are not inconsistent with this interpretation, there is a band centered at 264 cm−1 in the neutron spectrum for HCoC2, which is not observed in the infrared spectrum. Model calculations, based on a two-dimensional potential function in which the asymmetric stretching frequency is coupled to the symmetric stretching frequency, were unsuccessful owing to the magnitude of the coupling term required to account for the very large isotope effect.

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The structures of nanoporous carbon prepared by chlorination of TiC at five different temperatures (700–1100 °C) have been studied by means of reverse Monte Carlo modelling of neutron diffraction data S(q), 0.3

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A three-dimensional X-ray diffraction study of the s-modification of both (COOH)z.2H20 and (COOD)/. 2D20 has been made. For each substance, intensity data were collected with Cu K~. radiation out to 110 ° in 20 on a Picker automatic diffractometer. Positional and anisotropic thermal parameters for all atoms were refined on F 2 by full-matrix least-squares techniques. A correction for anisotropic extinction effects was included in the least-squares refinement. The weighted R factors on F 2 are 3.9%(547 observed reflections) fol 0c-(COOH)z.2H20 and 3-9% (555 observed reflections) for e-(COOD)2.2D20. The corresponding conventional R factors on F2 are 2.8% and 2.8% respectively; on Fthey are 2.0% and 2-3%. The oxalic acid molecules and water molecules are linked together by a three-dimensional network of hydrogen bonds. All three crystallographically independent O-H. • -O bond lengths expand significantly with deuteration while the bond lengths within the oxalate fragment remain unchanged. In e-(COOH)2.2H20, the O-H...O distances are 2-512 (1), 2-864 (2) and 2.883 (1)A" the corresponding O-D...O distances in ~-(COOD)2.2D20 are 2.531 (1), 2.880 (2) and 2.907 (1),~. 'in the final paper (Coppens, Sabine, Delaplane & Ibers, 1969) some comparisons are made between the X-ray and neutron results on oxalic acid dihydrate and their implications in terms of bonding effects are discussed. ExperimentalCrystals of e-POX were recrystallized from aqueous solution. About 0.35 g of anhydrous oxalic acid was dissolved in 2ml of 99.85 mole% D20 with heating, and the water was evaporated in vacuo. After repeating the procedure three times, a final recrystallization yielded crystals of e-DOX. Crystals of both substances were colorless monoclinic needles with the needle axis coincident with the b axis. Recrystallization of oxalic acid dihydrate from D20 has also been reported to produce rhomboidal crystals offl-DOX (Iwasaki & Saito, 1967;Iwasaki et al., 1967;Coppens & Sabine, 1969). The pres-* The anisot~opic crystal Type II extinction correction was applied in this refinement. 2430 AN X-RAY STUDY OF .-OXALIC ACID DIHYDRATE alent members (hkl) and (hfc[) of the {hkl} form were refined for four cycles yielding values of 6.5% and 5-8% averaged. The original 932 intensities were thus re-for R1 and Rz respectively. The final value for g is induced to 575 independent reflections. The R2 value on F z eluded in Table 6. for averaging was 1.4%. The structural parameters A second refinement was carried out which included were refined on F 2. A reflection was considered unob-the six components Gi~ of the tensor describing a Gausserved iflo < l'5cr(Io). For such reflections, a term A(F z) sian for a Type I crystal as variable parameters. Since = 1.5a(F~o)-F~ was included in the refinement when-the anisotropic extinction effects in the ~-POX and ever F~ > 2-0a(F~o). Atomic positional and anisotropie c~-DOX crystals appeared to be similar, the values for thermal parameters for each atom, an overall scale the components G;~ corresponding to the v.-DOX ...

The structure of amorphous Ge15Te85 has been studied by neutron and x-ray diffraction. Experimental data have been modelled simultaneously with the reverse Monte Carlo simulation method. The contrast between structure factors together with the application of some plausible physical constraints allowed the separation of the three partial pair correlation functions and determination of Ge and Te local environment.