Refinement of mercury fluoride hydroxide

Abstract

HgF(OH), orthorhombic, space group P212~2 ~, a = 4 .9568(6) , b = 5 .9042(7) , c = 6.8630 (11) A, V = 200.85 A 3, Z = 4, D x = 7.82 Mg m -3, g(Mo Ka) = 77.8 mm -1. For 441 observed reflections the final R = 0.066. The structure is built up of endless zig-zag chains of formula [Hg(OH)]] + with H g O = 2.10 and 2.12 A. The chains are connected by O H . . . F hydrogen bonds of 2.52 A and weak H g F and H g O contacts. Introduction. A refinement of the structure of HgF(OH) (Grdeni6 & Sikirica, 1973) has been performed as the earlier determination, based on a fairly limited number of intensities, resulted in rather large e.s.d.'s in the interatomic distances and high temperature factors for O and F. Pale-yellow crystals of HgF(OH) were obtained by dissolving yellow HgO in 10% HF and concentrating the solution on a water bath at 343 K. A prismatic single crystal, 0 .10 x 0.12 × 0.20 mm, was used in the diffractometer work. For the determination of the cell parameters and collection of the intensities a CAD-4 diffractometer was used with Zr-filtered Mo K radiation. The lattice parameters were determined by least-squares analysis of the 0 values for 50 reflections. The intensities were collected with the 09-20 scan technique and a peak scan interval Ao) = (0.70 + 0.70 tan 0) °. The maximum time spent on a reflection was 4.5 min. In one octant of reciprocal space all reflections with 3 o o(1) were measured. I and of f ) were calculated from fast prescans. Every second hour five standard reflections were measured. A decrease in their intensities was detected, but as it was irregular and the variation only between 2 and 7% during the two days of data collection, no correction was made. In the structure analysis 441 reflections with I > 3o(1) were used. Corrections were applied for Lorentz-polarization and absorption effects (g = 77.8 mm-1). The transmission factors, evaluated by numeri0567-7408/79/040949-03501.00 cal integration, varied between 0.005 and 0.047. The position of Hg, found by the Patterson method, was refined by least-squares calculations. As the resulting x coordinate was close to ~}, two peaks (x,y,z; 1⁄2 x, y, z) of nearly the same height were found for each of the O and F atoms in the difference syntheses. In the refinements, the lowest R was obtained with the coordinates given in Table 1, which thus represent the true structure. Considerably larger R values were found when the Hg coordinate was shifted to 1⁄2 x, combined with the earlier positions of O and F, as chosen by Grdeni6 & Sikirica (1973). The refinements were performed by full-matrix least-squares calculations with anisotropic temperature factors for Hg and isotropic ones for O and F. The H atom of the OH group was included with fixed parameters, the fractional coordinates derived from geometrical considerations, assuming an sp3-hybridized O atom. In the final refinement a parameter to correct for secondary extinction (Zachariasen, 1967) was included. The form factors for Hg, F and O were those of Doyle & Turner (1968) and for H that of Stewart, Davidson & Simpson (1965). An anomalous-dispersion correction for Hg (Cromer & Liberman, 1970) was also used. The refinement converged to R = 0.066 and R w = 0.077* with the * Lists of structure factors and anisotropic thermal parameters have been deposited with the British Library Lending Division as Supplementary Publication No. SUP 34159 (4 pp.). Copies may be obtained through The Executive Secretary, International Union of Crystallography, 5 Abbey Square, Chester CH 1 2HU, England. Table 1. Fractional coordinates and isotropic tempera tu re factors