Sodium copper pyrophosphate hexadecahydrate

Abstract

Na6CH(P207) 2. 16H20: F.W. 6776, triclinic, P i , a=6.842(I) , b=8.759(2), c=12.727(3) A, c~= 89.50(2), f l= 95.96(1), ~, = 112.58(1) °, (measured at 22 + 2 °C), Z = 1, dx = 2.02 (by flotation in benzene-methylene iodide), de= 1.99 g c m -3, F(000)=427, V=700.0 A 3. The pyrophosphate anion has a bridge P O P angle of 129.7(3) °, a mean P-O (bridge) distance of 1.620 A and a mean P-O (terminal) distance of 1.515/~. The copper ion is on a center of symmetry and is surrounded by oxygen atoms in a distorted octahedral arrangement. Two of the sodium atoms are surrounded by six oxygen atoms at mean distances of 2.449 and 2.402 A while the third sodium is surrounded by five oxygen atoms at a mean distance of 2.390 A. Introduction. Deep blue crystals were grown from aqueous solution at room temperature according to the procedure of Bassett, Bedwell & Hutchinson (1936). A crystal of approximate dimensions 0.1 × 0.1 × 0.1 mm was coated with a thin layer of Lubriseal high-vacuum grease to inhibit water loss. Intensity data were collected from 2396 reflections of which 2113 were considered observed by the criterion that the net intensity was greater than twice its standard deviation computed from counting statistics. A four-circle diffractometer was used in the 0-20 scan mode with nickel-filtered Cu K~ radiation (2 = 1.54050 A). The crystal was mounted so that its [011] direction was parallel to the axis of the diffractometer. The standard reflections monitored during the data collection showed no systematic change with time. There was no evidence for symmetry elements on precession-camera photographs and there were no systematic absences. Since no piezoelectric effect was detected the solution of the structure and the refinement were carried out in space group P 1. Absorption corrections were made to each reflection based on the carefully measured shape of the crystal and a calculated absorption coeffieient o f / z = 53.75 cm1. The maximum absorption factor [exp (/zR)] was 1.634 and the minimum was 1.373. Atomic scattering factors for Na +, Cu 2+, P, and O were taken from International Tables for X-ray Crystallography (1962) and corrected for anomalous dispersion according to Cromer & Liberman (1970). The scattering factors of Stewart, Davidson & Simpson (1965) were used for the hydrogen atoms. A Patterson map revealed the positions of all the copper and phosphorus atoms and Fourier maps based on the positions of these atoms revealed the location of all the sodium and oxygen atoms. The structure was refined by block-diagonal least-squares calculations with anisotropic thermal parameters, using only reflections considered as observed, to an R index (R= ~IAFI/Y~IFol) for the observed data of 0.083. A difference map at this stage revealed 13 out of the 16 hydrogen atom positions and these were introduced into the least-squares refinement with fixed isotropic thermal parameters of 2.5 A 2. The final R was 0.072 for the observed reflections and 0.093 for all reflections. The weighting scheme was w = 1/{1 + [(IFolel)/e2] 4} where P1 and P2 were adjusted to values of 40 and 25 respectively to give an R sensibly independent of IFol. The final coordinates of the hydrogen atoms are listed in Table 1 and the coordinates and anisotropic thermal parameters for the heavy atoms in Table 2.* The NRC * Tables of the coordinates of the corners of the crystal and observed and calculated structure factors have been deposited with the British Library Lending Division as Supplementary Publication No. SUP 30545 (12 pp., 1 microfiche). Copies may be obtained through The Executive Secretary, International Union of Crystallography, 13 White Friars, Chester CHI 1NZ, England. Table 1. Hydrogen-atom coordinates Estimated standard deviations in this and following tables are indicated in parentheses.