I. Nitta, K. Osaki
May 1, 1948
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Abstract
The strucutre of orthorhombic calcium formate was analysed by the method of Fourier series. Oscillation-rotation photographs were taken with Cu-Kα radiation around the three principal axes and the following unit cell dimensions and space group were obtained, which confirmed the results of the previous work (Nitta, 1927) ; a=10.163A., b=13.381A., c=6.27.1A. (at 18°C) ; space group, D152h—Pcab; Z=8. All the atoms are on the general positions 8 (c) :± (xyz; 1/2+x, 1/2-y, z; x, 1/2+y, 1/2-z; 1/2-x, y, 1/2+z) .with the parameters shown in Table I.The analysis was effectuated by the method of two-dimensional and three-dimensional Patterson syntheses, the latter being evaluated along lines through several points corresponding to peaks in P (xy) .The structure obtained may be explained as consisting of chains of the type shown in the figure parallel to the c-axis, which are laterally bound through formate ions to form a compact spatial network (Fig.2) . Three types of interionic linkage are found (Fig.3), two of which were already found in sodium formate, analysed by Zachariasen. A remarkable feature is the asymmetrical type of coordination (type II), which might be characteristic to ions of lower symmetry such as this. The calcium ions are surrounded by eight oxygen atoms as shown in Fig.4, one of them being somewhat more apart (Table III) . Pauling's rule concerning the stability of ionic crystals are shown to be strictly hold in its extended form. The shape of the formate, groups were found to be :C-C=1.25, 1.25, 1.25, 1.24 (±0.03A.) ; OCO=125°, 124° (±4°) .These results suggest an almost complete resonance between the two forms proposed by Pauling.