The Crystal Structure of Anhydrous Strontium Formate
1949 Volume 5 Issue 3-4 Pages 89-94
Details
1949 Volume 5 Issue 3-4 Pages 89-94
The crystal structure of orthorhombic anhydrous strontium formate Sr (HCOO) 2 was investigated by the method of X-ray Fourier analysis. Oscillation-rotation photographs were taken with filtered Cu-Kx radiation around each of the three principal axes, the dimensions of the unit cell and the space group. being, a=6.860 kX, b=8.730 kX, c=7.253 kX (at 20°C), D42-P212121, z=4. All the atoms are on the general positions: xyz; 1/2+x, 1/2-y, -z; 1/2-x, 1/2+y, 1/2-z; -x, -y, 1/2+z. By using the Patterson functions and the Fourier series projections of the electron density the atomic parameters were obtained, their final adjustment being made by intensity calculations:
Sr OI OII OIII OIV CI CII
x 0 0.145 0.384 0.268 0.130 0.245 0.132
y 0.0915 0.154 0.330 0.235 0.370 0.260. 0.303
z 0 0.358 0.350 0.828 0.057 0.420 0.906
The structure determined may be described as consisting of chains _??_ parallel to the c-axis which are bound laterally through the formate ions and the ones _??_ parallel to the a-axis, both chains forming a compact spacial network together. Two types of the linkage of the formate ions were found as shown in Fig. 3a and b. The former was found in the crystal structure of sodium formate by Zachariasen and of calcium formate by one of the authors (Nitta) and Osaki. The strontium ion is surrounded by eleven oxygen atoms, three of them being rather far apart, each oxygen atom is shared by two, three or four strontium ions, and the Pauling's rule concerning the stability of ionic crystals was found to hold in its extended form. The shape and size of formate ions were found to be;
HCOO (I) 1.26±0.03 kX 1.24±0.03 kX 126°±4°
HCOO (II) 1.25±0.03 kX 1.25±0.03 kX 127°±4°
That the two C-O distances in each HCOO radical are practically equal suggests almost complete resonance between the two valence bond structure
_??_ and _??_
