Abstract Generated abstract
Potassium and rubidium octafluororhenates were examined by X-ray powder diffraction, oscillation radiography, and reciprocal lattice radiography to characterize their crystallographic properties and compare the two salts. The study found orthorhombic unit cells for potassium octafluororhenate with parameters a = 8.70 kX, b = 5.91 kX, c = 12.53 kX, and for rubidium octafluororhenate with a = 9.10 kX, b = 6.10 kX, c = 12.97 kX, with possible space groups Pnma or Pn2a. Indexing of the diffraction spectra and density comparisons support the conclusion that the compounds are individual phases and are isomorphous with one another.
Full Text
CHEMISTRY
E. G. IPPOLITOV and P. A. KOZ’MIN
X-RAY STUDY OF POTASSIUM AND RUBIDIUM OCTAFLUORORHENATES
(Presented by Academician I. V. Tananaev, 24 VIII 1961)
Potassium and rubidium octafluororhenates, recently synthesized by Nikolaev and Ippolitov \((^{1})\), proved sufficiently stable in the open air to permit a detailed X-ray study of them. X-ray spectra of these salts were obtained by the powder method, as well as oscillation radiographs and reciprocal-lattice radiographs.
Fig. 1
To obtain X-ray spectra of potassium and rubidium octafluororhenates with filtered iron radiation, a URS-50-I ionization X-ray apparatus was used. Complete reproducibility of the spectra was observed on repeated exposures of the same specimen. The X-ray spectra obtained are shown in Fig. 1. The intensity of the reflections was determined by measuring the areas of the peaks, the intensity of the strongest reflection being taken as 100.
In the cited work \((^{1})\) a method was also described for obtaining coarsely crystalline potassium octafluororhenate, containing crystals up to 0.2 mm in size. These crystals were stable for a week in the open air. By contrast, in the isolated state rapid decomposition occurred as a result of the catalytic influence of traces of hydrogen fluoride, which decomposes octafluororhenate with liberation of rhenium hexafluoride \((^{2})\). Owing to the very high stability of single crystals in the open air, it was possible to obtain oscillation radiographs along three mutually perpendicular directions and reciprocal-lattice radiographs along two directions of the zero, first, and second layer lines. The oscillation and reciprocal-lattice radiographs were taken repeatedly on different crystals using unfiltered copper radiation.
Proceeding from the symmetry of the rotation and reciprocal-lattice radiographs and from the extinction conditions determined from the reciprocal-lattice radiographs, the following space groups are possible: \(D_{2h}^{16}=Pnma\) and \(C_{2v}^{9}=Pn2a\). The periods of the unit cell of potassium octafluororhenate were determined from rotation radiographs (Fig. 2) and were found to be \(a=8.70\) kX,
Table 1
Results of indexing the X-ray spectra
| \multicolumn{4}{c}{\(K_2ReF_8\)} | \multicolumn{4}{c}{\(Rb_2ReF_8\)} | \multicolumn{4}{c}{\(K_2ReF_8\)} | \multicolumn{4}{c}{\(Rb_2ReF_8\)} |
|---:|---:|---:|---:|---:|---:|---:|---:|---:|---:|---:|---:|---:|---:|---:|---:|
| intensity | \(\sin^2\theta\) obs. | \(hkl\) | \(\sin^2\theta\) calc. | intensity | \(\sin^2\theta\) obs. | \(hkl\) | \(\sin^2\theta\) calc. | intensity | \(\sin^2\theta\) obs. | \(hkl\) | \(\sin^2\theta\) calc. | intensity | \(\sin^2\theta\) obs. | \(hkl\) | \(\sin^2\theta\) calc. |
| 3 | 0.0190 | 101 | 0.0183 | 24 | 0.0300 | 011 | 0.0307 | 2 | 0.325 | 306 | 0.3256 | 6 | 0.322 | 233 | 0.3210 |
| 17 | 0.0334 | 011 | 0.0327 | 100 | 0.0323 | 102 | 0.0335 | 3 | 0.330 | 422 | 0.3284 | 6 | 0.331 | 512 | 0.3296 |
| 100 | 0.0361 | 102 | 0.0362 | 39 | 0.0414 | 111 | 0.0419 | | | 117 | 0.3309 | | | 423 | 0.3310 |
| 21 | 0.0454 | 111 | 0.0450 | 39 | 0.0447 | 200 | 0.0452 | 7 | 0.334 | 126 | 0.3337 | | | 503 | 0.3322 |
| 16 | 0.0491 | 200 | 0.0494 | 13 | 0.0487 | 201 | 0.0507 | 3 | 0.340 | 207 | 0.3413 | | | 331 | 0.3331 |
| 4 | 0.0563 | 201 | 0.0554 | 55 | 0.0602 | 112 | 0.0586 | 5 | 0.358 | 331 | 0.3577 | 17 | 0.339 | 325 | 0.3408 |
| 7 | 0.0652 | 112 | 0.0629 | 6 | 0.0623 | 103 | 0.0612 | | | 423 | 0.3582 | 12 | 0.345 | 415 | 0.3447 |
| 3 | 0.0676 | 103 | 0.0660 | 33 | 0.0672 | 202 | 0.0674 | | | 512 | 0.3594 | | | 226 | 0.3455 |
| 3 | 0.0732 | 202 | 0.0732 | 43 | 0.0701 | 210 | 0.0703 | 4 | 0.369 | 325 | 0.3670 | 9 | 0.354 | 008 | 0.3554 |
| 9 | 0.0758 | 210 | 0.0761 | 86 | 0.0734 | 013 | 0.0751 | | | 217 | 0.3680 | 5 | 0.367 | 108 | 0.2484 |
| 22 | 0.0807 | 013 | 0.0803 | 68 | 0.0754 | 211 | 0.0758 | 2 | 0.387 | 234 | 0.3853 | | | 035 | 0.6645 |
| 20 | 0.0818 | 211 | 0.0821 | 69 | 0.0868 | 113 | 0.0863 | 5 | 0.400 | 424 | 0.3999 | | | 424 | 0.3669 |
| 13 | 0.0929 | 113 | 0.0927 | 34 | 0.0887 | 004 | 0.0888 | | | 135 | 0.4018 | 6 | 0.380 | 333 | 0.3775 |
| 10 | 0.0951 | 004 | 0.0953 | 40 | 0.0946 | 203 | 0.0951 | 9 | 0.420 | 118 | 0.4203 | | | 406 | 0.3380 |
| 7 | 0.103 | 203 | 0.1030 | 26 | 0.100 | 104 | 0.1001 | | | 521 | 0.4217 | 4 | 0.395 | 514 | 0.3962 |
| 6 | 0.108 | 020 | 0.1069 | | | 020 | 0.1004 | 2 | 0.439 | 430 | 0.4382 | 10 | 0.403 | 208 | 0.3400 |
| | | 104 | 0.1077 | 5 | 0.111 | 301 | 0.1072 | | | 416 | 0.4388 | | | 040 | 0.4401 |
| 6 | 0.130 | 213 | 0.1297 | 6 | 0.120 | 213 | 0.1202 | | | 235 | 0.4389 | | | 326 | 0.0416 |
| | | 022 | 0.1307 | 15 | 0.125 | 114 | 0.1252 | | | 522 | 0.4396 | | | 416 | 0.4558 |
| 5 | 0.135 | 114 | 0.1344 | | | 302 | 0.1238 | 2 | 0.457 | 505 | 0.4577 | | | 522 | 0.4049 |
| | | 302 | 0.1350 | 4 | 0.130 | 311 | 0.1323 | | | 218 | 0.4573 | 14 | 0.413 | 601 | 0.4120 |
| 16 | 0.144 | 122 | 0.1431 | 30 | 0.133 | 122 | 0.1339 | 4 | 0.469 | 602 | 0.4685 | | | 431 | 0.4121 |
| | | 311 | 0.1439 | | | 204 | 0.1340 | | | 610 | 0.4714 | | | 334 | 0.4163 |
| | | 204 | 0.1447 | 6 | 0.147 | 220 | 0.1456 | | | 523 | 0.4693 | 11 | 0.445 | 515 | 0.4461 |
| 2 | 0.157 | 220 | 0.1563 | 10 | 0.158 | 214 | 0.1591 | 4 | 0.489 | 407 | 0.4895 | | | 240 | 0.4468 |
| 2 | 0.161 | 105 | 0.1613 | 13 | 0.162 | 123 | 0.1616 | | | 028 | 0.4881 | 6 | 0.476 | 327 | 0.4770 |
| | | 312 | 0.1617 | | | 015 | 0.1640 | 6 | 0.510 | 019 | 0.5092 | | | 019 | 0.4747 |
| | | 221 | 0.1623 | 9 | 0.170 | 222 | 0.1678 | | | 327 | 0.5099 | | | 417 | 0.4777 |
| 3 | 0.167 | 303 | 0.1648 | 4 | 0.173 | 115 | 0.1751 | | | 524 | 0.5100 | 7 | 0.482 | 426 | 0.4808 |
| 9 | 0.173 | 123 | 0.1729 | 4 | 0.176 | 313 | 0.1767 | 3 | 0.522 | 506 | 0.5232 | | | 613 | 0.4815 |
| | | 214 | 0.1714 | 7 | 0.185 | 205 | 0.1839 | | | 119 | 0.5215 | | | 318 | 0.4819 |
| 4 | 0.180 | 222 | 0.1802 | | | 401 | 0.1862 | | | 044 | 0.5229 | | | 506 | 0.4821 |
| 7 | 0.187 | 115 | 0.1880 | 31 | 0.191 | 024 | 0.1892 | 4 | 0.537 | 228 | 0.5375 | 19 | 0.488 | 119 | 0.4859 |
| 9 | 0.203 | 024 | 0.2022 | | | 304 | 0.1904 | | | 144 | 0.5353 | | | 044 | 0.4904 |
| | | 401 | 0.2036 | 17 | 0.198 | 223 | 0.1955 | 2 | 0.548 | 516 | 0.5500 | 8 | 0.506 | 137 | 0.509 |
| 12 | 0.226 | 106 | 0.2268 | | | 006 | 0.1998 | 3 | 0.565 | 614 | 0.5667 | | | 516 | 0.507 |
| 7 | 0.242 | 322 | 0.2419 | 32 | 0.210 | 215 | 0.2090 | | | 525 | 0.5646 | | | 620 | 0.507 |
| 10 | 0.252 | 403 | 0.2513 | | | 106 | 0.2111 | | | 336 | 0.5661 | 3 | 0.517 | 614 | 0.5204 |
| | | 224 | 0.2516 | 10 | 0.228 | 322 | 0.2242 | 8 | 0.603 | 506 | 0.6007 | | | 219 | 0.520 |
| | | 116 | 0.2535 | 30 | 0.235 | 224 | 0.2344 | | | 129 | 0.6017 | | | 531 | 0.514 |
| 5 | 0.270 | 125 | 0.2682 | 9 | 0.245 | 206 | 0.2450 | | | 623 | 0.6052 | 6 | 0.537 | 244 | 0.5356 |
| | | 323 | 0.2717 | | | 131 | 0.2427 | | | 533 | 0.6030 | | | 408 | 0.5358 |
| 3 | 0.277 | 132 | 0.2767 | 5 | 0.255 | 413 | 0.2557 | | | | | 3 | 0.544 | 237 | 0.5430 |
| | | 413 | 0.2780 | 13 | 0.269 | 404 | 0.2694 | | | | | | | 605 | 0.5452 |
| 3 | 0.287 | 315 | 0.2868 | | | 216 | 0.2701 | | | | | | | 435 | 0.5453 |
| 1 | 0.292 | 230 | 0.2900 | 10 | 0.274 | 315 | 0.2655 | | | | | 4 | 0.558 | 623 | 0.5568 |
| | | 216 | 0.2906 | 17 | 0.279 | 033 | 0.2759 | | | | | | | 329 | 0.5572 |
| | | 404 | 0.2929 | 8 | 0.288 | 420 | 0.2810 | | | | | | | 701 | 0.5588 |
| 5 | 0.296 | 033 | 0.2942 | | | 421 | 0.2866 | | | | | | | 418 | 0.5609 |
| | | 231 | 0.2959 | | | 133 | 0.2871 | | | | | 13 | 0.572 | 615 | 0.5703 |
| 6 | 0.305 | 107 | 0.3042 | | | 501 | 0.2878 | | | | | | | | |
| | | 420 | 0.3046 | | | 324 | 0.2908 | | | | | | | | |
| | | 225 | 0.3052 | 26 | 0.297 | 414 | 0.2945 | | | | | | | | |
| | | 133 | 0.3085 | | | 017 | 0.2971 | | | | | | | | |
| 5 | 0.318 | 017 | 0.3186 | 18 | 0.310 | 117 | 0.3083 | | | | | | | | |
| | | 414 | 0.3197 | 27 | 0.313 | 511 | 0.3129 | | | | | | | | |
| | | | | | | 126 | 0.3115 | | | | | | | | |
\(b=5.91\) kX, \(c=12.53\) kX. These data confirm the results of optical observations in polarized light, which showed that the crystal system of the crystals is rhombic \((^2)\). On the basis of the calculated unit-cell periods of potassium octafluororhenate and the possible space groups, the spectra of \(K_2ReF_8\) were indexed within the range from \(0\) to \(50^\circ\) of the angle \(\theta\). The indexing results are given in Table 1.
The external appearance of the X-ray spectrum of rubidium octafluororhenate indicated the probable isomorphism of this salt with potassium octafluororhenate. Proceeding
Fig. 2
DAN, vol. 142, No. 5. E. G. Ippolitov and P. A. Koz’min
From this assumption, the unit-cell periods of \(\mathrm{Rb_2ReF_8}\) were calculated from the most intense and characteristic reflections. As was to be expected, the periods increased and became \(a = 9.10\) kX, \(b = 6.10\) kX, \(c = 12.97\) kX. Using these values of the periods, all the remaining reflections of the spectrum of rubidium octafluororhenate were indexed. The results of the indexing are given in Table 1.
Since the atomic factor of rubidium is twice as large as the atomic factor of potassium, the intensities of reflections with identical \(hkl\) for the rubidium and potassium octafluororhenates may differ greatly. Therefore some weak reflections present in the spectrum of the potassium salt are not observed in the spectrum of the rubidium salt, and conversely. This becomes especially noticeable beginning with the angle \(\theta = 30^\circ\). It is possible that the unequal increase of all the unit-cell parameters of rubidium octafluororhenate also plays a role here.
Table 2
X-ray characteristics of potassium and rubidium octafluororhenates
| Formula | Crystal system | Fedorov group | Unit-cell periods in kX | Density, calculated, g/cm³ | Density, determined, g/cm³ | Number of molecules in the cell |
|---|---|---|---|---|---|---|
| \(\mathrm{K_2ReF_8}\) | Orthorhombic | \(\left\{\begin{array}{l}D_{2h}^{16}=Pnma\\ C_{2v}^{9}=Pn2a\end{array}\right.\) | \(a=8.70\) \(b=5.91\) \(c=12.53\) |
4.29 | \(4.33\pm0.03\) | 4 |
| \(\mathrm{Rb_2ReF_8}\) | Orthorhombic | the same | \(a=9.10\) \(b=6.10\) \(c=12.97\) |
4.70 | \(4.45\pm0.04\) | 4 |
On the basis of the obtained periods of the elementary-cell lattice, the densities of both salts were calculated. In Table 2 the results of these calculations are compared with the data obtained pycnometrically.
The results of the X-ray investigations confirm that potassium and rubidium octafluororhenates are individual compounds, isomorphous with one another. The investigation of the structure of potassium octafluororhenate is continuing.
Institute of General and Inorganic Chemistry
named after N. S. Kurnakov
Academy of Sciences of the USSR
Received
16 VIII 1961
CITED LITERATURE
- N. S. Nikolaev, E. G. Ippolitov, DAN, 140, No. 1 (1961).
- N. S. Nikolaev, E. G. Ippolitov, DAN, 136, No. 1, 111 (1961).