Reports of the Academy of Sciences of the USSR
1964. Volume 157, No. 4

CHEMISTRY

K. A. AVDUEVSKAYA, Academician I. V. TANANAEV, V. S. MIRONOVA

ON GERMANIUM ARSENATE

Arsenic-acid compounds of germanium have not been described in the literature. Meanwhile, the close similarity of H₃PO₄ and H₃AsO₄ and of many of their derivatives makes it possible to assume the existence of a germanium arsenate analogous to the described phosphate Ge(HPO₄)₂·H₂O (¹,²).

Saturation of a solution of H₃AsO₄ with germanium dioxide did not lead to the formation of a metastable solution, as occurred in the interaction of GeO₂ and H₃PO₄. As a result of two weeks’ stirring of a mixture of GeO₂ and H₃AsO₄ (4 mol/kg), a paste-like mass was formed. In the liquid phase, separated by suction on a porous filter No. 4, no germanium was found. Analysis of the solid phase, thoroughly washed with alcohol and ether and dried at 70°, established the following composition (in %): Ge 18.4; As 39.5; H₂O 9.5. For GeO₂·As₂O₅·2H₂O the calculated values are (in %): Ge 19.0; As 39.4; H₂O 9.7. Germanium was determined by the tannin method, arsenic iodometrically. The water content was determined directly from the loss in weight upon heating to 600°. As can be seen, the compound obtained has a composition analogous to that of the germanium phosphate separated from a metastable solution of GeO₂ in H₃PO₄.

Fig. 1. Thermogram of GeO₂·As₂O₅·2H₂O

GeO₂·As₂O₅·2H₂O is a finely crystalline powder, readily decomposed by water. Its thermogram is shown in Fig. 1. A series of successive endoeffects at 168, 224, and 275° corresponds to the removal of the first molecule of water; the crystalline structure changes hardly at all. At a temperature of 450° the remaining water is split off and the compound GeO₂·As₂O₅ is formed, which we designate as GeAs₂O₇-α.

The exothermic effect at 700°, as established by X-ray diffraction, is a consequence of a change in the crystalline structure. The compound formed at 700°, which we designate as GeAs₂O₇-β, is characterized by lower symmetry than GeAs₂O₇-α. Thermal decomposition of germanium pyroarsenate begins immediately after the exoeffect.

The endothermic effects at 835 and 925° are associated with the intense evolution of As₂O₅ and melting of the products formed. The composition of the product formed at 925° corresponds to the formula 4GeO₂·As₂O₅. Complete splitting off of As₂O₅ occurs after prolonged heating at ~1000°. Analysis showed that the final product of heating is GeO₂.

Figure 2 gives the schemes of the X-ray diffraction patterns of GeO₂·As₂O₅·2H₂O, GeAs₂O₇-α, and GeAs₂O₇-β. The values of the interplanar spacings d, the intensities I, and sin²θ are given in Table 1. The X-ray diffraction patterns were obtained with CuKα radiation in a camera 57.3 mm in diameter. The line intensities were estimated visually according to a nine-point system. Comparison of the X-ray diffraction pattern of Ge(HPO₄)₂·H₂O and GeP₂O₇-α with the X-ray diffraction patterns of GeO₂·As₂O₅·2H₂O and GeAs₂O₇-α indicates their similarity (there is no isomorphism), which is possibly connected with the isostructural nature of the compounds being compared. Mixing

lines toward smaller angles \(\theta\) (and, consequently, the increase in lattice periods), observed in the X-ray patterns of arsenic-acid compounds, is due to the increase in the radius of \(\mathrm{AsO_4^{3-}}\) as compared with the radius of \(\mathrm{PO_4^{3-}}\).

In Fig. 3A the IR absorption spectrum of \(\mathrm{GeO_2\cdot As_2O_5\cdot 2H_2O}\) is shown (wave numbers of the maxima and inflections: 740, 780, 800, 815, 850, 890, 900, 935, 1260, 1635 \(\mathrm{cm^{-1}}\)). The absorption band at 1635 \(\mathrm{cm^{-1}}\) belongs to deformation vibrations of water. In the spectrum of the compound of composition \(\mathrm{GeO_2\cdot As_2O_5\cdot H_2O}\), obtained by heating to \(250^\circ\), this absorption band is absent. Thus,

Fig. 2. Schemes of X-ray diffraction patterns of \(\mathrm{GeO_2\cdot As_2O_5\cdot 2H_2O}\) (1), \(\mathrm{GeAs_2O_7}\)-\(\alpha\) (2), \(\mathrm{GeAs_2O_7}\)-\(\beta\) (3)

one of the two water molecules in \(\mathrm{GeO_2\cdot As_2O_5\cdot 2H_2O}\) is chemically bound and, evidently, enters into the composition of the compound in the form of two \(\mathrm{HAsO_4^{2-}}\) ions.

The character of the IR spectrum of \(\mathrm{GeO_2\cdot As_2O_5\cdot 2H_2O}\) does not contradict the statement made, since it is known from the literature \((^3)\) that in the spectra of acid arsenates, alongside the most intense band at 920—800 \(\mathrm{cm^{-1}}\), weaker bands are present to the left and to the right of it. On the basis

Table 1

| \multicolumn{3}{c}{\(\mathrm{GeO_2\cdot As_2O_5\cdot 2H_2O}\)} | \multicolumn{6}{c}{\(\mathrm{GeAs_2O_7}\)-\(\alpha\)} | \multicolumn{9}{c}{\(\mathrm{GeAs_2O_7}\)-\(\beta\)} |
|---:|---:|---:|---:|---:|---:|---:|---:|---:|---:|---:|---:|---:|---:|---:|---:|---:|---:|
| \(I\) | \(\sin^2\theta\) | \(d,\ \text{Å}\) | \(I\) | \(\sin^2\theta\) | \(d,\ \text{Å}\) | \(I\) | \(\sin^2\theta\) | \(d,\ \text{Å}\) | \(I\) | \(\sin^2\theta\) | \(d,\ \text{Å}\) | \(I\) | \(\sin^2\theta\) | \(d,\ \text{Å}\) | \(I\) | \(\sin^2\theta\) | \(d,\ \text{Å}\) |
| 8 | 0.0097 | 7.810 | 4 | 0.334 | 1.332 | 6 | 0.0114 | 7.180 | 6 | 0.0114 | 7.18 | 4 | 0.173 | 1.85 | 1 | 0.430 | 1.17 |
| 3 | 0.0324 | 4.280 | 4 | 0.361 | 1.282 | 9 | 0.037 | 3.976 | 4 | 0.014 | 6.45 | 4 | 0.182 | 1.80 | 1 | 0.434 | 1.16 |
| 4 | 0.0361 | 4.048 | 1 | 0.377 | 1.256 | 5 | 0.033 | 4.225 | 3 | 0.022 | 5.17 | 2 | 0.189 | 1.77 | 1 | 0.465 | 1.13 |
| 8 | 0.049 | 3.480 | 4 | 0.392 | 1.231 | 4 | 0.050 | 3.433 | 4 | 0.032 | 4.28 | 3 | 0.201 | 1.72 | 1 | 0.481 | 1.11 |
| 1 | 0.059 | 3.163 | 2 | 0.399 | 1.220 | 5 | 0.072 | 2.879 | 9 | 0.038 | 3.94 | 3 | 0.212 | 1.67 | 2 | 0.505 | 1.08 |
| 5 | 0.083 | 2.668 | 5 | 0.442 | 1.159 | 8 | 0.097 | 2.475 | 1 | 0.039 | 3.84 | 3 | 0.228 | 1.61 | 3 | 0.530 | 1.06 |
| 9 | 0.095 | 2.493 | 2 | 0.475 | 1.118 | 5 | 0.111 | 2.313 | 5 | 0.047 | 3.54 | 1 | 0.234 | 1.59 | 1 | 0.540 | 1.05 |
| 1 | 0.101 | 2.422 | 2 | 0.497 | 1.094 | 4 | 0.135 | 2.098 | 7 | 0.049 | 3.46 | 4 | 0.242 | 1.56 | 2 | 0.576 | 1.02 |
| 3 | 0.106 | 2.361 | 1 | 0.530 | 1.059 | 1 | 0.166 | 1.890 | 4 | 0.060 | 3.15 | 4 | 0.248 | 1.55 | 1 | 0.591 | 1.003 |
| 2 | 0.119 | 2.237 | 3 | 0.539 | 1.050 | 2 | 0.209 | 1.688 | 5 | 0.067 | 2.98 | 3 | 0.259 | 1.52 | 2 | 0.607 | 0.990 |
| 3 | 0.134 | 2.107 | 1 | 0.599 | 0.995 | 5 | 0.233 | 1.596 | 4 | 0.074 | 2.83 | 3 | 0.272 | 1.48 | 2 | 0.630 | 0.966 |
| 5 | 0.146 | 2.018 | 2 | 0.626 | 0.975 | 3 | 0.269 | 1.485 | 5 | 0.083 | 2.64 | 1 | 0.283 | 1.45 | 1 | 0.659 | 0.950 |
| 4 | 0.162 | 1.912 | 3 | 0.638 | 0.965 | 7 | 0.292 | 1.426 | 6 | 0.091 | 2.55 | 5 | 0.291 | 1.43 | 1 | 0.694 | 0.926 |
| 3 | 0.180 | 1.812 | 4 | 0.687 | 0.930 | 4 | 0.307 | 1.391 | 6 | 0.097 | 2.48 | 2 | 0.299 | 1.44 | 2 | 0.721 | 0.909 |
| 4 | 0.200 | 1.723 | 2 | 0.694 | 0.926 | 5 | 0.389 | 1.234 | 6 | 0.109 | 2.34 | 2 | 0.309 | 1.39 | 1 | 0.750 | 0.891 |
| 1 | 0.211 | 1.677 | 3 | 0.758 | 0.885 | 4 | 0.429 | 1.176 | 3 | 0.115 | 2.27 | 1 | 0.317 | 1.37 | 1 | 0.859 | 0.832 |
| 2 | 0.230 | 1.607 | 1 | 0.795 | 0.864 | | | | 1 | 0.127 | 2.16 | 3 | 0.340 | 1.32 | 1 | 0.883 | 0.821 |
| 6 | 0.244 | 1.561 | 1 | 0.837 | 0.843 | | | | 4 | 0.119 | 2.23 | 4 | 0.352 | 1.30 | 1 | 0.935 | 0.796 |
| 3 | 0.260 | 1.510 | 1 | 0.848 | 0.837 | | | | 4 | 0.141 | 2.05 | 2 | 0.379 | 1.25 | | | |
| 3 | 0.278 | 1.463 | 4 | 0.885 | 0.819 | | | | 3 | 0.150 | 1.99 | 3 | 0.392 | 1.23 | | | |
| 7 | 0.291 | 1.427 | 3 | 0.921 | 0.803 | | | | 1 | 0.160 | 1.93 | 3 | 0.407 | 1.21 | | | |
| 5 | 0.300 | 1.406 | 3 | 0.935 | 0.797 | | | | 3 | 0.168 | 1.88 | 1 | 0.417 | 1.19 | | | |

From the foregoing, the compound $\mathrm{GeO_2 \cdot As_2O_5 \cdot 2H_2O}$ should be regarded as $\mathrm{Ge(HAsO_4)_2 \cdot H_2O}$. It was established by X-ray diffraction that removal of the water molecule leads only to a slight distortion of the crystal lattice, which makes it possible to assume the presence in the structure of the compound of channels or voids occupied by water.

Fig. 3. IR spectra of $\mathrm{GeO_2 \cdot As_2O_5 \cdot 2H_2O}$ (A) and $\mathrm{GeAs_2O_7}$-$\alpha$ (B)

Figure 3B gives the IR spectrum of $\mathrm{GeAs_2O_7}$-$\alpha$, obtained by dehydration of $\mathrm{Ge(HAsO_4)_2}$ at $500^\circ$. (Wave numbers of the maxima: 853, 910, and 1010 $\mathrm{cm^{-1}}$.)

The IR spectra of $\mathrm{Ge(HPO_4)_2H_2O}$ (?) and $\mathrm{Ge(HAsO_4)_2 \cdot H_2O}$ are very similar in form, which, together with the similarity of the X-ray diffraction patterns of the indicated compounds, attests to the identity of their structures.

Received
27 III 1964

REFERENCES CITED

1. K. A. Avduevskaya, I. V. Tananaev, ZhNKh, 8, 1020 (1963).
2. K. A. Avduevskaya, I. V. Tananaev, ZhNKh (1964).
3. F. A. Miller, C. H. Wilkins, Anal. chem., 24, 1253 (1952).