crystallized/recrystallized products, and crystal structure
Table 1 Solid products synthesized at different temperatures by reac-
tion between H TeO and H SO in different concentrations
refinements for TeO (I) and Te O (SO ).
6
6
2
4
3
2
3
4
wt% H SO
T/ЊC
Product
H TeO
2
4
Experimental
Syntheses
3
9
0–55
5
r.t.–136 (bp)
r.t.
6
6
6
H TeO
6
Telluric acid [H TeO Fluka, 99%; monoclinic, a = 649.34(5),
95
135
150–190 (bp)
200
210–290 (bp)
250
320
TeO ؒxH O, x = 1.58; amorphous
6
6
3 2
b = 931.90(6), c = 833.09(6) pm, β = 99.682(6)Њ], TeO [Fluka,
6
9
8
0–75
5
0–95
TeO ؒxH O, x = 1.37–1.58; crystalline
3 2
2
TeO (III); 5 wt% adsorbed H O
pract., >95%; tetragonal, a = 481.11(3), c = 761.04(7) pm],
3
2
TeO (III); 2–5 wt% adsorbed H O
3
2
TeCl (Alfa, 99%), tellurium powder [Fluka, purum, >99.7%;
4
ca. 100
ca. 100
TeO (II); 2 wt% adsorbed H O
3
2
2
hexagonal, a = 445.74(5), c = 592.8(1) pm], and conc. H SO4
TeO (I); 2 wt% adsorbed H O
3
2
(
Merck, p.a.; 95–97 wt%, the former value being used through-
out this paper) were used as starting chemicals for the syn-
theses. H SO concentrations in the range 30–95 wt% were
made by diluting with distilled water.
54
2
4
SCANPI program system. Indexation of unknown diffraction
55
patterns was attempted using the TREOR program. Unit-cell
parameters were refined using the CELLKANT program.
PXD intensity data for the refinement of the TeO (I) crystal
structure were collected with a Siemens D5000 diffractometer
equipped with primary germanium monochromator, position
sensitive detector, using Cu-Kα1 radiation and the sample in
cylinder (transmission) geometry.
With H TeO as starting chemical, 50 ml conc. H SO [origin-
56
6
6
2
4
ally 95 wt%; in some cases first heated at 320–325 ЊC for ca. 2 h
open system) to increase the concentration towards 100 wt%
H SO ] and 4.6 g of telluric acid were mixed. Such mixtures
3
(
2
4
were stirred in a round-bottomed flask equipped with a reflux
cooler at temperatures from room temperature (r.t.) to boiling
point (bp) for 1 d or longer. After cooling to r.t. (with frequent
intermediate stirring in order to avoid mass solidification
and sticking of the product to the glass of the reaction vessel)
a white–yellowish, non-hygroscopic precipitate was obtained.
Similar syntheses gave white products for reactions in 60–75
Powder neutron diffraction (PND) data for Te O (SO )
2
3
4
were collected with the high-resolution, two-axis diffractometer
PUS at the JEEP II reactor, Kjeller, Norway. Monochromatized
neutrons of wavelengths 155.4 pm were obtained by reflections
from Ge(511) and detected by two PSD banks, each covering
0Њ in 2θ. Diffraction data were measured at r.t., between
θ = 10 and 130Њ, and analysed in steps of ∆2θ = 0.05Њ. A
cylindrical sample holder was used and filled with ca. 1.5 g
sample.
Rietveld refinements of the PXD and PND data were
wt% H SO4 and white–yellowish products for 80–95 wt%
2
2
2
H SO . The liquid phase was removed by decantation and the
2
4
precipitate stirred with ca. 100 ml glacial acetic acid for 15 min,
filtered off, and washed with glacial acetic acid and acetone.
The entire washing procedure was repeated twice before the
product was dried and stored in a desiccator.
57
performed with the program GSAS. A pseudo-Voigt profile
A similar procedure was followed with tellurium dioxide as
starting chemical. 3.2 g TeO and 30–95 wt% H SO (50 ml)
function was used both for the PXD and PND data. Isotropic
thermal parameters were refined individually for the elements
of different kinds but no absorption correction was made.
2
2
4
were treated for periods of 1–2 d. After cooling to r.t., the
colourless to yellowish clear liquid phase was removed by
decantation. The white precipitate was treated as described
above. In the case of tellurium tetrachloride as starting
Thermoanalyses
chemical, 8.1 g TeCl were similarly treated with 50 ml 60–95
Thermogravimetric (TG) and differential thermal (DTA)
analyses were performed between 20 and 800 ЊC with a Perkin-
Elmer TGA 7 and DTA 7 system, respectively. The 15–40 mg
4
wt% H SO in the described reaction system. With tellurium
2
4
powder as starting chemical, mixtures of 5.1 g Te and 50 ml
0–95 wt% H SO were heated and stirred at different tem-
6
samples were placed in Al O crucibles, nitrogen was used as
2 3
Ϫ1
2
4
peratures (from r.t. to bp) for reaction periods of 2 h to one
week, depending on acid concentration and temperature,
usually judged by the amount of deposited white, non-
hygroscopic precipitate in the colourless solution.
atmosphere and the heating rate was 10 ЊC min .
Results and discussion
Duplicate experiments at r.t. were performed by treating
Telluric acid (H TeO ) as reactant
6
6
tellurium powder with 95 wt% H SO4 for one week, as
2
H TeO as reactant in 60–ca. 100 wt% H SO leads to at least
6
6
2
4
described above. The stirring was then stopped and the liquid
and solid phases were separated by filtering through a sintered-
glass funnel. The obtained violet solution was added to 150 ml
glacial acetic acid with stirring, and a bulky black precipitate
immediately separated. The solid product was filtered off,
washed with glacial acetic acid and dried in a desiccator.
The small amount of white solid product remaining on the
sintered-glass funnel was washed with 95 wt% H SO until no
four different solid reaction products [Table 1; TeO (I), TeO3
3
(
II), TeO (III) and TeO ؒxH O (in two forms, crystalline and
3 3 2
amorphous, x = 1.37–1.58), arranged according to decreasing
concentration of H SO and reaction temperature]. (In order
2
4
to avoid confusion with the literature where the designations A,
B, C, α, β and γ have been used to name different modifications
of TeO , the notations I, II and III are used to distinguish those
3
2
4
prepared in this study.) The yields were generally good for
violet colouring of the washing liquid could be seen, and then
washed with glacial acetic acid and dried in a desiccator.
Precipitated TeO3 was purified by washing with a con-
centrated KOH solution and thereafter with distilled water.
Afterwards it was washed with concentrated HCl and sub-
sequently with distilled water (until pH ca. 6). The products
after filtering were dried at 300 ЊC.
syntheses in 95 wt% H SO between 200 ЊC and bp, but lower
2
4
for less concentrated acid. For reaction temperatures below
00 ЊC (even for 95 wt% H SO ) the products became X-ray
2
2
4
amorphous and contained appreciable amounts of water.
For reactions attempted at r.t. the solid “product” proved to
be unchanged H TeO , but the low residual indicates some
6
6
dissolution of H TeO in 95 wt% H SO .
6
6
2
4
As the concentration of H SO was decreased the particle
2
4
Powder X-ray and neutron diffraction and refinements
size of the solid products decreased (recognized by PXD)
and their water contents increased gradually (see Table 1).
The H SO concentration and the reaction temperature play a
Characterization by powder X-ray diffraction (PXD) was
performed with Guinier–Hägg cameras (Cu-Kα1 radiation,
Si as internal standard). Positions of Bragg reflections
were obtained by means of a Nicolet L18 scanner using the
2
4
decisive role for the product obtained, in particular with respect
to the different forms of TeO3.
J. Chem. Soc., Dalton Trans., 2000, 4542–4549
4543