The structure of trithallium hydrogen bis(sulfate), Tl
3H(SO
4)
2, in the super-ionic phase has been analyzed by Rietveld analysis of the X-ray powder diffraction pattern. Atomic parameters based on the isotypic Rb
3H(SeO
4)
2 crystal in space group
Rm in the super-ionic phase were used as the starting model, because it has been shown from the comparison of thermal and electric properties in Tl
3H(SO
4)
2 and
M3H(SO
4)
2 type crystals (
M = Rb, Cs or NH
4) that the room-temperature Tl
3H(SO
4)
2 phase is isostructural with the high-temperature
Rm-symmetry
M3H(SO
4)
2 crystals. The structure was determined in the trigonal space group
Rm and the Rietveld refinement shows that an hydrogen-bond O—H
O separation is slightly shortened compared with O—H
O separations in isotypic
M3H(SeO
4)
2 crystals. In addition, it was found that the distortion of the SO
4 tetrahedra in Tl
3H(SO
4)
2 is less than that in isotypic crystals.
Supporting information
Crystals of Tl3H(SO4)2 were obtained from aqueous solutions of Tl2SO4
and H2SO4 in a molar ratio of 3:2. These crystals were grown by slow
evaporation from a saturated solution at 313 K after several
recrystallizations for purification.
The diffraction data were analyzed by the Rietveld method, with the atomic
parameters of the isotypic Rb3H(SeO4)2 in its super-ionic phase as a
starting model (Baranov et al., 1987). The profile shape was
represented by a pseudo-Voigt function. In addition to the profile, lattice
and structure parameters, the zero-point shift, ten background parameters, and
the scale factor were determined with corrections for preferred orientation
along (001) (the crystal shapes are very thin plates). Isotropic thermal
vibrations were assumed. The interatomic distances and bond angles were
calculated with ORFFE (Busing et al., 1964).
Data collection: RINT server software (Rigaku Corporation, 19??); cell refinement: RIETAN2000 (Izumi & Ikeda, 2000); data reduction: RINT server software; program(s) used to solve structure: RIETAN2000; program(s) used to refine structure: RIETAN2000; molecular graphics: ORTEP-3 for Windows (Farrugia, 2001); software used to prepare material for publication: RIETAN2000.
Trithallium hydrogen bis(sulfate)
top
Crystal data top
Tl3H(SO4)2 | Dx = 5.946 (1) Mg m−3 |
Mr = 806.28 | Cu Kα radiation, λ = 1.54184 Å |
Trigonal, R3m | T = 293 K |
Hall symbol: -R 3 2 | Particle morphology: plate-like |
a = 5.9376 (4) Å | white |
c = 22.0966 (9) Å | flat sheet, 15 × 20 mm |
V = 674.65 (6) Å3 | Specimen preparation: Prepared at 313 K |
Z = 3 | |
Data collection top
Rigaku RINT-1400 diffractometer | Data collection mode: reflection |
Radiation source: rotating-anode X-ray tube | Scan method: step |
Specimen mounting: packed powder pellet | 2θmin = 5.000°, 2θmax = 110.00°, 2θstep = 0.006° |
Refinement top
Refinement on Inet | Profile function: pseudo-Voigt |
Least-squares matrix: full with fixed elements per cycle | 38 parameters |
Rp = 0.065 | H-atom parameters not refined |
Rwp = 0.094 | (Δ/σ)max = 0.01 |
Rexp = 0.076 | Background function: square polynomial for each range |
χ2 = 1.513 | Preferred orientation correction: March-Dollase function, axis (001) (Dollase, 1986) |
17501 data points | |
Crystal data top
Tl3H(SO4)2 | V = 674.65 (6) Å3 |
Mr = 806.28 | Z = 3 |
Trigonal, R3m | Cu Kα radiation, λ = 1.54184 Å |
a = 5.9376 (4) Å | T = 293 K |
c = 22.0966 (9) Å | flat sheet, 15 × 20 mm |
Data collection top
Rigaku RINT-1400 diffractometer | Scan method: step |
Specimen mounting: packed powder pellet | 2θmin = 5.000°, 2θmax = 110.00°, 2θstep = 0.006° |
Data collection mode: reflection | |
Refinement top
Rp = 0.065 | 17501 data points |
Rwp = 0.094 | 38 parameters |
Rexp = 0.076 | H-atom parameters not refined |
χ2 = 1.513 | |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | Occ. (<1) |
Tl1 | 0.0 | 0.0 | 0.0 | 0.038 (2)* | |
Tl2 | 0.0 | 0.0 | 0.20754 (3) | 0.081 (2)* | |
S1 | 0.0 | 0.0 | 0.4063 (2) | 0.103 (6)* | |
O1 | −0.1489 (6) | 0.1489 (6) | 0.4334 (2) | 0.0929 (6)* | |
O2 | 0.0390 (2) | −0.0390 (2) | 0.3343 (4) | 0.0542 (8)* | 0.3333333 |
Geometric parameters (Å, º) top
Tl1—S1i | 3.788 (2) | S1—O1 | 1.644 (6) |
Tl2—S1ii | 3.621 (2) | S1—O2 | 1.641 (8) |
Tl1—O1iii | 2.913 (5) | O1—O1iv | 2.65 (1) |
Tl2—O1ii | 3.028 (3) | O1—O2v | 2.586 (7) |
Tl2—O2 | 2.830 (8) | O2—O2vi | 2.626 (6) |
| | | |
O1—S1—O1iv | 107.52 (6) | O1—S1—O2v | 103.85 (6) |
Symmetry codes: (i) x+1/3, y+2/3, z−1/3; (ii) y+1/3, x+2/3, −z+2/3; (iii) −y+1/3, x−y+2/3, z−1/3; (iv) −x+y, −x, z; (v) −y, x−y, z; (vi) y+1/3, x−1/3, −z+2/3. |
Experimental details
Crystal data |
Chemical formula | Tl3H(SO4)2 |
Mr | 806.28 |
Crystal system, space group | Trigonal, R3m |
Temperature (K) | 293 |
a, c (Å) | 5.9376 (4), 22.0966 (9) |
V (Å3) | 674.65 (6) |
Z | 3 |
Radiation type | Cu Kα, λ = 1.54184 Å |
Specimen shape, size (mm) | Flat sheet, 15 × 20 |
|
Data collection |
Diffractometer | Rigaku RINT-1400 diffractometer |
Specimen mounting | Packed powder pellet |
Data collection mode | Reflection |
Scan method | Step |
2θ values (°) | 2θmin = 5.000 2θmax = 110.00 2θstep = 0.006 |
|
Refinement |
R factors and goodness of fit | Rp = 0.065, Rwp = 0.094, Rexp = 0.076, χ2 = 1.513 |
No. of data points | 17501 |
No. of parameters | 38 |
No. of restraints | ? |
H-atom treatment | H-atom parameters not refined |
Selected geometric parameters (Å, º) topS1—O1 | 1.644 (6) | O1—O2ii | 2.586 (7) |
S1—O2 | 1.641 (8) | O2—O2iii | 2.626 (6) |
O1—O1i | 2.65 (1) | | |
| | | |
O1—S1—O1i | 107.52 (6) | O1—S1—O2ii | 103.85 (6) |
Symmetry codes: (i) −x+y, −x, z; (ii) −y, x−y, z; (iii) y+1/3, x−1/3, −z+2/3. |
The Tl3H(SO4)2 crystal is one of a family of M3H(XO4)2 compounds (M = Rb, Cs or NH4, and X = S or Se) known as zero-dimensional hydrogen-bonded systems. The M3H(XO4)2 crystals exhibit very interesting characteristics. Firstly, the hydrogen bonds are isolated. Secondly, deuterated crystals show a drastic isotope effect at the low-temperature phase transition. Thirdly, they undergo a super-ionic phase transition from the low-temperature ferroelastic phase of the monoclinic system to the high-temperature paraelastic phase of the trigonal system; for example, Rb3H(SeO4)2 and Cs3H(SeO4)2 undergo super-ionic phase transitions at 449 K and 456 K, respectively.
Recently, it was found that Tl3H(SO4)2 undergoes a super-ionic phase transition at 239 K and displays super-ionic conductivity even at room temperature (Matsuo et al., 2001), in spite of the fact that other M3H(XO4)2-type crystals are good insulators at room temperature. This interesting feature of the Tl3H(SO4)2 crystal would result from the change to the crystal structure due to placing Tl in the M site. Therefore, the determination of the crystal structure of the Tl3H(SO4)2 crystal in the super-ionic phase is very important for understanding the origin of the super-ionic phase transition in M3H(XO4)2-type crystals. However, no atomic coordinates of Tl3H(SO4)2 in the super-ionic phase were known, although the unit-cell parameters at room temperature had been previously determined by Peter & Jolibois (1973) from X-ray powder diffraction measurements. It is very difficult to prepare good quality single crystals of this compound. Therefore, we have measured the X-ray powder diffraction pattern and determined the crystal structure of Tl3H(SO4)2 in the super-ionic phase using Rietveld analysis.
It is known that M3H(XO4)2-type crystals belong to the trigonal system, space group R3 m, in the highest temperature phase below the melting point (Baranov et al., 1987; Merinov et al., 1990; Lukaszewicz et al., 1993). Chen et al. (2000) recently deduced that a new (NH4)3H(SO4)2 phase above 433 K also has R3 m symmetry. Moreover, (NH4)3H(SeO4)2, which is one of the M3H(XO4)2-type crystals, is known to undergo four phase transitions at TI—II = 335 K, TII-III = 308 K, TIII-IV = 275 K and TIV—V = 181 K (Gesi, 1977; Osaka et al., 1979). Phase I, space group R3 m, and phase II, space group R3, are super-ionic conductors (Pawłowski et al., 1990; Lukaszewicz et al., 1993). The phase transition at TI—II is characterized by a small change in the temperature gradients of the dielectric constant and of electrical conductivity (Pawłowski et al., 1990). The Tl3H(SO4)2 crystal also undergoes four phase transitions above 77 K, at TI—II = 267 K, TII-III = 239 K, TIII-IV = 196 K and TIV—V = 156 K (Matsuo et al., 2001).
In phases I and II, Tl3H(SO4)2 is a super-ionic conductor similar to (NH4)3H(SeO4)2. Furthermore, in the phase transition at TI—II = 269 K, the slopes of dielectric constant and electrical conductivity show the same temperature dependence as (NH4)3H(SeO4)2 (Matsuo et al., 2001). These facts indicate that the room temperature Tl3H(SO4)2 phase is isostructural with the high-temperature R3 m symmetry M3H(XO4)2 crystals. Therefore, a starting model based on the isotypic Rb3H(SeO4)2 crystal in the space group R3 m of the super-ionic phase was used in the determination of the structure of the super-ionic phase of Tl3H(SO4)2.
In the M3H(XO4)2-type crystal, it is also known that the O2 atom which forms the hydrogen bond statistically occupies three equivalent positions with probability 1/3 in the super-ionic phase (Baranov et al., 1987; Merinov et al., 1990). We used a similarly disordered model here. Selected geometric parameters are given in Table 1. The crystal structure is shown in Fig. 1 and the fitted diffraction profile for Tl3H(SO4)2 is shown in Fig. 2.
The structure of Tl3H(SO4)2 consists of isolated SO4 tetrahedra with Tl atoms distributed between them. The unit-cell volume of Tl3H(SO4)2 is 674.65 (6) Å3. This is very small in comparison with the unit-cell volumes of 733.5 Å3 for Rb3H(SeO4)2 (Baranov et al., 1987) and 839.0 Å3 for Cs3H(SeO4)2 (Merinov et al., 1990) in the super-ionic phase. In the subsequent discussion, the crystal data for Rb3H(SeO4)2 and Cs3H(SeO4)2 are taken from Baranov et al. (1987) and Merinov et al. (1990), respectively.
The O2—O2 bond lengths, which are hydrogen-bond lengths, are 2.626 (6) Å in Tl3H(SO4)2. This is slightly shorter than in the Rb3H(SeO4)2 [2.67 (2) Å] and Cs3H(SeO4)2 [2.71 Å] crystals. The S—O1 and S—O2 bond lengths in Tl3H(SO4)2 are 1.644 (6) and 1.641 (8) Å, respectively; thus, the S—O2 distance is very similar to the S—O1 distance. In contrast, in isotypic M3H(SeO4)2 crystals, the Se—O2 distances [1.682 (9) Å for Rb3H(SeO4)2 and 1.70 (2) Å for Cs3H(SeO4)2] are considerably longer than the Se—O1 distances [1.617 (3) Å for (Rb3H(SeO4)2) and 1.662 (8) Å for Cs3H(SeO4)2]. Thus, in Tl3H(SO4)2, the distortion of the SO4 tetrahedra is less than that of the isotypic M3H(SeO4)2 crystals.
It is known that the super-ionic phase transition is accompanied by a ferroelastic phase transition from the low-temperature ferroelastic phase to the high-temperature paraelastic phase. That is, the distortion in the crystal is closely related to the super-ionic phase transition. Therefore, the changes of the crystal structure accompanied by filling the M sites with Tl, in conjunction with the lesser distortion of the SO4 tetrahedra in comparison with the distortion of the tetrahedra in the isotypic crystals, would be the primary causes of the super-ionic phase transition at lower temperatures.
In this work, the coordinates of the H atom could not be determined, because H atoms migrate rapidly in the crystal in the super-ionic phase (Matsuo, 2001).