Well-ordered crystals of TaI5. The formation of the ternary iodide CsTaI6

Article abstract of DOI:10.1002/zaac.200700530

Well ordered single crystals of TaI₅ (orthorhombic, Pnma (no. 62), a = 1396.2(2), b = 2009.5(4), c = 660.7(1) pm, Z = 8, R₁ for 967 reflections with I₀2σ(I₀): 0.0381) were obtained from a reaction of the elements. The structure determination confirms Mueller's prediction of 1978. Single crystals of CsTaI₆ (monoclinic, C2/c (no. 15), a = 1362.3(2), b = 709.9(1), c = 1736.2(3) pm, β = 128.77(1)° , Z = 4, R₁ for 1140 reflections with I ₀2σ(I₀): 0.0378) were obtained by the oxidation of tantalum with CsI₃. Both crystal structures contain [TaI₆] octahedra which are edge-connected to Ta₂I₁₀ dimers in TaI₅ and isolated as [TaI₆]^- anions in the salt Cs[TaI₆] (CsWCl₆ type of structure).

Full text of DOI:10.1002/zaac.200700530

DOI: 10.1002/zaac.200700530
Well-Ordered Crystals of TaI5. The Formation of the Ternary Iodide CsTaI6
Katja Habermehla, Ingo Pantenburga, Peter Heldb, and Gerd Meyera,*
Köln, Institute für a Anorganische Chemie und b Kristallographie der Universität
Received November 26th, 2007.
Abstract. Well ordered single crystals of TaI5 (orthorhombic, Pnma
(no. 62), a ϭ 1396.2(2), b ϭ 2009.5(4), c ϭ 660.7(1) pm, Z ϭ 8, R1
for 967 reflections with I0>2σ(I0): 0.0381) were obtained from a
reaction of the elements. The structure determination confirms
Müller’s prediction of 1978. Single crystals of CsTaI6 (monoclinic,
C2/c (no. 15), a ϭ 1362.3(2), b ϭ 709.9(1), c ϭ 1736.2(3) pm, β ϭ
128.77(1)°, Z ϭ 4, R1 for 1140 reflections with I0>2σ(I0): 0.0378)
were obtained by the oxidation of tantalum with CsI3. Both crystal
structures contain [TaI6] octahedra which are edge-connected to
Ta2I10 dimers in TaI5 and isolated as [TaI6]Ϫ anions in the salt
Cs[TaI6] (CsWCl6 type of structure).
Keywords: Tantalum; Iodide; Crystal structure
This structure, as now determined from a well-ordered single crys-
tal of TaI5, was already predicted in 1978 by Müller [10], see Fig.
1 (bottom). It was confirmed in 1979 although from a crystal with
a one-dimensional disorder along [100] [2]. The sub-structure was
determined in the space group Ccmm with lattice constants of a ϭ
697 1, b ϭ 2007 1, c ϭ 661 1 pm. It was also predicted that the
true structure would have a doubled a axis and would have to be
described in space group Pnma [10, 2]. These lattice constants
would then be in accord with those reported by Rolsten in 1958
[11], a ϭ 665, b ϭ 1395, c ϭ 2010 pm (space group Pbnm), which
compare well with the lattice constants of our crystal, a ϭ
1396.2(2), b ϭ 2009.5(4), c ϭ 660.7(1) pm (space group Pnma).
Thus, starting with an ideal structure with space group
P63/m2/m2/c, the symmetry of the hexagonal closest packing, the
parallel orientation of the TaϪTa vectors leads via symmetry re-
duction of the 3- and 6-fold axes to an orthorhombic cell with a
feasible subgroup Cmcm (translationengleich, index 3). The loss of
half of the 16 symmetry elements of Cmcm generates the sub-group
Pmmn (klassengleich, index 2). Doubling of the unit cell creates
the sub-group Pnma (klassengleich, index 2). The respective
Bärnighausen family tree was already reported in Müller’s paper of
1978 [10].
The system tantalum/iodine contains Ϫ as one might have expected
Ϫ as the most oxidized compound tantalum pentaiodide, TaI5 [1].
The structure was previously determined from a one-dimensionally
disordered crystal [2]. It contains dimers of edge-connected
octahedra, Ta2I10. Ternary iodides ATaI6 (with A representing an
alkali-metal ion) have apparently not been investigated previously.
We have now obtained well ordered single crystals of TaI5 and of
the first ternary iodide of tantalum(V), CsTaI6 [3].
Results and Discussion
Dark brown single crystals of TaI5 were obtained from the elements
applying a 500Ϫ180 °C temperature gradient [4a], a procedure re-
ported with a slightly different temperature gradient in Brauer’s
handbook in 1962 [5]. The wall of a He-arc sealed tantalum tube
was oxidized with caesium triiodide, CsI3 at 390 °C whereby black
single crystals of CsTaI6 were obtained [4b].
The crystal structure of TaI5 [6] contains [TaI6] octahedra sharing
common edges to [I4/1TaI2/2TaI4/1] ϭ [Ta2I10] ϭ (TaI5)2 dimers,
Fig. 1. The octahedra are distorted subject to repulsive forces of
the high-charged tantalum atoms centering the octahedra with
d(TaϪTa) ϭ 445.9(1) pm. The distortion is represented by three
different sets of TaϪI distances, around 263 and 270 pm for the
terminal iodine atoms and 292 pm for the bridging iodine atoms in
the centrosymmetric [Ta2I10] dimers. These dimers are arranged as
Fig. 1 exhibits. An alternative description of the crystal structure
of TaI5 is that of a hexagonal closest packing of iodide spheres
with one fifth of the octahedral interstices occupied by TaV in a
way that the above-mentioned dimers occur.
The crystal structure of CsTaI6 [6] contains [TaI6]Ϫ octahedra (Fig.
2) with TaϪI distances between 274 and 276 pm with an average
of 274.8 pm, very close to the mean TaϪI distance in TaI5,
275.3 pm. These [TaI6]Ϫ octahedra are isolated from each other.
Csϩ ions are in a cuboctahedral environment (Fig. 2) with d(Cs-I)
ranging from 402 to 415 pm; the average distance CsϪI, 406.5 pm,
is larger than that observed in CsI (395.6 pm [12]), in accord with
an increase of the coordination number from 8 (CsI) to 12 (CsTaI6).
The crystal structure of CsTaI6 [6] (for atomic parameters see Tab.
1) is the same as observed for a large number of AIMVCl6 type
compounds with AI ϭ K, Tl, NH4, Rb, Cs and MV ϭ Nb, Ta, Sb
[13, 14]. It was first determined for CsWCl6 [15]. It may be under-
stood as a densest packing of, for the present example of CsTaI6,
Csϩ and IϪ spheres forming [CsI6] layers. These are stacked in the
fashion of a cubic-closest packing. One sixth of the octahedral
holes only produced by IϪ ions are occupied by Ta5ϩ ions, see
Fig. 2 and ref. [13].
* Prof. Dr. G. Meyer
Institut für Anorganische Chemie
Universität zu Köln
Greinstraße 6
D-50939 Köln
www.gerdmeyer.de
Z. Anorg. Allg. Chem. 2008, 634, 829Ϫ831
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
829

K. Habermehl, I. Pantenburg, P. Held, G. Meyer
Fig. 1 Top: The [Ta2I10] dimer in the crystal structure of TaI5.
Interatomic distances in pm and angles in degrees (with estimated
standard deviations in parentheses):
Fig. 2 Top: Details of the crystal structure of CsTaI6 in the neigh-
bourhood of the central Ta (left) and Cs atoms (right), respectively.
Interatomic distances in pm and angles in degrees (with estimated
standard deviations in parentheses):
Ta1ϪI7 ϭ 262.8(3), Ta1ϪI6 ϭ 264.3(3), Ta1ϪI5 ϭ 269.6(3), Ta1ϪI3 ϭ
270.7(3), Ta1ϪI2 ϭ 291.0(2), Ta1ϪI4 ϭ 293.1(2), I3ϪTa1ϪI5 ϭ 169.95(9),
I7ϪTa1ϪI4 ϭ 165.53(9), I6ϪTa1ϪI2 ϭ 169.53(9), I2ϪTa1ϪI7 ϭ 89.09(9),
I2ϪTa1ϪI4 ϭ 80.45(9), I2ϪTa1ϪI3 ϭ 86.66(9), I4ϪTa1ϪI5 ϭ 85.57(9),
I4ϪTa1ϪI6 ϭ 89.09(9), I4ϪTa1ϪI3 ϭ 85.53(9), I5ϪTa1ϪI2 ϭ 85.54(9),
I5ϪTa1ϪI6 ϭ 93.21(9), I5ϪTa1ϪI7 ϭ 93.21(9), I6ϪTa1ϪI7 ϭ 101.37(4),
I6ϪTaϪI3 ϭ 93.21(9), I7ϪTa1ϪI3 ϭ 92.98(9). Operator for generating
eqiuvalent atoms: (i) x, ϪyϪ1/2, z.
Ta1ϪI2 ϭ 273.89(8), 2x, Ta1ϪI1 ϭ 275.15(9), 2x, Ta1ϪI3 ϭ 275.45(9), 2x,
Cs1ϪI1 ϭ 401.9(1), 2x, Cs1ϪI3 ϭ 404.9(2), 2x, Cs1ϪI1 ϭ 405.3(1), 2x,
Cs1ϪI2 ϭ 406.1(1), 4x, Cs1ϪI3 ϭ 415.2(2), 2x, I2ϪTa1Ϫ I2 ϭ 180,
I2ϪTa1ϪI1 ϭ 90.47(3), I2ϪTa1Ϫ I1 ϭ 89.53(3), 2x, I2ϪTa1ϪI1 ϭ 90.47(3),
I1ϪTa1ϪI1
ϭ 180, I2ϪTa1ϪI3 ϭ 90.12(3), I2ϪTa1ϪI3 ϭ 89.88(3),
I1ϪTa1ϪI3 ϭ 90.20(3), 2x, I1ϪTa1ϪI3 ϭ 89.80(3), 2x, I2ϪTa1ϪI3 ϭ
89.88(3), I2ϪTa1ϪI3 ϭ 90.12(3), I3ϪTa1ϪI3 ϭ 180. Operators for genera-
ting equivalent atoms: (i) Ϫx, Ϫy, Ϫz, (ii) 1/2Ϫx, 1/2ϩy, 1/2Ϫz, (iii) Ϫ1/2ϩx,
1/2ϩy, z, (iv) Ϫx, y, 1/2Ϫz, (v) x, Ϫy, 1/2ϩz, (vi) Ϫx, 1ϩy, 1/2Ϫz, (vii) x, 1ϩy, z.
Middle: Perspective view of the crystal structure of TaI5 down
[001]. Bottom: The same view as above, taken from Müller [10].
Middle: Perspective view of the crystal structure of CsTaI6 exhibi-
ting the cuboctahedral environment of Csϩ and [TaI6]Ϫ octahedra.
Bottom: Second choice of the unit cell of CsTaI6 in the (010) plane.
The unit cell which was originally chosen for CsWCl6 (space group
C2/c) has a rather large β angle. For CsTaI6 the respective lattice
constants are:
Acknowledgements. This work was generously supported by the
State of Nordrhein-Westfalen and the Universität zu Köln.
a1 ϭ 1362.3(2), b1 ϭ 709.9(1), c1 ϭ 1736.2(3) pm, β1 ϭ 128.77(1)°.
A unit cell with the same volume may be chosen according to Fig.
2 (bottom) with lattice constants as follows, according to the trans-
formation matrix [Ϫ100, 0Ϫ10, 101]:
[1] R. E. McCarley, J. C. Boatman, Inorg. Chem. 1963, 2, 547.
[2] U. Müller, Acta Crystallogr. 1979, B35, 2502.
a2 ϭ a1, b2 ϭ b1, c2 ϭ 1381.2(2) pm, β2 ϭ 101.49(1)°.
830
www.zaac.wiley-vch.de
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 829Ϫ831

Well-Ordered Crystals of TaI5
[3] K. Habermehl, Diplomarbeit, Universität zu Köln, 2007.
[4] a) TaI5: 0.47 g of tantalum pieces and 2.5 g of iodine were
sealed in an evacuated Duran® glass ampoule of 15 cm length
under liquid-nitrogen cooling. The ampoule was put with its
ends in two furnaces which were put closely together. Both
furnaces were first heated to 500 °C for three days. Then a
temperature gradient of 500 °C (Ta) to about 180 °C (I2) was
applied for five days after which a dark crystalline substance
was secured in an argon-filled dry box.
Table 1 Atomic coordinates and equivalent temperature fac-
tor coefficients Ueq (10Ϫ4 pm2) for TaI5 and CsTaI6
Atom
x/a
y/b
z/c
Ueq
TaI5
Ta1
I2
I3
I4
I5
(8d)
(4c)
(8d)
(4c)
(8d)
(8d)
(8d)
Ϫ0.1252(1)
Ϫ0.0491(2)
0.0326(2)
Ϫ0.2058(2)
Ϫ0.2818(2)
Ϫ0.2096(2)
Ϫ0.0405(2)
Ϫ0.13905(3)
Ϫ1/4
0.5023(2)
Ϫ0.7353(3)
0.2666(3)
0.2703(4)
0.7379(2)
0.2508(2)
0.7539(2)
0.0217(2)
0.0227(8)
0.0314(6)
0.0235(7)
0.0312(6)
0.0309(8)
0.0332(9)
Ϫ0.1506(2)
Ϫ1/4
Ϫ0.1510(2)
Ϫ0.0553(2)
Ϫ0.0566(2)
b) CsTaI6: CsI3 was prepared as dark red crystals by slow
evaporation of a saturated solution of cesium iodide and
iodine in ethanol. 0.2 g of CsI3 (0.3 mmol), were filled under
dry-box conditions in a sealed tantalum tube which was then
jacketed by an evacuated Duran® glass ampoule. The ensem-
ble was heated to 390 °C for five days and then cooled slowly
to room temperature.
I6
I7
CsTaI6
1
Cs1
Ta1
I1
I2
I3
(4e)
(4a)
(8f)
(8f)
(8f)
0
0
0.3408(2)
0
0.1638(1)
Ϫ0.3171(1)
Ϫ0.1508(1)
/
4
0.0494(3)
0.0272(2)
0.0362(2)
0.0361(2)
0.0363(2)
0
0.2070(1)
0.1373(1)
Ϫ0.0700(1)
0.1695(1)
0.0356(1)
0.1054(1)
[5] G. Brauer, Handbuch der Präparativen Anorganischen Chemie,
Band II, S. 1152, F. Enke-Verlag, Stuttgart, 1962.
CsTaI6: 1075.26 g·molϪ1; diffractometer IPDS-I, Stoe, Darm-
stadt; Mo-Kα (graphite monochromator, λ ϭ 71.073 pm); T ϭ
293(2) K; 2θmax ϭ 56.3°; 150 images, 0° Յ ϕ Յ 300°; Δϕ ϭ
2°; indices: Ϫ17 Յ h Յ 17, Ϫ9 Յ k Յ 9, Ϫ22 Յ l Յ 22;
transmission (min, max) ϭ 0.0339, 0.0819; ρcalc ϭ 5.455 g
cmϪ3; 8865 reflection intensities measured of which 1436 were
symmetrically independent, Rint ϭ 0.0678, F(000) ϭ 1784, μ ϭ
25.225 mmϪ1. Monoclinic, C2/c (no. 15), a ϭ 1362.3(2), b ϭ
709.9(1), c ϭ 1736.2(3) pm, β ϭ 128.77(1)°, V ϭ 1309.2(4)
106 ·pm3, Z ϭ 4. R values: R1/wR2 for 1140 reflections with
[6] Suitable single crystals of both TaI5 and CsTaI6 were selected
under a microscope in a dry box and sealed in thin-walled
glass capillaries. The single crystals were transferred to a
single-crystal X-ray diffractometer (Stoe Image Plate Diffrac-
tion System, IPDS I) to collect a complete intensity data set
at ambient temperature. Structure solution and refinement was
performed with the programs SHELXS-97 (direct methods)
and SHELXL-97 [7], scattering factors were from Inter-
national Tables for X-ray Crystallogaphy [8]. Data corrections
were carried out for Lorentz and polarization factors
and absorption (numerical with the aid of the programs X-
RED and X-SHAPE [9]). Further details of the crystal struc-
ture determinations may be obtained from the Fach-
informationszentrum Karlsruhe, D-76344 Eggenstein-
Leopoldshafen, Germany (fax: (ϩ49)7247-808-666; e-mail:
crysdata@fizkarlsruhe.de), on quoting the depository numbers
ICSD-418486 (TaI5) and ICSD-418487 (CsTaI6), the authors
and the journal citation
I0>2σ(I0): 0.0378/0.0828 and for all data: 0.0527/0.876; Sall
ϭ
1.051; for atomic parameters see Table 1.
[7] G.M. Sheldrick, SHELXS-97, Program for Structure Analysis,
Universität Göttingen, Germany, 1998; SHELXL-97, Program
for Crystal Structure Refinement, Universität Göttingen, Ger-
many, 1997.
[8] A. J. C. Wilson (ed.), International Tables for Crystallography,
Vol. C, Kluwer Acad. Publ., Dordrecht, 1992.
[9] X-RED 1.22, Stoe Data Reduction Program (C), Stoe & Cie
GmbH, Darmstadt, 2001; X-Shape 1.06, Crystal Optimization
for Numerical Absorption Correction (C), STOE & Cie
GmbH, Darmstadt, 1999.
[10] U. Müller, Acta Crystallogr. 1978, A34, 256.
[11] R. F. Rolsten, J. Am. Chem. Soc. 1958, 80, 2952.
[12] A. Smakala, J. Kalnajs, Phys. Rev. 1955, 99, 1737.
[13] H.-Chr. Gaebell, G. Meyer, R. Hoppe, Z. Anorg. Allg. Chem.
1982, 493, 65.
TaI5: 815.45 g·molϪ1; diffractometer IPDS-I, Stoe, Darm-
stadt; Mo-Kα (graphite monochromator, λ ϭ 71.073 pm); T ϭ
293(2) K; 2θmax ϭ 56.3°; 100 images, 0° Յ ϕ Յ 200°; Δϕ ϭ
2°; indices: Ϫ17 Յ h Յ 18, Ϫ26 Յ k Յ 26, Ϫ8 Յ l Յ 7;
transmission (min, max) ϭ 0.0945, 0.1488; ρcalc ϭ 5.843 g
cmϪ3; 14219 reflection intensities measured of which 2226
were symmetrically independent, Rint ϭ 0.0935, F(000) ϭ
2704, μ ϭ 28.417 mmϪ1. Orthorhombic, Pnma (no. 62), a ϭ
1396.2(2), b ϭ 2009.5(4), c ϭ 660.7(1) pm, V ϭ 1853.8(5)
106 ·pm3, Z ϭ 8. R values: R1/wR2 for 967 reflections with
I0>2σ(I0): 0.0381/0.0841 and for all data: 0.1137/0.1011; Sall ϭ
0.793; for atomic parameters see Table 1.
[14] H. Henke, E. Buschmann, H. Bärnighausen, Acta Crystallogr.
1973, B29, 2622.
[15] W. Eichler, H.-J. Seifert, Z. Anorg. Allg. Chem. 1977, 431,
123.
Z. Anorg. Allg. Chem. 2008, 829Ϫ831
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
831