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Crystal structure of the quaternary compounds Li1.25Cd1.67In0.47Cl6 and Li0.21Mn1.71In0.79Cl6
Solid State Sciences 5 (2003) 827–832 www.elsevier.com/locate/ssscie
Crystal structure of the quaternary compounds Li1.25Cd1.67In0.47Cl6 and Li0.21Mn1.71In0.79Cl6 R. Nagel, Ch. Wickel, H.D. Lutz ∗ Universität Siegen, Anorganische Chemie I, 57068 Siegen, Germany Received 10 September 2002; received in revised form 16 January 2003; accepted 4 February 2003 Dedicated to Professor Bernt Krebs on the occasion of his 65th birthday
Abstract The quaternary chlorides “LiMInCl6 ” (M = Mg, Mn, Fe, Co, and Cd) reveal high lithium ion conductivity [Solid State Ionics 95 (1997) 173]. Single crystals of the cadmium and the manganese compounds are grown from melts of stoichiometric mixtures of the binary chlorides. The structures of the crystals were determined by X-ray single-crystal techniques. The obtained white Li1.25 Cd1.67 In0.47 Cl6 ¯ Z = 1, a = 379.2(1) and c = 1767.2(4) pm, R1 = 6.23%, crystals crystallize in a highly disordered CdCl2 -type structure (space group R 3m, 108 unique reflections (I > 2σI )). The octahedral metal ion 3a site of the structure is randomly occupied by Li+ , Cd2+ , and In3+ ions. An additional amount of Cd2+ ions is localized in the Van der Waals gap on the likewise octahedral interstitial 3b site. This CdCl2 -type structure obviously corresponds to the structure of the high-temperature polymorphs of the quaternary chlorides under discussion. The pale pink Li0.21 Mn1.71 In0.79 Cl6 crystals, the structure of which is obviously that of the room-temperature polymorphs of this series, crystallize in a filled AlCl3 -type, ordered CdCl2 superstructure (space group C2/m, Z = 2, a = 642.0(1), b = 1110.6(2), and c = 629.2(4) pm, β = 110.08(3)◦ , R1 = 3.83%, 423 unique reflections (I > 2σI )). Of the two metal ions sites the 2b site is occupied by the Li+ and In3+ ions, the 4g solely by Mn2+ ions. In the Van der Waals gap of this structure no electron density is observed. The distortion factors ρ and σ of CdCl2 type structures [J. Solid State Chem. 95 (1991) 176] are discussed with respect to occupation of interstitial sites in the Van der Waals gap. 2003 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.
1. Introduction Ternary lithium chlorides Li2 MCl4 (M = Mg, Mn and Cd) belong to the best lithium ion conductor known so far [1–4]. These compounds crystallize at ambient temperature in an inverse spinel-type structure with lithium ions on both the tetrahedral 8a and octahedral 16d sites and random distribution of the Li+ and M 2+ ions at the latter site. The electric conductivity of these compounds is in the range of 1 × 10−1 −1 cm−1 at 673 K [4]. It is increased in the case of lithium deficient compounds Li2−2x M1+x Cl4 [5] and of quaternary lithium chlorides Li2−x M1−x Mx Cl4 (M = Ga, In) [6]. In the course of our experiments of preparing materials with more increased ionic conductivity we obtained a serious of apparently stoichiometric quaternary compounds of the formula “LiMInCl6 ” with M = Mg, Mn, Fe, Co, and Cd [6]. Unexpectedly, the electric conductivities of the latter compounds are two orders of magnitude smaller than those * Corresponding author.
E-mail address: [email protected] (H.D. Lutz).
of the above-mentioned compounds with spinel-type structures [6,7]. We therefore assumed that these compounds do not crystallize in a spinel-type but in a layered structure. In addition, a phase transition at elevated temperatures was evidenced [6,7]. Unfortunately, we were not able to solve the crystal structure of these compounds because neither X-ray powder diffractograms could be indexed nor single crystals could be grown [7]. Very recent experiments, however, displayed that the quaternary lithium chlorides under investigation are not composed stoichiometricly according to the formula given above [8]. This is revealed by microprobe and ICP analyzes of small single-crystals. The crystal structures of the Li1.25Cd1.67 In0.47Cl6 and Li0.21Mn1.71In0.79Cl6 single crystals obtained are presented in this paper.
2. Experimental For preparation of the “LiMInCl6 ” single crystals (M = Mn, Cd) stoichiometric mixtures of the respective binary
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chlorides are fused in evacuated, closed silica glass ampoules and subsequently crystallized as follows. In the case of the cadmium compound, the samples were cooled down until 450 ◦ C in steps of 10◦ per day, annealed at that temperature for 11 months, and then quenched in ice water. The manganese compound was annealed at 300 ◦ C for 8 weeks. The composition of the obtained very small platelets was determined by using a Cam Scan (Cambridge, UK) CS44 SEM type microprobe in connection with both an EDAX (Cambridge, UK) DS-701 144-10 type EDX (energy dispersive) analyzer and a Microspec (Fremont, USA) WDX3PC type WDX (wave length dispersive) analyzer. Because of the very similar X-ray scattering factors of cadmium and indium the cadmium compound was additionally analyzed by solving a crystal with water and determining the Li, Cd, and In content with a Leeman Labs ICP-AES-type spectrograph. For details see [8]. The X-ray intensities were collected on a Stoe IPDS diffractometer with graphite-monochromatisized Mo Kα radiation. The crystal were scanned in the ϕ range from −1.0 to 360.5◦ with a ϕ increment of 1.5◦ . All reflections were corrected for Lorenz and polarization effects by using the program X-Red [9]. The structures were solved by direct methods and refined on the basis of the scattering factors of neutral atoms by using the program SHELXL97 [10].
3. Results The single crystals of the quaternary chlorides were obtained as very thin, white and pale pink platelets with 0.23 × 0.07× ∼ 0.01 mm3 and 0.2 × 0.1× ∼ 0.01 mm3 in size, respectively. The microprobe, ICP, and X-ray analyzes resulted in Li1.25Cd1.67 In0.47Cl6 and Li0.21 Mn1.71In0.79Cl6 as compositions of the crystals studied. 3.1. Li1.25 Cd1.67In0.47Cl6 The X-ray reflections of Li1.25 Cd1.67In0.47Cl6 were indexed in the hexagonal system with a = 379.2(1) pm and c = 1767.2(4) and Z = 1. The systematic extinctions evi¯ The structure was refined on the denced space group R 3m. basis of 108 unique reflections (I > 2σI ). The final R values R1 and wR2 are 6.50 and 13.39%, respectively. Further experimental data are given in Table 1, fractional atomic coordinates and anisotropic displacement parameters in Tables 2 and 3, selected distances and angles in Table 4. The refinement displayed a strongly disordered CdCl2 type structure (see Fig. 1). The Li+ , Cd2+ , and In3+ ions are randomly distributed on the fully occupied octahedral 3a site of the cubic eutactic arrangement of the chloride ions. The refinement shows significant additional electron density in the Van der Waals gap of the layer structure under discussion. This means that the likewise octahedral
Table 1 Crystallographic data and data of structure refinement of Li1.25 Cd1.67 In0.47 Cl6 and Li0.21 Mn1.71 In0.79 Cl6 Space group Z Lattice constants (pm, deg) Unit cell volume (pm3 ) Molar mass (in g mol−1 ) Calculated density (Mg m−3 ) Absorption coefficient (mm−1 ) F (000) Crystal size (mm3 ) Temperature T (K) Diffractometer Image plate distance (mm) ϕ-range (deg), ϕ (deg) 2θ range (deg) h k l ranges No. of reflections measured No. of unique reflections (I > 2σI ) Parameters refined R1 , wR2 (%) (I > 2σI ) R1 , wR2 (%) (all reflections) Goodness-of-fit (F 2 ) Extinction coefficient Residual electron density (e/106 pm3 ) a w = [σ 2 (F 2 ) + (0.0889P )2 ] with P = (F 2 + 2F 2 )/3. o o c b w = [σ 2 (F 2 ) + (0.0777P )2 ] with P = (F 2 + 2F 2 )/3. o o c
Li1.25 Cd1.67 In0.47 Cl6 ¯ (No. 166) R 3m 1 a = 379.2(1), c = 1767.2(4) 220.1(1) × 106 464.2 3.372 6.762 258 0.23 × 0.07× ∼ 0.01 293(2) STOE IPDS 50 −1.0–360.5, 1.5 6.92–60.74 −5 h 5, −5 k 5, −24 l 24 1563 108 9 6.23, 13.07a 6.50, 13.39a 1.326 0.33(7) +1.472, −1.326
Li0.21 Mn1.71 In0.79 Cl6 C2/m (No. 12) 2 a = 642.0(1), b = 1110.6(2), c = 629.2(1), β = 110.08(3) 421.4(1) × 106 397.7 3.135 6.467 367 0.2 × 0.1× ∼ 0.01 293(2) STOE IPDS 70 −1.0–360, 1.0 6.90–51.64 −7 h 7, −13 k 13, −7 l 7 2957 423 26 3.83, 10.75b 4.18, 10.99b 1.076 0.005(2) +1.564, −1.151
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Table 2 2 4 Fractional atomic coordinates, isotropic displacement parameters (in pm × 10 ) and occupations factors of Li1.25 Cd1.67 In0.47 Cl6 and Li0.21 Mn1.71 In0.79 Cl6 . Ueq is defined as Ueq = (1/3) i j Uij ai aj a ∗i a ∗j x
Atom
Site
Li1.25 Cd1.67 In0.47 Cl6 Cd(1) In Li Cd(2) Cl
3a 3a 3a 3b 6c
0 0 0 0 0
Li0.21 Mn1.71 In0.79 Cl6 In Mn Li Cl(1) Cl(2)
2b 4g 2b 4i 8f
0 0 0 0.2503(3) 0.2438(2)
y
z
Occ.
Ueq
0 0 0 0 0
0 0 0 0.5 0.2531(2)
0.426 0.157 0.417 0.131 1.0
0.037(1) 0.037(1) 0.037(1) 0.099(6) 0.047(1)
0.5 0.1665(1) 0.5 0 0.6643(1)
0 0 0 0.2368(3) 0.2374(3)
0.778 0.856 0.240 1.0 1.0
0.020(1) 0.018(1) 0.020(1) 0.021(1) 0.021(1)
Table 3 Anisotropic thermal displacement parametersa (in pm2 × 102 ) of Li1.25 Cd1.67 In0.47 Cl6 and Li0.21 Mn1.71 In0.79 Cl6 U11
U22
U33
Li1.25 Cd1.67 In0.47 Cl6 Cd(1) In Li Cd(2) Cl
2.8(1) 2.8(1) 2.8(1) 8.8(8) 4.2(1)
2.8(1) 2.8(1) 2.8(1) 8.8(8) 4.2(1)
5.6(1) 5.6(1) 5.6(1) 12(1) 5.7(2)
Li0.21 Mn1.71 In0.79 Cl6 In Mn Li Cl(1) Cl(2)
1.4(1) 1.3(1) 1.4(1) 1.5(1) 1.7(1)
1.2(1) 1.3(1) 1.2(1) 1.9(1) 1.5(1)
3.7(1) 2.9(1) 3.7(1) 3.2(1) 3.3(1)
U23 0 0 0 0 0 0 0 0 0 −0.2(1)
U13 0 0 0 0 0 1.2(1) 1.0(1) 1.2(1) 1.3(1) 1.0(1)
U12 1.4(1) 1.4(1) 1.4(1) 4.4(4) 2.1(1) 0 0 0 0 −0.3(1)
a U are defined according to T = exp[−2π 2 (h2 a ∗2 U + · · · + 2hka ∗ b∗ U + · · ·)]. ij 11 12
Table 4 Selected interatomic distances (in pm) and angles (in deg) of Li1.25 Cd1.67 In0.47 Cl6 (M = Li, Cd(1), In) and Li0.21 Mn1.71 In0.79 Cl6 (M = Li, In) Li1.25 Cd1.67 In0.47 Cl6 : 6 × M–Cl (3a site) 6 × Cd(2)–Cl (3b site) Cl–Cl
260.8(2) 267.0(2) 6 × 378.1(1) 3 × 360.5(3)a 3 × 371.5(3)b
6 × Cl(1)–M–Cl(1) 6 × Cl(1)–Cd(2)–Cl(1) 6 × Cl(1)–Cd(2)–Cl(1) 6 × Cl(1)–M–Cl(1) 3 × Cl(1)–M–Cl(1) 3 × Cl(1)–Cd(2)–Cl(1)
93.26(7) 90.50(7) 89.50(7) 86.74(7) 180.0 180.0
Li0.21 Mn1.71 In0.79 Cl6 : MCl6 octahedron (2b site): 4 × M–Cl(2) 2 × M–Cl(1)
253.1(1) 253.6(2)
2 × Cl(2)–M–Cl(2) 2 × Cl(2)–M–Cl(2) 4 × Cl(2)–M–Cl(1) 4 × Cl(2)–M–Cl(1)
87.75(6) 92.25(6) 87.66(5) 92.34(5)
MnCl6 octahedron (4g site): 2 × Mn–Cl(1) 2 × Mn–Cl(2) 2 × Mn–Cl(2) 2 × Cl(1)–Mn–Cl(2) 2 × Cl(2)–Mn–Cl(2) 2 × Cl(2)–Mn–Cl(2)
256.4(1) 257.1(1) 257.4(1) 93.08(5) 87.78(5) 93.02(5)
1 × Cl(1)–Mn–Cl(1) 2 × Cl(1)–Mn–Cl(2) 1 × Cl(2)–Mn–Cl(2) 2 × Cl(1)–Mn–Cl(2) 2 × Cl(1)–Mn–Cl(2) 1 × Cl(2)–Mn–Cl(2)
87.73(6) 93.13(5) 86.02(6) 86.12(5) 178.82(3) 178.90(4)
a Cl–Cl distance of the octahedron of the 3a site. b Cl–Cl distance of the octahedron of the 3b site.
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interstitial 3b site is also occupied by metal ions in some amounts. The coordinations of the two metal ions sites are shown in Fig. 2. Because of the relatively large distance of the 3b site to neighboring Cl− ions, viz. 267.0(2) pm, we assume that this position in the Van der Waals gap is mainly or solely occupied by cadmium ions. (The respective distances of Cd2+ , Li+ , and In3+ ions in the binary chlorides are 263.7 pm [11], 257.2 pm [12], and
252.6 pm [13].) Under this assumption about 13% of the 3b sites are occupied by Cd2+ ions. These ions, however, are either displaced from the center of the site, for example, towards adjacent Cl− ions or being relatively mobile. This is indicated from the relatively large thermal displacement parameters of > 9 × 10−2 pm2 (see Table 3) and concluded from the relatively large distance (see above). The M– Cl distance of the fully occupied 3a site is 260.8(2) pm. This is in agreement with the value of 259.8 pm, which is calculated from the M–Cl distances of the binary chlorides (see above) and the respective occupation factors, viz. 0.427 (Cd), 0.417 (Li), and 0.156 (In). The latter are derived from the composition of the crystal studied under consideration the amount of Cd on 3b sites. 3.2. Li0.21 Mn1.71In0.79Cl6
Fig. 1. Crystal structure of Li1.25 Cd1.67 In0.47 Cl6 ; shaded octahedra are due to the 3a site of the CdCl2 -type structure.
The X-ray data of Li0.21Mn1.71In0.79Cl6 were indexed in the monoclinic system with a = 642.0(1) pm, b = 1110.6(2) pm, c = 629.2(1) pm, and β = 110.08(3)◦ (Z = 2). From the systematic extinctions the space groups C2, Cm, and C2/m had to be considered but refinement in the centrosymmetric space group C2/m was possible without any complications. The final R values R1 and wR2 based on 423 unique reflections (I > 2σI ) are 3.83 and 10.75%, respectively. Further experimental data are given in Table 1, fractional atomic coordinates and anisotropic displacement parameters in Tables 2 and 3, selected distances and angles in Table 4. The refinement resulted in an deficient, ordered CdCl2 type superstructure, i.e., a filled AlCl3 -type structure of space group C2/m. Space group C2/m is a direct (trans¯ (CdCl2 -type lationengleich) subgroup of space group R 3m
Fig. 2. Coordination of the two metal ion sites 3a and 3b of Li1.25 Cd1.67 In0.47 Cl6 .
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Fig. 3. Coordination of the two metal ion sites 2b and 4g of Li0.21 Mn1.71 In0.79 Cl6 .
Waals gap, no electron density was observed in contrast to Li1.25Cd1.67 In0.48Cl6 .
4. Discussion
Fig. 4. Relation of the monoclinic and the pseudohexagonal unit cell of the AlCl3 -type structure.
structure). The unit-cell vectors of the pseudohexagonal cell of this structure are as ah = am , ch = 3cm cos(βm − 90) (see Fig. 4). In the monoclinic structure, the octahedral metal ion site of the aristo-type layered CdCl2 structure is occupied in an ordered manner by the Mn2+ ions at the 4g site, and the Li+ and In3+ ions randomly distributed at the 2b site. The coordination of the two octahedral MCl6 units is shown in Fig. 3. The position of the Li+ ions has been established considering both the M–Cl distances and the electron densities at the two metal ions sites. In the Van der
The monoclinic crystal structure of the Li0.21Mn1.71In0.79Cl6 crystal obviously represents the hitherto unknown structure of the low-temperature polymorphs of the LiM II InCl6 -type compounds prepared in 1995 [6,7]. The structure of the studied Li1.25Cd1.67In0.47Cl6 crystal resembles that of the high-temperature polymorph of “LiMnInCl6” [6]. Therefore the question arises whether the studied crystal has preserved the high-temperature structure on quenching to ambient temperature or the ordering of the metal ions in the C2/m space group structure could not be detected because of the very similar X-ray scattering factors of Cd2+ and In3+ . The partial occupation of the interstitial sites in the Van der Waals gap of Li1.25Cd1.67 In0.48Cl6 by additional cadmium ions is confirmed considering the distortion factors ρ and σ of the octahedra in CdCl2 -type structures (see Table 5). ρ means the ratio between the short and the long edge of the MCl6 octahedra, σ being the ratio between the free edge and the common edge of the edge connected octahedra [12]. In the case of Li1.25Cd1.67 In0.47Cl6 , both factors are increased compared with binary CdCl2 . This means that the MCl6 octahedra of Li1.25Cd1.67 In0.47Cl6 are flattened in c direction, which is caused by the positive
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Table 5 Distortion factors ρ and σ (see text) of some compounds with CdCl2 -type structure Compound NiCl2 CoCl2 FeCl2 MgCl2 CdCl2 Li1.25 Cd1.67 In0.47 Cl6
ρ
σ
Ref.
0.970 0.951 0.946 0.934 0.938 0.953
1.055 1.045 1.012 1.057 0.968 0.983
[14] [13] [15] [12] [12] This work
charge and bonding to adjacent Cl− ions of the Cd2+ ions in the Van der Waals gap. Acknowledgements The authors thank the Deutsche Forschungsgemeinschaft, contract number LU 140-27-3, and the Fonds der Chemischen Industrie for financial support.
References [1] R. Kanno, Y. Takeda, K. Tanaka, O. Yamamoto, J. Electrochem. Soc. 131 (1984) 469. [2] H.D. Lutz, P. Kuske, K. Wussow, Solid State Ionics 28–30 (1988) 1282. [3] A.R. West, Ber. Bunsen-Ges. Phys. Chem. 93 (1989) 1235. [4] H.D. Lutz, Nach. Chem. Tech. Lab. 43 (1995) 418. [5] Ch. Wickkel, Z. Zhang, H.D. Lutz, Z. Anorg. Allg. Chem. 620 (1994) 1537. [6] H.D. Lutz, H.-J. Steiner, Ch. Wickel, Solid State Ionics 95 (1997) 173. [7] Ch. Wickel, Doctoral Thesis, University of Siegen, Germany, 1995. [8] R. Nagel, Doctoral Thesis, University of Siegen, Germany, 2001. [9] X-Red, STOE&CIE, Darmstadt, 1997. [10] G.M. Sheldrick, SHELXL-97: Program for the Refinement of Crystal Structures, University of Göttingen, 1997. [11] H. Ott, Z. Phys. 24 (1923) 209. [12] D.E. Partin, M. O’Keeffe, J. Solid State Chem. 95 (1991) 176. [13] H.P. Beck, D. Wilhelm, Angew. Chem. 103 (1991) 897. [14] A. Ferrari, A. Braibanti, G. Bigliardi, Acta Crystallogr. 16 (1963) 846. [15] M.K. Wilkinson, J.W. Cable, E.O. Wollan, W.C. Koehler, Phys. Rev. 113 (1959) 497.
Crystal structure of the quaternary compounds Li1.25Cd1.67In0.47Cl6 and Li0.21Mn1.71In0.79Cl6 R. Nagel, Ch. Wickel, H.D. Lutz ∗ Universität Siegen, Anorganische Chemie I, 57068 Siegen, Germany Received 10 September 2002; received in revised form 16 January 2003; accepted 4 February 2003 Dedicated to Professor Bernt Krebs on the occasion of his 65th birthday
Abstract The quaternary chlorides “LiMInCl6 ” (M = Mg, Mn, Fe, Co, and Cd) reveal high lithium ion conductivity [Solid State Ionics 95 (1997) 173]. Single crystals of the cadmium and the manganese compounds are grown from melts of stoichiometric mixtures of the binary chlorides. The structures of the crystals were determined by X-ray single-crystal techniques. The obtained white Li1.25 Cd1.67 In0.47 Cl6 ¯ Z = 1, a = 379.2(1) and c = 1767.2(4) pm, R1 = 6.23%, crystals crystallize in a highly disordered CdCl2 -type structure (space group R 3m, 108 unique reflections (I > 2σI )). The octahedral metal ion 3a site of the structure is randomly occupied by Li+ , Cd2+ , and In3+ ions. An additional amount of Cd2+ ions is localized in the Van der Waals gap on the likewise octahedral interstitial 3b site. This CdCl2 -type structure obviously corresponds to the structure of the high-temperature polymorphs of the quaternary chlorides under discussion. The pale pink Li0.21 Mn1.71 In0.79 Cl6 crystals, the structure of which is obviously that of the room-temperature polymorphs of this series, crystallize in a filled AlCl3 -type, ordered CdCl2 superstructure (space group C2/m, Z = 2, a = 642.0(1), b = 1110.6(2), and c = 629.2(4) pm, β = 110.08(3)◦ , R1 = 3.83%, 423 unique reflections (I > 2σI )). Of the two metal ions sites the 2b site is occupied by the Li+ and In3+ ions, the 4g solely by Mn2+ ions. In the Van der Waals gap of this structure no electron density is observed. The distortion factors ρ and σ of CdCl2 type structures [J. Solid State Chem. 95 (1991) 176] are discussed with respect to occupation of interstitial sites in the Van der Waals gap. 2003 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.
1. Introduction Ternary lithium chlorides Li2 MCl4 (M = Mg, Mn and Cd) belong to the best lithium ion conductor known so far [1–4]. These compounds crystallize at ambient temperature in an inverse spinel-type structure with lithium ions on both the tetrahedral 8a and octahedral 16d sites and random distribution of the Li+ and M 2+ ions at the latter site. The electric conductivity of these compounds is in the range of 1 × 10−1 −1 cm−1 at 673 K [4]. It is increased in the case of lithium deficient compounds Li2−2x M1+x Cl4 [5] and of quaternary lithium chlorides Li2−x M1−x Mx Cl4 (M = Ga, In) [6]. In the course of our experiments of preparing materials with more increased ionic conductivity we obtained a serious of apparently stoichiometric quaternary compounds of the formula “LiMInCl6 ” with M = Mg, Mn, Fe, Co, and Cd [6]. Unexpectedly, the electric conductivities of the latter compounds are two orders of magnitude smaller than those * Corresponding author.
E-mail address: [email protected] (H.D. Lutz).
of the above-mentioned compounds with spinel-type structures [6,7]. We therefore assumed that these compounds do not crystallize in a spinel-type but in a layered structure. In addition, a phase transition at elevated temperatures was evidenced [6,7]. Unfortunately, we were not able to solve the crystal structure of these compounds because neither X-ray powder diffractograms could be indexed nor single crystals could be grown [7]. Very recent experiments, however, displayed that the quaternary lithium chlorides under investigation are not composed stoichiometricly according to the formula given above [8]. This is revealed by microprobe and ICP analyzes of small single-crystals. The crystal structures of the Li1.25Cd1.67 In0.47Cl6 and Li0.21Mn1.71In0.79Cl6 single crystals obtained are presented in this paper.
2. Experimental For preparation of the “LiMInCl6 ” single crystals (M = Mn, Cd) stoichiometric mixtures of the respective binary
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chlorides are fused in evacuated, closed silica glass ampoules and subsequently crystallized as follows. In the case of the cadmium compound, the samples were cooled down until 450 ◦ C in steps of 10◦ per day, annealed at that temperature for 11 months, and then quenched in ice water. The manganese compound was annealed at 300 ◦ C for 8 weeks. The composition of the obtained very small platelets was determined by using a Cam Scan (Cambridge, UK) CS44 SEM type microprobe in connection with both an EDAX (Cambridge, UK) DS-701 144-10 type EDX (energy dispersive) analyzer and a Microspec (Fremont, USA) WDX3PC type WDX (wave length dispersive) analyzer. Because of the very similar X-ray scattering factors of cadmium and indium the cadmium compound was additionally analyzed by solving a crystal with water and determining the Li, Cd, and In content with a Leeman Labs ICP-AES-type spectrograph. For details see [8]. The X-ray intensities were collected on a Stoe IPDS diffractometer with graphite-monochromatisized Mo Kα radiation. The crystal were scanned in the ϕ range from −1.0 to 360.5◦ with a ϕ increment of 1.5◦ . All reflections were corrected for Lorenz and polarization effects by using the program X-Red [9]. The structures were solved by direct methods and refined on the basis of the scattering factors of neutral atoms by using the program SHELXL97 [10].
3. Results The single crystals of the quaternary chlorides were obtained as very thin, white and pale pink platelets with 0.23 × 0.07× ∼ 0.01 mm3 and 0.2 × 0.1× ∼ 0.01 mm3 in size, respectively. The microprobe, ICP, and X-ray analyzes resulted in Li1.25Cd1.67 In0.47Cl6 and Li0.21 Mn1.71In0.79Cl6 as compositions of the crystals studied. 3.1. Li1.25 Cd1.67In0.47Cl6 The X-ray reflections of Li1.25 Cd1.67In0.47Cl6 were indexed in the hexagonal system with a = 379.2(1) pm and c = 1767.2(4) and Z = 1. The systematic extinctions evi¯ The structure was refined on the denced space group R 3m. basis of 108 unique reflections (I > 2σI ). The final R values R1 and wR2 are 6.50 and 13.39%, respectively. Further experimental data are given in Table 1, fractional atomic coordinates and anisotropic displacement parameters in Tables 2 and 3, selected distances and angles in Table 4. The refinement displayed a strongly disordered CdCl2 type structure (see Fig. 1). The Li+ , Cd2+ , and In3+ ions are randomly distributed on the fully occupied octahedral 3a site of the cubic eutactic arrangement of the chloride ions. The refinement shows significant additional electron density in the Van der Waals gap of the layer structure under discussion. This means that the likewise octahedral
Table 1 Crystallographic data and data of structure refinement of Li1.25 Cd1.67 In0.47 Cl6 and Li0.21 Mn1.71 In0.79 Cl6 Space group Z Lattice constants (pm, deg) Unit cell volume (pm3 ) Molar mass (in g mol−1 ) Calculated density (Mg m−3 ) Absorption coefficient (mm−1 ) F (000) Crystal size (mm3 ) Temperature T (K) Diffractometer Image plate distance (mm) ϕ-range (deg), ϕ (deg) 2θ range (deg) h k l ranges No. of reflections measured No. of unique reflections (I > 2σI ) Parameters refined R1 , wR2 (%) (I > 2σI ) R1 , wR2 (%) (all reflections) Goodness-of-fit (F 2 ) Extinction coefficient Residual electron density (e/106 pm3 ) a w = [σ 2 (F 2 ) + (0.0889P )2 ] with P = (F 2 + 2F 2 )/3. o o c b w = [σ 2 (F 2 ) + (0.0777P )2 ] with P = (F 2 + 2F 2 )/3. o o c
Li1.25 Cd1.67 In0.47 Cl6 ¯ (No. 166) R 3m 1 a = 379.2(1), c = 1767.2(4) 220.1(1) × 106 464.2 3.372 6.762 258 0.23 × 0.07× ∼ 0.01 293(2) STOE IPDS 50 −1.0–360.5, 1.5 6.92–60.74 −5 h 5, −5 k 5, −24 l 24 1563 108 9 6.23, 13.07a 6.50, 13.39a 1.326 0.33(7) +1.472, −1.326
Li0.21 Mn1.71 In0.79 Cl6 C2/m (No. 12) 2 a = 642.0(1), b = 1110.6(2), c = 629.2(1), β = 110.08(3) 421.4(1) × 106 397.7 3.135 6.467 367 0.2 × 0.1× ∼ 0.01 293(2) STOE IPDS 70 −1.0–360, 1.0 6.90–51.64 −7 h 7, −13 k 13, −7 l 7 2957 423 26 3.83, 10.75b 4.18, 10.99b 1.076 0.005(2) +1.564, −1.151
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Table 2 2 4 Fractional atomic coordinates, isotropic displacement parameters (in pm × 10 ) and occupations factors of Li1.25 Cd1.67 In0.47 Cl6 and Li0.21 Mn1.71 In0.79 Cl6 . Ueq is defined as Ueq = (1/3) i j Uij ai aj a ∗i a ∗j x
Atom
Site
Li1.25 Cd1.67 In0.47 Cl6 Cd(1) In Li Cd(2) Cl
3a 3a 3a 3b 6c
0 0 0 0 0
Li0.21 Mn1.71 In0.79 Cl6 In Mn Li Cl(1) Cl(2)
2b 4g 2b 4i 8f
0 0 0 0.2503(3) 0.2438(2)
y
z
Occ.
Ueq
0 0 0 0 0
0 0 0 0.5 0.2531(2)
0.426 0.157 0.417 0.131 1.0
0.037(1) 0.037(1) 0.037(1) 0.099(6) 0.047(1)
0.5 0.1665(1) 0.5 0 0.6643(1)
0 0 0 0.2368(3) 0.2374(3)
0.778 0.856 0.240 1.0 1.0
0.020(1) 0.018(1) 0.020(1) 0.021(1) 0.021(1)
Table 3 Anisotropic thermal displacement parametersa (in pm2 × 102 ) of Li1.25 Cd1.67 In0.47 Cl6 and Li0.21 Mn1.71 In0.79 Cl6 U11
U22
U33
Li1.25 Cd1.67 In0.47 Cl6 Cd(1) In Li Cd(2) Cl
2.8(1) 2.8(1) 2.8(1) 8.8(8) 4.2(1)
2.8(1) 2.8(1) 2.8(1) 8.8(8) 4.2(1)
5.6(1) 5.6(1) 5.6(1) 12(1) 5.7(2)
Li0.21 Mn1.71 In0.79 Cl6 In Mn Li Cl(1) Cl(2)
1.4(1) 1.3(1) 1.4(1) 1.5(1) 1.7(1)
1.2(1) 1.3(1) 1.2(1) 1.9(1) 1.5(1)
3.7(1) 2.9(1) 3.7(1) 3.2(1) 3.3(1)
U23 0 0 0 0 0 0 0 0 0 −0.2(1)
U13 0 0 0 0 0 1.2(1) 1.0(1) 1.2(1) 1.3(1) 1.0(1)
U12 1.4(1) 1.4(1) 1.4(1) 4.4(4) 2.1(1) 0 0 0 0 −0.3(1)
a U are defined according to T = exp[−2π 2 (h2 a ∗2 U + · · · + 2hka ∗ b∗ U + · · ·)]. ij 11 12
Table 4 Selected interatomic distances (in pm) and angles (in deg) of Li1.25 Cd1.67 In0.47 Cl6 (M = Li, Cd(1), In) and Li0.21 Mn1.71 In0.79 Cl6 (M = Li, In) Li1.25 Cd1.67 In0.47 Cl6 : 6 × M–Cl (3a site) 6 × Cd(2)–Cl (3b site) Cl–Cl
260.8(2) 267.0(2) 6 × 378.1(1) 3 × 360.5(3)a 3 × 371.5(3)b
6 × Cl(1)–M–Cl(1) 6 × Cl(1)–Cd(2)–Cl(1) 6 × Cl(1)–Cd(2)–Cl(1) 6 × Cl(1)–M–Cl(1) 3 × Cl(1)–M–Cl(1) 3 × Cl(1)–Cd(2)–Cl(1)
93.26(7) 90.50(7) 89.50(7) 86.74(7) 180.0 180.0
Li0.21 Mn1.71 In0.79 Cl6 : MCl6 octahedron (2b site): 4 × M–Cl(2) 2 × M–Cl(1)
253.1(1) 253.6(2)
2 × Cl(2)–M–Cl(2) 2 × Cl(2)–M–Cl(2) 4 × Cl(2)–M–Cl(1) 4 × Cl(2)–M–Cl(1)
87.75(6) 92.25(6) 87.66(5) 92.34(5)
MnCl6 octahedron (4g site): 2 × Mn–Cl(1) 2 × Mn–Cl(2) 2 × Mn–Cl(2) 2 × Cl(1)–Mn–Cl(2) 2 × Cl(2)–Mn–Cl(2) 2 × Cl(2)–Mn–Cl(2)
256.4(1) 257.1(1) 257.4(1) 93.08(5) 87.78(5) 93.02(5)
1 × Cl(1)–Mn–Cl(1) 2 × Cl(1)–Mn–Cl(2) 1 × Cl(2)–Mn–Cl(2) 2 × Cl(1)–Mn–Cl(2) 2 × Cl(1)–Mn–Cl(2) 1 × Cl(2)–Mn–Cl(2)
87.73(6) 93.13(5) 86.02(6) 86.12(5) 178.82(3) 178.90(4)
a Cl–Cl distance of the octahedron of the 3a site. b Cl–Cl distance of the octahedron of the 3b site.
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interstitial 3b site is also occupied by metal ions in some amounts. The coordinations of the two metal ions sites are shown in Fig. 2. Because of the relatively large distance of the 3b site to neighboring Cl− ions, viz. 267.0(2) pm, we assume that this position in the Van der Waals gap is mainly or solely occupied by cadmium ions. (The respective distances of Cd2+ , Li+ , and In3+ ions in the binary chlorides are 263.7 pm [11], 257.2 pm [12], and
252.6 pm [13].) Under this assumption about 13% of the 3b sites are occupied by Cd2+ ions. These ions, however, are either displaced from the center of the site, for example, towards adjacent Cl− ions or being relatively mobile. This is indicated from the relatively large thermal displacement parameters of > 9 × 10−2 pm2 (see Table 3) and concluded from the relatively large distance (see above). The M– Cl distance of the fully occupied 3a site is 260.8(2) pm. This is in agreement with the value of 259.8 pm, which is calculated from the M–Cl distances of the binary chlorides (see above) and the respective occupation factors, viz. 0.427 (Cd), 0.417 (Li), and 0.156 (In). The latter are derived from the composition of the crystal studied under consideration the amount of Cd on 3b sites. 3.2. Li0.21 Mn1.71In0.79Cl6
Fig. 1. Crystal structure of Li1.25 Cd1.67 In0.47 Cl6 ; shaded octahedra are due to the 3a site of the CdCl2 -type structure.
The X-ray data of Li0.21Mn1.71In0.79Cl6 were indexed in the monoclinic system with a = 642.0(1) pm, b = 1110.6(2) pm, c = 629.2(1) pm, and β = 110.08(3)◦ (Z = 2). From the systematic extinctions the space groups C2, Cm, and C2/m had to be considered but refinement in the centrosymmetric space group C2/m was possible without any complications. The final R values R1 and wR2 based on 423 unique reflections (I > 2σI ) are 3.83 and 10.75%, respectively. Further experimental data are given in Table 1, fractional atomic coordinates and anisotropic displacement parameters in Tables 2 and 3, selected distances and angles in Table 4. The refinement resulted in an deficient, ordered CdCl2 type superstructure, i.e., a filled AlCl3 -type structure of space group C2/m. Space group C2/m is a direct (trans¯ (CdCl2 -type lationengleich) subgroup of space group R 3m
Fig. 2. Coordination of the two metal ion sites 3a and 3b of Li1.25 Cd1.67 In0.47 Cl6 .
R. Nagel et al. / Solid State Sciences 5 (2003) 827–832
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Fig. 3. Coordination of the two metal ion sites 2b and 4g of Li0.21 Mn1.71 In0.79 Cl6 .
Waals gap, no electron density was observed in contrast to Li1.25Cd1.67 In0.48Cl6 .
4. Discussion
Fig. 4. Relation of the monoclinic and the pseudohexagonal unit cell of the AlCl3 -type structure.
structure). The unit-cell vectors of the pseudohexagonal cell of this structure are as ah = am , ch = 3cm cos(βm − 90) (see Fig. 4). In the monoclinic structure, the octahedral metal ion site of the aristo-type layered CdCl2 structure is occupied in an ordered manner by the Mn2+ ions at the 4g site, and the Li+ and In3+ ions randomly distributed at the 2b site. The coordination of the two octahedral MCl6 units is shown in Fig. 3. The position of the Li+ ions has been established considering both the M–Cl distances and the electron densities at the two metal ions sites. In the Van der
The monoclinic crystal structure of the Li0.21Mn1.71In0.79Cl6 crystal obviously represents the hitherto unknown structure of the low-temperature polymorphs of the LiM II InCl6 -type compounds prepared in 1995 [6,7]. The structure of the studied Li1.25Cd1.67In0.47Cl6 crystal resembles that of the high-temperature polymorph of “LiMnInCl6” [6]. Therefore the question arises whether the studied crystal has preserved the high-temperature structure on quenching to ambient temperature or the ordering of the metal ions in the C2/m space group structure could not be detected because of the very similar X-ray scattering factors of Cd2+ and In3+ . The partial occupation of the interstitial sites in the Van der Waals gap of Li1.25Cd1.67 In0.48Cl6 by additional cadmium ions is confirmed considering the distortion factors ρ and σ of the octahedra in CdCl2 -type structures (see Table 5). ρ means the ratio between the short and the long edge of the MCl6 octahedra, σ being the ratio between the free edge and the common edge of the edge connected octahedra [12]. In the case of Li1.25Cd1.67 In0.47Cl6 , both factors are increased compared with binary CdCl2 . This means that the MCl6 octahedra of Li1.25Cd1.67 In0.47Cl6 are flattened in c direction, which is caused by the positive
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Table 5 Distortion factors ρ and σ (see text) of some compounds with CdCl2 -type structure Compound NiCl2 CoCl2 FeCl2 MgCl2 CdCl2 Li1.25 Cd1.67 In0.47 Cl6
ρ
σ
Ref.
0.970 0.951 0.946 0.934 0.938 0.953
1.055 1.045 1.012 1.057 0.968 0.983
[14] [13] [15] [12] [12] This work
charge and bonding to adjacent Cl− ions of the Cd2+ ions in the Van der Waals gap. Acknowledgements The authors thank the Deutsche Forschungsgemeinschaft, contract number LU 140-27-3, and the Fonds der Chemischen Industrie for financial support.
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