Inorg. Chem. 2003, 42, 3036−3042
Na6TlSb4: Synthesis, Structure, and Bonding. An Electron-Rich Salt with a Chain Conformation and a Tl−Tl Bond Length Determined by the Cation Bin Li, Lisheng Chi, and John D. Corbett* Ames Laboratory-DOE1 and Department of Chemistry, Iowa State UniVersity, Ames, Iowa 50011 Received December 24, 2002
The title compound forms on fusion and annealing of a stoichiometric mixture of the elements. The structure was determined by single-crystal X-ray diffraction methods in the monoclinic space group C2/c, with a ) 15.154(3) Å, b ) 10.401(2) Å, c ) 17.413(4) Å, and β ) 113.57(3)°, Z ) 8. Four-membered Tl−Sb1−Sb4−Sb3 rings interlinked by pairs of Sb2 bridges generate swinglike repeat units [Tl2Sb8] that are further interlinked through external Tl−Tl bonds to form infinite one-dimensional chains. Cations play a major role in the structure. In contrast to the Zintlphase K6Tl2Sb3 with similar swinglike [Tl4Sb6] repeating units and Tl−Tl interlinkages, Na6TlSb4 has a more compact conformation of the chains and a notably smaller cell volume than expected. The new phase is metallic with two excess cations according to empirical electron counting, EHTB band calculations for the anion, and the compound’s measured resistivities and magnetic susceptibilities. The notably shorter Tl−Tl bond in the present salt (2.954 Å) can be directly attributed to the smaller cation and reduced intercation repulsions across that bond.
Introduction In recent years, a variety of ternary main group antimonides A-M-Sb (A ) alkali, alkaline-earth, or rare-earth metal; M ) triel or tetrel) have been reported.2 These constitute a subset to an even larger class of ternary maingroup pnictides in A-M-Pn systems (Pn ) P, As, Sb, Bi).3 Structures of the anionic frameworks among the former antimonides are generally low-dimensional and directly related to number, size, and charge of the cations and, in turn, to the atom proportions in the M-Sb anion and its valence electron count.2d,4-6 The useful Zintl-Klemm con* Author to whom correspondence should be addressed. E-mail: jdc@ ameslab.gov. (1) This research was supported by the Office of the Basic Energy Sciences, Materials Sciences Division, U.S. Department of Energy. Ames Laboratory is operated for DOE by Iowa State University under Contract W-7405-Eng-82. (2) (a) Ba7Ga4Sb9: Alemany, P.; Alvarez, S.; Hoffmann, R. Inorg. Chem. 1990, 29, 3070. (b) Na3InSb2: Cordier, G.; Ochmann, H. Z. Kristallogr. 1991, 195, 107. (c) Ca14AlSb11: Brock, S. L.; Weston, L. J.; Olmstead, M. M.; Kauzlarich, S. M. J. Solid State Chem. 1993, 107, 513. (d) SrSn3Sb4: Chow, D. T.; McDonald R.; Mar, A. Inorg. Chem. 1997, 36, 3750. (e) LaIn1-xSb2: Ferguson, M. J.; Ellenwood, R. E.; Mar, A. Inorg. Chem. 1999, 38, 4503. (f) EuSn3Sb4: Lam, R.; Zhang, J.; Mar, A. J. Solid State Chem. 2000, 150, 371. (g) BaGa2Sb2: Kim, S. J.; Kanatzidis, M. G. Inorg. Chem. 2001, 40, 3781. (3) Eisenmann, B.; Cordier, G. In Chemistry, Structure and Bonding of Zintl Phases and Ions; Kauzlarich, S. M., Ed.; VCH Publisher: New York, 1996; Chapter 3. (4) Cordier, G.; Scha¨fer, H.; Stelter, M. Z. Naturforsch. 1987, B42, 1268.
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cept accordingly work well for a large number of these ternary antimonides in accounting for the structure of the anionic framework, which may contain both strong M-M and Sb-Sb bonds.2g,7-9 On the other hand, this simple approximation in terms of classical (2-center-2-electron) bonding can sometimes fail, especially when there are highly charged cations, when there is a smaller difference in electronegativities, or if a delocalized bonding scheme is more appropriate. One must also consider the effect that formal nonbonding electron pairs have on increasing bond distances, for example, the two and one pairs on formal 2bSb- and 3b-Sb0, respectively. Here, we report the second compound exhibiting both Tl-Tl and Tl-Sb bonds with alkali metal cations, Na6TlSb4. The related Zintl-phase K6Tl2Sb310 contains one-dimensional anionic chains generated from a linkage of swinglike [Tl4Sb6] units [-Tl(Sb2)Sb2(Sb2)Tl-] by Tl-Tl bonds. Exploration for the isoelectronic Zintl(5) Cordier, G.; Ochmann, H.; Scha¨fer, H. ReV. Chim. Miner. 1984, 21, 282. (6) Cordier, G.; Ochmann, H. Z. Kristallogr. 1991, 197, 281 (Na2In2Sb3); 289 (K2Ga2Sb3); 291 (K2In2Sb3). (7) Cordier, G.; Ochmann, H.; Scha¨fer, H.; Stelter, M. Z. Anorg. Allg. Chem. 1984, 517, 118. (8) Cordier, G.; Scha¨fer, H.; Stelter, M. Z. Naturforsch. 1985, B40, 1100. (9) Cordier, G.; Ochmann, H.; Scha¨fer, H. Mater. Res. Bull. 1986, 21, 331. (10) Chi, L.; Corbett, J. D. Inorg. Chem. 2001, 40, 2705.
10.1021/ic020728b CCC: $25.00
© 2003 American Chemical Society Published on Web 04/05/2003
Na6TlSb4: Synthesis, Structure, and Bonding Table 1. Some Crystal and Structure Refinement Data for Na6TlSb4 fw space group, Z unit cell dimensionsa (Å, deg, Å3) a b c β V dcalcd (Mg/m3) µ (cm-1) final indices:b R1, wR2 [I > 2σ(I)] R1, wR2 (all data)
829.31 C2/c (No. 15), 8 15.154(3) 10.401(2) 17.413(4) 113.57(3) 2515.5(9) 4.380 213.96 0.039, 0.065 0.082, 0.073
a Refined from Guinier data with Si as internal standard, λ ) 1.540562 Å, 23 °C. b R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) ∑w(|Fo|2 - |Fc|2)2/ ∑w(Fo2)]1/2.
phase Na6Tl2Sb3 gave instead only the new Na6TlSb4 in the same space group but with appreciable changes in the conformation of similar chains and the electron count, magnetic susceptibility, and resistivity properties appropriate to a metallic salt. Experimental Section Synthesis. The samples were synthesized in niobium tubes from the elements (all from Alfa-Aesar): Na chunks (99.9%), Tl powder (99.999%), and Sb powder (99.95%). The general reaction techniques involving welded Nb containers within an evacuated silica jacket have been described elsewhere.11,12 Because some of the reagents and all of the products are very sensitive to air and moisture, all operations were performed in a N2- or He-filled glovebox with typical H2O levels at less than 0.1 ppm (vol). Powder patterns of products from exploratory Na-Tl-Sb reactions showed a new structure, and a single crystal of the compound was first obtained from the composition Na6Tl2Sb3 loaded so as to prepare an analogue of K6Tl2Sb3. In this, about 300 mg of the appropriate mixtures was first heated to 850 °C, held for 6 h, quenched, reheated to 450 °C, held for 166 h, and finally cooled at 3 °C/h to room temperature. A single-crystal X-ray diffraction study showed that the phase occurs in the same space group (C2/c) as does K6Tl2Sb3, but that the refined composition is Na6TlSb4 not Na6Tl2Sb3, and the unit cell orientation and the network are different. Once the stoichiometry had been so established, a single-phase sample of Na6Tl2Sb3 was obtained (judging from Guinier powder data) from a mixture with the refined stoichiometry and the same reaction conditions except for a longer annealing time, about 2 weeks. X-ray powder patterns for samples mounted between pieces of cellophane were collected with the aid of an Enraf-Nonius Guinier camera, Cu KR radiation (λ ) 1.540562 Å), and NIST silicon as an internal standard. Least-squares refinements of 27 lines indexed on the basis of the refined structural model resulted in the lattice constants given in Table 1. Structure Determination. A black, block-shaped crystal ca. 0.15 × 0.15 × 0.25 mm was mounted in a glass capillary inside the glovebox. The crystal was first checked by Laue photography for its singularity and then transferred to a Rigaku AFC6R automatic diffractometer for data collection, which took place at room temperature with monochromated Mo KR radiation. Provisional cell constants and an orientation matrix for data collection were determined by least-squares refinement of the setting angles of 25 centered reflections. The diffraction data were corrected for Lorentz (11) Corbett, J. D. Inorg. Synth. 1983, 22, 15. (12) Zhao, J. T.; Corbett, J. D. Inorg. Chem. 1995, 34, 378.
Table 2. Atomic Coordinates (×104) and Equivalent Isotropic Displacement Parameters (Å2 × 103) for Na6TlSb4
Tl1 Sb1 Sb2 Sb3 Sb4 Na1 Na2 Na3 Na4 Na5 Na6
x
y
z
U(eq)a
912(1) 964(1) 840(1) 2527(1) 1959(1) 3052(3) 2035(4) 1170(4) 3884(4) 9739(4) 9388(4)
3587(1) 6000(1) 1198(1) 3529(1) 9429(1) 1617(9) 8571(8) 946(9) 1195(9) 8579(8) 3662(9)
3254(1) 4231(1) 4180(1) 2669(1) 5823(1) 4453(4) 4031(4) 2406(4) 2652(4) 4176(4) 4113(4)
22(1) 18(1) 18(1) 19(1) 18(1) 29(2) 30(2) 28(2) 30(2) 28(2) 29(2)
a U(eq) is defined as one-third of the trace of the orthogonalized U ij tensor.
Table 3. Important Bond Lengths (Å) in Na6TlSb4 Tl1-Tl1 Tl1-Sb1 Tl1-Sb2 Tl1-Sb3
2.954(2) 3.015(2) 2.988(2) 3.005(1)
Sb1-Sb4 Sb2-Sb4 Sb3-Sb4
3.218(1) 3.250(2) 3.222(2)
and polarization effects and for absorption with the aid of three ψ-scans of reflections at different 2θ values. The diffraction analysis revealed that the crystal belonged to a C-centered monoclinic system, for which the systematic absences suggested possible space groups Cc (No. 9) or C2/c (No. 15). Intensity statistics gave a clear indication of the second centrosymmetric space group (〈E2 - 1〉 ) 1.012), and this gave satisfactory refinement results. Direct methods13 generated five positions, of which one was assigned to Tl and four to Sb atoms. Subsequent Fourier synthesis revealed six peaks that all were assigned to Na atoms according to the peak heights and approximate distances around each. Refinements, finally with anisotropic displacement parameters and a secondary extinction correction, converged at R1 ) 3.87%, wR2 ) 6.52% (I > 2σI). The largest residual peak and hole in the ∆F map were 2.28 and -1.77 e-Å-3 at distances of 0.53 and 0.74 Å from Sb4 and Tl, respectively. Some other details of the crystallographic and refinement parameters are given in Table 1. Table 2 contains the atomic positional and isotropic-equivalent displacement parameters, and Table 3 gives the important bond distances in the anion. The complete data collection, refinement, atomic displacement, and distance parameters are given in Supporting Information. Physical Properties. The resistivity of the phase was examined by the electrodeless “Q” method with the aid of a Hewlett-Packard 4342A Q meter.12 The method is particularly suitable for measurements on highly air-sensitive samples. For this purpose, 56 mg of a powdered sample with grain diameters between 150 and 250 µm was dispersed with chromatographic alumina and sealed under He in a Pyrex tube. Measurements were made at 34 MHz over the range 145-270 K. Magnetic susceptibility data were obtained from a 54.1-mg ground sample of the same product sealed under He in the container type described elsewhere.14 Magnetization data were obtained over the range 25-350 K on a Quantum Design MPMS SQUID magnetometer. EHTB Calculations. These were performed for the anion with the aid of the CAESAR program package developed by Whango and co-workers.15 The following atomic orbital energies and exponents were employed in the calculations (Hii ) orbital energy, (13) SHELXTL; Bruker AXS, Inc.: Madison, WI, 1997. (14) Sevov, S. C.; Corbett, J. D. Inorg. Chem. 1991, 30, 4875. (15) Ren, J.; Liang, W.; Whangbo, M.-H. CAESAR for Windows; PrimeColor Software, Inc., North Carolina State University: Raleigh, NC, 1998.
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Figure 1. ∼[010] view of the crystal structure in Na6TlSb4. The Tl, Sb, and Na atoms are colored black, green, and white, respectively, whereas the red dots represent intersections of the 2-fold axes along B b. (90% probability.)
eV; ξ ) Slater exponent): Tl 6s: -11.6, 2.32; 6p: -9.27, 1.6; Sb 5s: -18.8, 2.323; 5p: -11.7, 1.999. The Tl 6p energy utilized in the calculation was iterated to charge consistency against Sb16 to gain a value more suitable for this particular valence state.17 The result was more negative by 3.5 eV.
Results and Discussion Structure Description. The title compound Na6TlSb4 has a similar building block, Tl-Tl interconnections, space group, and Pearson symbol (mC88) as does K6Tl2Sb3,10 but Na6TlSb4 has a somewhat different conformation and orientation of the related infinite anionic chains along with two metallic electrons beyond simple valence rules. The basic anionic units in both salts, Tl2+xSb8-x, x ) 2 (K), 0 (Na), are interconnected into infinite (staggered) chains via isolated Tl-Tl bonds, as shown in Figure 1 for the new salt (Tl black, Sb green). Pairs of four-membered rings Tl-Sb1-Sb4-Sb3 (vs Tl1-Sb1-Tl2 -Sb3 with K10) slightly folded outward at Tl-Sb4 are interlinked by two Sb2 bridge atoms to generate an 8-ring and the swinglike repeat units (Tl2Sb8) shown in Figure 2a (vs [Tl4Sb6] before). The two anions are better compared when viewed along B b: Tl2Sb8 in Figure 2b relative to that of Tl4Sb6 in the potassium salt, Figure 2c. Two-fold axes along B b that bisect the Tl-Tl bonds are present in both structures, whereas a second 2-fold axis through the centers of the Tl4Sb6 units is replaced by a center of symmetry in the Tl2Sb8 units in the present case. The series of 2-folds that relate the centers of both the Tl4Sb6 units and Tl-Tl bonds in the K salt give a polar chain in the sense that Sb1 or Sb3 are always on the same side of the chain when viewed along B b (whereas adjoining chains along b c are reversed). On the other hand, the center of symmetry in each 8-ring means that these atoms reverse within the Tl2Sb8 units (16) Whangbo, J. H.; Li, J. CIBAND; North Carolina State University: Raleigh, NC, 1995. (17) Dong, Z.-C.; Corbett, J. D. J. Am. Chem. Soc. 1995, 117, 6447.
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Figure 2. (a) Swing-like repeat unit Tl2Sb8 in Na6TlSb4. There is a 2-fold axis out of the page that centers the Tl-Tl bonds at the extremes and an inversion center within each ring. (b) The anion chain in Na6TlSb4 as viewed along B b. (c) Chain repeat in anion in K6Tl2Sb3 viewed along B b. The presence of 2-fold axes centering both the Tl-Tl bonds and the 8-ring account for the differences from Na6TlSb4.
(compare Figure 2b,c). The individual Tl2Sb8 units in the sodium salt are seen to have the same general shape as they do in Tl4Sb6 but with a greater puckering between the connecting bonds. The chains in the latter stack alternately along B b, but the packing in both phases along b a and b c is complex. The Tl-Tl bond in Na6Tl2Sb8, 2.954(2) Å, is also notably (0.263(3) Å) shorter than that between Tl4Sb6 units in the K salt, 3.217(2) Å, a point to which we will return, whereas the Tl-Sb distances are fairly comparable in both, 2.99-3.25 Å. The occurrence of these two salts in the same C2/c space group may seem somewhat fortuitous. There is a sizable reapportionment of the monoclinic cell axes and angle in the process, from ∼10:17:20 Å (a:b:c) and 102° with potassium to ∼15:10:17 Å and 113° for sodium. Chains in the former lie parallel to b a whereas those with sodium lie parallel to the (101) body diagonal (Figure 1), whereby the ring symmetry changes from C2 to S2. The cations occupy different crystallographic positions in these two salts. In Na6TlSb4, there are six kinds of crystallographically independent sodium atoms, all in general positions, whereas there are seven independent potassium atoms in K6Tl2Sb3, two of which lie on the 2-fold axes. Cation Roles in the Structures. We believe that the differences in orientation of the anionic chains in the two salts arise directly from the change in countercations. There is also a disproportionate reduction in the cell volume in this change, from 3246 Å3 (K) to 2516 Å here. A classical but still useful way to compare these is in terms of the atom
Na6TlSb4: Synthesis, Structure, and Bonding
volumes deduced by Biltz.18 The expected “normal” cell volume difference per formula unit for the two can be approximated in terms of his values for K+ and Na+ plus Sb and Tl data taken from intermetallics, viz., V(K6Tl2Sb3) - V(Na6TlSb4) ) 6[V(K+) - V(Na+)]- + [V(Tl) - V(Sb)] ) 58.2 Å3 or 466 Å/cell (Z ) 8), which is only 64% of the observed difference, 730(1) Å3. The difference in the heavy atom volume term is very small, ∼10 Å3, and the alkali-metal cations provide the major effect. The change of the cations results in significantly different structures. The first difference is basic: Tl2 in the [Tl4Sb6] unit in K6Tl2Sb3 is substituted by Sb4 in the [Tl2Sb8] unit in Na6TlSb4, and this changes the charge type and basic electrical properties because of the presence of two additional electrons in the latter. The closely related, cation-poorer analogue Na4TlSb4 could not be obtained in any structure, suggesting again that packing in the present case is very important. The additional significant change in the ring conformation, Figure 2, and the accompanying large change in the Tl1-Tl1 bond length have already been noted. The result is a more compact structure than expected according to relative cation volumes. Modeling of the mechanics associated with these differences of phase stability and structure would appear to be a very difficult matter, but we can make some useful qualitative observations. Packing of the same number of smaller sodium cations about the chains is probably most important. We have noted elsewhere that the tight and specific alkali metal cation packing (coordination) about particularly several anionic polytrielide cluster and network structures is a major feature in determining stability and structure, and their differences can give rise to an array of diverse structures.19-21 A considerable discrimination among the polyanions is found in terms of cation size, that is, in the competitive positioning of mixed cations about the polyanions and also in affording compositions that are stable only with certain cation sizes. The smaller and higher field sodium cations naturally exhibit shorter distances to anion atoms and appear to have the greatest effects or to afford unique compositions. (We have not yet studied lithium examples.) The cation placements and distances about atoms in the anions appear particularly informative in the present cases. The Sb1, 2, and 3 atoms in both structures have eight cation neighbors, the Tl2 or Sb4 atoms only six (below), and the 4b-Tl atoms in the Tl-Tl bonds just three close A+ each (plus two more distant Na1), evidently because they are relatively protected. The most striking feature about the TlTl distances is that separate Na3 (or K5), Na4 (or K4), and Na6 (or K7) atoms make close contacts with each Tl1 atom in the bridge at 3.22 Å (×3) for Na, Figure 3a, vs 3.43 Å (18) Biltz, W. Raumchemie der festen Stoffe; Leopold Voss: Leipzig, Germany, 1934, pp 239, 241. (19) Corbett, J. D. Angew. Chem., Int. Ed. 2000, 39, 670. (20) Chi, L.; Corbett, J. D. Inorg. Chem. 2001, 40, 3596. (21) Li, B.; Corbett, J. D. Inorg. Chem. 2002, 41, 3944.
Figure 3. Cations, Tl, and Sb atoms within 4.0 Å of the center of the Tl-Tl bond in (a) Na6TlSb4 and (b) K6Tl2Sb3. Heavier and lighter lines mark the shorter and more distant cation-Tl contacts in each, respectively. (The exterior Tl-Na1 bond lengths are intermediate, 3.60 and 3.70 Å.)
(×2) and 3.65 Å (K7) with K, Figure 3b. Each of these is marked by heavier lines. Both distance sets are relatively short compared with A-Tl and A-Sb separations elsewhere in each structure. Each of the six cations about the Tl pairs actually forms a very asymmetric bridge across the Tl-Tl bond, with a second long contact (thin lines) to the other Tl at 3.9-4.0 Å for Na and 4.2-4.5 Å for K. Most importantly, these evidently attractive interactions also explain the dependence of Tl-Tl bond lengths on the cations because these are limited by a pair of comparatively short A‚‚‚A closed shell contacts that occur across the Tl-Tl bond for each A cation, averaging 3.53, 3.62, and 3.73 Å for Na‚‚‚ Na and 3.85, 3.87, and 3.95 Å for K‚‚‚K. These ranges approach the shortest single A‚‚‚A distances elsewhere in the structure, 3.45 and 3.80 Å, respectively. Thus, the large (0.26 Å) difference in the interconnecting Tl-Tl bond lengths is clearly governed by the six independent A‚‚‚A repulsions between cations that tightly solvate each Tl atom, a matrix effect. The second long A-Tl contacts across the Tl-Tl bond in both structures (thin lines) are similarly limited by A‚‚‚A cations riding on each other. For comparison, the average A-Sb distances is the two structures differ by a comparable 0.30 vs 0.36 Å for the difference in crystal radii of K+ vs Na+,22 a reasonable variance considering some A-Sb covalency is probably also present. The 2.954(2)Å Tl-Tl distance appears about as short as known for this type of compound in which it is fairly unencumbered by extraneous effects. The single-bond metal(22) Shannon, R. D. Acta Crystallogr. 1976, A32, 751.
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lic diameter of Tl is given as 2.96 and a covalent bond distance as 3.10 Å.24 Interestingly, a family of persilyl-Tl(II) dithallanes exhibit comparable distances: R2Tl-TlR2, d ) 2.935 Å (295 K) for R ) (Me3Si)3Si,25 2.966 Å for R′ ) (t-BuSi)3Si,26 etc. Similar distances, 2.85-2.94 Å, are found in R′4Tl3Cl and R′6Tl6Cl2 molecules that consist of Tl3Cl rings or condensed Tl6Cl2 polyhedra, respectively, each with several similar Tl-Tl bond lengths.27 Longer distances are found in simple 3-D solids, for example, in Sr5Tl3 (3.00 Å)28 and in NaTl (3.24 Å)29 (from a substantial matrix effect), whereas a wide range of distances, ∼3.06-3.44 Å, is found in many electron-deficient and unligated polyhedral thallium anions.16,19,30 The oxidation state dependence of these distances is not so clear. The hypersilyl dimers are Tl2+ in a polar sense but 3b-Tl0 in Zintl usage and electrondeficient, in contrast to 4b-Tl- in the present salts. However, both types with short distances occur with relatively strong electron-withdrawing groups, persilyl or Sb, in contrast to the electron pair repulsion effects on Tl(I) that are often cited in earlier studies with longer bonds.25 The only 3-bonded atoms in the two structures, Sb4 (Na) and Tl2 (K), both show some unusual cation dispositions that we can attribute to the presence of an apparent sterically active “lone pair”. These centers are pyramidal in their bonding to Sb, with average angles of 102.2° at Sb4 and 105.9° at Tl2. Both centers are also six-coordinate to cations, as opposed to eight about the other antimony atoms, even though they are relatively well-exposed. A survey of cation distances to other Sb atoms in the respective chains shows that dh(A-Sb) values elsewhere are 0.08 and 0.11 Å less than the average Na-Sb4 and K-Tl2 distances of 3.40 and 3.73 Å, respectively, despite the reduced coordination number. Figure 4a,b shows the nearest cations around Sb4 and Tl2, respectively, within a 4.0-Å radius. (The next nearest cations lie below in both figures.) As seen, the angular and distance correlations about each certainly support a lone-pair notion if the usual implication of a spatial gap in the coordination sphere is employed. The Sb4 coordination is irregular, with five Na+ at 3.30-3.44 Å lying fairly low and unsymmetrically and a sixth cation at 3.55 Å in the opposite direction, leaving quite an open “hole”. The effect around Tl2 is even more pronounced, with three close cations (3.58-3.72 Å) almost at the waist about Tl2, and three more distance ones (3.80-3.88 Å) above, leaving a clear open region. One more puzzle is the stoichiometry of the sodium salt in which the same chain, albeit with a slightly different (23) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell University Press: Ithaca, NY, 1960; p 403. (24) Emsley, J. The Elements, 3rd ed.; Clarendon Press: Cambridge, England, 1998; p 208. (25) Henkel, S.; Klinkhammer, K. W.; Schwarz, W. Angew. Chem., Int. Ed. Engl. 1994, 33, 681. (26) Wiberg, N.; Blank, T.; Amelunxen, K.; No¨th, H.; Schno¨ckel, H.; Baum, E.; Purath, A.; Fenske, D. Eur. J. Inorg. Chem., 2002, 341. (27) Wiberg, N.; Blank, T.; Lerner, H.-W.; Fenske, D.; Linti, G. Angew. Chem., Int. Ed. 2001, 40, 1232. (28) Bruzzone, G.; Franceschi, E.; Merlo, F. J. Less-Common Met. 1978, 60, 59. (29) Schmidt, P. C.; Baden, W.; Weiden, N.; Weiss, A. Phys. Status Solidi 1985, 92A, 205. (30) Dong, Z.-C.; Corbett, J. D. Inorg. Chem. 1996, 35, 1444.
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Figure 4. Cation contacts
