Thermal Iodine Loss Cascade of W5I16 - ACS Publications - American

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Cite This: Inorg. Chem. 2017, 56, 14300-14305

Thermal Iodine Loss Cascade of W5I16 Markus Ströbele and Hans-Jürgen Meyer* Institute of Inorganic Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany

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ABSTRACT: Tungsten iodide compounds feature a surprising diversity of binary compounds. Their formation conditions and phase equilibria depend very much on the surrounding iodine partial pressure and temperature. Herein we focus on squarepyramidal tungsten iodide cluster compounds with their iodine loss, structural rearrangements, cross-linking behavior, and final transformation into the octahedral cluster compound β-W6I12 at elevated temperatures. Reactions depart from W5I16 at different iodine pressures and temperatures. The thermal decomposition of W5I16 at low iodine pressure passes through a number of cluster compounds (W5I15, W5I13·xI2, β-W5I12, and W5I11) under release of iodine. At higher iodine pressures, only one intermediate compound (α-W5I12) was found. Thermal decomposition of W5I16 was examined by differential thermal/thermogravimetric analysis, differential scanning calorimetry, and X-ray diffraction (XRD) measurements. New compounds (W5I15, W5I13·xI2, and W5I11) were structurally characterized by means of XRD techniques. The crystal structure of W5I11 reveals a nice relationship to its transformation product W6I12.

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a silica tube (l ≈ 4 cm; V ≈ 1.7 cm3) and flame-sealed under vacuum while cooled with liquid nitrogen. The tube was heated at 275 °C for 100 h, with a heating and cooling rate of 2 °C/min. The ampule was opened in a glovebox under argon. The sintered black solid was ground in an agate mortar, and the powder was transferred in a Schlenk vessel with two gas inlets. Afterward, the side product I2 was removed by heating the mixture in a water bath under flowing argon (95 °C). W5I16 was obtained as a single-phase product and was stable in air according to the powder XRD (PXRD) pattern. W5I15 was prepared by thermal decomposition of the cluster compound W5I16. Approximately 150 mg (0.05 mml) of W5I16 was flame-sealed in a silica tube (l ≈ 7 cm; V ≈ 3 cm3) and treated in a temperature gradient 210 to 25 °C for 24 h (heating rate 2 °C/min; cooling rate 0.5 °C/min). The excess of I2 appeared in the room temperature region of the tube and was manually removed from the otherwise X-ray-pure W5I15. W5I15 was obtained as a single-phase product and was stable in air, according to the PXRD pattern. Yield: 95%. W5I15 can be dissolved in acetone, ethanol, and methanol but does not dissolve in water. W5I13·xI2 was prepared by thermal decomposition of the cluster compound W5I16. Approximately 150 mg (0.05 mml) of W5I16 was sealed in a silica tube (l ≈ 7 cm; V ≈ 3 cm3) and treated in a temperature gradient 232 to 25 °C for 1 h (heating and cooling rate 2 °C/min). The excess of I2 appeared in the room temperature region of the tube and was manually removed. α-W5I12 was prepared by thermal decomposition of the cluster compound W5I16. Approximately 200 mg (0.07 mmol) of W5I16 was sealed in a silica tube (l ≈ 4 cm; V ≈ 1.5 cm3) and treated in a temperature gradient 325 to 25 °C for 1 h (heating and cooling rate 2 °C/min). The excess of I2 appeared in the room temperature region of the tube and was manually removed. The black powder was stable in air according to the PXRD pattern. Yield: 95%.

INTRODUCTION Among binary molybdenum and tungsten halide compounds, octahedral metal clusters with the [M6X8] (M = Mo, W) core are most frequently obtained for X = Cl,1,2 Br,3,4 and I.5−7 Studies on other clusters were reported for a number of binary tungsten iodide compounds comprising [W3I6],8,9 [W4I7],7,10 [W5I8],7,12,13 and [W6I8]7,11 cluster cores. For binary tungsten iodides with the [W5I8] core, only three binary compounds, W5I167 with the connectivity [W5I8]I3a(I3)2/2a‑a·I2] (i = innen or inner and a = außen or outer), W15I4712 with the connectivity [(W5I8i)Ia(I3)2a(I3)2/2a−a][(W5I8i)I2a(I3)3/2a−a]2, and α-W5I1213 with the connectivity [(W5I8i)I3aI2/2a‑a], are reported. A few complex compounds like (C12H28N)[W5I13], (C12H28N)[W5I13]·THF, and (C12H28N)2[W5I13]7 were also published. Because of a new halide exchange route, using WCl6 and SiI4 as starting materials, trigonal tungsten iodide clusters with the [W3I6] core, such as the compound W3I12, can be prepared on a large scale.8 The thermal transformation of W3I12, is the gateway to a plethora of tungsten iodides. Departing from this compound, we aim to get a better and more complete understanding on existing compounds and phase relationships in the W−I system because thermal transformations of this compound revealed the successive formation of tetra-, penta-, and hexanuclear clusters.8 Moreover, several yet undiscovered binary tungsten iodide cluster compounds are quite likely to exist in this system. In this work, we investigate the W−I system with respect to existing phase relationships and new square-pyramidal tungsten clusters that appear during the thermal treatment of W5I16.

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EXPERIMENTAL SECTION Received: September 21, 2017 Published: November 9, 2017

W5I16 was prepared by the thermal conversion of the cluster compound W3I12. A total of 4 g of W3I12 (≈2 mmol) was filled into © 2017 American Chemical Society

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β-W5I12 was prepared by thermal decomposition of the cluster compound W5I16. A total of 150 mg (0.05 mml) of W5I16 was sealed in a silica tube (l ≈ 7 cm; V ≈ 3 cm3) and treated in a temperature gradient 425 to 25 °C for 1 h (heating and cooling rate 2 °C/min.). The excess of I2 appeared in the room temperature region of the tube and was manually removed. The black powder was stable in air according to the PXRD pattern. Yield: 95%. W5I11 was prepared by the thermal decomposition of the cluster compound W5I16. Approximately 150 mg (0.05 mml) of W5I16 was sealed in a silica tube (l ≈ 7 cm; V ≈ 3 cm3) and treated in a temperature gradient 525 to 25 °C for 1 h (heating rate 2 °C/min; cooling rate 0.5 °C/min). The excess of I2 appeared in the room temperature region of the tube. Yield: ≈5% black single crystals; ≈90% W5I11 powder; side phase β-W5I12; stable in air. X-ray Crystallography. All reaction products were investigated by PXRD using a StadiP diffractometer (Stoe, Darmstadt, Germany) with Ge-monochromated Cu Kα1 radiation and a Mythen1 detector. The structure solution of W5I15 was accomplished by using the crystallographic data of W5I16 as starting values, followed by a full Rietveld refinement (see Table S2 and Figure S2). Black single crystals of W5I14.12(2), W5I14.04(1), and W5I11 were measured with a single-crystal X-ray diffractometer (STOE-IPDS IIT) at room temperature (T = 293 K) using Mo Kα radiation (λ = 0.71073 Å). Crystal structure refinements and solutions were performed with direct methods (SHELXS) and least-squares refinements on F2 (SHELXL).14 Some results and the final R values are shown in Table S2 for W5I15, Table S3 for W5I14.12(2), Table S4 for W5I14.04(1), and Table S5 for W5I11. Differential Scanning Calorimetry (DSC) Measurements. Samples were enclosed in gold-plated (5 μm) steel autoclaves (volume 100 μL; BFT 94; Bächler Feintech AG, Hölstein, Switzerland) under a dry argon atmosphere (glovebox). Samples were heated and cooled at a rate of 2 °C/min in a differential scanning calorimeter (DSC 204 F1 Phoenix; Fa. Netzsch, Selb, Germany). Monitored thermal effects were assigned by PXRD patterns from separately prepared samples. Measurements could only be done up to 450 °C to avoid the reaction of elemental iodine with the gold plating and hereafter with the steel container. The DSC system was calibrated using the sensitivity and temperature calibration software Fa. Netzsch version 6.1.0 (11.02.2014). As calibration substances, elementary gallium (ABCR; 99.9999%), KNO3 (Riedel-de-Haen; 99.9%), RbNO3 (Aldrich; 99.7%), KClO4 (Sigma-Aldrich; ≥99%), and CsCl (Merck; 99.5%) were used. Measured was the energy of the transformation reaction or phase transition. Differential Thermal Analysis/Thermogravimetric Analysis (DTA/TGA) Measurements. Samples were filled into homemade SiO2 containers with a small (⌀ 3 mm) opening on top of the container (Figure S1) and heated and cooled with a rate of 2 °C/min with an argon flow of 60 mL/min in a differential thermal analysis system (STA 449F3 Jupiter; Fa. Netzsch, Selb, Germany). Monitored thermal effects were assigned by PXRD patterns from separately prepared samples. Elemental Analysis (EA). Samples were filled in commercially purchased sintered Al2O3 containers (volume 0.3 mL; 99.7% Al2O3; Fa. Netzsch, Selb, Germany) and heated and cooled with a rate of 2 °C/min in a flow mixture of argon (120 mL/min) and oxygen (60 mL/min) up to 1050 °C in a differential thermal analysis system (STA449F3 Jupiter; Fa. Netzsch, Selb, Germany). The amount of tungsten in the sample was calculated from the resulting mass of X-ray-pure WO3. The amount of iodine resulted from the weight difference of the starting material and the calculated weight of elemental tungsten in the sample. EA of β-W5I12: W5I12.04, and W5I11.93. Ampule Pressure. To estimate the iodine pressure in the sealed silica tubes, the general gas equation pV = nRT was used. The used parameters and the results are listed in Table S6.

Article

RESULTS AND DISCUSSION

The iodine-rich cluster compound W5I16 used as the starting material in our studies was prepared by thermal conversion of W3I12 at 275 °C for 100 h in a fused silica ampule. Thermal transformations of W5I16 were unknown until now; only the direct synthesis of α-W5I12 by decomposition of W5I16 was published in 2016.13 Intermediate stages or compounds of the thermal transformation of W5I16 were studied by DTA/TGA and DSC measurements, whose thermal effects are supposed to show certain reaction stages. For the synthesis and identification of intermediate compounds, we performed separate preparations under given conditions in silica tubing. Crystalline powders were structurally characterized by XRD techniques. Because thermal transformation reactions of tungsten iodides depend very much on the surrounding iodine pressure, which is generated by the release of iodine, we explored the impact of lower and higher iodine partial pressure conditions. Decomposition at Lower Iodine Pressure. DTA/TGA measurements of W5I16 were performed in homemade silica containers, revealing five distinguishable steps of transformation reactions, shown in Figure 1. The fact that our silica containers are equipped with a small opening ensures low iodine pressure conditions during reactions (Figure S1).

Figure 1. DTA/TGA measurement of W5I16 (113 mg) in a homemade silica container with a small opening, ensuring low iodine pressure. The formation of W5I13·xI2 was not detected in the DTA/TGA measurement but only in separate reactions.

The first stage of iodine loss (onset at 235 °C; maximum at 270 °C) corresponds to a mass loss of 4.3% in combination with a slight endothermic effect. This mass loss is in good agreement with the loss of 1/2 I2 (calculated mass loss of 4.3%) per formula unit, corresponding to the composition W5I15. The second step of iodine loss, also in combination with an endothermic effect (onset at 295 °C, maximum at 320 °C), corresponds to a mass loss of 16.7% relative to the starting mass. This mass loss is in good agreement with the loss of 2 I2 per formula unit (calculated mass loss for 2 I2: 16.5%), resulting in a composition equal to W5I12. The third step of iodine loss (onset at 545 °C; maximum at 555 °C) displays a mass loss of 21.7% relative to the starting mass, in combination with a strong endothermic effect. This mass loss is in agreement with the loss of 2.5 I2 per formula unit (calculated mass loss for 2.5 I2: 21.5%), resulting in the composition W5I11. 14301

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Figure 2. Superposition of recorded XRD patterns of crystalline powders obtained from W5I16 decomposition reactions under lower I2 pressure, at various temperatures.

The fourth step of iodine loss (onset at 600 °C; maximum at 610 °C) displays a mass loss of 26% relative to the starting mass, also in combination with a strong endothermic effect. This mass loss is in agreement with the thermal transformation of W5I16 into W6I12, with a calculated mass loss of 25.8%. The fifth, and last step, with a mass loss of 69% relative to the starting mass, is the result of the decomposition of W6I12 into elementary tungsten and elementary iodine (calculated mass loss: 68.8%) at temperatures higher than 850 °C and displays a strong and sharp endothermic signal. A PXRD pattern recorded of the resulting gray powder confirmed the powder to be X-raypure elemental tungsten. The same decomposition process of W5I16 was investigated by means of XRD measurements, based on products of separate reactions in fused silica tubes. For these reactions, approximately 150 mg (0.05 mml) of W5I16 was fused into silica tubing (l ≈ 7 cm; V ≈ 3 cm3) and heated at certain temperatures (see the temperature axis in Figure 2) with a holding time of 1 h (heating and cooling rate 2 °C/min). One end of the silica ampule was exposed to the lower temperature region of the furnace to collect the released I2. Figure 2 displays a superposition of PXRD patterns of reaction products. Below 200 °C, no change of the starting material W5I16 is observed. The pattern at 210 °C was assigned as W5I15, according to the result of the structure refinement from an X-ray-pure, black crystalline powder (annealed at 210 °C for 24 h). Similar patterns cover the region from 210 to 230 °C (displayed in blue in Figure 2). The temperature range between 250 and 350 °C shows a strong iodine loss signal in the DTA/TGA measurement. Only two stronger reflections are observed in the corresponding PXRD pattern (green patterns in Figure 2). Separately done reactions in silica tubes at 290 °C for 1 h yielded black single crystals. Single-crystal structure refinements on two different crystals resulted in the compositions W5I14.12(2) and W5I14.04(1), confirming decomposition of W5I15 by the loss of iodine. The temperature range from 375 to 500 °C is dominated by the PXRD pattern of β-W5I12. The structure of this compound

is unknown until now, but elemental analyses (see Experimental Section) revealed compositions W5I12.04 and W5I11.93. Between 525 and 550 °C, the PXRD patterns can be assigned to a mixture of W5I11 (side phase), β-W5I12, and βW6I12. The PXRD pattern above 575 °C is fully consistent with that of β-W6I12 (shown in yellow in Figure 2). Decomposition at Higher Iodine Pressure. DSC measurements of W5I16 (51.7 mg) were executed while enclosed in gold-plated (5 μm) steel autoclaves with a small volume (V ≈ 100 μL), resulting in higher iodine pressure conditions. The DSC pattern revealed only two distinguishable thermal effects, displayed in Figure 3.

Figure 3. DSC measurement of W5I16 enclosed in a gold-plated (5 μm) steel autoclave, corresponding to higher iodine pressure.

The strong endothermic effect in the range 300−350 °C with an energy of 66 kJ/mol is assigned to the formation of α-W5I12 by means of PXRD patterns (green in Figure 3). The exothermic effect at around 400 °C with an energy of −5.5 kJ/mol corresponds to the thermal transformation of α-W5I12 14302

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Figure 4. Superposition of recorded XRD patterns of crystalline powders obtained from W5I16 decomposition reactions under higher iodine pressure at various temperatures.

into β-W6I12. The presence of β-W6I12 is indicated by the red pattern in Figure 4. Crystal Structures. All W5Ix compounds (x = 16, 15.67, 15, 13 + x, 12, 11) are basically composed of a [W5I8] cluster core with five apical iodido ligands. The cluster, as already described by Holm et al.,7 consists of a metal−metal-bonded W5 square pyramid. The four triangular faces are capped by μ3-bonded iodido ligands, and the basal edges are capped by μ2-bonded iodido ligands. Each tungsten atom is terminally coordinated by one iodido ligand (Figure 5). The [W5I8] core can be related to the well-known [W6I8] core of W6I12, as was already described by Holm et al.7 Figure 6. Segment of the W5I16 structure.

Two notable features are the angled asymmetric bridging I3 unit [bonding distances 289.0(4) and 293.3(4) pm; I12−I14− I9 angle 163.1(1)°] and the unusually long W1−I9 contact [326.4(7) pm]. This may give rise to considering W5I16 as a dipolar ion with a positive charge on the [W5I8] cluster core and a negative charge distributed on the bridging I3 ligands. Contrary to theby usexpected loss of the coordinated I2 molecule, the bridging triiodido ligand is cleaved in the first decomposition step, resulting in the loss of one iodine atom per formula unit and the composition W5I15. W5I15 was obtained as an X-ray-pure black powder from reactions in silica tubes at 210 °C for 24 h, and the crystal structure was refined from PXRD data. The structure of W5I15 is almost identical with the structure of W5I16, and the connectivity could be described as [W5I8]I5a·I2 (Figure 7). The refined I−I distance of I2 (I14− I15) of 275.6(9) pm is identical with the distance of I2 in W5I16 [276.0(4) pm], but the distance to the adjacent iodido ligand (I14−I11) is shorter [328(1) pm] than the coordination distance I11−I15 [332.5(4) pm] in W5I16. A notable point is the shortening of the W1−I9 distance in W5I15 by almost 10 pm [from 326.4(7) to 316.4(5) pm in W5I15]. Still, these distances appear to be unusually large. A most likely explanation may be interactions between the iodido ligand I9

Figure 5. [W5I13] unit as a main building block in W5Ix compounds (x = 16, 15.67, 15, 13 + x, 12, 11).

In W5I16, two terminal triiodido ligands interconnect two adjacent clusters (via I9 and I12; Figure 6). In addition, one I2 molecule unit is situated in the vicinity of I11. The resulting connectivity can be described as [W5I8]I3a(I3)2/2a‑a·I2. The refined I−I distance (I15−I16) of 276.0(4) pm of the I2 molecule is slightly elongated in comparison with the intramolecular I−I distance in solid I2 at 25 K [272.1(1) pm].15 14303

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implemented in the structure of W5I11. The compound W5I11 crystallizes in the monoclinic space group Pnma (Z = 4). As was already noticed by Holm et al.7 for the [W5I13]1−,2− ions, compounds with the [W5I8] core bear an obvious structural relationship to [W6I14]2− by removal of a [WI]1−,0 fragment. For W5I11, the relationship to W6I12 with the connectivity [W6I8i]I2aI4/2a‑a is even tighter because the W5I11 structure is already based on a layered connectivity and the [W5I8] cluster cores are interconnected to each other by four terminal bridging iodido ligands, resulting in the connectivity [W5I8i]IaI4/2a‑a (Figure 9).

Figure 7. Segment of the W5I15 ([W5I8i]I5a·I2) structure.

with four μ2-capping inner iodido ligands of the adjacent cluster at I−I distances below 400 pm (Figure S4). The next step of iodine loss is the already expected loss of the I2 molecule. This was confirmed after some black, block like single crystals could be selected from the thermal treatment of W5I16 in a temperature gradient from 232 to 25 °C for 1 h. Single-crystal structure refinements performed on two crystals, selected from the same reaction product, allowed two interpretations of the iodine loss. One possible explanation is a loss of some I2 molecules without a significant structural change (Figure 8, left). Refinement of the site occupation factors of the two distinct iodide atoms of I2 (I14−I15) on 4a Wyckoff positions revealed almost identical values around 50%, leading to the composition [W5I8i]I5a·1/2I2 (Figure 8, left). Structure refinement of the site occupation factors of the corresponding iodine atoms of the second single crystal revealed values of 37(1)% for I14 and 75(1)% for I15. This result may be basically understood with the loss of one iodide atom with the formation of a bridging triiodide-like unit, similar to that obtained in the structure of W5I16 (Figure 8, right). A further loss of iodine results in the direct connectivity of adjacent clusters via two apical iodido ligands, as implemented in the structure of α-W5I12 as [W5I8i]I3iI2/2a‑a, whose structure was already described by us in detail.13 The structure of β-W5I12 is unknown until now, but elemental analyses (see the Experimental Section) on separately prepared samples (at 350 °C for 1 h and at 400 °C for 1 h) yielded the compositions W5I12.04 and W5I11.93. A further reduction of the cluster by a loss of iodine requires more than two direct Ia‑a bonds between adjacent clusters, as

Figure 9. Section of the crystal structure of W5I11 depicting the connectivity by four apical iodido ligands shared by two clusters in a layered structure. Inner iodido ligands are omitted for clarity.

The average W−W distance [263.51(8) pm] in W5I11 is around 2 pm shorter than the average W−W distances in W5I16, W5I15, and W5I14.04(1) [265.8(3), 265.3(8), and 265.3(3) pm] and around 4 pm shorter than the average W−W distance in W6I12 [267.1(5) pm]. This shortening of the W−W distance is in good agreement with the shrinkage of the average W−W distance by 3 pm in the case of the reduction of [W5I11]−, with 18e− in the metal−metal bonding energy states to [W5I11]2− and 19e− in the metal−metal bonding energy states, as described by Holm et al.7 and Ströbele and Meyer.12 The average W−Ii distances for μ3- and μ2-bridging iodido ligands [279.3(1) and 275.7(4) pm] are in the range of the μ3- and μ2bridging iodido ligands of other W5Ix compounds discussed in

Figure 8. Two possibilities for the iodine loss in the crystal structure of W5I13·xI2. An approximately half-occupied I2 position for [W5I8i]I5a·1/2I2 (left) or the loss of one iodide atom with the formation of a triiodide bridge (right). The inner iodido ligands are omitted in the left-hand cluster of the right-side drawing for more clarity. The refined compositions, based on two distinct crystals inspected by single-crystal refinements, yielded the compositions W5I14.04(1) and W5I14.12(2). 14304

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contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

this paper (Table S1) and in W6I12 [279.2(7) pm]. The average W−Ia distance [286.0(1) pm] of the four basal terminal iodido ligands is slightly elongated in relation to the other W5Ix compounds discussed in this paper. The W−I distance of the apical iodido ligand [279.6(1) pm] lies in the range of the W−I distances of the apical iodido ligands of W15I47, α-W5I12, (Pr4N)[W5I11], and (Pr 4N)2[W5I11] [284.3(3)/279.3(2), 281.8(6), 280.0(4), and 281.6(2) pm] but is shorter than the W−I distances of the apical iodido ligands in W5I16, W5I15, and W5I14.04(1) [326.4(7), 316.4(5), and 297.1(5) pm]. The unit cell of W5I11 is shown in Figure 9. A comparison of the W5Ix structures described in this paper is given in Figure S3, and the average W−W and W−I distances are summarized in Table S1.

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Corresponding Author

*E-mail: [email protected]. ORCID

Markus Ströbele: 0000-0002-5147-5677 Hans-Jürgen Meyer: 0000-0003-2450-4011 Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. These authors contributed equally.

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Notes

CONCLUSIONS W5I16 was synthesized using W3I12 as the starting material. Thermal decomposition of W5I16 via the release of iodine under lower iodine pressures revealed the new compounds W5I15, W5I13·xI2 (0 < x ≤ 1), β-W5I12, and W5I11 as characterized by single-crystal XRD or PXRD methods. At higher iodine pressures, only the known compound α-W5I12 was detected. The final transformation (of W5I11 and of α-W5I12) results with the formation of the long-known β-W6I12, in both cases. Structural transformations of tungsten iodide clusters with the square-pyramidal W5 core proceed with the loss of iodine under simultaneous reduction of the cluster. During this process, the I3− and I2 units are successively removed from structures (W5I15 and W5I13·xI2), before cross-linking between clusters is obtained. In this way, the crystal structure of α-W5I12 is represented by a [W5I8i]I3iI2/2a‑a connectivity by two shared apical iodide ligands (Ia‑a). Further cross-linking via four shared iodide bridges is achieved in the structure of W5I11, represented as [W5I8i]IaI4/2a‑a. This connectivity pattern shows a remarkable similarity to the corresponding connectivity pattern [W6I8i]I2aI4/2a‑a in the structure of W6I12. Further details of the crystal structure investigation may be obtained from the Fachinformationszentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany (fax +49 7247-808-666; email crysdata@fiz-karlsruhe.de; web page http://www.fizkarlsruhe.de/request_for_deposited_data.html) on quoting the depository numbers 433543 for W5I15, 433548 for W5I14.12(2), 433547 for W5I14.04(1), and 433546 for W5I11.

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AUTHOR INFORMATION

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was supported by the Deutsche Forschungsgemeinschaft (Bonn, Germany) via Grant ME 914/27-1. REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b02417. Homemade SiO2 container, Rietveld structure refinement plot, comparison of the different W5Ix compounds, short I−I contacts between two clusters in W5I15, homemade furnace with a silica ampule, average W−W and W−I distances for W5Ix compounds, crystal data and structure refinement for W5I15, W5I14.12(2), W5I14.04(1), and W5I11, and parameters and equations used for the pressure estimation (PDF) Accession Codes

CCDC 1576685 and 1576703−1576705 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/ cif, or by emailing [email protected], or by 14305

DOI: 10.1021/acs.inorgchem.7b02417 Inorg. Chem. 2017, 56, 14300−14305