Article pubs.acs.org/IC
Facile Way of Synthesis for Molybdenum Iodides Markus Ströbele, Robert Thalwitzer, and H.-Jürgen Meyer* Section for Solid State and Theoretical Inorganic Chemistry, Institute of Inorganic Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany S Supporting Information *
ABSTRACT: Molybdenum iodides are prepared based on a new way of synthesis, namely, via reductive metathesis reaction of MoCl5 with SiI4. MoI3 was formed at 150 °C. Mo6I12 and the new molybdenum iodides Mo6I16 and Mo6I18 with the well-known [Mo6I8]4+ cluster core were obtained in the temperature range 550−600 °C. Compounds were structurally characterized by powder and single-crystal X-ray diffraction techniques.
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INTRODUCTION Three main synthesis routes are reported in the literature for the preparation of molybdenum iodides. Among them are the reaction of MoCl5 with HI1 and the reaction of Mo(CO)6 with elemental iodine at 105 °C,2 which can be both carried out only in small scale. The most common synthesis of molybdenum iodides is based on the direct reaction of elemental molybdenum with elemental iodine in a fused silica container resulting in the formation of a mixture of MoI3 and Mo6I12.3 The practical performance of this way of synthesis contains the risk of an explosion of the silica tube, due to the high iodine pressure and the poor reactivity of molybdenum powder (depending on the particle size and purity) at elevated temperatures. Molybdenum iodide compounds based on octahedral molybdenum clusters have gained more and more attention during the past years. The [(Mo6I8i)I6a]2− anion is based on an octahedral cluster of molybdenum atoms with eight facecapping inner (i = innen) iodido ligands and six apical or outer (a = aussen) iodido ligands. The outer ligands are more weakly bound to the cluster core, making extensive ligand exchange chemistry possible, which has led to the development of ligandsubstituted molybdenum iodides having the general formula [Mo6I8(L)6]2−. A comprehensive synthesis of this type of cluster was recently described for (TBA)2[Mo6I8(NCS)6] (TBA = tetrabutyl ammonium).4 Materials containing this type of cluster anion represent powerful photosensitizers whose properties are strongly influenced by the nature of the apical l i g a n d ( L ) . 5 , 7 T h e p h o t o p h y s ic a l p r o p e r t i e s o f (TBA) 2 [(Mo 6 I 8 )(C 3 F 7 COO) 6 ] 6 and (TBA) 2 [(Mo 6 I 8 ) (CF3COO)6]7 in solutions were reported to involve high phosphorescence quantum yields (ΦL > 0.59) and high quantum yields of singlet oxygen (a1Δg) production (ΦΔ > © XXXX American Chemical Society
0.8) in the presence of oxygen. These remarkable properties have gained interest for a deeper understanding of optical phenomena and to explore potential applications of these compounds like photocatalysis,8,9 photodynamic inactivation of bacteria,10 photodynamic therapy of cancer,11,33 X-ray-induced PDT,12 oxygen sensing,13,14 lighting,15 solar energy harvesting,16 organic synthesis,17 catalysis,18 luminescent nanoparticles,19,34 photoreduction of CO2,20 etc. The requirement of larger quantities of high-quality molybdenum iodides is addressed in this work by a new facile route for the preparation of molybdenum iodides MoI3, Mo6I12, Mo6I18, and Mo6I16, adapted from the recently reported preparation of tungsten iodides.21 Crystal structures of MoI3 and the new compounds Mo6I18 and Mo6I16 are reported.
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EXPERIMENTAL SECTION
MoCl5 (ABCR, 99.6%), SiI4 (ChemPUR, 99%), I2 (Merck, 99.8%), and Mo (Sigma-Aldrich, 99.99%) were used without further purification. All preparations were carried out in a glovebox under a dry argon atmosphere. MoI3. MoI3 was prepared by grinding 2.0 g (7.3 mmol) of MoCl5 and 4.9 g (9.2 mmol) of SiI4 in an agate mortar. The homogeneous mixture was filled in a Schlenk flask equipped with two gas inlet pipes with PTFE faucets and heated at 150 °C for 16 h in a hot air cabinet. Afterwards, byproducts (elemental iodine and silicon chlorides) were removed under moderate heating (water bath) under flowing argon to yield 3.8 g of MoI3 (88% based on MoCl5) which appeared as black crystal needles. Classical Method (for high-crystalline samples): A mixture of 2 g (20 mmol) of elementary molybdenum and 8 g (63 mmol) of I2 was sealed into an evacuated silica tube (l = 15 cm, V ≈ 20 cm3) and heated in a temperature gradient (400 °C to room temperature) for 2 Received: September 15, 2016
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DOI: 10.1021/acs.inorgchem.6b02229 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry weeks. Afterwards, the tube was cooled to room temperature at a rate of 2 °C/min. Good crystalline fibrous MoI3 (yield ≈ 5%) was found in the low-temperature region of the tube and removed mechanically. Mo6I12 (Orthorhombic Phase). Mo6I12 was synthesized by a solid state metathesis reaction of 200.0 mg (0.732 mmol) of MoCl5 and 490.2 mg (0.915 mmol) of SiI4. The mixture was sealed into a silica ampule (V ≈ 2 cm3) under vacuum. Afterward, the mixture was heated at 600 °C for 24 h (heating rate 2 °C/min), and cooled to room temperature at a rate of 2 °C/min. Excess of iodine was carefully sublimed off to obtain X-ray pure Mo6I12 as a red powder. Mo6I16. A mixture of 300.0 mg (0.63 mmol) of MoI3 and 1.0 g (3.94 mmol) of I2 was sealed into an evacuated silica tube (V ≈ 2 cm3), heated at 550 °C for 24 h (heating rate 2 °C/min), and cooled to room temperature at a rate of 2 °C/min. Mo6I16 was obtained as a red-brown crystalline powder together with I2, which was carefully sublimed off. Mo6I18. was synthesized by a solid state metathesis reaction of 100.0 mg (0.366 mmol) of MoCl5 and 245.1 mg (0.458 mmol) of SiI4. The mixture was sealed into a silica ampule (V ≈ 2 cm3) under vacuum. Afterwards, the mixture was heated at 590 °C for 24 h (heating rate 2 °C/min), and cooled to room temperature at a rate of 2 °C/min. Excess of iodine was carefully sublimed off to obtain X-ray pure Mo6I18, appearing as a dark reddish-brown powder. Powder X-ray Diffraction. Diffraction patterns of all reaction products were investigated by powder X-ray diffraction (XRD) using a StadiP diffractometer (Stoe, Darmstadt) with Ge-monochromated Cu Kα1 radiation and a Mythen detector. The crystal structure of MoI3 was indexed isotypically to ZrI322 and Mo6I18 isotypically to W6I18.23 Atom positions were refined by global refinement (Winplotr, FullProf Suite).24 Further details of the crystal structure investigations may be obtained from the Fachinformationszentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany (Fax: +49 7247-808-666; Email: crysdata@fiz-karlsruhe.de, http://www.fiz-karlsruhe.de) on quoting the depository number CSD-431 486 for MoI3 and CSD-431 014 for Mo6I18. Single-Crystal X-ray Diffraction. An orange single-crystal of Mo6I16 was measured with a single-crystal X-ray diffractometer (STOE-IPDS) at room temperature (T = 293 K) using Mo Kα radiation (λ = 0.71073 Å). The crystal structure refinement and solution were performed with direct methods (SHELXS) and leastsquares refinements on F2 (SHELXL).25 Further details of the crystal structure investigation may be obtained from the Fachinformationszentrum Karlsruhe, 76344 EggensteinLeopoldshafen, Germany (Fax: +49 7247-808-666; E-mail: crysdata@ fiz-karlsruhe.de, http://www.fiz-karlsruhe.de) on quoting the depository number CSD-430 947 for Mo6I16.
examined in depth for tungsten iodides by Long and Holm in 1995.11 The disadvantage of this route, as already mentioned by Long and Holm, is the risk of violent explosions and the formation of inhomogeneous product mixtures. In this paper we present a new and facile synthesis route for the preparation of molybdenum iodides, especially for MoI3, based on a reductive solid state metathesis reaction between MoCl5 and SiI4 in a Schlenk flask under mild heating in a hot air cabinet. Advantages of this route are easy performance, the negligible iodine pressure in the reaction vessel, and the possibility to synthesize gram amounts of molybdenum iodides in high purity. The crystal structure of MoI3 was first described isotypic with MoBr330 on the basis of similar powder patterns by Smith et al. in 1960,3 but no crystallographic data (like atom positions or lattice constants) were given. Tachikawa indexed the powder pattern with a hexagonal cell (a = b = 712 pm, c = 641 pm),11 ̀ assigned the structure isotypic to MoBr3 with a = and Evstafev 712 pm, b = 1233 pm, and c = 641 pm,31 but also no space group or atomic positions were given. The powder pattern of a crystalline MoI3 sample, obtained from our preparation was indexed and refined hexagonally with space group P63/mcm (No. 193), consistent with the β-TiCl3type structure which is commonly assigned for many trihalides. However, some weak reflections ( 2σ(I)] R indices (all data) largest diff. peak and hole (e·Å−3)
563.59(2) 4 145.295 5.6173 5−55° 436 39 27 4.1218, 5.4952 2.4564 1.1592
Mo6I16 2606.0 293(2) 71.073 monoclinic P21/c (No. 14) a = 1091.27(3) b = 1047.04(2) c = 1312.28(4) β = 98.021(2)° 1484.75(7) 2 19.085 5.829 2.5−25° 2613 100
154.060 orthorhombic Pmmn (No. 59) a = 1233.7(1) b = 641.31(1) c = 712.31(1)
Mo6I18 2860.0 154.060 monoclinic P21/m (No. 11) a = 1046.18(2) b = 1791.09(3) c = 1047.23(2) β = 118.850(1)° 1719.72(6) 2 144.234 5.523 2.5−60° 3738 64 52 3.3724, 4.1797 3.8424 1.9315
1.074 R1 = 0.0355, wR2 = 0.0847 R1 = 0.0413, wR2 = 0.0876 1.528 and −1.960 C
DOI: 10.1021/acs.inorgchem.6b02229 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
refined for the first time. The formation of these iodides is obtained via auto reduction of MoI3 when I2 elimination is obtained at elevated temperatures. This includes the preparation of Mo6I12, a compound of particular interest for the preparation of desired [Mo6X8L6]n− clusters (L = organic or inorganic ligand) which are showing remarkable photophysical properties.6,32
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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.6b02229. (CIF) (CIF) (CIF) Comparison of the crystal data and structure refinement for MoI3 in the space groups P63/mcm and Pmmn (PDF)
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Figure 4. I2 molecules situated in between layers of the structure of Mo6I16.
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This research was supported by the Deutsche Forschungsgemeinschaft (Bonn) via grant ME 914/27-1. REFERENCES
(1) Guichard, M. Sur un iodure de molybdène. Compt. Rend. 1896, 123, 821−823. Guichard, M. Biiodure de Molybdène. Ann. Chim. Phys. 1901, 23, 498−574. (2) Djordjevic, C.; Nyholm, R. S.; Pande, C. S.; Stiddard, M. H. B. Reaction of Iodine with Group VI Hexacarbonyls: Tri-iodides of Molybdenum and Tungsten and their Derivatives. J. Chem. Soc. A 1966, 16−17. (3) Lewis, J.; Machin, D. J.; Nyholm, R. S.; Pauling, P.; Smith, P. W. Preparation and properties of molybdenum triiodide. Chem. Ind. 1960, 259. (4) Riehl, L.; Ströbele, M.; Enseling, D.; Jüstel, T.; Meyer, H.-J. Molecular Oxygen Modulated Luminescence of an Octahedrohexamolybdenum Iodide Cluster having Six Apical Thiocyanate Ligands. Z. Anorg. Allg. Chem. 2016, 642, 403−408. (5) Brückner, P.; Preetz, W.; Pünjer, M. Darstellung, Kristallstrukturen, NMR-, Schwingungsspektren und Normalkoordinatenanalyse der Clusteranionen [(Mo6I8i)Y6a]2−, Ya = F, Cl, Br, I. Z. Anorg. Allg. Chem. 1997, 623, 8−17. Efremova, O. A.; Shestopalov, M. A.; Chirtsova, N. A.; Smolentsev, A. I.; Mironov, Y. V.; Kitamura, N.; Brylev, K. A.; Sutherland, A. J. A highly emissive inorganic hexamolybdenum cluster complex as a handy precursor for the preparation of new luminescent materials. Dalton Trans. 2014, 43, 6021−6025. (6) Sokolov, M. N.; Mihailov, M. A.; Peresypkina, E. V.; Brylev, K. A.; Kitamura, N.; Fedin, V. P. Highly luminescent complexes [Mo6X8(nC3F7COO)6]2− (X = Br, I). Dalton Trans. 2011, 40, 6375−6377. (7) Kirakci, K.; Kubát, P.; Langmaier, J.; Polívka, T.; Fuciman, M.; Fejfarova, K.; Lang, K. A comparative study of the redox and excited state properties of (nBu4N)2[Mo6X14] and (nBu4N)2[Mo6X8(CF3COO)6] (X = Cl, Br, or I). Dalton Trans. 2013, 42, 7224−7232. (8) Liqiang, J.; Yichun, Q.; Baiqi, W.; Shudan, L.; Baojiang, J.; Libin, Y.; Wei, F.; Honggang, F.; Jiazhong, S. Review of photoluminescence performance of nano-sized semiconductor materials and its relation-
Figure 5. Crystal structure refinement plot of Mo6I18. Red circles represent measured data points which are superimposed with the calculated powder pattern (black line). Green lines represent the Bragg positions; difference curve is shown as a blue line.
Figure 6. Cluster chain in the structure of Mo6I18.
= 277.1(5); Mo−Ia = 285.8(5) pm) than in W6I18 (W−Ii = 279.1(7); W−Ia = 282.8(2) pm).
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CONCLUSION A new synthesis route is established for the preparation of molybdenum iodides. The reaction involves a reductive metathesis reaction between MoCl5 and SiI4 which is easily performed. On the basis of this method, described for the preparation of MoI3, it is possible to synthesize a number of octahedral molybdenum clusters with the [Mo6I8]4+ core in a single step, and crystal structures of MoI3, Mo6I16, Mo6I18 are D
DOI: 10.1021/acs.inorgchem.6b02229 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry ships with photocatalytic activity. Sol. Energy Mater. Sol. Cells 2006, 90, 1773−1787. (9) Barras, A.; Cordier, S.; Boukherroub, R. Fast photocatalytic degradation of rhodamine B over [Mo6Br8(N3)6]2− cluster units under sun light irradiation. Appl. Catal., B 2012, 123−124, 1−8. (10) Pohl, J.; Preuss, A.; Röder, B. In Singlet Oxygen: Applications in Biosciences and Nanosciences; Nonell, S., Flors, C., Eds.; Royal Society of Chemistry, 2016. (11) Kirakci, K.; Kubát, P.; Kučeráková, M.; Šícha, V.; Gbelcová, H.; Lovecká, P.; Grznárová, P.; Ruml, T.; Lang, K. Water-soluble octahedral molybdenum cluster compounds Na2[Mo6I8(N3)6] and Na2[Mo6I8(NCS)6]: Syntheses, luminescence, and in vitro studies. Inorg. Chim. Acta 2016, 441, 42−49. (12) Kirakci, K.; Kubát, P.; Fejfarová, K.; Martinčík, J.; Nikl, M.; Lang, K. X-ray Inducible Luminescence and Singlet Oxygen Sensitization by an Octahedral Molybdenum Cluster Compound: A New Class of Nanoscintillators. Inorg. Chem. 2016, 55, 803−809. (13) Feng, Y.; Cheng, J.; Zhou, L.; Zhou, X.; Xiang, H. Ratiometric optical oxygen sensing: a review in respect of material design. Analyst 2012, 137, 4885−4901. (14) Zhang, P.; Osborn, D. J.; Baker, G. L.; Ghosh, R. N. High Temperature Oxygen Sensing Using K2Mo6Cl14 Luminescence. Sens., 2005 IEEE 2005, 628−631. (15) Kuttipillai, P. S.; Zhao, Y.; Traverse, C. J.; Staples, R. J.; Levine, B. G.; Lunt, R. R. Light-Emitting Diodes: Phosphorescent Nanocluster Light-Emitting Diodes. Adv. Mater. 2016, 28, 320−326. (16) Renaud, A.; Grasset, F.; Dierre, B.; Uchikoshi, T.; Ohashi, N.; Takei, T.; Planchat, A.; Cario, L.; Jobic, S.; Odobel, F.; Cordier, S. Inorganic Molybdenum Clusters as Light-Harvester in All Inorganic Solar Cells: A Proof of Concept. Chemistry Select 2016, 1, 2284−2289. (17) DeRosa, M. C.; Crutchley, R. J. Photosensitized singlet oxygen and its applications. Coord. Chem. Rev. 2002, 233−234, 351−371. (18) Kamiguchi, S.; Nagashima, S.; Chihara, T. Characterization of Catalytically Active Octahedral Metal Halide Cluster Complexes. Metals 2014, 4, 84−107. (19) Aubert, T.; Cabello-Hurtado, F.; Esnault, M.-A.; Neaime, C.; Lebret-Chauvel, D.; Jeanne, S.; Pellen, P.; Roiland, C.; Le Polles, L.; Saito, N.; Kimoto, K.; Haneda, H.; Ohashi, N.; Grasset, F.; Cordier, S. Extended Investigations on Luminescent Cs2[Mo6Br14]@SiO2 Nanoparticles: Physico-Structural Characterizations and Toxicity Studies. J. Phys. Chem. C 2013, 117, 20154−20163. Kuttipillai, P. S.; Zhao, Y.; Traverse, C. J.; Staples, R. J.; Levine, B. G.; Lunt, R. R. Phosphorescent Nanocluster Light-Emitting Diodes. Adv. Mater. 2016, 28, 320−326. (20) Kumar, P.; Kumar, S.; Cordier, S.; Paofai, S.; Boukherroub, R.; Jain, S. L. Photoreduction of CO2 to methanol with hexanuclear molybdenum [Mo6Br14]2‑ cluster units under visible light irradiation. RSC Adv. 2014, 4, 10420−10423. (21) Ströbele, M.; Castro, C.; Fink, R. F.; Meyer, H.-J. A facile method for the synthesis of binary tungsten iodides. Angew. Chem. 2016, 128, 4894−4897. et al. Angew. Chem. Int. Ed. (Engl.) 2016, 65, 4814−4816. (22) Lachgar, A.; Dudis, D. S.; Corbett, J. D. Revision of the Structure of Zirconium Triiodide. The Presence of Metal Dimers. Inorg. Chem. 1990, 29, 2242−2246. (23) Franolic, J. D.; Long, J. R.; Holm, R. H. Comprehensive Tungsten-Iodine Cluster Chemistry: Isolated Intermediates in the Solid-state Nucleation of [W6I14]2‑. J. Am. Chem. Soc. 1995, 117, 8139−8153. (24) Roisnel, T.; Rodríquez-Carvajal, J. WinPLOTR: A Windows tool for powder diffraction patterns analysis. Mater. Sci. Forum 2001, 378-381, 118−123. Recent developments of the program FULLPROF; Commission on powder diffraction (IUCr), Newsletter, 2001. (25) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. (26) Riche, M. A. Le Tungstène et ses composes. Ann. Chim. Phys. 1857, 3, 5−80. (27) Sato, T.; Fukui, H.; Sasaki, H.; Tachikawa, T. Preparation of molybdenum iodides. Denki Kagaku Oyobi Kogyo Butsuri Kagaku 1988, 56, 860−863.
(28) Defacqz, E. Sur un nouvel iodure de tungstène. C. R. Acad. Sci. 1898, 127, 510−512. (29) Schäfer, H.; Schulz, H.-G. Das System Wolfram/lod. Z. Anorg. Allg. Chem. 1984, 516, 196−200. (30) Babel, D. Die Verfeinerung der MoBr3-Struktur. J. Solid State Chem. 1972, 4, 410−416. ̀ V. K. Dissertation, Nikolaev, Institut for Inorganic (31) Evstafev, Chemistry, 2004. (32) Kirakci, K.; Kubát, P.; Dušek, M.; Fejfarová, K.; Šícha, V.; Mosinger, J.; Lang, K. A Highly Luminescent Hexanuclear Molybdenum Cluster − A Promising Candidate toward Photoactive Materials. Eur. J. Inorg. Chem. 2012, 2012, 3107−3111. (33) Solovieva, A. O.; Vorotnikov, Y. A.; Trifonova, K. E.; Efremova, O. A.; Krasilnikova, A. A.; Brylev, K. A.; Vorontsova, E. V.; Avrorov, P. A.; Shestopalova, L. V.; Poveshchenko, A. F.; Mironov, Y. V.; Shestopalov, M. A. Cellular internalisation, bioimaging and dark and photodynamic cytotoxicity of silica nanoparticles doped by {Mo6I8}4+ metal clusters. J. Mater. Chem. B 2016, 4, 4839−4846. (34) Vorotnikov, Y. A.; Efremova, O. A.; Vorotnikova, N. A.; Brylev, K. A.; Edeleva, M. V.; Tsygankova, A. R.; Smolentsev, A. I.; Kitamura, N.; Mironov, Y. V.; Shestopalov, M. A. On the synthesis and characterisation of luminescent hybrid particles: Mo6 metal cluster complex/SiO2. RSC Adv. 2016, 6, 43367−43375.
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