Next Article in Journal
Shear Strength of Exterior Plywood Panels Pressed at Low Temperature
Next Article in Special Issue
Hydroisomerization of n-Butane over Platinum-Promoted Cesium Hydrogen Salt of 12-Tungstophosphoric Acid
Previous Article in Journal
Nitrate-Melt Synthesized HT-LiCoO2 as a Superior Cathode-Material for Lithium-Ion Batteries
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Materials
Volume 2
Issue 3
10.3390/ma2030869
materials-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Efficient Syntheses of [(n-C4H9)4N]4[α-Mo8O26] and [(n-C4H9)4N]2[Mo2O7]

by
Shusaku Ikegami
and
Atsushi Yagasaki
*
Department of Chemistry, Kwansei Gakuin University, Sanda 669-1337, Japan
*
Author to whom correspondence should be addressed.
Materials 2009, 2(3), 869-875; https://doi.org/10.3390/ma2030869
Submission received: 16 June 2009 / Revised: 30 June 2009 / Accepted: 27 July 2009 / Published: 28 July 2009
(This article belongs to the Special Issue Polyoxometalate Compounds)
Browse Figure
Versions Notes

Abstract

:
Efficient and simple syntheses of [(n-C4H9)4N]4[α-Mo8O26] (I) and [(n-C4H9)4N]2[Mo2O7] (II) from MoO3 and aqueous [(n-C4H9)4N]OH are described. The yield is 72% for I and 73% for II.

1. Introduction

The tetrabutylammonium salts of [α-Mo8O26]4- [1,2,3] and [Mo2O7]2- [4] are important starting materials in the synthesis of variety of polyoxometalates and metal-organic hybrid materials. By virtue of their solubility in aprotic organic solvents, these salts have found widespread application [5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27]. In the method currently employed for the preparation of [(n-C4H9)4N]4[α-Mo8O26] (I) (Scheme 1), Na2MoO4 and [(n-C4H9)4N]Br are used as starting materials [28]. Because of this, large amounts of sodium salts are produced as byproducts.
Scheme 1. Classical synthesis of [(n-C4H9)4N]4[α-Mo8O26] (I).
Scheme 1. Classical synthesis of [(n-C4H9)4N]4[α-Mo8O26] (I).
8Na2MoO4 + 12HCl + 4[(n-C4H9)4N]Br → [(n-C4H9)4N]4[α-Mo8O26] + 12NaCl + 4NaBr + 6H2O
These byproducts tend to make the final yield low and to fluctuate from one preparation to another. In order to prepare [(n-C4H9)4N]2[Mo2O7] (II), one has to first prepare I (Scheme 2) [28].
Scheme 2. Classical synthesis of [(n-C4H9)4N]2[Mo2O7] (II).
Scheme 2. Classical synthesis of [(n-C4H9)4N]2[Mo2O7] (II).
[(n-C4H9)4N]4[α-Mo8O26] + 4[(n-C4H9)4N]OH → 4[(n-C4H9)4N]2[Mo2O7] + 2H2O
Although the conversion rate is moderate (69%), the need to first prepare I makes the overall yield of II based on the initial starting material, Na2MoO4, as low as 44%. We report here preparations that are more convenient and more efficient than those currently employed.

2. Results and Discussion

Compound I was efficiently synthesized by mixing MoO3 and [(n-C4H9)4N]OH (Scheme 3).
Scheme 3. New synthesis of [(n-C4H9)4N]4[α-Mo8O26] (I).
Scheme 3. New synthesis of [(n-C4H9)4N]4[α-Mo8O26] (I).
8MoO3 + 4[(n-C4H9)4N]OH → [(n-C4H9)4N]4[α-Mo8O26] + 2H2O
The pH of the suspension decreased from 7.8 to 6.1 as the reaction proceeded and the solid acid consumed OH-. The color of the suspension also changed during this period from light gray to bright white. Compound I is insoluble in water, and it seems that what little amount of I formed by the reaction of MoO3 and [(n-C4H9)4N]OH immediately precipitated out from the solution. In fact, the powder obtained by filtering the suspension after its color changed to bright white gave IR spectra identical to that of pure I. When the molar ratio of [(n-C4H9)4N]OH to MoO3 was increased to 1, II was obtained in high yield (Scheme 4).
Scheme 4. New synthesis of [(n-C4H9)4N]2[Mo2O7] (II).
Scheme 4. New synthesis of [(n-C4H9)4N]2[Mo2O7] (II).
2MoO3 + 2[(n-C4H9)4N]OH → [(n-C4H9)4N]2[Mo2O7] + H2O
Again, the pH of the suspension decreased from 7.5 to 6.6 and the color changed to white as the reaction proceeded. However, the solid left undissolved in this aqueous suspension was not II and the IR spectrum showed that it was actually I. This observation suggests that II does not form when the reaction medium is water, even if the molar ratio of [(n-C4H9)4N]OH to MoO3 is optimal for its formation. It seems that, even in such a case, I forms first and it then reacts with the remaining [(n-C4H9)4N]OH to form [(n-C4H9)4N]2[MoO4], which is highly soluble in water. In other words, the substance obtained by evaporating the suspension was probably a mixture of I and [(n-C4H9)4N]2[MoO4]. Compound II was obtained only after re-dissolving the substance in acetonitrile, whereupon I reacts with [(n-C4H9)4N]2[MoO4] to form II (Scheme 5)
Scheme 5. Formation of [(n-C4H9)4N]2[Mo2O7] (II).
Scheme 5. Formation of [(n-C4H9)4N]2[Mo2O7] (II).
4[(n-C4H9)4N]2[MoO4] + [(n-C4H9)4N]4[α-Mo8O26] → 6[(n-C4H9)4N]2[Mo2O7]
Both compounds I and II prepared by the current method gave satisfactory elemental analyses. They both have characteristic IR absorptions in the 1,000–400 cm-1 range and thus can be conveniently identified by their IR spectra (Figure 1). However, care should be taken when measuring these IR spectra, as compounds I and II both react with KBr under pressure and give different spectra when they are recorded as KBr pellets [29].
Materials 02 00869 g001 1024
Figure 1. IR spectra of [(n-C4H9)4N]4[α-Mo8O26] (I, left column) and [(n-C4H9)4N]2[Mo2O7] (II, right column) from ATR [(a) and (d)], Nujol mull [(b) and (e)], and KBr pellet [(c) and (f)].
Figure 1. IR spectra of [(n-C4H9)4N]4[α-Mo8O26] (I, left column) and [(n-C4H9)4N]2[Mo2O7] (II, right column) from ATR [(a) and (d)], Nujol mull [(b) and (e)], and KBr pellet [(c) and (f)].
Materials 02 00869 g001
The current reactions for preparing I and II proceed relatively slowly because they are heterogeneous reactions. However, the overall time necessary to obtain analytically pure I in a crystalline form is not very different from that of the conventional method. The time required to obtain II is much shorter and the overall yield has been improved significantly in the current method, because there is no need to prepare I first.
In addition to providing simple and efficient methods for synthesizing I and II, the current study demonstrates that MoO3 is a good starting material for obtaining polymolybdates soluble in aprotic organic solvents, although MoO3 itself is insoluble in those solvents. In fact, [(n-C4H9)4N]5[IMo6O24] has recently been prepared in a good yield using MoO3 as a starting material [30].

3. Experimental

3.1. General

The following were purchased from commercial sources and used without further purification: MoO3 (Nakarai), P2O5 (Kishida), and 10% aqueous [(n-C4H9)4N]OH (Wako). Acetonitrile (Wako) was dried over 3-Å molecular sieves. Diethyl ether (Kishida) was dried over 4-Å molecular sieves. The pH of the reaction mixtures was measured with METTLER DELTA340 pH meter. IR spectra were recorded on a Shimadzu FTIR-8400 spectrometer. The numerical values given below are for the spectra recorded from mineral oil (Nujol) mulls between KBr plates. Absorptions are described as follows: very strong (vs), strong (s), medium (m), weak (w), and shoulder (sh). Elemental analyses were performed by Toray Research Center Inc., Shiga, Japan.
Preparation of [(n-C4H9)4N]4[α-Mo8O26] (I): Molybdenum(VI) oxide (MoO3, 1.2 g, 8.3 mmol) was mixed with aqueous [(n-C4H9)4N]OH (10 mL, 4.1 mmol). The mixture was stirred for 60 h, during which time the pH of the mixture went down from 7.8 to 6.1 and the slightly gray suspension turned bright white. The precipitate was collected on a fine-porosity filter with suction and dried in vacuo over P2O5. This crude product (2.1 g) was dissolved in 15 mL of acetonitrile. After a small amount of insoluble material was filtered off with a fine-porosity filter, the filtrate was stored overnight at – 35 °C. The clear, colorless, block-shaped crystals that formed were collected on a medium-porosity filter with suction and dried in vacuo over P2O5 for 8 h to yield 1.6 g of the product (0.74 mmol, 72%). Anal. calcd. for C64H144N4Mo8O26: C, 35.70; H, 6.74 N, 2.60; Mo, 35.6. Found: C, 35.67, H, 6.75; N, 2.77; Mo, 35.6. IR (400 – 1,000 cm-1): 501 (m), 562 (m), 659 (vs), 722 (m), 735 (m), 807 (s), 854 (m), 881 (w), 905 (s), 920 (s), 950 (m).
Preparation of [(n-C4H9)4N]2[Mo2O7] (II): Molybdenum(VI) oxide (MoO3, 0.59 g, 4.1 mmol) was mixed with aqueous [(n-C4H9)4N]OH (10 mL, 4.1 mmol). The mixture was left stirring overnight, during which time the pH of the mixture went down from 7.5 to 6.6 and the slightly gray suspension turned bright white. The mixture was then evaporated to dryness under vacuum, and the solids thus obtained were dissolved in acetonitrile (5 mL). After a small amount of insoluble material was filtered off with a fine porosity filter, diethyl ether (23 mL) was added to the filtrate. The mixture was then stored overnight at –35 °C. The colorless crystals that formed were collected on a medium-porosity filter with suction and dried in vacuo over P2O5 for 4 h to yield 1.2 g of the product (1.5 mmol, 73%). Anal. calcd. for C32H72N2Mo2O7: C, 48.73; H, 9.20 N, 3.55. Found: C, 48.63, H, 9.33; N, 3.64. IR (400–1,000 cm-1): 746 (m), 770 (s), 867 (vs), 927 (w).

4. Conclusions

Direct reactions between MoO3 and [(n-C4H9)4N]OH in stoichiometric ratios have been proven to be a facile and convenient way to prepare tetra-n-butylammonium salts of [α-Mo8O26]4- and [Mo2O7]2- in high yields. The current study, together with the report of the successful synthesis of the tetra-n-butylammonium salt of [IMo6O24]5- by a similar method [30], demonstrates the potential of MoO3 as a starting material for the general syntheses of non-aqueous polymolybdates.

References and Notes

  1. Fuchs, J.; Hartl, H. Structure of tetrabutylammonium octamolybdate. Angew. Chem. Int. Ed. Engl. 1976, 15, 375–376. [Google Scholar] [CrossRef]
  2. Klemperer, W.G.; Shum, W. Synthesis and interconversion of the isomeric α- and β-Mo8O264- ions. J. Am. Chem. Soc. 1976, 98, 8291–8293. [Google Scholar] [CrossRef]
  3. Day, V.W.; Fredrcih, M.F.; Klemperer, W.G.; Shum, W. Structural and dynamic stereochemistry of α-Mo8O264-. J. Am. Chem. Soc. 1977, 99, 952–953. [Google Scholar] [CrossRef]
  4. Day, V.W.; Fredrcih, M.F.; Klemperer, W.G.; Shum, W. Synthesis and characterization of the dimolybdate ion, Mo2O72-. J. Am. Chem. Soc. 1977, 99, 6146–6148. [Google Scholar] [CrossRef]
  5. Nugent, W.A. In situ-generated molybdenum(VI) reagent for cis-chlorination of alkenes. Tetrahedron Lett. 1978, 37, 3427–3430. [Google Scholar] [CrossRef]
  6. Day, V.W.; Fredrich, M.F.; Klemperer, W.G.; Liu, R.S. Polyxomolybdate-hydrocarbon interactions. Synthesis and structure of the CH2Mo4O15H3- anion and related methylene-dioxymolybdates. J. Am. Chem. Soc. 1979, 101, 491–492. [Google Scholar]
  7. Do, Y.; Simhon, E.D.; Holm, R.H. Oxo/Sulfido ligand substitutuion in [Mo2O7]2-: Reaction sequence and characterization of the final product, [MoS3(OSiM3)]-. Inorg. Chem. 1985, 24, 1831–1838. [Google Scholar] [CrossRef]
  8. Che, T.M.; Day, V.W.; Francesconi, L.C.; Fredrich, M.F.; Klemperer, W.G.; Shum, W. Synthesis and structure of the [CpTi(Mo5O18)]3- and [CpTi(W5O18)]3- anions. Inorg. Chem. 1985, 24, 4055–4062. [Google Scholar] [CrossRef]
  9. Liu, S.; Shaikh, S.N.; Zubieta, J. Polyoxomolybdate-o-benzoquinone interactions. Synthesis and structure of a diacetal derivative, [Mo4O15(OH)(C14H8)]3-, from 9,10-phenanthrenequinone carbonyl insertion. Comparison to the reaction products with tetrachloro-1,2-benzoquinone, the ligand-bridged binuclear complexes [(MoO2Cl2)2L]2-, L = (C6Cl2O4)2- and (C2O4)2-, formed via carbonyl insertion and chloride transfer. Inorg. Chem. 1988, 27, 3064–3066. [Google Scholar]
  10. Chen, Q.; Liu, S.; Zhu, H.; Zubieta, J. Carbomolybdate clusters formed by carbonyl insertion into molybdenum-oxygen bonds. Structural investigation of the [RMo4O15X]3- core (R = -C9H4O, X = OCH3; R = -C14H10, X = -C7H5O2; R = C14H8, X = -OH). Polyhedron 1989, 8, 2915–2923. [Google Scholar]
  11. Ichida, H.; Yagasaki, A. Synthesis and structure of the novel polymolybdate which contains five-coordinated Mo(VI). J. Chem. Soc., Chem. Commun. 1991, 27–28. [Google Scholar]
  12. Kitamura, A.; Ozeki, T.; Yagasaki, A. β-Octamolybdate as a building block. Synthesis and structural characterization of rare earth–molybdate adducts. Inorg. Chem. 1997, 36, 4275–4279. [Google Scholar]
  13. Proust, A.; Thouvenot, R.; Herson, P. Revisiting the synthesis of [Mo6Cp*O18]-. X-Ray structural analysis, UV-visible, electrochemical and multinuclear NMR characterization. J. Chem. Soc., Dalton Trans. 1999, 51–55. [Google Scholar]
  14. Wang, X.-J.; Chen, Z.-F.; Kang, B.-S.; Liang, H.; Liu, H.-Q.; Yu, K.-B.; Su, C.-Y.; Chen, Z.-N. Chemistry of 2-mercaptophenol (H2mp). Part iii. One dimensional arrays of binuclear anions of Mo (VI) linked by bis (2-hydroxyphenyl) disulfide via hydrogen bondings. Polyhedron 1999, 18, 647–655. [Google Scholar]
  15. Ozeki, T.; Sakaguchi, M.; Yagasaki, A. Synthesis and structure of a novel dimeric molybdenum oxyhalide anion. Polyhedron 2000, 19, 43–45. [Google Scholar] [CrossRef]
  16. Nishikawa, K.; Kinoshita, I.; Nishioka, T.; Isobe, K. Synthesis and X-ray analysis of Mn-Mo mixed metal oxide cluster with cubic framework. Chem. Lett. 2000, 1342–1343. [Google Scholar] [CrossRef]
  17. Wei, Y.; Lu, M.; Cheung, C.F.; Barnes, C.L.; Peng, Z. Functionalization of [MoW5O19]2- with aromatic amines: Synthesis of the first arylimido derivatives of mixed-metal polyoxometalates. Inorg. Chem. 2001, 40, 5489–5490. [Google Scholar] [CrossRef] [PubMed]
  18. Hasenknopf, B.; Delmont, R.; Herson, P.; Gouzerh, P. Anderson-type heteropolymolybdates containing tris(alkoxo) ligands: Synthesis and structural characterization. Eur. J. Inorg. Chem. 2002, 1081–1087. [Google Scholar] [CrossRef]
  19. Liang, H.; Chen, Z.-F.; Hu, R.-X.; Yu, Q.; Zhou, Z.-Y.; Zhou, X-G. Synthesis, crystal structure and spectroscopic characterization of mono- and tetra-nuclear molybdenum(VI) complexes with 2-mercaptopyridine N-oxide: (n-Bu4N)2[MoO2(PT)2·Mo4O8(μ-O)2(μ3-O)2(PT)2]. Trans. Met. Chem. 2002, 27, 102–104. [Google Scholar]
  20. Marcoux, P.R.; Hasenknopf, B.; Vaissermann, J.; Gouzerh, P. Developing remote metal binding sites in heteropolymolybdates. Eur. J. Inorg. Chem. 2003, 2406–2412. [Google Scholar] [CrossRef]
  21. Bustos, C.; Hasenknopf, B.; Thouvenot, R.; Vaissermann, J.; Proust, A.; Gouzerh, P. Lindqvist-type (aryldiazenido)polyoxomolybdates - synthesis, and structural and spectroscopic characterization of compounds of the type (nBu4N)3[Mo6O18(N2Ar)]. Eur. J. Inorg. Chem. 2003, 2757–2766. [Google Scholar] [CrossRef]
  22. Roh, S.-G.; Proust, A.; Robert, F.; Gouzerh, P. Coordination chemistry of amidoximes. Molybdenum complexes of (alkyl)aminoacetamidoximes and fumaromonoamidoxime. Inorg. Chim. Acta 2003, 342, 311–315. [Google Scholar] [CrossRef]
  23. Laurencin, D.; Fidalgo, E.G.; Villanneau, R.; Villain, R.; Herson, P.; Pacifico, J.; Stoeckli-Evans, H.; Benard, M.; Rohmer, M.-M.; Suess-Fink, G.; Proust, A. Framework fluxionality of organometallic oxides: Synthesis, crystal structure, EXAFS, and DFT studies on [{Ru(η6-arene)}4Mo4O16] complexes. Chem. Eur. J. 2004, 10, 208–217. [Google Scholar] [CrossRef] [PubMed]
  24. Wu, P.; Li, Q.; Ge, N.; Wei, Y.; Wang, Y.; Wang, P.; Guo, H. An easy route to monofunctionalized organoimido derivatives of the lindqvist hexamolybdate. Eur. J. Inorg. Chem. 2004, 2819–2822. [Google Scholar] [CrossRef]
  25. Li, Q.; Wu, P.; Xia, Y.; Wei, Y.; Guo, Y. Synthesis, spectroscopic studies and crystal structure of a polyoxoanion cluster incorporating para-bromophenylimido ligand, (Bu4N)2[Mo6O18(NC6H4Br-p)]. J. Organomet. Chem. 2006, 691, 1223–1228. [Google Scholar] [CrossRef]
  26. Qui, Y.; Xu, L.; Gao, G.; Wang, W.; Li, F. A new arylimido derivative of polyoxometalate (Bu4N)2[Mo6O17(NAr)2] [Ar = 2,6-(CH3)2C6H3]: Synthesis, structure and physicochemical properties. Inorg. Chim. Acta 2006, 359, 451–458. [Google Scholar] [CrossRef]
  27. Xu, L.; Lu, M.; Xu, B.; Wei, Y.; Peng, Z.; Powell, D.R. Towards main-chain-polyoxometalate-containing hybrid polymers: A highly efficient approach to bifunctionalized organoimido derivatives of hexamolybdates. Angew. Chem. Int. Ed. Eng. 2002, 41, 4129–4132. [Google Scholar] [CrossRef]
  28. Klemperer, W.G. Tetrabutylammonium isopolyoxometalates. Inorg. Syntheses 1990, 27, 74–85. [Google Scholar]
  29. Compound I does not react with KBr when the latter is thoroughly dried and a spectrum of pure I is obtained. See ref. [2]
  30. Honda, D.; Ikegami, S.; Inoue, T.; Ozeki, T.; Yagasaki, A. Protonation and methylation of an anderson-type polyoxoanion [IMo6O24]5-. Inorg. Chem. 2007, 46, 1464–1470. [Google Scholar] [CrossRef] [PubMed]

Share and Cite

MDPI and ACS Style

Ikegami, S.; Yagasaki, A. Efficient Syntheses of [(n-C4H9)4N]4[α-Mo8O26] and [(n-C4H9)4N]2[Mo2O7]. Materials 2009, 2, 869-875. https://doi.org/10.3390/ma2030869

AMA Style

Ikegami S, Yagasaki A. Efficient Syntheses of [(n-C4H9)4N]4[α-Mo8O26] and [(n-C4H9)4N]2[Mo2O7]. Materials. 2009; 2(3):869-875. https://doi.org/10.3390/ma2030869

Chicago/Turabian Style

Ikegami, Shusaku, and Atsushi Yagasaki. 2009. "Efficient Syntheses of [(n-C4H9)4N]4[α-Mo8O26] and [(n-C4H9)4N]2[Mo2O7]" Materials 2, no. 3: 869-875. https://doi.org/10.3390/ma2030869

APA Style

Ikegami, S., & Yagasaki, A. (2009). Efficient Syntheses of [(n-C4H9)4N]4[α-Mo8O26] and [(n-C4H9)4N]2[Mo2O7]. Materials, 2(3), 869-875. https://doi.org/10.3390/ma2030869

Article Metrics

Back to TopTop