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• W2090216500 abstract "first_page settings Order Article Reprints Font Type: Arial Georgia Verdana Font Size: Aa Aa Aa Line Spacing:    Column Width:    Background: Open AccessArticle 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 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) Download Download PDF Download PDF with Cover Download XML Download Epub 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. Keywords: α-octamolybdate; dimolybdate; synthesis; tetra-n-butylammonium 1. IntroductionThe 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 DiscussionCompound 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]. 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)]. 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. GeneralThe 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. ConclusionsDirect 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. 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[2]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] © 2009 by the authors; licensee Molecular Diversity Preservation International, Basel, Switzerland. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/). 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 Find Other Styles Article Metrics No No Article Access Statistics For more information on the journal statistics, click here. Multiple requests from the same IP address are counted as one view." @default.
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