Crystal structures of two new heptamolybdates and of a pyrazole incorporating a γ-octamolybdate anion

doi:10.1016/S0020-1693(99)00329-1

Inorganica Chimica Acta

Volume 295, Issue 1, 15 November 1999, Pages 106-114

https://doi.org/10.1016/S0020-1693(99)00329-1 Get rights and content

Abstract

Two new heptamolybdates, one containing calcium and imidazole and the other with urea and ammonium cations, have been prepared. X-ray crystallographic studies of single crystals of both compounds have been carried out. In the mixture of calcium and imidazole [(Himi)₄][Ca(H₂O)₆(μ-O)₂][Mo₇O₂₄]·2(imi)·3H₂O (1), the calcium(II) cation is surrounded by six water molecules and two oxygen atoms from the polyanion, and bridges in trans position two [Mo₇O₂₄]⁶⁻ polyanions forming a linear composite with alternating Mo₇O₂₄ and Ca(H₂O)₆ units. The urea compound [CO(NH₂)₂H]₃(NH₄)₉[Mo₇O₂₄]₂·5[CO(NH₂)₂]·4H₂O (2) presents [Mo₇O₂₄]⁶⁻ heptamolybdate anions bound by hydrogen bonds from NH₄⁺, [CO(NH₂)H] cations and H₂O molecules. A new crystalline phase of a γ-octamolybdate containing pyrazole coordinatively bound to molybdenum has also been prepared [(Hpyr)₄][(pyr)₂(Mo₈O₂₆)]CH₃COCH₃·2H₂O (3). The structure has been solved by X-ray diffraction from a single crystal. The MoN bond length is 2.262(3) Å. All compounds have been characterised by IR, ¹H NMR and thermal analysis.

Introduction

It is interesting to study the interaction between MoO₃ and molecules of biological interest such as imidazole (in the presence of the calcium(II) cation) and pyrazole. Moreover, the interaction between MoO₃ and urea, to our knowledge, has not been previously described. This study is of interest because of the biological importance of both molybdenum(VI) and urea. Moreover, MoO₃ can act as a catalyst in the transformation of small molecules such as methanol, which is oxidised to formaldehyde [1]. Here, we present a study of the possible changes produced in the urea molecule by MoO₃, including its hydrolysis acid [2] by the effect of the H⁺ proceeding from MoO₃ in aqueous solution. Urea is one of the world’s most important chemicals because of its wide use in different areas [3].

As a result of our study, we report on two new heptamolybdates, one of them with imidazole and calcium [(Himi)₄][Ca(H₂O)₆(μ-O)₂][Mo₇O₂₄]·2(imi)·3H₂O (1), and the other with urea and ammonium cations [CO(NH₂)₂H]₃(NH₄)₉[Mo₇O₂₄]₂·5[CO(NH₂)₂]·4H₂O (2). We also report a new γ-octamolybdate of pyrazole [(Hpyr)₄][(pyr)₂Mo₈O₂₆]CH₃COCH₃·2H₂O (3).

To the best of our knowledge, no data for isomolybdates of mixed organic and calcium cations as well as urea and ammonium are available, this being the first time that a linear composite with alternating Mo₇O₂₄ and Ca(H₂O)₆ units is described.

Moreover, organic isopolymolybdates draw great interest because of their photochemical and photochromic properties as well as being potential antitumour and anti-VIH agents [4], [5], [6], [7].

Section snippets

General procedures and instrumentation

All chemicals were commercially available reagent grade. Deionized water was used for all syntheses. Elemental analyses (C, H and N) were performed with an EA 1108 CHNS-O automatic analyser. Calcium was determined using a Varian Spectra-10 PLUS atomic absorption spectrometer. IR spectra were recorded in the range 4000–250 cm⁻¹ on a Nicolet 710 FTIR spectrophotometer using KBr pellets. ¹H NMR spectra were collected on a Bruker WP-200 SY at 400 MHz with TMS as internal standard after dilution of

Preparation of [(Himi)₄][Ca(H₂O)₆(μ-O)₂][Mo₇O₂₄]·2(imi)·3H₂O (1)

A suspension of molybdenum trioxide (2.88 g, 20 mmol), imidazole (2.72 g, 40 mmol) and 10 cm³ of sulfuric acid (18 M) in deionized water (1.1 l), was heated under reflux for 4 h. The initial pH 2.5 was raised to pH 5.8 by adding calcium hydroxide; then the suspension was filtered and from the solution, by slow evaporation at room temperature, colourless crystals suitable for X-ray analyses were obtained. Anal. Calc. for 1, C₁₈H₄₆Mo₇N₁₂O₃₅Ca: C, 12.7; H, 2.7; Ca, 2.4; N, 9.9. Found: C, 12.4; H,

Crystal structures determination and refinement

For compounds 1–3, irregular prismatic colourless crystals for 1 and 3 (0.07×0.5×0.4 and 0.07×0.05×0.04 mm, respectively) and hexagonal colourless crystals for 2 (0.4×0.25×0.25 mm) were mounted on a glass fiber and used for data collection. Cell constants and an orientation matrix for data collection were obtained by least-squares refinement of the diffraction data from 25 reflections in the range 10<θ<25° for 1 and 3, in a Stoe Siemens AED-2 diffractometer and in the range of 10<θ<19° in an

Synthesis

One of the main advantages of wet chemistry methods to obtain polyoxometalates is that weak interactions (hydrogen bonds, van der Waals, hydrophile–hydrophobic interactions, etc.) are not broken at temperatures below ca. 70°C. They are involved in the self-assembling of molecular precursors and play an important role during the formation of the polyanion network or of supramolecular associations [17].

The preparations for all compounds were similar, with the exception of the heptamolybdates

Supplementary material

Crystallographic data (without structure factors) of the structures described in this publication have been deposited with the Cambridge Crystallographic Data Centre as no. CCDC-125423 (1), CCDC-125424 (2) and CCDC-125425 (3). Copies of the data can be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-1223-336-033; e-mail: [email protected]). Figures S1 and S2 are available from the authors upon request.

Acknowledgements

P.G. gratefully acknowledges support from the Gobierno de Canarias (Project No. 245-108/98). Thanks are also due to Mrs P. Agnew for correcting the English text.

References (28)

E. McCarron et al.
Polyhedron
(1986)
P. Gili et al.
Polyhedron
(1992)
J. Livage
Coord. Chem. Rev.
(1998)
P.A. Lorenzo Luis et al.
Inorg. Chim. Acta
(1998)
R.T. Morrison, R.N. Boyd, Organic Chemistry, 5th ed., Allyn and Bacon Inc., Boston,...
M.D. Joesten, D.O. Johnston, J.T. Netterville, J.L. Wood, Chemistry: Impact on Society, Saunders College Publishing,...
Chem. Rev., An issue of the Journal devoted to Polyoxometalates 98...
H.-K. Fung et al.
Acta Crystallogr., Sect. C
(1996)
X. You et al.
Acta Crystallogr., Sect. C
(1989)
P.Y. Zavalij et al.
Acta Crystallogr., Sect. C
(1997)

P. Martı́n-Zarza, J.M. Arrieta, M.C. Muñoz-Roca, P. Gili, J. Chem. Soc., Dalton Trans. (1993)...

M.K. Ehlert et al.

Inorg. Chem.

(1993)

G.H. Stout, L.H. Jensen, X-Ray Structure Determination. A Practical Guide, 2nd ed., Wiley, New York, 1989, p....

G.M. Sheldrick, shelxs86, Acta Crystallogr., Sect. A 46 (1990)...

Cited by (41)

Oxidation vs. coordination chemistry of the {MoV<inf>2</inf>O<inf>4</inf>}2+ species: A structural study
2022, Journal of Molecular Structure
Citation Excerpt :
Many [MoVI7O24]6–-containing compounds are known [51–60]. The majority are salts with protonated organic bases such as propan-1-amine [53], pyrrolidine [51], dabco [61], imidazole [62], 2-aminopyridine [54,55,58], etc. The geometric parameters of heptamolybdate in MoVI7MoVI agree well with the reported values [51,58,63].
The reaction systems consisting of mononuclear [Mo^VOCl₄(H₂O)]^–, carboxylate-based ligand and acetonitrile have afforded three novel polyoxomolybdate compounds. All three were characterized by X-ray structure analysis on single-crystal. The combination with phthalic acid has produced (Et₃NH)₈[Mo^V₄Mo^VI₁₂O₅₀]·2Py (Mo^V,VI₁₆, Et₃NH⁺ = a protonated triethylamine, Py = pyridine), a compound with the mixed-valence hexadecanuclear cluster anion. Its four pentavalent sites form part of well-known {Mo^V₂O₄}²⁺ units, the remaining twelve metal ions are fully-oxidized. The quinaldinate system has led to a genuine {Mo^V₂O₄}²⁺ complex with the carboxylate ligand, (Et₃NH)[Mo^V₂O₄(quin)₃]·CH₃OH (Mo^V₂, quin^– = a deprotonated form of quinoline-2-carboxylic acid), and to a fully-oxidized compound, (PipeH)₈[Mo^VI₇O₂₄][Mo^VIO₄]·CH₃CN (Mo^VI₇Mo^VI, PipeH⁺ = a protonated piperidine). The latter compound contains a very rare combination of two oxomolybdate(VI) species, heptamolybdate [Mo^VI₇O₂₄]^6– and monomolybdate [Mo^VIO₄]^2–.
Oxidation of sulfides in aqueous media catalyzed by pyrazole-oxidoperoxido-molybdenum(VI) complexes
2020, Inorganica Chimica Acta
Citation Excerpt :
All of these pyrazole-derived ligands and their respective coordination modes can be found in a wide selection of mononuclear and dinuclear oxidomolybdenum(VI) complexes [9–22], with representative examples being [MoO2Cl2(L1)2], [MoO2Cl2(L2)], [(L3)MoO3], [MoO2Cl(L3)]n+, [MoO(O2)2(L1)2], [(MoO2Cl(L1)2)2(μ2-O)] and [(MoO2(L3))2(μ2-O)]n+, where L1 indicates a monodentate ligand (e.g. pzH, 3-methylpyrazole (Mepz) or 3,5-dimethylpyrazole (dmpz)), L2 indicates a bidentate ligand (e.g. bis(pyrazolyl)alkane (bpza)), and L3 indicates a tridentate ligand (e.g. HC(pz)3 or HC(3,5-Me2pz)3). The structural diversity of discrete oxidomolybdenum(VI) complexes bearing coordinatively bound pyrazole-derived ligands extends to high-nuclearity molecules such as the tetranuclear complex [Mo4O16(dmpz)6] (consisting of a symmetrical {MoO(μ-O)(O2)(dmpz)}2 binuclear core to which two [MoO2(O2)(dmpz)2] units are connected) [16,18], the compounds [HL1]4[Mo8O26(L1)2] which incorporate γ-octamolybdate anions [19,23], and the tetraperoxido-octamolybdate derivatives [HL1]4[Mo8O22(O2)4(L1)2]·nH2O [18,19]. Oxido- and oxidoperoxido-molybdenum(VI) complexes with organic ligands are well known for their catalytic activity in olefin epoxidation with hydroperoxides [24–26].
The complex [MoO(O₂)₂(pyrazole)₂] (1) is an effective catalyst for the oxidation of organic sulfides (methylphenylsulfide and diphenylsulfide). Reactions can be run in water as the only medium, at low temperature (25 °C), with low catalyst loadings (0.2 mol%) and excellent H₂O₂ efficiency with no significant non-productive decomposition of the oxidant. Under conditions that favor sulfone formation, the overall process, including isolation of the precipitated product (by filtration or centrifugation) and recycling of the aqueous phase containing the catalyst, can be performed in the absence of organic or ionic liquid solvents. Catalytic results with the recycled aqueous phase were the same as those obtained in the first cycle. With water as the sole solvent, 1 is a superior catalyst to the 3,5-dimethylpyrazole complexes [MoO(O₂)₂(dmpz)₂] (2) and [Hdmpz]₄[Mo₈O_25.8(O₂)_0.2(dmpz)₂]·4H₂O (3). Crystal structures for 1 and 3 are presented.
Directing role of the synthetic route on the self-assembly process of MoO<inf>4</inf>2− units to Mo<inf>7</inf>O<inf>24</inf>2− or Mo<inf>22</inf>O<inf>74</inf>16− ions
2020, Inorganica Chimica Acta
Different synthetic routes, solution-based methods performed at room temperature, under reflux or hydrothermally at 110 °C, along with mechanochemically accelerated (hand grinding or liquid-assisted ball milling) vapour-assisted aging, yielded polyoxomolybdate [Co(en)₃]₂[Mo₇O₂₄]·8H₂O (1) as the final product. The new heptamolybdate 1 was the only product of the reaction between sodium molybdate, tris(ethylendiamine)cobalt(III) chloride and succinic acid when the used molar ratio of Mo: Co: acid was 1:1:1 or 1:6:1, regardless to the employed synthetic route (solution vs. solid state). From the literature known polyoxomolybdate [Co(en)₃]₅Na[Mo₇O₂₄(μ-Mo₈O₂₆)Mo₇O₂₄]·nH₂O (2) was also isolated as the main product only from the solution based methods where the sodium molybdate was present in an excess (molar ratio 6:1:1) and in the case when the reaction was conducted at elevated temperature and by employing the excess of succinic acid (molar ratio 1:1:6). All products were characterized by means of elemental analysis, IR spectroscopy as well as powder and single crystal X-ray diffraction analysis.
Application of central composite design to the partition of perrhenate anion in aqueous two phase system Na <inf>2</inf> MoO <inf>4</inf>  + PEG 4000 + H <inf>2</inf> O
2019, Journal of Molecular Liquids
Citation Excerpt :
On the other hand, molybdenum can be present as polyoxometalates, whose form a class of inorganic compounds that are unique in terms of molecular and electronic structural versatility, reactivity, and relevance for the analytical chemistry, catalysis, biology, medicine, geochemistry, materials science, topology, nanomaterials and supramolecular chemistry [2,3]. Moreover, hybrid organic isopolymolybdates arouse great interest due to their photochemical and photo-chromic properties as well as being potential antitumour and anti-HIV agents [4]. Rhenium is recovered during pyrometallurgical processing of molybdenum sulfide and copper sulfide ores; the traditional technology involves removing rhenium (VII) oxide, Re2O7, from the sulfurous gas phase generated during roasting process (in molybdenum processing) and smelting (in copper processing) [5,6].
Rhenium and molybdenum are valuable metals present in the earth's crust in very low concentration and are increasingly used in industry thanks to their multiple properties, but due to the harmful aspects of the production process, there is a need to develop systems of concentration or purification of salts of these elements. For this work a PEG/Na₂MoO₄ aqueous two phase system (ATPS) was used for the partition of ReO₄^- anion. By using a central composite design, the effects of PEG concentration, sodium molybdate concentration, temperature, pH and their possible interaction on the partition coefficient were studied, also to estimate the optimal configuration of the factors that influence the process. At the same time, experimental density, sound velocity and isentropic compressibility were also obtained for top and bottom phases. The results showed that the optimal conditions for the partition of ReO₄⁻ anion using the ATPS formed by PEG and Na₂MoO₄ were 14.7 wt% PEG 4000, 16.3 wt% Na₂MoO₄, 35 °C and pH 6. For these conditions, the partition coefficient (K) obtained was up to 17.8 ± 0.78. The order of factors with high significance on the partition coefficient was: Na₂MoO₄ concentration > PEG concentration > temperature > pH > interaction between Na₂MoO₄ and PEG concentrations; the effect of these parameters mainly is related with the speciation, salting-out effect and hydrophobicity. The influence of these factors on the density, and sound velocity of the top phase was minimal, unlike its influence on the properties of the bottom phase, not isentropic compressibility and effect of PEG and Na₂MoO₄ concentrations on sound velocity. The evaluation of the partitioning behavior was made by experimental design, applying statistical regression analysis and analysis of variance (ANOVA). The statistical models for partition coefficient and for phase densities (and the other properties) as function of parameters with significant effects were obtained, and also a good correlation between experimental and correlated data was observed (R-Squared = 0.9379, ReO₄⁻ partition coefficient; 0.9882, bottom phase; and 0.9836 upper phase). This work is oriented to the possible application in stripping of a top phase provided for a co-extraction of rhenium and molybdenum by ATPS in acidic media or in solutions with high contend of Mo such as those provided by pressure oxidative leaching of molybdenite in basic media.
Stabilization of β-octamolybdate with large counterions
2017, Journal of Molecular Structure
Two new organic-inorganic compounds [H₂NC(N(CH₃)₂)₂]₄[Mo₈O₂₆]·2H₂O (1) and (C₆H₁₁NH₃)₄[Mo₈O₂₆] (2) have been synthesized at room temperature and characterized by single-cristal X-ray diffraction, thermal and elemental analyses. We show that the β-[Mo₈O₂₆]⁴⁻ isomer can be stabilized by counterions which are either small or large. This observation is contradictory to the common rule which states that the β isomer should be stabilized by small counterions. Thus, we show that the organic counterion in both compounds (1) and (2) are large, but its ammonium group stabilize the β form owing to its localization in a specific nucleophilic site.
The Anderson-Evans polyoxometalate: From inorganic building blocks via hybrid organic-inorganic structures to tomorrows "Bio-POM"
2016, Coordination Chemistry Reviews
Citation Excerpt :
Interestingly, when ZnII and NiII were used as heteroatoms and tris-CH3 and tris-CH2OH as organic ligands, double-sided χ-isomers were also obtained despite using the route involving re-arrangement of octamolybdate (Fig. 7, C4) which resulted in loss of the threefold symmetry [86]. There exist 177 crystal structures of “extended” (see Section 2.2) structures in the AlIIIMo6 [61,69,74,76–78,81,82,173,191–205], CrIIIMo6 [56,60,63,65–69,73,76,79,81,173,177,191,194,195,199,201,204,206–217], NiIIMo6 [93,175,218–220], CoII/IIIMo6 [221–223] FeIIIMo6 [224], CuIIMo6 [174,225–229], ZnIIMo6 [230], AsIIIMo6 [229–232], Mo7 [112,176,193,233–245], TeVIMo6 [70,246–250], TeVIW6 [70,75,251–253], IVIIMo6 [82,97,193,214,254–257], W7 [172,258], PtIVMo6 [259,260] and PtIVW6 [261] systems as of March 2015. The following paragraphs looks into some interesting organic-inorganic compounds in terms of structure and crystal packing.
One of the most common polyoxometalates (POMs) is the Anderson–Evans archetype with the general formula [H_y(XO₆)M₆O₁₈]ⁿ⁻, where y = 0–6, n = 2–8, M = addenda atoms (Mo^VI or W^VI) and X = a central heteroatom. The Anderson–Evans archetype is a highly flexible POM cluster that allows modification from several point-of-views; (i) it can incorporate a large number of different heteroatoms differing in size and oxidation state, (ii) it can incorporate inorganic and organic cations and molecules demonstrating different coordination motifs, and (iii) covalent attachment with tris(hydroxymethyl)methane ligands allows it to be combined with specific organic functionalities. The catalog of available heteroatoms, counter cations and organic ligands has witnessed a tremendous expansion during the last years ranging from small inorganic anions that act as building-blocks for larger structures to anions in the nanometer range exhibiting multifunctional properties. This in-depth review discusses synthesis approaches and looks into existing Anderson–Evans structures with a special emphasis on structure-property relationship that tris(hydroxymethyl)methane functionalized structures bring. It also covers the successful use of the Anderson–Evans archetype in various fields of classical applications and describes its superiority to other POM archetypes especially in biological applications.

View all citing articles on Scopus

View full text

Article preview

Inorganica Chimica Acta

Abstract

Introduction

Section snippets

General procedures and instrumentation

Preparation of [(Himi)₄][Ca(H₂O)₆(μ-O)₂][Mo₇O₂₄]·2(imi)·3H₂O (1)

Crystal structures determination and refinement

Synthesis

Supplementary material

Acknowledgements

References (28)

Polyhedron

Polyhedron

Coord. Chem. Rev.

Inorg. Chim. Acta

Acta Crystallogr., Sect. C

Acta Crystallogr., Sect. C

Acta Crystallogr., Sect. C

Inorg. Chem.

Cited by (41)

Oxidation vs. coordination chemistry of the {Mo<sup>V</sup><inf>2</inf>O<inf>4</inf>}<sup>2+</sup> species: A structural study

Oxidation of sulfides in aqueous media catalyzed by pyrazole-oxidoperoxido-molybdenum(VI) complexes

Directing role of the synthetic route on the self-assembly process of MoO<inf>4</inf><sup>2−</sup> units to Mo<inf>7</inf>O<inf>24</inf><sup>2−</sup> or Mo<inf>22</inf>O<inf>74</inf><sup>16−</sup> ions

Application of central composite design to the partition of perrhenate anion in aqueous two phase system Na <inf>2</inf> MoO <inf>4</inf>  + PEG 4000 + H <inf>2</inf> O

Stabilization of β-octamolybdate with large counterions

The Anderson-Evans polyoxometalate: From inorganic building blocks via hybrid organic-inorganic structures to tomorrows "Bio-POM"

Crystal structures of two new heptamolybdates and of a pyrazole incorporating a γ-octamolybdate anion

Abstract

Introduction

Section snippets

General procedures and instrumentation

Preparation of [(Himi)4][Ca(H2O)6(μ-O)2][Mo7O24]·2(imi)·3H2O (1)

Crystal structures determination and refinement

Synthesis

Supplementary material

Acknowledgements

Polyhedron

Polyhedron

Coord. Chem. Rev.

Inorg. Chim. Acta

Acta Crystallogr., Sect. C

Acta Crystallogr., Sect. C

Acta Crystallogr., Sect. C

Inorg. Chem.

Preparation of [(Himi)₄][Ca(H₂O)₆(μ-O)₂][Mo₇O₂₄]·2(imi)·3H₂O (1)