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Polyoxometalates and Polyoxometalate-Based Systems
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Polyoxometalates and Polyoxometalate-Based Systems

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Inorganic Chemistry".

Deadline for manuscript submissions: closed (30 April 2019) | Viewed by 29703

Special Issue Editor

Dr. Santiago Reinoso

E-Mail Website
Guest Editor
Departamento de Ciencias & Institute for Advanced Materials and Mathemathics (InaMat2), Universidad Pública de Navarra (UPNA), Pamplona, Spain
Interests: polyoxometalates; coordination chemistry of transition metals and rare earths; synthetic inorganic chemistry; single-crystal X-ray diffraction
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Polyoxometalates are a class of molecules that have fascinated researchers for decades. Despite being first described centuries ago, this type of anionic metal–oxygen clusters continues to represent a highly vibrant research domain because of their unmatched collection of versatile properties. The vast polyoxometalate family encompasses molecular species with very diverse sizes (from small dimetalates to clusters comparable to small proteins) and manifold structures (often with highly symmetric topologies) that tend to show rich solution equilibria, significant chemical and thermal stability, and the ability to act as proton–electron sinks thanks to their fast and reversible proton-coupled redox processes. These properties can usually be fine-tuned at the atomic level through systematic compositional modifications performed in the cluster skeleton. Moreover, the possibility of generating vacant metallic sites in a controlled manner allows polyoxometalates to be used as robust, fully-inorganic polydentate ligands toward a range of electrophilic moieties (e.g., transition-metal cations, rare earths, p-block organoderivatives, etc.), thus paving the way for endowing the clusters with tailored additional properties brought by such electrophiles. The combination of all these features confers an intrinsic multifunctional nature on polyoxometalates that places these clusters at the frontier between an exceptionally wide range of scientific disciplines, such as inorganic chemistry, physics, crystallography, catalysis, biology or medicine. As such, they offer virtually endless options for future applied developments in these areas, and hence, they are continuously selected as the active molecule of choice for constructing new advanced materials upon integration with, for example, polymers, oxides, or carbonaceous supports. This Special Issue is intended to focus on the most recent advances in polyoxometalate chemistry and polyoxometalate-based systems by covering different aspects from fundamentals (synthetic methods, reactivity, spectroscopic or spectrometric studies, structures, mechanistic insights) to potential applications (redox and acid-base catalysis, photo- and electrochemistry, magnetism, electronics, optics, bio-medicine, energy conversion and storage, sorption and separation, environmental remediation). Full papers, communications, and reviews on these topics are welcome.

Dr. Santiago Reinoso
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Polyoxometalates and derivatives
  • Synthesis and reactivity
  • Spectroscopic and spectrometric studies
  • Crystallochemistry
  • Computational modeling
  • Redox and acid-base catalysis
  • Photo- and electrochemistry
  • Magnetism
  • Electronics and optics
  • Batteries and capacitors
  • Sorption and separation
  • Environment
  • Bio-medical applications

Published Papers (7 papers)

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Research

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13 pages, 3134 KiB  
Article
Toward Advanced Functional Systems: Honeycomb-Like Polymeric Surfaces Incorporating Polyoxovanadates with Surface-Appended Copper-Cyclam Complexes
by Leire Ruiz-Rubio, Beñat Artetxe, Leyre Pérez-Álvarez, Jagoba Martín-Caballero, Tatsumi Ishihara, Juan M. Gutiérrez-Zorrilla and José Luis Vilas-Vilela
Molecules 2019, 24(12), 2313; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules24122313 - 22 Jun 2019
Cited by 3 | Viewed by 2645
Abstract
In this work the immobilization of hybrid polyoxometalates (POMs) onto functional polymeric surfaces is exposed and discussed. Thus, various hybrid polymer‒inorganic films were prepared by anchoring selected hybrid POMs onto tailored polymeric surfaces that consisted of breath figures (BFs) made of polystyrene-b-poly(acrylic acid)/polystyrene [...] Read more.
In this work the immobilization of hybrid polyoxometalates (POMs) onto functional polymeric surfaces is exposed and discussed. Thus, various hybrid polymer‒inorganic films were prepared by anchoring selected hybrid POMs onto tailored polymeric surfaces that consisted of breath figures (BFs) made of polystyrene-b-poly(acrylic acid)/polystyrene (PS-b-PAA/PS) blends. Functionalization of the BF films was performed by selective arrangement of acrylic acid groups of the amphiphilic block copolymer on the surface pores because of their affinition for the water condensed during breath figure formation. These carboxylic acid functional groups contained within the PAA blocks were then employed to anchor [Cu(cyclam)][{Cu(cyclam)}2(V10O28)]·10H2O (1-CuV10) and [{Cu(cyclam)}(VO3)2]·5H2O (1-CuV1), hybrid POMs by immersing the films into aqueous solutions of the in situ formed hybrid clusters, resulting in the hybrid films BF1 and BF2, respectively. Superficial analysis of these hybrid polymeric films was carried out by the sophisticated ion beam-based technique time-of-flight secondary ion mass spectrometry (ToF-SIMS) that was revealed to be an excellent method for the superficial compositional mapping of patterned surfaces. Full article
(This article belongs to the Special Issue Polyoxometalates and Polyoxometalate-Based Systems)
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14 pages, 1622 KiB  
Article
A Comprehensive Study on the Dye Adsorption Behavior of Polyoxometalate-Complex Nano-Hybrids Containing Classic β-Octamolybdate and Biimidazole Units
by Shuang Liang, Yan-Mei Nie, Sang-Hao Li, Jian-Liang Zhou and Jun Yan
Molecules 2019, 24(4), 806; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules24040806 - 22 Feb 2019
Cited by 9 | Viewed by 3293
Abstract
Six new hybrids based on β-[Mo8O26]4− polyoxometalates, [Ni(H2biim)3]2[β-Mo8O26]•8DMF(1); (DMA)2[M(H2biim)2(H2O)2][β-Mo8O26]•4DMF (M = Ni [...] Read more.
Six new hybrids based on β-[Mo8O26]4− polyoxometalates, [Ni(H2biim)3]2[β-Mo8O26]•8DMF(1); (DMA)2[M(H2biim)2(H2O)2][β-Mo8O26]•4DMF (M = Ni (2), Co (3)), DMA = dimethyl-ammonium, H2biim=2,2′-biimidazole); [M(H2biim)(DMF)3]2[β-Mo8O26]•2DMF (M = Zn (4), Cu (5)); [(DMA)2[Cu(DMF)4][β-Mo8O26]•2DMF]n (6), have been successfully synthesized and characterized. Compounds 2–5 show favorable capacity to adsorb methylene blue (MB) at room temperature, and they can selectively capture MB molecules from binary-mixture solutions of MB/MO (MO = Methyl Orange), or MB/RhB (RhB = Rhodamine B). Compound 3 can uptake up to 521.7 mg g−1 MB cationic dyes rapidly, which perform the maximum adsorption in an hour among the reported materials as far as we know. The compounds are stable and still work very efficiently after three cycles. For compound 3, the preliminary adsorption mechanism studies indicated that the adsorption is an ion exchange process and the adsorption behavior of polyoxometalate-complex can be benefited from additional exchangeable protons in the complex cations. Full article
(This article belongs to the Special Issue Polyoxometalates and Polyoxometalate-Based Systems)
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11 pages, 2679 KiB  
Article
A New 3-D Open-Framework Zinc Borovanadate with Catalytic Potentials in α-Phenethyl Alcohol Oxidation
by Xinxin Liu, Biao Guo, Xuejiao Sun, Le Zhang and Hongming Yuan
Molecules 2019, 24(3), 531; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules24030531 - 01 Feb 2019
Cited by 5 | Viewed by 2294
Abstract
A novel 3-D open-framework zinc borovanadate [Zn6(en)3][(VIVO)6(VVO)6O6(B18O36(OH)6)·(H2O)]2·14H2O (1, en = ethylenediamine) was hydrothermally obtained and [...] Read more.
A novel 3-D open-framework zinc borovanadate [Zn6(en)3][(VIVO)6(VVO)6O6(B18O36(OH)6)·(H2O)]2·14H2O (1, en = ethylenediamine) was hydrothermally obtained and structurally characterized. The framework was built from [V12B18O54(OH)6(H2O)]10− polyanion clusters bridged by Zn(en) complex fragments. The compound not only possessed a three-dimensional open-framework structure with unique plane-shaped channels, but also exhibited excellent catalytic activities for the oxidation of α-phenethyl alcohol. Full article
(This article belongs to the Special Issue Polyoxometalates and Polyoxometalate-Based Systems)
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14 pages, 5254 KiB  
Article
Substitution Effect on the Charge Transfer Processes in Organo-Imido Lindqvist-Polyoxomolybdate
by Patricio Hermosilla-Ibáñez, Kerry Wrighton-Araneda, Walter Cañón-Mancisidor, Marlen Gutiérrez-Cutiño, Verónica Paredes-García and Diego Venegas-Yazigi
Molecules 2019, 24(1), 44; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules24010044 - 22 Dec 2018
Cited by 3 | Viewed by 3596
Abstract
Two new aromatic organo-imido polyoxometalates with an electron donor triazole group ([n-Bu4N]2[Mo6O18NC6H4N3C2H2]) (1) and a highly conjugated fluorene ([n-Bu [...] Read more.
Two new aromatic organo-imido polyoxometalates with an electron donor triazole group ([n-Bu4N]2[Mo6O18NC6H4N3C2H2]) (1) and a highly conjugated fluorene ([n-Bu4N]2[Mo6O18NC13H9]) (2) have been obtained. The electrochemical and spectroscopic properties of several organo-imido systems were studied. These properties were analysed by the theoretical study of the redox potentials and by means of the excitation analysis, in order to understand the effect on the substitution of the organo-imido fragment and the effect of the interaction to a metal centre. Our results show a bathochromic shift related to the charge transfer processes induced by the increase of the conjugated character of the organic fragment. The cathodic shift obtained from the electrochemical studies reflects that the electronic communication and conjugation between the organic and inorganic fragments is the main reason of this phenomenon. Full article
(This article belongs to the Special Issue Polyoxometalates and Polyoxometalate-Based Systems)
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19 pages, 2758 KiB  
Article
A Charge-Transfer Salt Based on Ferrocene/Ferrocenium Pairs and Keggin-Type Polyoxometalates
by Beñat Artetxe, Amaia Iturrospe, Pablo Vitoria, Estibaliz Ruiz-Bilbao, José S. Garitaonandia and Juan M. Gutiérrez-Zorrilla
Molecules 2018, 23(12), 3150; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23123150 - 30 Nov 2018
Cited by 5 | Viewed by 4267
Abstract
A new hybrid inorganic-organometallic salt has been obtained from the reaction of the Keggin-type silicotungstate anion with ferrocene in a water/methanol mixture as a result of the partial oxidation of ferrocene molecules to ferrocenium cations. Single-crystal X-ray diffraction analysis reveals the presence of [...] Read more.
A new hybrid inorganic-organometallic salt has been obtained from the reaction of the Keggin-type silicotungstate anion with ferrocene in a water/methanol mixture as a result of the partial oxidation of ferrocene molecules to ferrocenium cations. Single-crystal X-ray diffraction analysis reveals the presence of four ferrocenium (FeIII) cations and one ferrocene (FeII) molecule per plenary Keggin anion in the crystal structure of [FeIII (Cp)2]4[SiW12O40]·[FeII(Cp)2]·2CH3OH (1). Compound 1 thus constitutes the first example in the literature in which ferrocenium and ferrocene species coexist in the structure of a polyoxometalate-based salt. The two crystallographically independent ferrocenium species in the asymmetric unit of 1 exhibit different configurations: One displays an eclipsed conformation with ideal D5h symmetry, whereas the conformation in the other one is staggered D5d. The crystal packing of 1 can be best described as an organometallic sub-lattice of ferrocenium and ferrocene species linked by a network of π-π interactions that generates rectangular cavities of about 14 × 10 Å in which strings of Keggin anions and methanol molecules are hosted, further connected to each other via weak OPOM···CMeOH-OMeOH···OPOM type hydrogen bonds. The charge-transfer nature of the salt has been studied by solid-state diffuse reflectance UV-Vis spectroscopy and the presence of magnetically isolated FeIII/FeII centres has been confirmed by Mössbauer spectroscopy. A topological study carried out on all of the pristine ferrocenyl species deposited in the Cambridge Structural Database (CSD) has allowed two main conclusions to be drawn: (1) these species tend to adopt extreme conformations (either eclipsed or staggered) with less than a 15% of examples showing intermediate states and (2) the oxidation state of the iron centres can be unequivocally assigned on the basis of a close inspection of the Fe···Cp distances, which allows ferrocene neutral molecules and ferrocenium cations to be easily distinguished. Full article
(This article belongs to the Special Issue Polyoxometalates and Polyoxometalate-Based Systems)
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9 pages, 615 KiB  
Article
Thermochemical Measurements of Alkali Cation Association to Hexatantalate
by Dylan J. Sures, G. P. Nagabhushana, Alexandra Navrotsky and May Nyman
Molecules 2018, 23(10), 2441; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules23102441 - 24 Sep 2018
Cited by 2 | Viewed by 3409
Abstract
Ion association is an important process in aqueous dissolution, precipitation, and crystallization of ionic inorganic, organic, and biological materials. Polyoxometalates (POMs) are good model compounds for understanding the complex relationships between lattice energy, ion-pairing in solution, and salt solubility. Here we perform calorimetric [...] Read more.
Ion association is an important process in aqueous dissolution, precipitation, and crystallization of ionic inorganic, organic, and biological materials. Polyoxometalates (POMs) are good model compounds for understanding the complex relationships between lattice energy, ion-pairing in solution, and salt solubility. Here we perform calorimetric measurements to elucidate trends in cluster stability, lattice energy, and ion-pairing behavior studies of simple hexatantalate salts in neat water, parent hydroxide solutions, and molybdate melts, extending previous studies on the isostructural hexaniobates. High temperature calorimetry of alkali salts of hexatantalate reveals that the enthalpies of formation from oxides of the K, Rb, and Cs salts are more similar to each other than they are for their niobate analogues and that the tantalate cluster is energetically less stable than hexaniobate. Aqueous dissolution calorimetry reveals that the cesium salt of hexatantalate has a similar concentration dependence on its dissolution enthalpy to that of hexaniobate. However, unlike rubidium hexaniobate, rubidium hexatantalate also exhibits increased concentration dependence, indicating that hextantalate can undergo increased ion-pairing with alkali salts other than cesium, despite the dilute environments studied. Dissolution enthalpies of POM salts in the parent alkali hydroxides shows that protonation of clusters stabilizes lattices even more than the strongly associating heavy alkali cations do. Additionally, neither weak nor strong lattice ion associations necessarily correlates with respectively high or low aqueous solubility. These studies illuminate the importance of considering ion-pairing among the interrelated processes in the aqueous dissolution of ionic salts that can be extended to serving as a model of cation association to metal oxide surfaces. Full article
(This article belongs to the Special Issue Polyoxometalates and Polyoxometalate-Based Systems)
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Review

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26 pages, 6299 KiB  
Review
Polyoxometalate-Based Catalysts for CO2 Conversion
by Yanwei Cao, Qiongyao Chen, Chaoren Shen and Lin He
Molecules 2019, 24(11), 2069; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules24112069 - 30 May 2019
Cited by 49 | Viewed by 9344
Abstract
Polyoxometalates (POMs) are a diverse class of anionic metal-oxo clusters with intriguing chemical and physical properties. Owing to unrivaled versatility and structural variation, POMs have been extensively utilized for catalysis for a plethora of reactions. In this focused review, the applications of POMs [...] Read more.
Polyoxometalates (POMs) are a diverse class of anionic metal-oxo clusters with intriguing chemical and physical properties. Owing to unrivaled versatility and structural variation, POMs have been extensively utilized for catalysis for a plethora of reactions. In this focused review, the applications of POMs as promising catalysts or co-catalysts for CO2 conversion, including CO2 photo/electro reduction and CO2 as a carbonyl source for the carbonylation process are summarized. A brief perspective on the potentiality in this field is proposed. Full article
(This article belongs to the Special Issue Polyoxometalates and Polyoxometalate-Based Systems)
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