Open Access
The effects of halogen substituents on the catalytic oxidation of benzylalcohols in the presence of dinuclear oxidovanadium(IV) complex
(Elsevier, 2017) Bikas, Rahman; Shahmoradi, Elaheh; Noshiranzadeh, Nader; Emami, Marzieh; Reinoso, Santiago; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
A new dinuclear complex of oxidovanadium(IV), namely [(VO)2(HL)(l-O)] (1), has been synthesized by the reaction of VO(acac)2 with the heptadentate N4O3-donor Schiff base ligand, 2-(5-Bromo-2-hydroxyphenyl)-1,3-bis(2-(5-bromo-2-hydroxybenzylideneamino)ethyl)imidazolidine (H3L). The complex has been characterized by elemental analysis, spectroscopic methods and single-crystal X-ray diffraction. The latter technique revealed that the vanadium ions have distorted octahedral geometry and are connected together by oxido and phenolic oxygen atoms. The bridging oxido ligand shares the equatorial positions of the two metal centers while the oxygen atom of the bridging phenol group connects the axial positions. The catalytic activity of this complex has been tested for the oxidation of some benzyl alcohol derivatives by using H2O2 as a green oxidant. In order to maximize the yields, the effects of various influential parameters in catalytic reactions such as the oxidant-to-substrate molar ratio, the temperature and the solvent, were studied. Moreover, the electronic and steric effects of halogen substituents on the phenyl group of the substrate were also explored by analyzing the oxidation of benzyl alcohol derivatives with F, Cl and Br atoms in the relative para-position (electronic effect), and of another set of substrates with a Cl substituent in relative ortho-, meta, and para-positions (steric effect). The results of these catalytic studies show that complex 1 catalyzes the oxidation of benzyl alcohol derivatives to the corresponding benzaldehydes with little amounts of the benzoic acid being detectable in the reaction mixture. Both the reaction conditions and the substituents on the phenyl group of the benzyl alcohols affect the selectivity and the activity of this catalytic system.
Open Access
A simple approach to develop tailored mesoporosity in nanostructured heteropolysalts
(Wiley, 2017) Alcañiz Monge, Juan; Trautwein, Guido; El Bakkali, Bouchra; Reinoso, Santiago; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
In this study, we describe a very simple approach to the development of tailored mesoporosity in any nanostructured heteropolysalt with control over both the mesoporous volume and the pore size. This approach, which consists in the treatment of a solid microporous precursor with a basic agent, has been tested on the ammonium salt of the Keggin‐type [PMo12O40]3− heteropolyanion and constitutes a novel procedure for the preparation of mesoporous solids with no precedents. The results obtained in this study allow two main conclusions to be drawn: 1) the micro‐ and mesoporous structures in the heteropolysalt nanoparticles are independent from each other and 2) the development of mesoporosity in the solid material must be related to a process of alkaline degradation within the core of the nanocrystals that aggregate into the particles. These results afford valuable additional information to the present model of porosity that has been established for heteropolysalts.
Open Access
Thermally-triggered crystal dynamics and permanent porosity in the first heptatungstate-metalorganic three-dimensional hybrid framework
(Wiley, 2017) Martín Caballero, Jagoba; Artetxe, Beñat; Reinoso, Santiago; San Felices, Leire; Castillo, Óscar; Beobide, Garikoitz; Vilas, José Luis; Gutiérrez Zorrilla, Juan M.; Institute for Advanced Materials and Mathematics - INAMAT2
The hybrid compound [{Cu(cyclam)}3(W7O24)]⋅15.5 H2O (1) (cyclam=1,4,8,11-tetraaza-cyclotetradecane) was synthesized by reacting the {Cu(cyclam)}2+ complex with a tungstate source in water at pH 8. Compound 1 exhibits an unprecedented three-dimensional covalent structure built of heptatungstate clusters linked through metalorganic complexes in a POMOF-like framework that displays water-filled channels. This dynamic architecture undergoes two sequential single-crystal-to-single-crystal transformations upon thermal evacuation of water molecules to result in the partially dehydrated [{Cu(cyclam)}3(W7O24)]⋅12 H2O (2) and anhydrous [Cu(cyclam)]0.5[{Cu(cyclam)}2.5(W7O24)] (3) crystalline phases. These transitions are associated with cluster rotations and modifications in the CuII coordination geometries, which reduce the dimensionality of the original lattice to layered systems but preserving the porous nature. Phase 3 reverts to 2 upon exposure to ambient moisture, whereas the transition between 1 and 2 proved to be irreversible. The permanent microporosity of 3 was confirmed by gas sorption measurements (N2, CO2), which reveal a system of parallel channels made of wide cavities connected through narrow necks that limit the adsorption process. This observation is in good agreement with Grand Canonical Monte Carlo simulations.
Open Access
The effect of the orientation of the Jahn-Teller distortion on the magnetic interactions of trinuclear mixed-valence Mn(II)/Mn(III) complexes
(Royal Society of Chemistry, 2019) Bikas, Rahman; Shahmoradi, Elaheh; Reinoso, Santiago; Emami, Marzieh; Lezama, Luis; Sanchiz, Joaquín; Noshiranzadeh, Nader; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Two new trinuclear manganese complexes, [Mn3(L1)(μ-OCH3)2(N3)2]·CH3OH (1) and [Mn3(L2)(μ-OCH3)2(N3)2]·CH3OH (2), have been obtained from the reaction of Mn(OAc)2 4H2O, NaN3 and the preformed N6O4-donor H4L1 or H4L2 compartmental ligands, which are synthesized via Schiff base condensation of pentaethylenehexamine with 2-hydroxybenzaldehyde or 2-hydroxy-3-methoxybenzaldehye, respectively. Complexes 1 and 2 have been characterized by spectroscopic methods and single-crystal X-ray analysis. The structural studies indicate that both 1 and 2 are mixed-valence complexes containing angular Mn(III)-Mn(II)-Mn(III) cores in which the metal centers are connected to each other by phenoxido and methoxido bridging groups. The coordination environment around the manganese ions is analogous in both complexes, but for a change in the direction of the Jahn-Teller distortion around the external Mn(III) ions when going from 1 to 2, which is mainly attributed to the steric effect of different substituents on the phenyl rings of the ligands. The analysis of the magnetic susceptibility data indicates the presence of antiferromagnetic intramolecular coupling in both complexes, but the interaction in 1 was found to be nearly one order of magnitude weaker than that in 2. This fact is rationalized on the basis of the different orientation of the Jahn-Teller distortion, which modifies the magnetic exchange pathway through the phenoxido bridges from the equatorial-axial connection type observed in 1 to the axial-axial linkages displayed by 2.
Open Access
Monokristal-monokristal eraldaketak polioxometalatoetan oinarritutako sistemetan: termikoki aktibatutako zenbait adibide
(Universidad del País Vasco, 2019) Fernández Navarro, Leticia; Ruiz Bilbao, Estíbaliz; Artetxe, Beñat; San Felices, Leire; Iturrospe, Amaia; Reinoso, Santiago; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Kanpo-estimuluen bitartez aktibatutako fase-trantsizioak, eta haien artean kristal bakun izaera mantentzen duten kasuak, hots monokristal-monokristal (MKMK) eraldaketak, interes handikoak dira; izan ere, gai dira i) ezaugarri berriak dituzten produktuak emateko eta ii) materialaren propietateetan gertatzen diren aldaketak, egitura kristalinoak jasaten dituenekin erlazionatzeko. Polioxometalatoen (POMen) kasuan bezala, egiturei zurruntasuna ematen dieten oinarrizko unitateak erabiltzea bide egokia da prozesuan zehar gerta litekeen kristalinitatearen galera saihesteko. Gaur egun POMetan oinarritutako sistemetan aurki daitezkeen MKMK eraldaketa urrien artean, aipatzekoak dira termikoki aktibatutako adibideak. Lan honetan azken hauek laburbilduko dira eta bereziki gure ikerketa taldean prestatutako konposatuak eta haien erabilerak (katalisia eta gasen xurgapen selektiboa) goraipatuko ditugu.
Open Access
Polioxometalatoak: elhuyar anaien ametsak bizirik dirau!
(Universidad del País Vasco, 2017) Artetxe, Beñat; Reinoso, Santiago; Gutiérrez Zorrilla, Juan M.; Institute for Advanced Materials and Mathematics - INAMAT2
Polioxometalatoak (POMak) kimika ez-organikoaren munduan ezagunak diren metalez eta oxigenoz osatutako kluster anionikoak dira. Azaldu ohi duten forma, konposizio eta propietate aniztasunaren ondorioz, POMek aplikazio ugari dituzte teknologiari, ekonomiari edo ingurugiroari lotutako arlo ezberdinetan. Nahiz eta aspaldidanik aplikazio katalitikoetan erabili, gaur egun etorkizunerako garrantzitsuak izango diren esparru oso ezberdinetarako ikertzen ari dira, besteak beste, hondakin-uren tratamenduan, medikuntzan, konputazio kuantikoan, energia-iturri berriztagarrietan edota sentsore kimiko lumineszenteetan. Horrengatik guztiagatik, polioxometalatoen kimika, etorkizun handiko kimika ezorganikoaren alorreko esparru dinamikoenetariko bat dela baiezta genezake.
Open Access
Thermostructural behavior in a series of lanthanide-containing polyoxotungstate hybrids with copper(II) complexes of the tetraazamacrocycle cyclam: a single-crystal-to-single-crystal transformation study
(American Chemical Society, 2019) Martín Caballero, Jagoba; Artetxe, Beñat; Reinoso, Santiago; San Felices, Leire; Vitoria, Pablo; Larrañaga, Aitor; Vilas, José Luis; Gutiérrez Zorrilla, Juan M.; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
A series of 14 isostructural [Cu(cyclam)](2)[{Cu(cyclam)}4{(a-GeW11O39)Ln(H2O)-(OAc)(12)].18H(2)O (1-Ln, where Ln = La Lu; cyclam = 1,4,8,11-tetraazacyclotetradecane) polyoxometalate-based hybrids reported herein represent (i) the first example of a twodimensional covalent hybrid lattice involving the [{(aXWI 1039)Ln(H2O)(OAc)}2in- archetype and (ii) the first structural characterization of such a dimeric polyoxotungste for Ln = La and Pr as well as for the combination of X = Ge and Ln = Ce, Nd, Sm, or Lu. Compounds 1-Ln have been characterized by elemental analyses, infrared spectroscopy, and thermogravimetric analysis, and their thermostructural behavior has been monitored by powder and single-crystal Xray diffraction. The title compounds undergo two single-crystal-to-single-crystal transformations triggered dehydration leading to the [{Cu(cydam)}6{(alpha-GeW11O39)Ln(H2O)(OAc)}2]-4H(2)O intermediate (2-Ln, where Ln = Eu or Er) and [Cu(cyclam)]0.5[{Cu(cyclam)}55{(alpha-GeW11O39)Ln(0Ac)}2] (3-Ln, where Ln = Ce or Eu) final anhydrous phases, the latter evidencing a coordinatively unsaturated derivative of the dimeric archetype for the first time. These transitions involve formation and disruption of Cu Opom bonds that result in different {Cu(cydam)}(2+) moieties grafting onto and being released from Keggin surfaces, which reduces the dimensionality of 1-Ln to one-dimensional covalent assemblies for 2-Ln and 3-Ln. While all 3-Ln phases rehydrate fully upon exposure to air for 24 h, the kinetics governing the crystal transitions back toward 1Ln through 2-Ln depend on the nature of Ln. Under ambient moisture, the anhydrous structures fully revert back to the parent framework for Ln = La Sm, while the samples containing Eu to Lu afford mixtures of 1-Ln and 2-Ln and require immersion in water for the structural reversion to reach completion. Single-crystal X-ray diffraction analyses of the rehydrated 1R-Ln samples (Ln = Ce, Eu, and Er) support these observations.
Open Access
Zirconia-supported tungstophosphoric heteropolyacid as heterogeneous acid catalyst for biodiesel production
(Elsevier, 2018) Alcañiz Monge, Juan; El Bakkali, Bouchra; Trautwein, Guido; Reinoso, Santiago; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
A series of materials based on the immobilization of the 12-tungstophosphoric heteropolyacid over zirconia supports have been prepared and applied as heterogeneous acid catalysts in the esterification of palmitic acid with methanol as a model reaction for the preliminary stage of the biodiesel production. The title materials have been obtained through the sol-gel method combined with a subsequent hydrothermal treatment at mild conditions, which affords catalysts with larger porosity and higher thermal and chemical stability under the esterification reaction conditions than other preparative approaches. Generating the zirconia support by hydrolysis of an alkoxyde precursor in the presence of the heteropolyacid leads to materials with homogeneously well-dispersed clusters, as well as to an increasing contribution of the tetragonal ZrO2 crystalline phase, a decreasing size of the nanoparticles and larger microporous volumes as the loading of the Keggin-type species increases. The 12-tungstophosphoric acid retains its catalytic activity in the esterification of palmitic acid with methanol at 60 °C upon immobilization over zirconia and conversions even higher than those observed under homogeneous conditions are obtained due to the active contribution of the support. The sample with a 30% mass percentage of heteropolyacid has been identified as the most efficient catalyst because it affords conversions above the 90% and shows the lower loss of activity over successive reaction runs among all of our materials. This loss of activity has been analyzed on the basis of the leaching of the catalyst and the fouling of the materials.
Open Access
Zirconia-supported 11-molybdovanadophosphoric acid catalysts: effect of the preparation method on their catalytic activity and selectivity
(Wiley, 2018) El Bakkali, Bouchra; Trautwein, Guido; Alcañiz Monge, Juan; Reinoso, Santiago; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa; Gobierno de Navarra / Nafarroako Gobernua
The oxidation of adamantane with hydrogen peroxide catalyzed by zirconia-supported 11-molybdovanadophosphoric acid is shown to be a suitable green route for the synthesis of adamantanol and adamantanone. This work evaluates how the catalyst activity and selectivity are affected by some of its preparative parameters, such as the method for supporting the catalytically active heteropoly acid over the zirconia matrix or the pretreatments applied to the resulting materials before being used as heterogeneous catalysts. Our results indicate that the most effective catalysts able to maintain their activity after several reaction runs are those prepared by following the sol-gel route, whereas the most selective catalysts are those obtained by impregnation methods. Moreover, the calcination temperature has also been identified as a relevant parameter influencing the performance of catalysts based on supported heteropoly acids. The increasing catalytic activity observed over several consecutive reaction runs has been attributed to the formation of peroxo derivatives of polyoxometalate clusters at the surface of the catalyst and their accumulation after each reaction cycle.
Open Access
Immobilization of polyoxometalates on tailored polymeric surfaces
(MDPI, 2018) Aguado-Ureta, Saioa; Rodríguez-Hernández, Juan; Campo, Adolfo del; Pérez-Álvarez, Leyre; Ruiz-Rubio, Leire; Vilas, José Luis; Artetxe, Beñat; Reinoso, Santiago; Gutiérrez Zorrilla, Juan M.; Ciencias; Zientziak
Herein we describe the preparation of hybrid polymer–inorganic interfaces by the immobilization of polyoxometalate nanoclusters on functionalized polymer surfaces. The polymeric surfaces were made of polystyrene-b-poly(acrylic acid)/polystyrene (PS-b-PAA/PS) blends by spin coating on a silicon wafer. The functionalization of the polymer film was obtained by interfacial migration of the amphiphilic block copolymer toward the interface upon water vapor annealing. The carboxylic acid functional groups contained in the PAA block were then employed to anchor the [LnIII(α-SiW11O39)]5− polyoxometalates (Ln: Ce, Er). This purpose was achieved by immersing the films in aqueous solutions of the in situ-formed inorganic nanoclusters. X-ray photoelectron and confocal Raman spectroscopies, together with atomic force microscopy, confirmed the immobilization of the inorganic species at the interface.