BUSCADOR RECOLECTA

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 (Fe) cations and one ferrocene (Fe) molecule per plenary Keggin anion in the crystal structure of [Fe (Cp)][SiWO]·[Fe(Cp)]·2CHOH (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 D symmetry, whereas the conformation in the other one is staggered D. 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 O···C-O···O 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 Fe/Fe 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., This work was funded by UPV/EHU (grants PPG17/37 and GIU17/050), Eusko Jaurlaritza/Gobierno Vasco (PIBA2018-59) and Ministerio de Economía, Industria y Competitividad (grant MAT2017-89553-P)., Peer Reviewed

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., Phase transitions induced by external stimuli in which crystallinity is retained, so-called single-crystal-to-single-crystal transformations (SCSC), are being widely studied because they allow for i) obtaining products with novel characteristics and ii) correlating structural changes with how a given property of the material is modified. The use of building blocks that provide robustness to the system such as polyoxometalates (POM) are a suitable option to avoid the loss of crystallinity throughout the process. Among the scarce SCSC transformations reported to date for POM-based systems, it is worth highlighting the temperature-triggered examples. This work reviews the later cases with strong focus on the compounds obtained in our research group and their applications (catalysis and selective gas sorption)., Artikulu hau Eusko Jaurlaritzak Estibaliz Ruiz-Bilbaori eskainitako doktorego-aurreko diru-laguntzari esker (PRE_2018_1_0143) burutu da. Egileek UPV/EHU (PPG17/37, GIU17/050), Eusko Jaurlaritzaren (PIBA2018-59, KK-2018/00054) eta Ekonomia, Industria eta Lehiakortasun Ministerioaren (MAT2017-89553-P) finantziazioa eskertu nahi dute. Santiago Reinosok Obra Social la Caixa, Fundación Caja Navarra eta Nafarroako Unibertsitate Publikoaren «Captación de Talento» programaren bidez jasotako diru-laguntza eskertzen du.

A hydrothermal reaction between the monolacunary polyoxometalate [SiW11O39]8-, a copper(II) salt, and 1,4,8,11-tetraazacyclotetradecane (cyclam) affords the first example of a hybrid compound combining metal complexes of such an N4-tetradentate macrocyclic ligand and Keggin-type clusters, namely, [Cu(cyclam)(H2O)][{Cu(cyclam)}2SiW11O39Cu(H2O)]·5H2O (1). This compound has been characterized by infrared spectroscopy and thermal and elemental analyses. Single-crystal X-ray diffraction (scXRD) reveals a layered crystal packing made of corrugated two-dimensional covalent grids in which four octahedral {Cu(cyclam)}2+ bridging moieties connect copper(II)-monosubstituted {SiW11O39Cu(H2O)}6- polyanions to four adjacent clusters, and additional [Cu(cyclam)(H2O)]2+ square-pyramidal counterions are embedded into square-like grid voids. Thermostructural analyses confirm the presence in the 130-250 °C temperature range of a stable and crystalline anhydrous phase, which displays a diffraction pattern different from that of 1. This thermally triggered phase transition proceeds through a single-crystal to single-crystal transformation pathway, which according to scXRD, involves not only the release of water molecules, but also the cleavage and formation of Cu-O bonds induced by the rotation of Keggin-type anions. These modifications fully dismantle the parent two-dimensional covalent assembly to result in the neutral, discrete [{Cu(cyclam)}3SiW11O39Cu] hybrid species (2), in which the cluster exhibits three square-pyramidal {Cu(cyclam)}2+ decorating moieties grafted at its surface. This species must display a five-coordinated copper(II) center in the Keggin skeleton, and therefore, it constitutes one of the scarce examples of such type of coordinatively unsaturated substituted cluster observed in the solid state. The irreversibility of the phase transition has been confirmed by combined thermal and diffractometric analyses, which evidenced also the great flexibility of the supramolecular framework of 2, as this anhydrous phase is able to adsorb up to six water molecules per cluster to lead to the hydrated derivative [{Cu(cyclam)}3SiW11O39Cu(H2O)]·5H2O (2h) without any significant alteration in its cell parameters, nor in its crystalline structure., This work was funded by Eusko Jaurlaritza/Gobierno Vasco (EJ/GV, Grants IT1291-19 and PIBA2018-59) and Ministerio de Ciencia, Innovación y Universidades (Grant MAT2017-89553-P). L.F.N. and E.R.B. are indebted to EJ/GV for their predoctoral fellowships (PRE_2019_1_0106 and PRE_2018_1_0143).

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., This work was funded by Eusko Jaurlaritza/Gobierno Vasco (Grant PIBA2018-59 and ELKARTEK bG18 10(2018/00054), MINECO (Grant MAT2017-89553-P), and UPV/EHU (Grants PPG17/37 and GIU17/050). S.R. thanks Obra Social la Caixa, Fundacion Caja Navarra, and UPNA for a research contract in the framework of the program "Captación del Talento". Technical and human support provided by SGIker (UPV/EHU) is gratefully acknowledged.

Polioxometalatoen (POMen) konposizio eta egitura aniztasun ikaragarria, ur disoluzioan aurkezten dituzten oreka kimiko dinamikoen emaitza dira. Izan ere, beraien eraketa prozesuak ingurune azidotan gertatzen diren oxoanioien kondentsazio konplexuetan oinarrituta daude eta ondorioz, pH baldintza jakinetan zenbait metal-oxigeno kluster ezberdin daude orekan. Hortaz, POMei dagozkien topologia garrantzitsuenen ikuspegi orokorra aurkezten da lan honetan, pHaren arabera ur disoluzioan agertzen diren espezie nagusiei erreparatuz. Lehenik, ohiko iso- eta hetero-polioxobanadato, -polioxomolibdato eta ¿polioxowolframatoak aztertu dira eta bukatzeko hain konbentzionalak ez diren POM familietan jarri da arreta; hala nola, molibdato erraldoiak, uranio peroxo-klusterrak eta metal noblez osatutako egiturak.., The large compositional and structural diversity of polyoxometalates (POMs) is strongly related to their dynamic chemical equilibria in aqueous solution. In fact, their formation process involves complex oxoanion condensation reactions in acidic media and thus, more than one metal-oxo cluster species coexist in a given pH condition. Thus, a general overview of the most common structural archetypes of POMs is provided in this work, with strong focus on the main species found in aqueous solution as a function of the pH. First, traditional iso- and hetero-polyoxovanadates, -polyoxomolybdates and -polyoxotungstates are reviewed, followed by the analysis of less conventional families, such as giant molybdates, uranium peroxoclusters and noble-metal POMs., (PRE_2018_1_0143; PRE_2019_1_0106) burutu da. Egileek Ekonomia, Industria eta Lehiakortasun Ministeritzaren (MAT2017-89553-P) eta Eusko Jaurlaritzaren (IT-1291-19 eta KK-2020/00008) finantziazioa eskertu nahi dute.

The unprecedented heptavanadate cluster has been isolated from reactions between trisalkoxide ligands and vanadatein water at pH = 2 as a series of alkylammonium [HxV7O18(H2O)((OCH2)3CR)](4−x)‑salts (1−3,R=CH2OH;4,R=CH3). Their structures have been determined and the partial stability of4 in water assessed by a combination of multinuclear NMR spectroscopyand ESI-MS. The heptavanadate unit reported herein could represent an intermediate species in the formation of decavanadate thatis blocked by attachment of tripodal ligands., Eusko Jaurlaritza/Gobierno Vasco (EJ/GV, IT-1291-19 and KK-2020/00008) and Ministerio de Economı́a, Industria y Competitividad (MAT2017-89553-P). L.F.N. and E.R.B. thank EJ/GV for their predoctoral fellowships.