A Robust Framework Based on Polymeric Octamolybdate Anions and Copper(II) Complexes of Tetradentate N-donor Ligands

A new organic-inorganic compound based on octamolybdate building blocks and copper(II) complexes of tetradentate N-donor ligands has been hydrothermally synthesized, namely [Cu(cyclam)](2)[Mo8O26]center dot 1.5H(2)O (1), (cyclam: 1,4,8,11-tetraazacyclotetradecane). Compound 1 has been chemically (elemental and thermal analyses), spectroscopically (infrared spectroscopy), and structurally (single crystal and powder X-ray diffraction) characterized. The crystal packing of 1 shows a covalent framework structure formed by [Mo8O26](n)(4n-) chains running along the 100 direction which are linked to each other through the coordination spheres of {Cu(cyclam)}(2+) complexes leading to a three-dimensional open network. This structural assembly generates voids that can be described as a succession of cavities communicated through narrow bottlenecks with approximate cross section of 4 x 7 angstrom(2) where the hydration water molecules are hosted. The robust open structure of 1 remains virtually unaltered upon thermal evacuation of guest solvent molecules at 130 degrees C, resulting in the anhydrous phase [Cu(cyclam)](2)[Mo8O26] (1a) with potentially accessible micropores as demonstrated by single-crystal X-ray diffraction measurements. Electron paramagnetic resonance spectroscopy analysis of 1 has also been assessed.This work was funded by UPV/EHU (Grant PPG17/37 and GIU17/050) and University of Tunis El Manar (predoctoral fellowship to N.D., including a three-month stay at Universidad del Pais Vasco, UPV/EHU). B.A. thanks UPV/EHU for a postdoctoral fellowship within the program "Convocatorias de Ayudas para la Especializacion de Personal Investigador". Technical and human support provided by SGIker (UPV/EHU) is gratefully acknowledged

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

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

Polioxometalatoak ingurune urtsuan: egitura esanguratsuenak

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.; Polioxometalatoen (PoMen) konposizio eta egitura aniztasun ikaragarria ur disoluzioan aurkezten dituzten oreka kimiko dinamikoen emaitza da. Izan ere, haien eraketa prozesuak ingurune azidotan gertatzen diren oxoanioien kondentsazio konplexuetan oinarrituta daude, eta, ondorioz, pH baldintza jakinetan zenbait metal-oxigeno kluster daude orekan. Hortaz, PoMei dagozkien topologia garrantzitsuenen ikuspegi orokorra aurkezten da lan honetan, pH-aren 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 erraldoietan, uranio peroxo-klusterretan eta metal noblez osatutako egituretan

Single-Crystal to Single-Crystal Reversible Transformations Induced by Thermal Dehydration in Keggin-Type Polyoxometalates Decorated with Copper(II)-Picolinate Complexes: The Structure Directing Role of Guanidinium

Three new hybrid inorganic-metalorganic compounds containing Keggin-type polyoxometalates, neutral copper(II)-picolinate complexes and guanidinium cations have been synthesized in bench conditions and characterized by elemental analysis, infrared spectroscopy and single-crystal X-ray diffraction: the isostructural [C(NH2)(3)](4)[{XW12O40}{Cu-2(pic)(4)}] . [Cu-2(pic)(4)(H2O)](2) .6H(2)O [X = Si (1), Ge (3)] and [C(NH2)(3)]8[{SiW12O40}(2){Cu(pic)(2)}3{Cu-2(pic)4(H2O)}(2)] .8H(2)O (2). The three compounds show a pronounced two-dimensional character owing to the structure-directing role of guanidinium. In 1 and 3, layers of [{XW12O40}{Cu-2(pic)(4)}] n(4n-) hybrid POM chains and layers of [Cu-2(pic)(4)(H2O)] complexes and [C(NH2)(3)](+) cations pack alternately along the z axis. The hydrogen-bonding network established by guanidinium leads to a trihexagonal tiling arrangement of all copper(II)-picolinate species. In contrast, layers of [C(NH2)(3)](+)-linked [{SiW12O40}(2){Cu(pic)(2)}(3)] n(8n-) double chains where each Keggin cluster displays a {Cu-2(pic)(4)(H2O)} moiety pointing at the intralamellar space are observed in 2. The thermal stability of 1-3 has been studied by thermogravimetric analyses and variable temperature powder X-ray diffraction. Compounds 1 and 3 undergo single-crystal to single-crystal transformations promoted by reversible dehydration processes and the structures of the corresponding anhydrous phases 1a and 3a have been established. Despite the fact that the [Cu-2(pic)(4)(H2O)] dimeric complexes split into [Cu( pic)(2)] monomers upon dehydration, the packing remains almost unaltered thanks to the preservation of the hydrogen-bonding network established by guanidinium and its associated Kagome-type lattice. Splitting of the dimeric complexes has been correlated with the electron paramagnetic resonance spectra.This work was funded by Eusko Jaurlaritza/Gobierno Vasco (grant IT477- 10 and predoctoral fellowship to A. P.), Ministerio de Economia y Competitividad (grant MAT2013-48366-C2-2P) and Universidad del Pais Vasco UPV/EHU (grant UFI11/53). Technical and human support provided by SGIker (UPV/EHU) is gratefully acknowledged

Reversible First-Order Single Crystal to Single Crystal Thermal Phase Transition in [(CH3)3CNH3]4[V4O12]

[EN] The well-known compound tetrakis(tert-butylammonium)-cyclo-tetrametavanadate (V), [(CH3)3CNH3]4[V4O12] (1h_RT), which crystallizes in the tetragonal I4/m space group, undergoes an irreversible solid state transformation upon heating, constituting one of the few examples in which the initial and the final stages are structurally characterized by sc-XRD. Now, we observed the ability of the same compound to undergo an additional single-crystal-to-single-crystal (SCSC) transformation upon thermal stimuli, but this time at low temperatures (153 K). Compound 1h_RT contains a discrete unprotonated [V4O12]4− tetrahedral anion in which V and O bridging atoms are coplanar. In both phases, these tetrameric anions are linked through tert-butylammonium cations in an extensive network of hydrogen bonds, but at low temperatures, this phase loses its characteristic O-V-O coplanarity, with the resulting rearrangement of the crystal packing and hydrogen-bond network which provide its reversibility at low temperatures. Again, the initial and final stages have been characterized structurally by sc-XRD.This research was funded by IT1722-22, KK-2022/00045 and MCIN, grant MAT2017-89553-P

Monokristal-monokristal eraldaketak polioxometalatoetan oinarritutako sistemetan: termikoki aktibatutako zenbait adibide.

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)

Naphthyl-Containing Organophosphonate Derivatives of Keggin-Type Polyoxotungstates

New organophosphonate derivatives of monovacant Keggin-type polyoxotungstates that contain naphthyl groups have been synthesized and characterized in both solid state and solution. Single-crystal structural analysis shows that two phosphonate groups occupy the vacant position of the lacunary cluster unit in the isostructural compounds [N(C4H9)(4)](3)[H(POC11H9)(2)(-HBW11O39)] (TBA-1) and [N(C4H9)(4)](3)[H(POC11H9)(2)(-SiW11O39)] (TBA-2). Liquid-solution UV-Vis transmittance and solid-state diffuse reflectance spectroscopy studies reveal the presence of a new absorption band in the visible region, the charge transfer character of which has been further confirmed by time-dependent density functional theory (TD-DFT) calculations. The latter evidence that the charge transfer process is dominated by transitions from the highest occupied molecular orbital (HOMO), localized in the aromatic ring of the organic group, to the lowest unoccupied molecular orbital (LUMO), localized in the Keggin anion. Photoluminescence studies show that the fluorescent properties of the 1-naphthylmethylphosphonate group are quenched upon its incorporation into the inorganic oxo-tungstate skeleton. The solution stability of the hybrid clusters has been evaluated by a combination of H-1-, C-13- and P-31-Nuclear Magnetic Resonance spectroscopy and Electrospray Ionization-Mass Spectrometry. The hybrid polyanion [H(POC11H9)(2)(-HBW11O39)](3-) (1) herein constitutes the first structurally characterized organo-p-block containing borotungstate, and hence it confirms that this strategy for the organic functionalization of polyoxometalate clusters can be applied to new platforms belonging to the family of group-13 heteropolyoxotungstates

Consecutive single-crystal-to-single-crystal isomerization of novel octamolybdate anions within a microporous hybrid framework with robust water sorption properties

The 3D hybrid framework [{Cu(cyclam)}3(kMo8O27)]· 14H2O (1) (cyclam=1,4,8,11-tetraazacyclotetradecane) undergoes sequential single-crystal-to-singlecrystal transformations upon heating to afford two different anhydrous phases (2 a and 3a). These transitions modify the framework dimensionality and enable the isomerization of k-octamolybdate (k-Mo8) anions into λ (2 a) and μ (3 a) forms through metal migration. Hydration of 3 a involves condensation of one water molecule to the cluster to afford the γ-Mo8 isomer in 4, which dehydrates back into 3a through the 6a intermediate. In contrast, 2a reversibly hydrates to form 5, exhibiting the same Mo8 cluster as that of 1. It is remarkable that three of the Mo8 clusters (k, λ and μ) are new and that up to three different microporous phases can be isolated from 1 (2 a, 3a, and 6a). Water vapor sorption analyses show high recyclability and the highest uptake values for POM-based systems. The isotherms display an abrupt step at low humidity level desirable for humidity control devices or water harvesting in drylands.Funded by Eusko Jaurlaritza/Gobierno Vasco (EJ/GV, grants IT1722-22 and KK-2022/00045). E.R.B. thanks EJ/GV for her doctoral fellowship (PRE_2018_1_0143)

Single-Crystal-to-Single-Crystal Cluster Transformation in a Microporous Molybdoarsenate(V)-Metalorganic Framework

[EN]The hybrid compound [Cu(cyclam)(H2O)(2)](0.5)[{Cu(cyclam)}(1.5){B-H2As2Mo6O26(H2O)}].9H(2)O (1) (cyclam = 1,4,8,11- tetraazacyclotetradecane) was synthesized in aqueous solution by reacting the {Cu(cyclam)}(2+) complex with a mixture of heptamolybdate and an arsenate(V) source. Crystal packing of 1 exhibits a supramolecular open-framework built of discrete covalent molybdoarsenate/metalorganic units and additional [Cu(cyclam)-(H2O)(2)](2+) cations, the stacking of which generates squarelike channels parallel to the z axis with an approximate cross section of 10 x 11 A(2) where all the hydration water molecules are hosted. Thermal evacuation of solvent molecules yields a new anhydrous crystalline phase, but compound 1 does not preserve its singlecrystalline nature upon heating. However, when crystals are dehydrated under vacuum, they undergo a structural transformation that proceeds via a single-crystal-to-single-crystal pathway, leading to the anhydrous phase [{Cu(cyclam)}(2)(A-H2As2Mo6O26)] (2). Total dehydration results in important modifications within the inorganic cluster skeleton which reveals an unprecedented solid-state B to A isomerization of the polyoxoanion. This transition also involves changes in the CuII bonding scheme that lead to covalent cluster/metalorganic layers by retaining the open-framework nature of 1. Compound 2 adsorbs ambient moisture upon air exposure, but it does not revert back to 1, and the hydrated phase [{Cu(cyclam)}(2)(A-H2As2Mo6O26)]center dot 6H(2)O (2h) is obtained instead. Structural variations between 1 and 2 are reflected in electron paramagnetic resonance spectroscopy measurements, and the permanent microporosity of 2 provides interesting functionalities to the system such as the selective adsorption of gaseous CO2 over N-2.This work was funded by Eusko Jaurlaritza/Gobierno Vasco (EJ/GV, Grants IT-1291-19 and KK-2020/00008, together with a predoctoral fellowship to E.R.-B.), Ministerio de Economia, Industria y Competitividad (Grant MAT2017-89553-P), and University of Tunis El Manar (predoctoral fellowship to N.D. including a research stay at UPV/EHU)