Study of monodimensional compounds based on group 6 tetraoxometalates with Cu(cyclam) complexes

Synthesis, chemical and structural characterisation, and magnetic properties of novel chromate, molibdate and tungstate copper-cyclam complexes

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

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)

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)

Structural Characterization of Mono and Dihydroxylated Umbelliferone Derivatives

Coumarin derivatives are a class of compounds with a pronounced wide range of applications, especially in biological activities, in the medicine, pharmacology, cosmetics, coatings and food industry. Their potential applications are highly dependent on the nature of the substituents attached to their nucleus. These substituents modulate their photochemical and photophysical properties, as well as their interactions in their crystalline form, which largely determines the final field of application. Therefore, in this work a series of mono and dihydroxylated coumarin derivatives with different chemical substituents were synthesized and characterized by UV-Visible spectroscopy, thermal analysis (differential scanning calorimetry (DSC) and TGA), 1H NMR and X-Ray Diffraction to identify limitations and possibilities as a function of the molecular structure for expanding their applications in polymer science.This research was funded by the Basque Government within the framework ELKARTEK through the research project KK-2018/00108 and KK-2019/00077. This work was also funded by the Ministry of Economy and Competitiveness—Spain (MINECO) through the research Projects RTC-2016-4887-4 and RTI2018-096636-J-100 within the framework of the National Programme for Research Aimed at the Challenges of Society

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

Slow Magnetic Relaxation and Luminescent Properties of Mononuclear Lanthanide-Substituted Keggin-Type Polyoxotungstates with Compartmental Organic Ligands

This work was funded by Eusko Jaurlaritza/Gobierno Vasco (EJ/GV, grants IT1291-19 and KK-2020/00008) and Ministerio de Ciencia e Innovación (MCIN, grant MAT2017–89553-P). E.R.B. is indebted to EJ/GV for her predoctoral fellowship (PRE_2018_1_0143). E.C. thanks MCIN/AEI/10.13039/501100011033/ “FEDER Una manera de hacer Europa” (project PGC2018 102052-B-C21) and the I+D+i FEDER program 2018 of Junta de Andalucı́a (Project A-FQM-172-UGR18) for financial support.The reaction of mid to late lanthanide ions with the N,N′-dimethyl-N,N′-bis(2-hydroxy-3-formyl-5-bromobenzyl)ethylene-diamine organic ligand and monolacunary Keggin type [α-SiW11O39]8- anion affords a series of isostructural compounds, namely, K5[LnIII(α-SiW11O39)(C20H22Br2N2O4)]·14H2O (1-Ln, Ln = Sm to Lu). The molecular structure of these sandwich-type complexes is formed by the LnIII ion in a biaugmented trigonal prismatic geometry, which occupies the external O4 site of the organic ligand and the vacant site of the lacunary polyoxometalate (POM) unit. The empty N2O2 coordination site of the organic ligand allows its unprecedented folding, which displays a relative perpendicular arrangement of aromatic groups. Weak Br···Br and ?-πinteractions established between adjacent molecular units govern the crystal packing, which results in the formation of assemblies containing six hybrid species assembled in a chairlike conformation. 1-Gd and 1-Yb display slow relaxation of the magnetization after the application of an external magnetic field with maxima in the out-of-phase magnetic susceptibility plots below ?5-6 K, which is ascribed to the presence of various relaxation mechanisms. Moreover, photoluminescent emission is sensitized for 1-Sm and 1-Eu in the visible region and 1-Er and 1-Yb in the NIR. In contrast, the quenching of metal-centered luminescence in the 1-Tb derivative has been attributed to the out-of-pocket coordination mode of the lanthanide center within the POM fragment. It is demonstrated that the 1-Yb dual magneto-luminescent material represents the first lanthanide-containing POM reported to date with simultaneous slow magnetic relaxation and NIR emission. Solution stability of the hybrid molecular species in water is also confirmed by ESI-mass spectrometry experiments carried out for 1-Tb and 1-Tm.Eusko Jaurlaritza/Gobierno Vasco IT1291-19, KK-2020/00008I+D+i FEDER A-FQM-172-UGR18Ministerio de Ciencia e Innovación MAT2017–89553-P, PGC2018 102052-B-C2

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 (κ-Mo8 O27 )] ⋅ 14H2 O (1) (cyclam=1,4,8,11-tetraazacyclotetradecane) undergoes sequential single-crystal-to-single-crystal transformations upon heating to afford two different anhydrous phases (2 a and 3 a). These transitions modify the framework dimensionality and enable the isomerization of κ-octamolybdate (κ-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 3 a through the 6 a intermediate. In contrast, 2 a reversibly hydrates to form 5, exhibiting the same Mo8 cluster as that of 1. It is remarkable that three of the Mo8 clusters (κ, λ and μ) are new and that up to three different microporous phases can be isolated from 1 (2 a, 3 a, and 6 a). 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). Technical and human support from SGIker (UPV/EHU) is gratefully acknowledged.Peer reviewe

Study of monodimensional compounds based on group 6 tetraoxometalates with Cu(cyclam) complexes

Synthesis, chemical and structural characterisation, and magnetic properties of novel chromate, molibdate and tungstate copper-cyclam complexes

Thermally induced structural transitions between single-crystalline states in the first hybrid compound combining Keggin-type clusters with metal-cyclam complexes: From two-dimensional covalent assemblies to discrete molecular species

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, Innovacion 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).Peer reviewe