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.

The unprecedented heptavanadate cluster has been isolated from reactions between trisalkoxide ligands and vanadate in water at pH = 2 as a series of alkylammonium [H x V 7 O 18 (H 2 O)((OCH 2 ) 3 CR)] (4–x)- salts ( 1 – 3 , R = CH 2 OH; 4 , R = CH 3 ). Their structures have been determined and the partial stability of 4 in water assessed by a combination of multinuclear NMR spectroscopy and ESI-MS. The heptavanadate unit reported herein could represent an intermediate species in the formation of decavanadate that is blocked by attachment of tripodal ligands.

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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.

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.