The first decavanadate-based microporous hybrid, namely, [Cu(cyclam)][{Cu(cyclam)}2(V10O28)]·10H2O(1, cyclam = 1,4,8,11-tetraazacyclotetradecane) has been prepared by reaction of (VO3) -anions and {Cu(cyclam)} 2+ complexes in NaCl (aq) at pH 4.6-4.7, and characterized by elemental analyses, thermogravimetry, and X-ray diffraction techniques (powder, single-crystal). Compound 1 exhibits a POMOF-like supramolecular open-framework built up of covalent decavanadate/metalorganic layers with square-like voids, the stacking of which is aided by interlamellar cementing complexes and generates water-filled channels with approximate cross-sections of. 10.4 × 8.8 Å 2 . The framework is robust enough to remain virtually unaltered upon thermal evacuation of all water molecules of hydration, as demonstrated through single-crystal X-ray diffraction studies on the anhydrous phase 1a. This permanent microporosity renders interesting functionality to 1, such as selective adsorption of CO2 over N2 and remarkable activity as heterogeneous catalyst toward the H2O2-based oxidation of the highly-stable, tricyclic alkane adamantane.Porous crystalline materials such as metal organic frameworks (MOFs) have attracted great attention due to their wide range of relevant applications. 1 These materials are constructed by coordination of metal ions or metalcontaining units (nodes) to organic bridging ligands (linkers) to form open crystalline frameworks with permanent porosity. This feature qualifies them as suitable candidates for gas storage and separation, ion exchange, host-guest chemistry, magnetism, biomedicine and catalysis. 2 However, the synthesis of MOFs usually requires harsh conditions (e.g. high temperature or pressure, prolonged reaction times, harmful solvents, etc.), and removal of guest molecules from their cavities often leads to the collapse of the porous structure when flexible linkers are used. In this context, the incorporation of rigid and voluminous species such as metal clusters could increase the overall robustness

Eleven dimetallic Zn(II)-Ln(III) complexes of the general formula [Zn(µ-L)(µ-OAc)Ln(NO3)2]·CH3CN (Ln(III) = Pr (1), Nd (2), Sm (3), Eu (4), Gd (5), Tb (6), Dy (7), Ho (8), Er (9), Tm (10), Yb (11)) have been prepared in a one-pot reaction from the compartmental ligand N,N'-dimethyl-N,N'-bis(2-hydroxy-3-formyl-5-bromo-benzyl)ethylenediamine (H2L). In all these complexes, the Zn(II) ions occupy the internal N2O2 site whereas the Ln(III) ions show preference for the O4 external site. Both metallic ions are bridged by an acetate bridge, giving rise to triple mixed diphenoxido/acetate bridged Zn(II)Ln(III) compounds. The Nd, Dy, Er and Yb complexes exhibit field induced single-ion magnet (SIM) behaviour, with Ueff values ranging from 14.12 to 41.55 K. The Er complex shows two relaxation processes, but only the second relaxation process with an energy barrier of 21.0 K has been characterized. The chromophoric L(2-) ligand is able to act as an "antenna" group, sensitizing the near-infrared (NIR) Nd(III) and Yb(III)-based luminescence in complexes 2 and 11 and therefore, both compounds can be considered as magneto-luminescent materials. In addition, the Sm(III), Eu(III) and Tb(III) derivatives exhibit characteristic emissions in the visible region.

Reaction of mid- to late lanthanide ions with GeO2 and Na2WO4 in NaOAc buffer results in a library of [Ln2 (GeW10O38)](6-) clusters (Ln2), which consist of dilacunary Keggin fragments stabilized by the insertion of 4f atoms in the vacant sites and show the ability to undergo cation-directed self-assembly processes. In the presence of Na(+), two β-Ln2 subunits assemble by means of Ln-O(WO5)-Ln bridges to form the chiral [Ln4(H2O)6(β-GeW10O38)2](12-) dimeric anions (ββ-Ln4, Ln = Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu). When Cs(+) is present, two Ln4-like dimers further assemble into the [{Ln4(H2O)5(GeW10O38)2}2](24-) species (Ln8, Ln = Ho, Er, Tm, Yb, Lu). Two types of tetramers coexist in the solid state: One shows a full ββ-Ln8 architecture, whereas the other one is a mixed αβ-Ln8 assembly in which each β-subunit is linked to its corresponding α-Ln2 derivative. Regardless of differences in isomeric forms and the relative arrangement of Ln2 subunits, all anions display virtually identical {Ln4} cores as a common structural feature. A combination of ESI mass spectrometry and (183)W NMR spectroscopy experiments indicates that Ln8 tetramers fragment into Ln4 dimers upon dissolution, which undergo partial dissociation into Ln2 monomers and slow dimer/monomer equilibration. This is most likely followed by β-to-α isomerization of Ln2 clusters with consequent reassembly, as indicated by isolation of three additional αα-Ln4 derivatives. Magnetic and photoluminescence properties in the Na-ββ-Ln4 series are also discussed.

Two new hybrid compounds constructed from Keggin type polyoxometalates and copper(II) complexes of tetradentate ligands containing amine and pyridyl groups, namely [Cu(bpmen)(H2O)][SiW12O40{Cu(bpmen)}] (1) and [SiW12O40{Cu(bpmpn)(H2O)}2]·3H2O (2) (bpmen, N,N'-dimethyl-N,N'-bis-(pyridin-2-ylmethyl)-1,2-diaminoethane; bpmpn, N,N'-dimethyl-N,N'-bis(pyridin-2-ylmethyl)-1,3-diaminopropane), have been synthesized under hydrothermal conditions and characterized by elemental analyses and infrared and Raman spectroscopy. Thermal stability of 1 and 2 has been studied by means of thermogravimetric analyses and variable temperature powder X-ray diffraction. Both compounds undergo single-crystal to single-crystal transformations promoted by reversible dehydration processes that have been followed by single-crystal X-ray diffraction. Structures of 1 and 2, and also of their corresponding anhydrous phases 1a and 2a, have been established. The layered structure of 1 shows rows of monodecorated polyanions with complex cations occupying intralamellar spaces, whereas trans-didecorated species in 2 lead to stacked honeycomb-like metal-organic layers forming channels where Keggin clusters are accommodated. Structural differences relate to changes in the complex geometry and ligand conformation when going from bpmen to bpmpn. Dehydration of 1 promotes coordination of the complex countercation and consequent formation of a cis-didecorated species in 1a, whereas changes in the structure of 2a are more subtle. Structural variations upon dehydration are reflected in the electron paramagnetic resonance spectra.

Single‐crystal‐to‐single‐crystal transformations are solid‐state phase transitions between different crystalline states in which the crystal integrity and the long‐range structural order are retained through the whole transformation process. Such a phenomenon constitutes the structural response that some compounds afford when being exposed to a given external stimulus (temperature, pressure, light, etc.) and, therefore, its study has become a relevant focus of interest within crystal engineering because it allows for monitoring how certain properties (colour, magnetism, luminescence, porosity) of the stimuli‐responsive material are modified as the structure evolves into the activated form. A range of organic, inorganic and hybrid systems have been found to undergo such phase transitions, but these examples only include a small number of compounds that incorporate polyoxometalate anions, among which the removal of guest solvent molecules (dehydration) stands out as the most common external stimulus able to induce the occurrence of a single‐crystal‐to‐single‐crystal transformation. This feature article compiles the examples of dehydration‐triggered single‐crystal‐to‐single‐crystal transformation studies that have been reported to date for polyoxometalate‐based compounds and reviews some of their most relevant structural aspects.