Beñat Artetxe

Cation-Directed Dimeric versus Tetrameric Assemblies of Lanthanide-Stabilized Dilacunary Keggin Tungstogermanates

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.

A Robust Open Framework Formed by Decavanadate Clusters and Copper(II) Complexes of Macrocyclic Polyamines: Permanent Microporosity and Catalytic Oxidation of Cycloalkanes

The first decavanadate-based microporous hybrid, namely, [Cu(cyclam)][{Cu(cyclam)}2(V10O28)]·10H2O (1, cyclam = 1,4,8,11-tetraazacyclotetradecane) was 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 (powder, single-crystal) techniques. Compound 1 exhibits a POMOF-like supramolecular open-framework built 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.

Rearrangement of a Krebs-Type Polyoxometalate upon Coordination of N,O-Bis(bidentate) Ligands

Selective coordination of 2,3-pyzdc to the Krebs-type [{Ni(H2O)3}2(WO2)2(SbW9O33)2](10-) anion promotes a skeletal rearrangement that results in the [(2,3-pyzdc)2{NaNi2(H2O)4Sb2W20O70}2](22-) (Ni4) hybrid dimer showing a novel dinickel containing a 20-tungsto-2-antimonate(III) framework stabilized by N,O-bis(bidentate) bridging ligands. The solution stability and magnetism of Ni4 is discussed.

Crown‐Shaped Tungstogermanates as Solvent‐Controlled Dual Systems in the Formation of Vesicle‐Like Assemblies

Reaction of early lanthanides, GeO2 , and Na2 WO4 in a NaOAc buffer results in large crown-shaped polyoxometalates based on [Ln2 GeW10 O38 ](6-) subunits. By using Ni(2+) as a crystallizing agent, [Na⊂Ln12 Ge6 W60 O228 (H2 O)24 ](35-) (Na⊂Ln12 ) hexamers formed by alternating β(1,5)/β(1,8) subunits were obtained for Ln=Pr, Nd. The addition of K(+) led to a similar anion for Ln=Sm, namely, [K⊂Sm12 Ge6 W60 O228 (H2 O)22 ](35-) (K⊂Sm12 ) and [K⊂K7 Ln24 Ge12 W120 O444 (OH)12 (H2 O)64 ](52-) (K⊂Ln24 ) dodecamers that consist of a central core identical to K⊂Sm12 decorated with six external γ(3,4) subunits for Ln=Pr, Nd. These anions dissociate in water into hexameric cores and monomeric entities, as shown by ESI mass spectrometry. The former self-assemble into spherical, hollow, and single-layered blackberry-type structures with radii of approximately 75 nm, as monitored by laser light scattering (LLS) and TEM techniques. Analogous studies performed for K⊂Nd24 in water/acetone mixtures show that the dodecamers remain stable and form in turn their own type of blackberries with sizes that increase from approximately 20 to 50 nm with increasing acetone content. This control over both the composition and size of the vesicle-like assemblies is achieved for the first time by modifying the architecture of the species that undergoes supramolecular association through the solvent polarity.

New Perspectives for Old Clusters: Anderson-Evans Anions as Building Blocks of Large Polyoxometalate Frameworks in a Series of Heterometallic 3 d-4 f Species.

A series of nine [Sb7W36O133Ln3M2(OAc)(H2O)8](17-) heterometallic anions (Ln3M2; Ln=La-Gd, M=Co; Ln=Ce, M=Ni and Zn) have been obtained by reacting 3 d metal disubstituted Krebs-type tungstoantimonates(III) with early lanthanides. Their unique tetrameric structure contains a novel {MW9O33} capping unit formed by a planar {MW6O24} fragment to which three {WO2} groups are condensed to form a tungstate skeleton identical to that of a hypothetical trilacunary derivative of the ɛ-Keggin cluster. It is shown, for the first time, that classical Anderson-Evans {MW6O24} anions can act as building blocks to construct purely inorganic large frameworks. Unprecedented reactivity in the outer ring of these disk-shaped species is also revealed. The Ln3M2 anions possess chirality owing to a {Sb4O4} cluster being encapsulated in left- or right-handed orientations. Their ability to self-associate in blackberry-type vesicles in solution has been assessed for the Ce3Co2 derivative.

Sequential single-crystal-to-single-crystal transformations promoted by gradual thermal dehydration in a porous metavanadate hybrid

TheE porous hybrid metavanadate [{Cu(cyclam)}(VO3)2]·5H2O (1) (cyclam = 1,4,8,11-tetraazacyclotetradecane) undergoes thermally-triggered sequential single-crystal-to-single-crystal (SCSC) transformations upon gradual dehydration to produce three new porous crystalline phases, namely [{Cu(cyclam)}(VO3)2]·3H2O (2), [{Cu(cyclam)}(VO3)2]·1.3H2O (3) and [{Cu(cyclam)}(VO3)2] (4). Compound 1 has a three-dimensional structure formed by metavanadate chains linked by {Cu(cyclam)} moieties in a hybrid open framework with two different types of hexagonal channels where water molecules of hydration are hosted. The SCSC transformations cause a rearrangement o/f the metavanadate chains in such a way that they contract when going from 1 to 2 and stretch back when 2 transforms into 3. The size of the channels is also modified as the hybrid dehydrates. The transition from 2 to 3 leads to the cleavage of a Cu–O bond and consequent coordination of a {Cu(cyclam)} moiety to a different {VO4} unit, which drastically decreases the size of the channel in the process. In contrast, total dehydration of 3 enlarges the channel in the anhydrous phase 4 due to the migration of another Cu atom. The reversibility of such transformations has been monitored by a combination of thermogravimetric and powder X-ray diffraction analyses. While 1 and 3 are stable in open-air conditions, 2 transforms back into 1 upon exposure to air for three weeks. The anhydrous phase 4 rapidly rehydrates into 3 when in contact with ambient moisture. Furthermore, 3 can also be transformed into the parent hybrid 1 when soaked in water for seven days. Therefore, all crystal transitions described herein are fully reversible by applying the appropriate conditions.

trans-Di­aqua­bis­(pyridazine-3-carboxyl­ato-κ2N2,O)cobalt(II) dihydrate

The title compound, [Co(C5H3N2O2)2(H2O)2]·2H2O, contains a CoII ion on an inversion center, exhibiting an octahedral coordination geometry. The equatorial plane is formed by two trans-related N,O-bidentate pyridazine-3-carboxylate ligands and the axial positions are occupied by two water molecules. The CoII complex molecules are stacked in a column along the a-axis direction by an O—H⋯N hydrogen bond between the non-coordinating pyridazine N atom and the coordinating water molecule. These columns are further connected into a layer parallel to the ac plane by additional hydrogen bonds involving the coordinating and non-coordinating water molecules, and the non-coordinating carboxylate O atom. The crystal packing is completed by interlayer weak C—H⋯O interactions.

Diaquabis(1H-imidazole-4-carboxylato-κ2N3,O)cobalt(II)

The title compound, [Co(C4H3N2O2)2(H2O)2], contains a CoII cation on a twofold rotation axis, exhibiting a distorted octahedral coordination geometry. The equatorial plane is formed by two N,O-bidentate 1H-imidazole-4-carboxylate ligands and the axial positions are occupied by water molecules. The crystal packing consists of a three-dimensional network stabilized by O—H⋯O and N—H⋯O hydrogen bonds, together with weak π–π interactions [centroid–centroid distance = 3.577 (2) Å] between the imidazole rings.

Thermally-Triggered Crystal Dynamics and Permanent Porosity in the First Heptatungstate-Metalorganic Three-Dimensional Hybrid Framework

The hybrid compound [{Cu(cyclam)}3 (W7 O24 )]⋅15.5 H2 O (1) (cyclam=1,4,8,11-tetraaza-cyclotetradecane) was synthesized by reacting the {Cu(cyclam)}2+ complex with a tungstate source in water at pH 8. Compound 1 exhibits an unprecedented three-dimensional covalent structure built of heptatungstate clusters linked through metalorganic complexes in a POMOF-like framework that displays water-filled channels. This dynamic architecture undergoes two sequential single-crystal-to-single-crystal transformations upon thermal evacuation of water molecules to result in the partially dehydrated [{Cu(cyclam)}3 (W7 O24 )]⋅12 H2 O (2) and anhydrous [Cu(cyclam)]0.5 [{Cu(cyclam)}2.5 (W7 O24 )] (3) crystalline phases. These transitions are associated with cluster rotations and modifications in the CuII coordination geometries, which reduce the dimensionality of the original lattice to layered systems but preserving the porous nature. Phase 3 reverts to 2 upon exposure to ambient moisture, whereas the transition between 1 and 2 proved to be irreversible. The permanent microporosity of 3 was confirmed by gas sorption measurements (N2 , CO2 ), which reveal a system of parallel channels made of wide cavities connected through narrow necks that limit the adsorption process. This observation is in good agreement with Grand Canonical Monte Carlo simulations.

Crystal structure of trans-di­aqua­bis­(1H-pyrazole-3-carboxyl­ato-κ2N,O)copper(II) dihydrate

In the title compound, [Cu(C4H3N2O2)2(H2O)2]·2H2O, the CuII ion is located on an inversion centre and exhibits an axially elongated octahedral coordination geometry. The equatorial plane is formed by two N,O-bidentate 1H-pyrazole-3-carboxylate ligands in a trans configuration. The axial positions are occupied by two water molecules. The mononuclear complex molecules are arranged in layers parallel to the ab plane. Each complex molecule is linked to four adjacent species through intermolecular O—H⋯O and N—H⋯O hydrogen bonds that are established between the coordinating water molecules and carboxylate O atoms or protonated N atoms of the organic ligands. These layers are further connected into a three-dimensional network by additional hydrogen bonds involving solvent water molecules and non-coordinating carboxylate O atoms.