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-SiW 11 O 39 ] 8– anion affords a series of isostructural compounds, namely, K 5 [Ln III (α-SiW 11 O 39 )(C 20 H 22 Br 2 N 2 O 4 )]·14H 2 O ( 1 -Ln, Ln = Sm to Lu). The molecular structure of these sandwich-type complexes is formed by the Ln III ion in a biaugmented trigonal prismatic geometry, which occupies the external O 4 site of the organic ligand and the vacant site of the lacunary polyoxometalate (POM) unit. The empty N 2 O 2 coordination site of the organic ligand allows its unprecedented folding, which displays a relative perpendicular arrangement of aromatic groups. Weak Br···Br and π–π interactions 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.

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.

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.

The hybrid compound [Cu(cyclam)(H 2 O) 2 ] 0.5 [{Cu(cyclam)} 1.5 { B -H 2 As 2 Mo 6 O 26 (H 2 O)}]·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)(H 2 O) 2 ] 2+ cations, the stacking of which generates squarelike channels parallel to the z axis with an approximate cross section of 10 × 11 Å 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 single-crystalline 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 -H 2 As 2 Mo 6 O 26 )] ( 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 Cu II 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 -H 2 As 2 Mo 6 O 26 )]·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 CO 2 over N 2 .