Shaping Solid-State Supramolecular Cavities: Chemically Induced Accordionlike Movement of gamma-Zirconium Phosphate Containing Polyethylenoxide Pillars

The hydrophilic oxygen atoms of polyethylenoxide chains inserted as pillars in gamma-zirconium phosphate form hydrogen bonds with the acid groups of the host. As a result the pillars are almost perpendicular to the gamma layers. Upon changing the pH level of the supernatant solution the hydrogen bonds are broken and the pillars become almost perpendicular to the layers (shown schematically). Thus there is a reversible enlargement-shortening of the interlayer space.     

Hydrogen Bonding in the Dimer and Monohydrate of 2-Adamantanol: A Test Case for Dispersion-Corrected Density Functional Methods

Weakly-bound intermolecular clusters constitute reductionist physical models for non-covalent interactions. Here we report the observation of the monomer, the dimer and the monohydrate of 2-adamantanol, a secondary alcohol with a bulky ten-carbon aliphatic skeleton. The molecular species were generated in a supersonic jet expansion and characterized using broadband chirped-pulse microwave spectroscopy in the 2–8 GHz frequency region. Two different gauche-gauche O-H···O hydrogen-bonded isomers were observed for the dimer of 2-adamantanol, while a single isomer was observed for the monomer and the monohydrate. The experimental rotational parameters were compared with molecular orbital calculations using density functional theory (B3LYP-D3(BJ), B2PLYP-D3(BJ), CAM-B3LYP-D3(BJ), ωB97XD), additionally providing energetic and electron density characterization. The shallow potential energy surface makes the dimer an interesting case study to benchmark dispersion-corrected computational methods and conformational search procedures.     

Relative Permeabilities for Strictly Hyperbolic Models of Three-Phase Flow in Porous Media

Traditional mathematical models of multiphase flow in porous media use a straightforward extension of Darcys equation. The key element of these models is the appropriate formulation of the relative permeability functions. It is well known that for one-dimensional flow of three immiscible incompressible fluids, when capillarity is neglected, most relative permeability models used today give rise to regions in the saturation space with elliptic behavior (the so-called elliptic regions). We believe that this behavior is not physical, but rather the result of an incomplete mathematical model. In this paper we identify necessary conditions that must be satisfied by the relative permeability functions, so that the system of equations describing three-phase flow is strictly hyperbolic everywhere in the saturation triangle. These conditions seem to be in good agreement with pore-scale physics and experimental data.     

The Hydrogen Bond and Beyond: Perspectives for Rotational Investigations of Non-Covalent Interactions

In the last decade, experiment and theory have expanded our vision of non-covalent interactions (NCIs), shifting the focus from the conventional hydrogen bond to new bridging interactions involving a variety of weak donor/acceptor partners. Whereas most experimental data originate from condensed phases, the introduction of broadband (chirped-pulse) microwave fast-passage techniques has revolutionized the field of rotational spectroscopy, offering unexplored avenues for high-resolution studies in the gas phase. We present an outlook of hot topics for rotational investigations on isolated intermolecular clusters generated in supersonic jet expansions. Rotational spectra offer very detailed structural data, easily discriminating the isomeric or isotopic composition and effectively cancelling any solvent, crystal, or matrix bias. The direct comparison with quantum mechanical predictions provides insight into the origin of the inter- and intramolecular interactions with much greater precision than any other spectroscopic technique, simultaneously serving as test-bed for fine-tuning of theoretical methods. We present recent examples of rotational investigations around three topics: oligomer formation, chiral recognition, and identification of halogen, chalcogen, pnicogen, or tetrel bonds. The selected examples illustrate the benefits of rotational spectroscopy for the structural and energetic assessment of inter-/intramolecular interactions, which may help to move from fundamental research to applications in supramolecular chemistry and crystal engineering.     

Luminescence of Eu3+ and Tb3+ Complexes of Two Macrobicyclic Ligands Derived from a Tetralactam Ring and a Chromophoric Antenna

Two macrobicyclic ligands derived from an 18‐membered tetralactam ring and 2,2′‐bipyridine or 2,6‐bis(pyrazol‐1‐yl)pyridine moieties, 1 and 2 , respectively, form stable complexes with Gd^III, Eu^III, and Tb^III ions in aqueous solution. The ligand‐based luminescence is retained in the Gd^III cryptates, whereas this radiative deactivation is quenched in the Eu^III and Tb^III cryptates by ligand‐to‐metal energy transfer, resulting in the usual metal‐centered emission spectra. Singlet‐ and triplet‐state energies, emission‐decay lifetimes, and luminescence yields were measured. [Tb⊂ 1 ]³⁺ cryptate shows a long luminescence lifetime (τ=1.12 ms) and a very high metal luminescence quantum yield (Φ=0.25) in comparison with those reported in the literature for Tb³⁺ complexes sensitized by a bipyridine chromophore. By comparison to [Ln⊂ 1 ]³⁺, [Ln⊂ 2 ]³⁺ presents markedly lower luminescence properties, due to worse interaction between the 2,6‐bis(pyrazol‐1‐yl)pyridine unit and the metal ion. Moreover, the luminescent metal and the triplet ligand energy levels of [Eu⊂ 2 ]³⁺ do not match. The effects of H₂O molecules coordinated to the metal centre and of thermally activated decay processes on nonradiative deactivation to the ground‐state are also reported.     

Magnesium optical one-shot sensor based on a coumarin chromoionophore

The characterization of a new irreversible optical absorption-based one-shot sensor for magnesium is described. The magnesium photoactive probe is 7-diethylamino-3-(3,4-ethylendioxybenzoyl)coumarin immobilized in a plasticized polymeric membrane. The magnesium selectivity can be explained in terms of size and charge density of magnesium and charge-separated resonance forms contribution in the excited state of coumarin. The selectivity obtained for magnesium over a variety of naturally occurring species in natural waters meets the requirements for the determination of this ion in water. The one-shot sensor responds between 0.14 and 14mgL(-1) with a sensor-to-sensor reproducibility of 1.3% as [Formula: see text] , at the medium level of the range. The performance of the optical one-shot sensor was tested in the analysis of magnesium in different types of natural waters and soft drinks validating results against a reference procedure.     

Palladium(II) coordination and cyclometallated complexes derived from 3- and 5-aryl-substituted pyrazoles

Palladium(II) coordination complexes of nine 3- or 5-arylpyrazoles (phenyl, 2-bromophenyl, or 3-methoxyphenyl), as well as of 3,5-diphenylpyrazole, are reported. A cis-trans mixture of [PdL₂Cl₂] isomers is found in the case of 3-aryl-1-methylpyrazoles, the cis-isomers being transformed into trans by heating. Only trans isomers are isolated with the other ligands. Cyclopalladation of 3-ary]-1-methylpyrazoles can be performed with palladium(II) acetate, and the resultant μ-acetate bridged dimers can be transformed into μ-chloro bridged dimers or acetylacetonate monomers. The structures of the complexes have been characterized by ¹H- and ¹³C-NMR spectroscopy.