Lanthanide‐Based Coordination Polymers Assembled by a Flexible Multidentate Linker: Design,Structure, Photophysical Properties,and Dynamic Solid‐State Behavior

Flexible director : A flexible multidentate linker containing picolinate chromophores directs the selective formation of luminescent 1D lanthanide‐based polymers. Partial protonation significantly decreases the preorganization of the linker, thus leading to supramolecular 1D and 2D isomers (see scheme). The lanthanide‐containing 1D polymers undergo reversible structural modification in the hydration/dehydration process, which is also associated with significant differences in the luminescence emission.

     

Wetting behavior of low-index cubic SiC surfaces

We report on the interaction of water molecules with polar and nonpolar stoichiometric surfaces of cubic silicon carbide, as described by ab initio molecular dynamics at finite temperature. Our calculations show that, irrespective of coverage, in the gas phase water spontaneously dissociates on both polar Si-terminated (001) and nonpolar (110) surfaces, following similar mechanisms. The specific geometric arrangement of atoms on the outermost surface layer is responsible for water orientation and coordination and thus plays a major role in determining surface reactivity. This is found to be the case also for water on a computer-generated amorphous-SiC surface. In addition, from a macroscopic standpoint, the ability of the two crystalline surfaces with different polarities to induce water dissociation can be related to the similarities of their ionization potentials.     

Surface vibrations of Na(001) and K(001) surfaces

We present the results of a theoretical study of the dynamics of the atom motion of Na(001) and K(001) surfaces. The total electronic energy is calculated using a pseudopotential approach with a confined electron gas as unperturbed system. With this theory the dynamical matrix can he derived without resorting to empirical parametrizations. Surface phonon dispersion curves are reported for the high symmetry directions of the two-dimensional Brillouin zone for ideal and relaxed configurations. The calculated spectra are compared with the results of semi-empirical force constant calculations. The effects of single and multilayer relaxations on the location and the nature of the main surface bands are examined.     

Versatile electrochemiluminescent organic emitters

Organic luminophores for electrochemiluminescence (ECL), namely polycyclic aromatic hydrocarbons, have been the first molecules investigated since the beginning of ECL studies. Moving from organic solvents to water-based solutions in view of analytical applications, the attention on ECL emitters shifted to soluble inorganic complexes, which prevailed in both fundamental and applied research. However, the investigation of organic molecules has recently revived owing to new synthetic procedures and concepts. Polymeric nanoparticles, surface functionalisation, aggregation-induced emission (AIE), and thermally activated delayed fluorescence (TADF) sparked the research with renovated interest for organic molecules. Here, we introduce and summarise these new concepts behind organic emitters for ECL.     

Relating structural and thermodynamic effects of the Pb(II) lone pair: a new picolinate ligand designed to accommodate the Pb(II) lone pair leads to high stability and selectivity

The crystal and molecular structure and the stability of lead and calcium complexes of two chelates containing picolinate chelating groups in different geometries have been investigated in order to relate the ligand affinity and selectivity for lead over calcium with the ability of the ligand to accommodate a stereochemically active lone pair. The crystal structures of the lead complexes of the diprotonated and monoprotonated tripodal ligand tpaa2- show that the three picolinate arms of the tripodal ligand coordinate the lead in an asymmetric way leaving a gap in the coordination sphere to accommodate the lead lone pair. As a consequence of this binding mode, one picolinate arm is very weakly bound and therefore can be expected to contribute very little to the complex stability. Conversely, the geometry of the dipodal ligand H2dpaea is designed to accommodate the lead lone pair; in the structure of the [Pb(dpaea)] complex the donor atoms of the ligand occupy only a quarter of the coordination sphere, reducing the sterical interaction between the lead lone pair with respect to the H3tpaa complexes. As a result, in the lead structures of H2dpaea all the ligand donor atoms are strongly bound to the metal ion leading to increased stability. The high value of the formation constant measured for the lead complex of the dipodal dpaea2- (log beta11(Pb)=12.1(3)) compared to the lower value found for the one of the tripodal tpaa3- (log beta11(Pb)=10.0(1)) provides direct evidence of the influence of the stereochemically active lead lone pair on complex stability. As a result, since the ligand geometry has little effect on the stability of the calcium complex, a remarkable increase in the Pb/Ca selectivity is observed for dpaea-(10(6.6)) compared to tpaa3- (10(1.5)), making the dipodal ligand a good candidate for application as extracting agent for the lead removal from contaminated water.     

Structure,reactivity and luminescence studies of triphenylsiloxide complexes of tetravalent lanthanides

Among the 14 lanthanide elements (Ce–Lu), until recently, the tetravalent oxidation state was readily accessible in solution only for cerium while Pr(iv), Nd(iv), Dy(iv) and Tb(iv) had only been detected in the solid state. The triphenylsiloxide ligand recently allowed the isolation of molecular complexes of Tb(iv) and Pr(iv) providing an unique opportunity of investigating the luminescent properties of Ln(iv) ions. Here we have expanded the coordination studies of the triphenylsiloxide ligand with Ln(iii) and Ln(iv) ions and we report the first observed luminescence emission spectra of Pr(iv) complexes which are assigned to a ligand-based emission on the basis of the measured lifetime and computational studies. Binding of the ligand to the Pr(iv) ion leads to an unprecedented large shift of the ligand triplet state which is relevant for future applications in materials science.

The first observed luminescence emission spectra of Pr(iv) complexes are assigned to a ligand-based emission. Binding of the triphenylsiloxide ligand to the Pr(iv) ion leads to an unprecedented large red shift of its triplet state.     

Cation assisted binding and cleavage of dinitrogen by uranium complexes

The role of alkali promoters in N₂ cleavage by metal complexes remains poorly understood despite its relevance to the industrial production of ammonia from N₂. Here we report a series of alkali bound-oxo-bridged diuranium(iii) complexes that provide a unique example of decreasing N₂ binding affinity with increasing cation size (from K to Cs). N₂ binding was found to be irreversible in the presence of K. A N₂ complex could be isolated in the solid state in the presence of the Rb cation and crystallographically characterized, but N₂ binding was found to be reversible under vacuum. In the presence of the Cs cation N₂ binding could not be detected at 1 atm. Electrochemical and Computational studies suggest that the decrease in N₂ binding affinity is due to steric rather than electronic effects. We also find that weak N₂ binding in ambient conditions does not prevent alkali assisted N₂ cleavage to nitride from occurring. More importantly, we present the first example of cesium assisted N₂ cleavage leading to the isolation of a N₂ derived multimetallic U/Cs bis-nitride. The nitrides readily react with protons and CO to yield ammonia, cyanate and cyanide.

N₂ binding affinity decreases markedly in a series of isostructural U(iii)–alkali ions complexes with increasing cation size. N₂ binding is undetectable in the Cs analogue, but the first example of cesium-assisted N₂ cleavage to bis-nitride was observed at ambient condition.     

Farming for Pharming: Novel Hydroponic Process in Contained Environment for Efficient Pharma-Grade Production of Saffron

Soilless cultivation of saffron (Crocus sativus) in a controlled environment represents an interesting alternative to field cultivation, in order to obtain a standardized high-quality product and to optimize yields. In particular, pharma-grade saffron is fundamental for therapeutic applications of this spice, whose efficacy has been demonstrated in the treatment of macular diseases, such as Age-related Macular Degeneration (AMD). In this work, a hydroponic cultivation system was developed, specifically designed to meet the needs of C. sativus plant. Various cultivation recipes, different in spectrum and intensity of lighting, temperature, photoperiod and irrigation, have been adopted to study their effect on saffron production. The experimentation involved the cultivation of corms from two subsequent farm years, to identify and validate the optimal conditions, both in terms of quantitative yield and as accumulation of bioactive metabolites, with particular reference to crocins and picrocrocin, which define the ‘pharma-grade’ quality of saffron. Through HPLC analysis and chromatography it was possible to identify the cultivation parameters suitable for the production of saffron with neuroprotective properties, evaluated by comparison with an ISO standard and the REPRON^® procedure. Furthermore, the biochemical characterization was completed through NMR and high-resolution mass spectrometry analyses of saffron extracts. The whole experimental framework allowed to establish an optimized protocol to produce pharma-grade saffron, allowing up to 3.2 g/m² harvest (i.e., more than three times higher than field production in optimal conditions), which meets the standards of composition for the therapy of AMD.     

Anhydrous Conditions Enable the Catalyst-Free Carboxylation of Aromatic Alkynes with CO2 under Mild Conditions

The direct carboxylation of aromatic alkynes with CO₂, a cheap and widely available C1 source, is the most attractive method for the synthesis of carboxylic acids. Here we show that direct carboxylation of terminal alkynes can be simply performed in near-quantitative yield in four hours with anhydrous Cs₂CO₃ under mild conditions without need of a metal catalyst.