Current trends in the computational modelling of polyoxometalates

Computational chemistry applied to the study of polyoxometalates has achieved its maturity in the last years. During two decades, important advances have been made using theoretical tools in the comprehension and interpretation of many relevant issues. In the present mini-review, we want to stress that different techniques have been incorporated to the routine of computation: from the very first Hartree?CFock LCAO-SCF calculation on the decavanadate anion, followed by numerous density functional theory?Cbased studies on increasingly complex systems, also applying correlated ab initio techniques for magnetism and, more recently, using molecular dynamics to analyse properties in liquid media, the information provided by computational chemistry gets more and more relevant.     

Determination of betaines in vegetable oils by capillary electrophoresis tandem mass spectrometry--application to the detection of olive oil adulteration with seed oils

A CE–tandem mass spectrometry (MS²) methodology enabling the simultaneous determination of betaines (glycine betaine, trigonelline, proline betaine and total content of carnitines) in vegetable oils was developed. Betaines were derivatized with butanol previous to their baseline separation in 10 min using a 0.1 M formic acid buffer at pH 2.0. Ion trap conditions were optimized in order to maximize the selectivity and sensitivity. Analytical characteristics of the proposed method were established by evaluating its selectivity, linearity, precision (RSDs ranged from 4.8 to 10.7% for corrected peak areas) and accuracy by means of recovery studies (from 80 to 99%) and LODs and LOQs at 0.1 ppb level. The method was applied for the determination of the selected betaines in seed oils and extra virgin olive oils. MS² experiments provided the fingerprint fragmentation for the betaines identified in vegetable oils. In extra virgin olive oils, carnitines were not detected, making it possible to propose them as a feasible novel marker for the detection of adulterations of olive oils. Application of the developed method for the analysis of different mixtures of extra virgin olive oil with seed oil (between 2 and 10%) enabled the detection and quantitation of the total content of carnitines. The results obtained show the high potential of the developed method for the authentication and quality control of olive oils.     

Syntheses, crystal structures, transport properties and first-principles electronic structure study of the (tTTF)2X (X=Br, I) low-dimensional antiferromagnets

An efficient synthetic procedure for the preparation of unsymmetrically substituted tetrathiafulvalene (TTF) donors has been used to obtain the trimethylene-tetrathiafulvalene (tTTF) donor with high purity. Good quality crystals of the two (tTTF)(2)X (X = Br, I) salts have been obtained by electrocrystallization. The two salts are isomorphous and contain tTTF layers which are built from (tTTF)(2) dimeric units. Both systems are low-dimensional antiferromagnets with the highest Ne?el temperatures for TTF based radical cation salts: ≈ 35 K (Br salt) and ≈43 K (I salt). The resistivity is found to substantially decrease with pressure although both salts still have activated conductivity at 25 kbar. First-principles Density Functional Theory (DFT) calculations have been used to investigate the relative strength of the three different types of magnetic interactions in the tTTF layers as well as the potential magnetic ground states. These calculations successfully predict the nature of the ground state and suggest a possible correlation between structural details and Ne?el temperatures for the bromine and iodine salts. Remarkably, the calculated antiferromagnetic ground state can be predicted from the nesting properties of the Fermi surface for the hypothetical Pauli paramagnetic metallic state.     

Role of axially coordinated surface sites for electrochemically controlled carbon monoxide adsorption on single crystal copper electrodes

The adsorption of CO on low index copper single crystals in electrochemical environments has been investigated. The results, analysed through a combination of in situ infrared spectroscopy, DFT and cyclic voltammetry, reveal a unique adsorption behaviour when compared to previous studies on copper and the more widely studied noble metal surfaces. By employing small, weakly specifically adsorbed electrolytes, it is shown that carbon monoxide is adsorbed over a much wider electrode potential range than previously reported. The electrochemical Stark shift (δν/δE) observed is similar for the three Cu(hkl) surfaces examined despite different surface coverages. Most notably, however, is an electrochemical feature observed at ca. -1.0 V (vs. Ag/AgCl) on the (110) surface. It is proposed that this voltammetric feature arises from the reduction/oxidation of Cu(δ+) surface sites involved in the binding of carbon monoxide with the participation of the electrolyte anion. This provides additional specific sites for CO adsorption. DFT calculations support the proposed presence of low-coordination copper sites stabilised by electrolyte anions. An experimental electron transfer rate constant of 4.2 s(-1) to the Cu(δ+) surface sites formed was found. These new observations concerning the surface electrochemistry of CO on Cu indicate that the electrocatalytic behaviour of Cu electrodes in processes such as CO(2) reduction need to be re-evaluated to take account of the rich adsorption behaviour of CO, including the co-adsorption of the electrolyte anion to these sites.     

A multipurpose gold(I) precatalyst

[Au(tmbn)(2)](SbF(6)) is the first gold(I) complex supported by two nitrile ligands that is indefinitely stable at room temperature. This is a highly versatile precatalyst that can be used for the preparation of active and robust solid-supported gold(I) catalysts.     

RNAs' uracil quartet model with a non-essential metal ion

We have recently communicated the resemblance of 1-hexyluracil in the crystal state with a lipid bilayer (CrystEngComm, 2010, 12, 362-365). Treatment of this molecule with silver nitrate yields a model, using a non-essential metal ion, of a uracil quartet with geometric parameters comparable to those previously found in RNA strands.     

Reactivity of metallic nitride endohedral metallofullerene anions: electrochemical synthesis of a Lu3N@Ih-C80 derivative

Electrochemically generated Lu(3)N@I(h)-C(80) dianions react with the electrophile, PhCHBr(2), to produce a methano derivative of Lu(3)N@I(h)-C(80)(CHC(6)H(5)) (1) with high regioselectivity. The compound was characterized by MALDI-TOF, NMR, and UV-vis-NIR absorption spectroscopy. Electrochemical characterization of this Lu(3)N@I(h)-C(80)(CHC(6)H(5)) derivative showed the typical irreversible reductive behavior of the pristine Lu(3)N@I(h)-C(80), similar to those observed for Bingel adducts of Lu(3)N@I(h)-C(80). Using the same conditions, the reaction between Sc(3)N@I(h)-C(80) dianions and PhCHBr(2) was conducted for comparison. Unexpectedly, no nucleophilic reaction was observed, indicating that Sc(3)N@I(h)-C(80) dianions are not reactive toward the electrophile. Theoretical studies for both dianionic Lu(3)N@I(h)-C(80) and Sc(3)N@I(h)-C(80) showed that the HOMO is more highly localized on the fullerene cage for [Lu(3)N@I(h)-C(80)](2-) and more localized on the inside cluster for [Sc(3)N@I(h)-C(80)](2-), providing an explanation for the drastically different reactivities observed.     

The first ruthenium-alkyne-dihydride reported is now recognized as an intermediate in the homogeneous hydrogenation of diphenylacetylene: Crystal structure of (μ-H)2Ru3(CO)9(μ3-η2-∥-C2Ph2)

The title complex (complex1) was the first alkyne-substituted triruthenium dihydrido cluster to be reported and was characterized by spectroscopy as a triangular cluster with the alkyne parallel to a Ru-Ru edge. Recently, we have found that1 is a key intermediate in the homogeneous hydrogenation of diphenylacetylene catalyzed by tetrahedral Ru₄ and FeRu₃ clusters. Since the discovery of1, a great number of complexes with alkynes parallel to a cluster edge have been reported; at present this is the more common bonding mode for alkynes on trinuclear clusters. The structural features of1 allow a comparison with those of other ruthenium-containing derivatives and help to draw suggestions of the role of1 in hydrogenation catalysis.     

Hydrogen bonding in 2‐(2‐oxothiazolidin‐3‐yl)‐4,5‐dihydrothiazolium hydrogen sulfate monohydrate

The asymmetric unit of the title compound, C₆H₉N₂OS₂⁺·HSO₄⁻·H₂O, contains a heterocyclic cation, a hydrogen sulfate anion and a water molecule. There are strong hydrogen bonds between the hydrogen sulfate anions and water molecules, forming an infinite chain along the [010] direction, from which the cations are pendent. The steric, electronic and geometric features are compared with those of similar compounds. In this way, structural relationships are stated in terms of the influence of the sulfate group on the protonation of the heterocycle and on the tautomeric equilibrium in the solid state.     

Thermodynamics of (1-alkanol + linear monoether) systems

Densities, ρ, and speeds of sound, u, of systems formed by 1-heptanol, or 1-octanol, or 1-decanol and dibutylether have been measured at a temperature of (293.15, 298.15, and 303.15) K and atmospheric pressure using a vibrating tube densimeter and sound analyser Anton Paar model DSA-5000. The ρ and u values were used to calculate excess molar volumes, V^E, and deviations from the ideal behaviour of the thermal expansion coefficient, Δα_p and of the isentropic compressibilities, Δκ_S. The available database on molar excess enthalpies, H^E, and V^E for (1-alkanol + linear monoether) systems was used to investigate interactional and structural effects in such mixtures. The enthalpy of the OH?O bonds is lower for methanol solutions, and for the remainder systems, it is practically independent of the mixture compounds. The V^E variation with the chain length of the 1-alkanol points out the existence of structural effects for systems including longer 1-alkanols. The ERAS model is applied to the studied mixtures. ERAS represents quite accurately H^E and V^E data using parameters which consistently depend on the molecular structure.