Incorporation of pyramidal heteroanions in mixed-metal polyoxometalate based cages

Abstract available: p.x-xi

Differentiation of Epoxide Enantiomers in the Confined Spaces of an Homochiral Cu(II) MOF by Kinetic Resolution

TAMOF-1, a homochiral metal-organic framework (MOF) constructed from an amino acid derivative and Cu(II), was investigated as a heterogeneous catalyst in kinetic resolutions involving the ring opening of styrene oxide with a set of anilines. The branched products generated from the ring opening of styrene oxide with anilines and the unreacted epoxide were obtained with moderately high enantiomeric excesses. The linear product arising from the attack on the non-benzylic position of styrene oxide underwent a second kinetic resolution by reacting with the epoxide, resulting in an amplification of its final enantiomeric excess and a concomitant formation of an array of isomeric aminodiols. Computational studies confirmed the experimental results, providing a deep understanding of the whole process involving the two successive kinetic resolutions. Furthermore, TAMOF-1 activity was conserved after several catalytic cycles. The ring opening of a mesoepoxide with aniline catalyzed by TAMOF-1 was also studied and moderate enantioselectivities were obtained

Homochiral Metal-Organic Frameworks for Enantioselective Separations in Liquid Chromatography

Selective separation of enantiomers is a substantial challenge for the pharmaceutical industry. Chromatography on chiral stationary phases is the standard method, but at a very high cost for industrial-scale purification owing to the high cost of the chiral stationary phases. Typically, these materials are poorly robust, expensive to manufacture and often too specific for a single desired substrate, lacking desirable versatility across different chiral analytes. Here we disclose a porous, robust homochiral metal-organic framework (MOF), TAMOF-1, built from copper(II) and an affordable linker prepared from natural L-histidine. TAMOF-1 has shown to be able to separate a variety of model racemic mixtures, including drugs, in a wide range of solvents of different polarity, outperforming several commercial chiral columns for HPLC separations. Although not exploited in the present article, it is worthy to mention that the preparation of this new material is scalable to the multikilogram scale, opening unprecedented possibilities for low-energy chiral separation at the industrial scale

Directed self-assembly, symmetry breaking, and electronic modulation of metal oxide clusters by pyramidal heteroanions

Mixed valence/metal polyoxometalate (POM) clusters are one of the most interesting host species showing the ability to incorporate a wide range of heteroatoms of various charges and geometries. We report herein, the incorporation of different pyramidal EO32- heteroanions (E = PH, S, Se, Te) which are responsible not only for directing the templated assembly of a family of mixed-metal POMs but also for the symmetry-breaking of the traditional Dawson architecture and modulation of the electronic characteristics of the cluster's shell. The isolated family of POMs consists of four members: (Me2NH2)5Na2[Mo11V7O52(HPO3)]·MeOH·5H2O (1), (NH4)7[Mo11V7O52(SO3)]·12H2O (2), K7[Mo11V7O52(SeO3)]·31H2O (3), (Me2NH2)6Na[Mo11V7O52(TeO3)]·15H2O (4), and were characterized by X-ray structural analysis, electrospray ionization mass spectrometry (ESI-MS), thermogravimetric analysis (TGA), UV-vis, IR, elemental and flame atomic absorption spectroscopy (FAAS) analysis, and inductively coupled plasma optical emission spectroscopy (ICP-OES). Cyclic voltammetry (CV) and electron paramagnetic resonance (EPR) spectroscopic studies in concert with density functional theoretical (DFT) calculations elucidate the effect of the heteroatom on the electronic properties of the cluster

COVID-19 vaccine effectiveness against hospitalization due to SARS-CoV-2: A test-negative design study based on Severe Acute Respiratory Infection (SARI) sentinel surveillance in Spain

Background: With the emergence of SARS-CoV-2, influenza surveillance systems in Spain were transformed into a new syndromic sentinel surveillance system. The Acute Respiratory Infection Surveillance System (SiVIRA in Spanish) is based on a sentinel network for acute respiratory infection (ARI) surveillance in primary care and a network of sentinel hospitals for severe ARI (SARI) surveillance in hospitals. Methods: Using a test-negative design and data from SARI admissions notified to SiVIRA between January 1 and October 3, 2021, we estimated COVID-19 vaccine effectiveness (VE) against hospitalization, by age group, vaccine type, time since vaccination, and SARS-CoV-2 variant. Results: VE was 89% (95% CI: 83-93) against COVID-19 hospitalization overall in persons aged 20 years and older. VE was higher for mRNA vaccines, and lower for those aged 80 years and older, with a decrease in protection beyond 3 months of completing vaccination, and a further decrease after 5 months. We found no differences between periods with circulation of Alpha or Delta SARS-CoV-2 variants, although variant-specific VE was slightly higher against Alpha. Conclusions: The SiVIRA sentinel hospital surveillance network in Spain was able to describe clinical and epidemiological characteristics of SARI hospitalizations and provide estimates of COVID-19 VE in the population under surveillance. Our estimates add to evidence of high effectiveness of mRNA vaccines against severe COVID-19 and waning of protection with time since vaccination in those aged 80 or older. No substantial differences were observed between SARS-CoV-2 variants (Alpha vs. Delta).The data of the study was originally collectedas part of the following projects run by the European Centre for Disease Prevention and Control:“Establishing Severe Acute Respiratory Infections (SARI) surveillance and performing hospital-based COVID-19 transmission studies”, “Developing an infrastructure and performing vaccine effectiveness studies for COVID-19 vaccines in the EU/EEA”, and the “Vaccine Effectiveness, Burden and Impact Studies(VEBIS) of COVID-19 and Influenza".S

Design and assembly of covalently functionalised polyoxofluorovanadate molecular hybrids

Mixed-valent polyoxometalate (POM) clusters are one of the most interesting host species showing a wide range of structural features and properties. We report the facile preparation and functionalization of a mixed-valent polyoxofluorovanadates where two electrons are trapped to antipodal sites of the clusters. The first members of this family of clusters with the general formula, [VV12VIV2O16(μ-O)10(μ3-O)10(μ3-F)2(L)2]6-, where L: py = pyridine (1); pyr = pyrazine (2); im = imidazole (3), are unique organic-inorganic hybrids with the addition of a N-donor ligand at either end of the polyoxofluorovanadate. The composition and connectivity of 1 - 3 were characterized by single-crystal X-ray diffractometry and electrospray ionization mass spectrometry. Electron paramagnetic resonance spectroscopy revealed the two well-separated VIV ions in each cluster are fully uncoupled with J = 0 giving a degenerate singlet-triplet ground state. This attenuation of the exchange interaction is probed with density functional theoretical calculations that detail the inclusion of the fluoride ion in the cluster produces a bond pathway biased toward destructive interference between competing ferromagnetic and antiferromagnetic interactions. These robust molecular materials are the ideal combination of desirable electronic properties with an organic handle with which they can be integrated into spintronic circuitry for molecular devices

Controlling the self-assembly of a mixed-metal Mo/V-selenite family of polyoxometalates

Five mixed-metal mixed-valence Mo/V polyoxoanions, templated by the pyramidal SeO32- heteroanion have been isolated: K10MoVI12VV10O58(SeO3)8]center dot 18?H2O (1), K7MoVI11VV5VIV2O52(SeO3)]center dot 31?H2O (2), (NH4)7K3MoVI11VV5VIV2O52(SeO3)(MoV6VV- O22)]center dot 40?H2O (3), (NH4)19K3MoVI20VV12VIV4O99(SeO3)10]center dot 36?H2O (4) and Na3(H2O)5{Mo18-xVxO52(SeO3)} {Mo9-yVyO24(SeO3)4}] (5). All five compounds were characterised by single-crystal X-ray structure analysis, TGA, UV/Vis and FT-IR spectroscopy, redox titrations, and elemental and flame atomic absorption spectroscopy (FAAS) analysis. X-ray studies revealed two novel coordination modes for the selenite anion in compounds 1 and 4 showing eta,mu and mu,mu coordination motifs. Compounds 1 and 2 were characterised in solution by using high-resolution ESI-MS. The ESI-MS spectra of these compounds revealed characteristic patterns showing distribution envelopes corresponding to 2- and 3- anionic charge states. Also, the isolation of these compounds shows that it may be possible to direct the self-assembly process of the mixed-metal systems by controlling the interplay between the cation shrink-wrapping effect, the non-conventional geometry of the selenite anion and fine adjustment of the experimental variables. Also a detailed IR spectroscopic analysis unveiled a simple way to identify the type of coordination mode of the selenite anions present in POM-based architectures

Assembly of a family of mixed metal {Mo : V} polyoxometalates templated by TeO₃^2-: {Mo₁₂V₁₂Te₃}, {Mo₁₂V₁₂Te₂} and {Mo₁₇V₈Te}

The influence of the pyramidal heteroanion, TeO<sub>3</sub><sup>2−</sup> in the self-assembly of mixed metal (Mo/V) systems, is demonstrated by the isolation of three novel mixed-metal, mixed-valence architectures, {Mo<sub>12</sub>V<sub>12</sub>Te<sub>3</sub>} (<b>1</b>), {Mo<sub>12</sub>V<sub>12</sub>Te<sub>2</sub>} (<b>2</b>) and {Mo<sub>17</sub>V<sub>8</sub>Te} (<b>3</b>) with the tellurium centres exhibiting the novel µ8-TeO4 and µ9-TeO<sub>3</sub> coordination modes while compounds 1 and 2 were discovered utilizing ESI mass spectrometry

Spontaneous Magnetization in Homometallic u6-oxalate Coordination Polymers

Reaction of 1,2,4-triazole and NaF with M(ox) (M = transition metal dication; ox = oxalate dianion) under hydrothermal conditions has lead to the isolation of a variety of hybrid organic-inorganic coordination polymers. Four structurally different 3D networks were obtained, depending on the transition metal, with stoichiometry: [M2(H2O)(m2-ox)][M2(m3-trz)6] (M = Fe (1), Co(2), Ni (3)), [Zn2(H2O)(m3-trz)2(m2-ox)] (4), [Mn3(m3-trz)2(m6-ox)(m3-F)2] (5) and [Fe3(m3-trz)2(m6-ox)(m2-F)2] (6). In all cases, the magnetic behavior is dominated by antiferromagnetic exchange interactions between paramagnetic centers. Remarkably, 5 and 6 present a novel magnetic connectivity around the oxalate anion: a 6-bridging mode. This magnetic geometry promotes multiple triangular arrangements among antiferromagnetically coupled spin carriers resulting in a complex magnetic network due to the presence of competing interactions. These materials exhibit spontaneous magnetization below 9 and 66 K, respectively.</p