Guest-Tunable Dielectric Sensing Using a Single Crystal of HKUST-1

There is rising interest on low-k dielectric materials based on porous metal-organic frameworks (MOFs) for improved electrical insulation in microelectronics. Herein, we demonstrate the concept of MOF dielectric sensor built from a single crystal of HKUST-1. We study guest encapsulation effects of polar and non-polar molecules, by monitoring the transient dielectric response and AC conductivity of the crystal exposed to different vapors (water, I2, methanol, ethanol). The dielectric properties were measured along the crystal direction in the frequency range of 100 Hz to 2 MHz. The dielectric data show the efficacy of MOF dielectric sensor for discriminating the guest analytes. The time-dependent transient response reveals dynamics of the molecular inclusion and exclusion processes in the nanoscale pores. Since dielectric response is ubiquitous to all MOF materials (unlike DC conductivity and fluorescence), our results demonstrate the potential of dielectric MOF sensors compared to resistive sensors and luminescence-based approaches.Comment: 6 pages, 5 figure

Hidden negative linear compressibility in lithium L-tartrate†

Development of artificial muscles, next-generation pressure sensors and precision optics relies on advances in materials with anomalous mechanical properties. Negative linear compressibility, NLC, is one such rare, counterintuitive phenomenon, in which a material expands along one axis under hydrostatic pressure. Both classical and recent NLC materials face a pay-off between the active pressure range and magnitude of NLC, and in the vast majority of cases the NLC effect decreases with pressure. By decoupling the mechanical behaviour of building units for the first time in a winerack framework containing two different strut types, we show that lithium L-tartrate exhibits NLC with a maximum value, Kmax = -21 TPa^-1, and an overall NLC capacity, χNLC = 5.1 %, that are comparable to the most exceptional materials to date. Furthermore, the contributions from molecular strut compression and angle opening interplay to give rise to so-called “hidden” negative linear compressibility, in which NLC is absent at ambient pressure, switched on at 2 GPa and sustained up to the limit of our experiment, 5.5 GPa. Analysis of the changes in crystal structure using variable-pressure synchrotron X-ray diffraction reveals new chemical and geometrical design rules to assist the discovery of other materials with exciting hidden anomalous mechanical properties

Exploiting in-situ NMR to monitor the formation of a metal-organic framework

The formation processes of metal–organic frameworks are becoming more widely researched using in situ techniques, although there remains a scarcity of NMR studies in this field. In this work, the synthesis of framework MFM-500(Ni) has been investigated using an in situ NMR strategy that provides information on the time-evolution of the reaction and crystallization process. In our in situ NMR study of MFM-500(Ni) formation, liquid-phase 1H NMR data recorded as a function of time at fixed temperatures (between 60 and 100 °C) afford qualitative information on the solution-phase processes and quantitative information on the kinetics of crystallization, allowing the activation energies for nucleation (61.4 ± 9.7 kJ mol−1) and growth (72.9 ± 8.6 kJ mol−1) to be determined. Ex situ small-angle X-ray scattering studies (at 80 °C) provide complementary nanoscale information on the rapid self-assembly prior to MOF crystallization and in situ powder X-ray diffraction confirms that the only crystalline phase present during the reaction (at 90 °C) is phase-pure MFM-500(Ni). This work demonstrates that in situ NMR experiments can shed new light on MOF synthesis, opening up the technique to provide better understanding of how MOFs are formed

Hybrid glasses from strong and fragile metal-organic framework liquids

This is the final version of the article. It first appeared from NPG via http://dx.doi.org/10.1038/ncomms9079Hybrid glasses connect the emerging field of metal-organic frameworks (MOFs) with the glass formation, amorphization and melting processes of these chemically versatile systems. Though inorganic zeolites collapse around the glass transition and melt at higher temperatures, the relationship between amorphization and melting has so far not been investigated. Here we show how heating MOFs of zeolitic topology first results in a low density ?perfect? glass, similar to those formed in ice, silicon and disaccharides. This order?order transition leads to a super-strong liquid of low fragility that dynamically controls collapse, before a subsequent order?disorder transition, which creates a more fragile high-density liquid. After crystallization to a dense phase, which can be remelted, subsequent quenching results in a bulk glass, virtually identical to the high-density phase. We provide evidence that the wide-ranging melting temperatures of zeolitic MOFs are related to their network topologies and opens up the possibility of ?melt-casting? MOF glasses.The authors would like to thank Trinity Hall (TDB); HRH Sheikh Saud Bin Saqr Al Qasimi (TDB and AKC); Wuhan University of Science and Technology (YY and GNG), ERC grant number 259619 PHOTO EM (CD); Alexander von Humboldt Foundation (SH); The World Premier International Research Center Initiative on Materials Nanoarchitectronics (WPI-MANA) from MEXT, Japan (HHMY)

Impact of opioid-free analgesia on pain severity and patient satisfaction after discharge from surgery: multispecialty, prospective cohort study in 25 countries

Background: Balancing opioid stewardship and the need for adequate analgesia following discharge after surgery is challenging. This study aimed to compare the outcomes for patients discharged with opioid versus opioid-free analgesia after common surgical procedures.Methods: This international, multicentre, prospective cohort study collected data from patients undergoing common acute and elective general surgical, urological, gynaecological, and orthopaedic procedures. The primary outcomes were patient-reported time in severe pain measured on a numerical analogue scale from 0 to 100% and patient-reported satisfaction with pain relief during the first week following discharge. Data were collected by in-hospital chart review and patient telephone interview 1 week after discharge.Results: The study recruited 4273 patients from 144 centres in 25 countries; 1311 patients (30.7%) were prescribed opioid analgesia at discharge. Patients reported being in severe pain for 10 (i.q.r. 1-30)% of the first week after discharge and rated satisfaction with analgesia as 90 (i.q.r. 80-100) of 100. After adjustment for confounders, opioid analgesia on discharge was independently associated with increased pain severity (risk ratio 1.52, 95% c.i. 1.31 to 1.76; P < 0.001) and re-presentation to healthcare providers owing to side-effects of medication (OR 2.38, 95% c.i. 1.36 to 4.17; P = 0.004), but not with satisfaction with analgesia (beta coefficient 0.92, 95% c.i. -1.52 to 3.36; P = 0.468) compared with opioid-free analgesia. Although opioid prescribing varied greatly between high-income and low- and middle-income countries, patient-reported outcomes did not.Conclusion: Opioid analgesia prescription on surgical discharge is associated with a higher risk of re-presentation owing to side-effects of medication and increased patient-reported pain, but not with changes in patient-reported satisfaction. Opioid-free discharge analgesia should be adopted routinely

High Pressure Crystal Structure and Electrical Properties of a Single Component Molecular Crystal [Ni(dddt)₂] (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate)

Single-component molecular conductors form an important class of materials showing exotic quantum phenomena, owing to the range of behavior they exhibit under physical stimuli. We report the effect of high pressure on the electrical properties and crystal structure of the single-component crystal [Ni(dddt)2] (where dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate). The system is isoelectronic and isostructural with [Pd(dddt)2], which is the first example of a single-component molecular crystal that exhibits nodal line semimetallic behavior under high pressure. Systematic high pressure four-probe electrical resistivity measurements were performed up to 21.6 GPa, using a Diamond Anvil Cell (DAC), and high pressure single crystal synchrotron X-ray diffraction was performed up to 11.2 GPa. We found that [Ni(dddt)2] initially exhibits a decrease of resistivity upon increasing pressure but, unlike [Pd(dddt)2], it shows pressure-independent semiconductivity above 9.5 GPa. This correlates with decreasing changes in the unit cell parameters and intermolecular interactions, most notably the π-π stacking distance within chains of [Ni(dddt)2] molecules. Using first-principles density functional theory (DFT) calculations, based on the experimentally-determined crystal structures, we confirm that the band gap decreases with increasing pressure. Thus, we have been able to rationalize the electrical behavior of [Ni(dddt)2] in the pressure-dependent regime, and suggest possible explanations for its pressure-independent behavior at higher pressures

Chiral, Racemic, and <i>Meso</i>-Lithium Tartrate Framework Polymorphs: A Detailed Structural Analysis

Following our previous report of five anhydrous lithium tartrates <b>1</b>–<b>5</b> (tart = C₄H₄O₆ ^2–), we have synthesized and solved the single crystal structures of four new I¹O² inorganic–organic frameworks, all with the same chemical formula, Li₂(tart). Reactions between lithium acetate and the meso, chiral, and racemic isomers of tartaric acid in water:ethanol mixtures have yielded two new polymorphs of Li₂(<i>meso</i>-tart) in space groups <i>P</i>2₁/<i>c</i> <b>6</b> and <i>Cc</i> <b>7</b>, racemic Li₂(d,l-tart) in <i>P</i>2₁/<i>c</i> <b>8</b>, and chiral Li₂(l-tart) in <i>C</i>2 <b>9</b>. Hydrogen bond graph set analysis was adapted for use with framework materials and employed here to examine the motifs displayed by the eight anhydrous dilithium tartrates <b>2</b>–<b>9</b>. A variety of hydrogen-bonding patterns and dimensionalities are observed in this system, and the relative hydrogen bond strengths are found to correlate well with O–H stretching frequency shifts in the FTIR spectra. The relative formation energies of the framework isomers have been calculated by DFT methods, using schemes that include dispersion correction, zero-point vibrational energy, and thermal vibrations at room temperature. Although the energy ordering depends slightly on the scheme used, it is generally found to relate to the differences in crystallographic density and hydrogen bond strength rather than other structural features