Modulation of Prins Cyclization by Vibrational Strong Coupling

Light-molecule strong coupling has emerged within the last decade as a new method to control chemical reactions. A few years ago it was discovered that chemical reactivity could be altered by vibrational strong coupling (VSC). Only a limited number of reactions have been investigated under VSC to date, including solvolysis and deprotection reactions. Here the effect of VSC on a series of aldehydes and ketones undergoing Prins cyclization, an important synthetic step in pharmaceutical chemistry, is investigated. A decrease of the second-order rate constant with VSC of the reactant carbonyl stretching groups is observed. We also observe an increased activation energy due to VSC, but proportional changes in activation enthalpy and entropy, suggesting no substantive change in reaction pathway. The addition of common cycloaddition reactions to the stable of VSC-modified chemical reactions is another step towards establishing VSC as a genuine tool for synthetic chemistry.     

Magnetism and the magnetocaloric effect in PrMn1.6Fe0.4Ge2

The magnetic and magnetocaloric properties of PrMn_1.6Fe_0.4Ge₂around the ferromagnetic transitions T _C ^inter ~ 230 K and T _C ^Pr ~ 30 K have been investigated by magnetisation, ⁵⁷Fe Mössbauer spectroscopy and electron paramagnetic resonance (EPR) measurements over the temperature range 5–300 K. The broad peaks in magnetic entropy around T_C ^inter (intralayer antiferromagnetism of the Mn sublattice to canted ferromagnetism) and T_C ^Pr (onset of ferromagnetic order of Pr sublattice in addition to ferromagnetically ordered Mn sublattice) are typical of second order transitions with maximum entropy values of -ΔS _M ~ 2.0 J/kg K and -ΔS _M ~ 2.2 J/kg K respectively for ΔB = 0–6 T. The EPR signal around T = 48 K of g value g ~ 0.8 is consistent with paramagnetic free ion Pr^3?+?. Below T_C ^Pr ~ 30 K the g value increases steadily to g ~ 2.5 at 8 K as saturation of the Pr^3?+? ion is approached. The EPR measurements indicate additional effects in this system below T ~ 20 K with the appearance of EPR signals of low g value g ~ 0.6.     

A novel tin (II) dithioether complex

Organotin and related tin containing compounds are a recurring motif in organometallic chemistry. Here we report a new complex resulting from the reaction of tin (II) chloride with a dithioether diallyl ether ligand created as a side product from other research in our lab. This new complex is reasonably stable and can be synthesized on the bench top with no extraordinary measures required to exclude air or moisture. Its crystal structure reveals a five coordinate pseudo-square pyramidal geometry around tin, with the ligand binding the metal through its thioether sulfurs and the chlorides bridging.     

Recent experiments with transient NMRON

High resolution magnetic and electric hyperfine interaction distributions are determined for single crystal⁵⁴MnNi with diffused impurity concentrations of 0.14 and 0.40 at%, and for a 0.1 µm layer of⁶⁰CoFe co-plated onto single crystal Fe. High quality gamma detected nuclear spin echoes recorded for the⁶⁰CoFe specimen demonstrate that a reduced influence of the RF skin effect far outweighs any magnetic hyperfine field interaction broadening associated with the co-plating process.     

The Nature of Line Broadening in Thermally Detected 57FeFe NMR

⁵⁷FeFe with isotopic concentrations from 15 to 95% is studied using NMR thermally detected by nuclear orientation. Lines are found to be consistently homogeneous. The contrast with previous inhomogeneous ⁵⁷FeFe lines from Mössbauer detected NMR is explained by differences in radio frequency field strength.     

Ground‐State Chemical Reactivity under Vibrational Coupling to the Vacuum Electromagnetic Field

The ground‐state deprotection of a simple alkynylsilane is studied under vibrational strong coupling to the zero‐point fluctuations, or vacuum electromagnetic field, of a resonant IR microfluidic cavity. The reaction rate decreased by a factor of up to 5.5 when the Si?C vibrational stretching modes of the reactant were strongly coupled. The relative change in the reaction rate under strong coupling depends on the Rabi splitting energy. Product analysis by GC‐MS confirmed the kinetic results. Temperature dependence shows that the activation enthalpy and entropy change significantly, suggesting that the transition state is modified from an associative to a dissociative type. These findings show that vibrational strong coupling provides a powerful approach for modifying and controlling chemical landscapes and for understanding reaction mechanisms.     

Sequence Effects in Conjugated Donor–Acceptor Trimers and Polymers

To investigate the sequence effect on donor–acceptor conjugated oligomers and polymers, the trimeric isomers PBP and BPP , comprising dialkoxy phenylene vinylene ( P ), benzothiadiazole vinylene ( B ), and alkyl endgroups with terminal olefins, are synthesized. Sequence effects are evident in the optical/electrochemical properties and thermal properties. Absorption maxima for PBP and BPP differ by 41 nm and the electrochemical band gaps by 0.1 V. The molar emission intensity is five times greater in PBP than BPP . Both trimers are crystalline and the melting points differ by 17 °C. The PBP and BPP trimers are used as macromonomers in an acyclic diene metathesis polymerization to give PolyPBP and PolyBPP . The optical and electrochemical properties are similar to those of their trimer precursors—sequence effects are still evident. These results suggest that sequence is a tunable variable for electronic materials and that the polymerization of oligomeric sequences is a useful approach to introducing sequence into polymers.

     

Elucidating Inorganic Nanoscale Species in Solution: Complementary and Corroborative Approaches

The challenge of defining a length on the nanoscale is non‐trivial. For a well‐defined inorganic nanoscale species, a size measurement can describe a number of different dimensions (core, shell, solvation sphere). Often size is reported out of context or even inadvertently misrepresented. Since many of the techniques used to measure size depend on significant and sometimes destructive sample preparation, an additional challenge is defining “what size means” for a nanoscale species in solution. In this Concept, the distinction is made between complementary techniques that can be used together to unveil more information about the material in question, and corroborative techniques, which are used to make multiple measurements of the same property. Additionally, corroborative techniques can be used to measure the same property in and out‐of solution so as to reveal details about solution behaviour. We highlight various approaches to this characterization challenge in the context of three case studies that demonstrate the use of both complementary and corroborative techniques to elucidate the various functional dimensions of different types of inorganic nanoscale species in solution.