The rate of the light-induced spin transition in a coordination polymer network solid dramatically increases when included as the core in mesoscale core-shell particles. A series of photomagnetic coordination polymer core-shell heterostructures, based on the light-switchable Rb Co[Fe(CN)] · mHO (RbCoFe-PBA) as core with the isostructural K Ni[Cr(CN)] · nHO (KNiCr-PBA) as shell, are studied using temperature-dependent powder X-ray diffraction and SQUID magnetometry. The core RbCoFe-PBA exhibits a charge transfer-induced spin transition (CTIST), which can be thermally and optically induced. When coupled to the shell, the rate of the optically induced transition from low spin to high spin increases. Isothermal relaxation from the optically induced high spin state of the core back to the low spin state and activation energies associated with the transition between these states were measured. The presence of a shell decreases the activation energy, which is associated with the elastic properties of the core. Numerical simulations using an electro-elastic model for the spin transition in core-shell particles supports the findings, demonstrating how coupling of the core to the shell changes the elastic properties of the system. The ability to tune the rate of optically induced magnetic and structural phase transitions through control of mesoscale architecture presents a new approach to the development of photoswitchable materials with tailored properties.

A series of photomagnetic coordination polymer core–shell heterostructures, based on the light-switchable Prussian blue analogue Rb a Co b [Fe­(CN)6] c ·mH2O (RbCoFe-PBA) as the core and the ferromagnetic K j Ni k [Cr­(CN)6] l ·nH2O (KNiCr-PBA) as the shell, was studied using powder X-ray diffraction, down to 100 K, and magnetometry, down to 2 K, to investigate the influence of the shell thickness on light-induced magnetization changes and gain insight into the mechanism. The core material is known to undergo a charge-transfer-induced spin transition (CTIST), and synchrotron powder diffraction was used to monitor structural changes in both the core and the shell associated with the thermally and optically induced CTIST of the core. Significant lattice contraction in the RbCoFe-PBA core upon cooling through the high-spin to the low-spin state transition near ∼260 K induces strain on the KNiCr-PBA shells. This lattice strain in the shell can be relieved either by thermal cycling back to high temperature or by using light to access the metastable high-spin state of the core at low temperature. The different extents of strain in the KNiCr-PBA shell are reflected in low-temperature, low-field magnetization versus temperature data in the light and dark states. A broader magnetic transition at T c ≈ 70 K in the dark state relative to the light state reflects the greater dispersion of nearest-neighbor contacts and exchange energies induced by the structural distortions of the strained state. Analyses for different shell thicknesses, coupled with high-field magnetization data, support a mechanism whereby the light-induced magnetization changes in the KNiCr-PBA shell are due to realignment of the local magnetic anisotropy as a result of the structural changes in the shell associated with the optical CTIST of the core. Through magnetization and structural analyses, the depth to which the properties of the shell are influenced by the core–shell architecture was estimated to be between 40 and 50 nm.

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Weak partial agonists that promote a desensitized state of the α7 nicotinic acetylcholine receptor (nAChR) have been associated with anti-inflammatory effects. Exemplar compounds feature a tertiary or quaternary ammonium group. We report the synthesis, structure, and electrophysiological evaluation of 1-ethyl-4-phenylthiomorpholin-1-ium triflate, a weak partial agonist with a sulfonium isostere of the ammonium pharmacophore. These results offer new insights in understanding nAChR-ligand interactions and provide a new chemical space to target the α7 nAChR.

New nanometer scale heterostructure particles of the two-dimensional Hofmann-like Fe(ii) spin-crossover network, Fe(phpy)[Ni(CN)]·0.5HO {phpy = 4-phenylpyridine}, and the Prussian blue analogue KNi[Cr(CN)]·nHO (NiCr-PBA) have been developed, exhibiting synergistic photomagnetic effects, whereby the LIESST (light-induced electron spin-state trapping) effect in the Hofmann-like material induces a magnetization change in the NiCr-PBA. A variety of microscopic and spectroscopic techniques demonstrate the heterogeneous growth of the NiCr-PBA on the Hofmann seed particles and show the Hofmann compound retains its thermal and photoinduced spin transition properties in the heterostructure. The photoinduced magnetization change in the NiCr-PBA network arises from coupling of the two lattices despite dissimilar structure types. Isothermal magnetization minor hysteresis loop studies at 5 K show light absorption leads to changes in the local anisotropy of NiCr-PBA magnetic domains, providing direct evidence for a general magnetomechanical mechanism of light-switchable magnetism in coordination polymer heterostructures combining a photoactive material with a magnet.

2016-11-03T14:11:40

Spin-transition heterostructures have shown promise for inducing large switchable stresses at the nanoscale with a volumetric work density similar to piezoelectrics, but before practical applications are feasible, how heterostructure interfaces and geometry influence the transmission of stress and, in return, how they affect the spin-transition actuator itself, must be better understood. Here, four series of cubic spin-transition Prussian blue analogue (PBA) core–shell heterostructures were developed in order to probe the scaling behavior of the strain induced in the shell by the spin transition of the core. Cubic Rb x Co­[Fe­(CN)6] y·nH2O (RbCoFe-PBA) particles ranging 100–600 nm were used to prepare separate series of Rb x Co­[Fe­(CN)6] y ·nH2O@KjNi­[Cr­(CN)6] k ·mH2O (RbCoFe@KNiCr-PBA) core–shell particles with magnetic KNiCr-PBA shells ranging from 15 to 130 nm. A model fit to the strain-modified magnetization extracts the “strained volume” of the shell, and the results are compared with structural changes observed with powder X-ray diffraction. A linear relationship is found between the strained volume of the shell and the volume of the core for thicker shells, where the magnetic KNiCr-PBA shell is influenced to depths greater than 100 nm in response to the spin transition of the RbCoFe-PBA core. For thin shells, the relationship is more complicated, as the volume change in the actuating core and the strain it induces in the shell become interdependent and a function of shell thickness.

A one-dimensional NiII coordination polymer has been prepared via solvothermal synthesis using dimethyl sulfoxide as solvent. The coordination polymer forms double-chains along [010] and exhibits π–π stacking and C—H⋯π inter­actions forming the inter­ior of the double-chains, separated from a C—H⋯π hydrogen-bonding network in the space between the double-chains.