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A surrounding matrix is known to alter nanoparticle spin transitions, the solid state structural phase changes associated with transitions between high spin (HS) and low spin(LS) states. To better quantify how the spin transition solid and surrounding matrix interact, several series of core‐shell particles were prepared based on RbxCo[Fe(CN)6]z ⋅ nH2O, RbCoFe‐PBA, as spin transition core with isostructural shells of different compositions and thicknesses. Synchrotron PXRD through the thermal high HS to LS, the LS to photoexcited high spin (PXHS), and thermal PXHS to LS transitions, show the activation energy is lowered as shells become thicker and stiffer. Calorimetry data coupled with transition state theory analysis indicate the core stiffens in the core‐shell particles relative to the uncoated particles. The conclusion is supported by microstrain analysis that shows stiffer shells limit the extent to which the core distorts as individual sites transition, leading to the lower activation energy. Finally, differences in lattice mismatch with different shell materials are shown to alter the mechanism by which the transition progresses. [ABSTRACT FROM AUTHOR]

We propose a chelation-assisted assembly of multidentate CNs into metal-organic nanoparticles (MONs). Multidentate CNs functionalized with coordination sites participate equally as organic linkers in MON construction, which is driven by chelation between metal ions and coordination sites. MONs assembled from Au nanoparticles display particle number- and size-dependent optical properties. In addition, the resulting CN-assembled MONs give evidence that assembly was dictated by the multidentate surface ligand rather than the size, shape or material of CNs. With this chelation-assisted strategy, it is possible to control the number of assembled CNs and build the connections between them.

Here, we employed the nudged elastic band (NEB) method to simulate the diffusion of ferrocene through vanadyl phosphate (VOPO4), with a focus on understanding the diffusion pathways arising from the complex structure of ferrocene. We systematically evaluated a total of 36 potential diffusion paths, categorizing them into three groups based on their directional orientation: 15 paths between V sites along the [110] direction, 15 paths from V to P sites along the [100] direction, and 6 paths between P sites also along the [110] direction. Our analysis revealed that the energy barriers for diffusion along the [110] direction typically ranged between 0.25 and 0.35 eV, which are notably higher than those observed for pathways along the [100] direction, where the energy barriers ranged from 0.11 to 0.20 eV. To further elucidate the complex deformation of ferrocene during diffusion, we established four key measures to characterize the structural conformation: the angle of the axis of the ferrocene molecule relative to the [010] direction within the (001) plane, the dihedral angle between the two cyclopentadienyl rings, the orientation angle of the -CH bonds with respect to the [001] direction, and the angle between two -CH bonds from the two cyclopentadienyl rings. [ABSTRACT FROM AUTHOR]

Metastable phases of the photoswitchable molecular magnet K0.3Co[Fe(CN)6]0.77 ⋅ nH2O in sub-micrometer particles have been structurally investigated by synchrotron powder x-ray diffraction (PXRD) measurements. The K0.3Co[Fe(CN)6]0.77 ⋅ nH2O bulk compound (studied here with a sample having average particle size of 500 nm) undergoes a charge transfer coupled spin transition (CTCST), where spin configurations change between a paramagnetic CoII (S = 3/2) –FeIII (S = 1/2) high-temperature (HT) state and a diamagnetic CoIII (S = 0) –FeII (S = 0) low-temperature (LT) state. The bulk compound exhibits a unique intermediate (IM) phase, which corresponds to a mixture of HT and LT spin states that depend on the cooling rate. Several hidden metastable HT states emerge as a function of thermal and photo stimuli, namely: (1) a quench (Q) state generated from the HT state by flash cooling, (2) a LTPX state obtained by photoexcitation from the LT state derived by thermal relaxation from the Q state, and (3) an IMPX state accessed by photo-irradiation from the IM state. A sample with a smaller particle size, 135 nm, is investigated for which the particles are on the scale of the coherent LT domains in the IM phase within the larger 500 nm sample. PXRD studies under controlled thermal and/or optical excitations have clarified that the reduction of the particle size profoundly affects the structural changes associated with the CTCST. The unusual IM state is also observed as segregated domains in the 135 nm particle, but the collective structural transformations are more hindered in small particles. The volume change decreases to 2%–3%, almost half the value found for 500 nm particles (5%–8%), even though the linear thermal expansion coefficients are larger for the smaller particles. Furthermore, photoexcitation from the IM and LT states does not turn into single phases in the smaller particles, presumably because of the multiple interfaces and/or internal stress generated by the coexistence of small CoII–FeIII and CoIII–FeII domains in the lattice. Since the reduced particle size limits cooperativity and domain growth in the lattice, CTCST in the small particle sample becomes less sensitive to external stimuli. [ABSTRACT FROM AUTHOR]

We report the compressibility of two Prussian blue analogs (PBAs) under hydrostatic pressure, one with small and one with a relatively large cubic unit cell among PBAs, and investigate the modification of their elastic properties when the two lattices are coupled within a heteroepitaxial core–shell structure. Bulk modulus (K0) values are derived from x-ray powder diffraction experiments using a diamond anvil cell with silicone oil as a pressure-transmitting medium. The pressure–volume curves fitted to Murnaghan equations of states show that K0 inversely scales with the crystal packing for the rubidium cobalt hexacyanoferrate and rubidium nickel hexacyanochromate samples (K0 ∼ 29 GPa for Co-Fe PBA, a0 = 9.95 Å and ∼20 GPa for Ni-Cr PBA, a0 = 10.48 Å with a0 being the lattice constant at ambient pressure). The two single-phase samples undergo a cubic-to-rhombohedral phase transition above ∼0.8 GPa, which correlates fairly well with the build-up of nonhydrostatic pressure contributions in the cell. Within the core–shell structure, the volume change observed for the core scales with that of the shell because of the configuration close to the case of a solid pressure-transmitting medium. The Ni-Cr PBA shell layer exhibits an increased rhombohedral distortion with respect to the single-phase reference possibly associated with shearing at the core–shell interface. Its bulk modulus is not significantly modified with respect to that of the single-phase sample despite the presence of defects associated with the growth mode, whereas the P-V curve of the core suggests a stiffening of the Co-Fe PBA lattice. [ABSTRACT FROM AUTHOR]

Strain is often used to alter material properties in applications ranging from bandgap tuning for semiconductor electronics to performing work through mechanical actuation. Spin transitions are accompanied by volume changes in the solid state and are being explored in actuation as a source of mechanical strain inducible by the many controllable stimuli known to trigger spin state changes. There is still much to understand, especially at small length scales, about how strain is transmitted from one material to another across a mechanically coupled interface. Theoretical efforts modeling spin-transition particles in a matrix provide significant insights, but this remains an area where systematic experimental studies are limited. This Perspective highlights the progress using cobalt hexacyanoferrate network solids, or Prussian blue analogues (CoFe-PBA), as a framework for investigating spin transition induced strain in nanometer scale and mesoscale heterostructures. Using a family of isostructural cyanometallate networks to form heterostructures with well-defined interfaces, measurements of the altered properties in response to strain generated by the thermally or optically induced spin state change of the CoFe-PBA provide the chance to experimentally interrogate factors that control interface transmitted strain. [ABSTRACT FROM AUTHOR]

The light-induced magnetization changes in cobalt ferrite nanoparticles are reinvestigated to probe the mechanism of photomagnetic behavior and to uncover the essential criteria required to observe the effect. Irradiation with white light results in pronounced demagnetization as evidenced by a decrease in the coercivity (ΔHc ∼ 3 kOe at 10 K) and a drop in the high field magnetization at 70 kOe. Wavelength dependent studies show the optical excitation driving the effect is broad in nature. Power and temperature (T) dependent measurements reveal strikingly different photomagnetic behaviors for the high field magnetization and coercive fields with energy scales of 25 K and 200 K, respectively. Importantly, the magnitude of the light-induced change in the magnetization is found to be specific to the synthesis protocol, with aggregated nanoparticles showing a larger effect than isolated particles. Mössbauer spectroscopy provides additional evidence of the differences between the aggregated and isolated nanoparticle samples. For T ≲ 25 K , the photo-response arises from magnetic disorder generated by an elevated electronic temperature in the surface layer of the particles, thereby leading to a decrease in magnetic volume. For 25 K ≲ T ≲ 200 K , the electronic and phononic reservoirs are more intimately coupled, so the photo-induced magnetic response follows the temperature dependence of the magneto-crystalline anisotropy. A similar response in manganese ferrite suggests that the mechanism is general. [ABSTRACT FROM AUTHOR]

The structural and magnetic constituents of three ladder-like coordination polymers are described along with an analysis of their spin formations. The findings reveal the effect of the character and geometry of the non-bridging ligands on the spin exchange relationship between Cu[super 2+] ions linked by the same double end-on azide bridge.

The utility of oxidative cyclization reactions for construction of tetrahydrofuran rings is examined. The results show that alcohol nucleophiles were found to be most effective traps for radical cation intermediates generated from both, enol and ketene dithioacetal groups. It is proposed that the anodic oxidation of enol ethers and ketene dithiacetal groups in the presence of alcohol nucleophile creates a unique method for construction of both tetrahydrofuran rings and quaternary carbons.

A two-dimensional iron-nickel cyanide-bridged network at the air-water interface is formed due to the result of reaction of a Langmuir monolayer of an amphiphitic pentacyanoferrate complex with Ni2+ ions from the subphase. Characterization of these networks by different techniques was done, and it was found that air-water interface can function as a structure-directing element in the assembly of new supramolecular network solids and may help in the development of nanoscale materials.

The scope of enantioselective cyclopentannelation reaction that uses allenyl ether derived nucleophiles is studied, and two different versatile mechanisms are seen. The results show that for gamma-substituted allene ethers that are axially chiral, very high enantiomeric excesses of cyclopentenone products are observed in the matched cases.

Research has been conducted on the manganese tetraphenylporphyrin monoleyer films. The preparation of these films has been carried out and their use as supported oxidation catalysts is described.

A study using antiferromagnetic resonance (AFMR) was conducted to characterize the canted antiferromagnetic state to analyze the magnetostructural correlations within a series of layered solids. The findings verify the suitability of AFMR in providing a microscopic probe of antiferromagnetic materials given its advantages such as high sensitivity to subtle differences in magnetic interactions and the ability to work with a minimum amount of material.

A study on the preparation and structural characterization of octadecylphosphonate bilayers with divalent metals was conducted using the Langmuir-Blodgett (LB) films method. Results showed that octadecylphosphonate LB bilayers were isostructural with their corresponding metal phosphonate analogs in solid state. These findings demonstrated that the structural properties of each octadecylphosphonate LB film were dependent on the identity of metal ion and the solid state materials.

An analysis of the function of the template layer in forming self-assembled films involved use of self-assembly of organophosphonate acid molecules at a zirconium octadecylphosphonate Langmuir-Blodgett (LB) film to constant organophosphonate monolayer and multilayer films. A surface with a high density of zirconium bonding regions is evident because the zirconated LB template layer is well-ordered and close-packed with Zr:P ratio of 1:1.