Crystal size versus paddle wheel deformability: selective gated adsorption transitions of the switchable metal-organic frameworks and † Switchable pillared layer metal-organic frameworks M 2 (2,6-ndc) 2 (dabco) (DUT-8(M), M ¼ Ni, Co, 2,6-ndc ¼ 2,6naphthalenedicarboxylate, dabco ¼ 1,4-diazabicyclo-[2.2.2]octane, DUT -Dresden University of Technology) were synthesised in two different crystallite size regimes to produce particles up to 300 mm and smaller particles around 0.1 mm, respectively. The textural properties and adsorption-induced switchability of the materials, obtained from both syntheses, were studied by physisorption of N 2 at 77 K, CO 2 at 195 K and nbutane at 273 K, revealing pronounced differences in adsorption behavior for Ni and Co analogues. While the smaller nano-sized particles (50-200 nm) are rigid and show no gating transitions confirming the importance of crystallite size, the large particles show pronounced switchability with characteristic differences for the two metals resulting in distinct recognition effects for various gases and vapours. Adsorption of various vapours demonstrates consistently a higher energetic barrier for the "gate opening" of DUT-8(Co) in contrast to , as the "gate opening" pressure for Co based material is shifted to a higher value for adsorption of dichloromethane at 298 K. Evaluation of crystallographic data, obtained from single crystal and powder X-ray diffraction analysis, showed distinct geometric differences in the paddle wheel units of the respective MOFs.These differences are further disclosed by solid-state UV-vis, FT-IR and Raman spectroscopy. Magnetic properties of DUT-8(Co) and DUT-8(Ni) were investigated, indicating a high-spin state for both materials at room temperature. Density functional theory (DFT) simulations confirmed distinct energetic differences for Ni and Co analogues with a higher energetic penalty for the structural "gate opening" transformation for DUT-8(Co) compared to DUT-8(Ni) explaining the different flexibility behaviour of these isomorphous MOFs.underlying structural phase transitions are triggered by adsorption or desorption of guest molecules and generally characterised by an activation energy barrier, which causes hysteresis in physisorption experiments. Due to their switchable nature, so porous crystals are oen discussed as materials with huge application potential in gas storage, 11 separation processes, 12,13 sensor technology 14,15 and catalysis. 16 Despite rapidly growing research in the eld of exible MOFs, 1,17-21 the role of critical factors inuencing and controlling framework switchability are barely understood. 22 As MOFs are modular networks, the exibility of the linker but also the hinges of the metal node are key features that affect switchability. The importance of metal-node hinges and their energetics for framework switchability has been widely investigated for compounds such as M(bdp) (M ¼ Co, Fe, bdp ¼ 1,4-benzenedipyrazolate), 11,23,24 M(m-OH)(bdc) (MIL-53, M ¼ Cr, Al, Fe, bdc ¼ 1,4-benzenedicarboxylate)...

We propose a simple hydrothermal synthesis of nanoflakes composed of alternating sulfide and hydroxide quasi-monolayers and their aqueous colloids, as a prospective family of novel multifunctional 2D materials.

The pillared layer framework DUT-8(Zn) (Zn2(2,6-ndc)2(dabco), 2,6-ndc = 2,6-naphthalenedicarboxylate, dabco = 1,4-diazabicyclo-[2.2.2]-octane, DUT = Dresden University of Technology) is a prototypical switchable MOF, showing characteristic adsorption and desorption induced open...

We introduce here a multifunctional material composed of alternating atomic sulfide sheets close to CuFeS2 and Mg-based hydroxide ones (valleriite), which are assembled due to their electric charges of opposite sign. Valleriite particles of 50-200 nm in the lateral size and 10-20 nm thick were synthesized via a simple hydrothermal pathway using various concentrations of precursors and dopants, and examined with XRD, TEM, EDS, X-ray photoelectron spectroscopy, reflection electron energy loss spectroscopy (REELS), Mössbauer, Raman and UV-vis-NIR spectroscopies, magnetic, dynamic light scattering, zeta potential measurements. The electronic, magnetic and optical characteristics are found to be critically dependent of the charge (electron density) at the narrow-gap sulfide layers containing Cu+ and Fe3+ cations, and can be tuned via the composition of hydroxide part. Particularly, substitution of Mg2+ with Al3+ increases the negative charge of the hydroxide layers and reduces the content of Fe3+-OH centers (10-45% of total iron); the effects of Cr and Co dopants entering both layers are more complicated. Mössbauer doublets of paramagnetic Fe3+ detected at room temperature transform to several Zeeman sextets at 4.2 K; the hyperfine fields up to 500 kOe and complex magnetic behavior, but not pure paramagnetism or antiferromagnetism, were observed for valleriites with the higher positive charge of the sulfide sheets, probably due to the depopulation of the minority-spin 3d states of S-bonded Fe3+ ions. Aqueous colloids of valleriite show optical absorption at 500 - 750 nm, which, along with the peaks at the same energies in REELS, may arise due to quasi-static dielectric resonance involving the vacant Fe 3d band and being dependent on the composition of both layers too. These and other findings call attention to the of valleriites as a new rich family of 2D materials for a variety of potential applications.

According to in situ Raman experiments, in certain pressure ranges open (op) and closed pore (cp) phases coexist in DUT-8(Ni) crystals.

This paper reports Raman spectroscopy investigation of phase transitions in Rb2NaYF6 crystal. The experimental spectra were compared with the calculated one. The spectra were obtained in temperature range from 8 to 300 K. The Raman spectra shows anomalous temperature‐dependent behavior at T1 = 154 and T2 = 122 K. Soft mode restoration has been found, which allows us to attribute first transition at 154 K to displacive type. Detailed analysis temperature dependencies of the line positions and widths have been performed. We found no effects of possible lattice disorder anywhere, except narrow (about 20 K) range above the T1 temperature. The Raman spectra of Rb2NaYF6 crystal have been obtained and analyzed under hydrostatic pressure up to 4.33 GPa (at T = 295 K). The high pressure experiment up to 4.33 GPa did not disclose any effects associated with phase transitions. The lattice vibration spectra were calculated up to 10 GPa. The calculation has been demonstrated that the Rb2NaYF6 does not undergo high pressure phase transition. Copyright © 2013 John Wiley & Sons, Ltd.

Raman spectra of a HoFe3(BO3)4 crystal chip has been investigated at simultaneously high temperature and high pressure (up to 7.1 GPa and 560 K). On the basis of Raman analysis, the assignment to one of the two possible crystal phases has been made. The experimental p–T phase diagram of HoFe3(BO3)4 was established. An increase in the pressure leads to an increase in the temperature of transition. The phase boundary equation was obtained. Neither triple points nor a phase with new symmetry was revealed in the phase diagram. A critical point with the temperature T = 560 K and the pressure p = 2.53 GPa was found. The nanocrystals with different shapes began to grow on crystal surface after reaching that point. The composition of new nanocrystals is identical to the composition of initial crystal. Copyright © 2017 John Wiley & Sons, Ltd.

The crystal structure of the first-synthesized compound EuErCuS3 was determined from X-ray powder diffraction data: orthorhombic crystal system, space group Pnma, structural type Eu2CuS3: a = 10.1005(2) Å, b = 3.91255(4) Å, c = 12.8480(2) Å; V = 507.737(14) Å3, Z = 4, and ρx = 6.266g/cm3. The temperatures and enthalpies of reversible polymorphic transitions and of incongruent melting of the compound were determined by DSC: