Oceanic Salt Switch (original) (raw)
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24 J Phys Chem B 2004 108 20465-20470
This study focuses on the clear, stable mother liquors obtained after completion of crystallization of nanocrystalline sodalite, zeolite A, and zeolite Y. Characterization of the freeze-dried mother liquors by highresolution transmission electron microscopy showed regions of crystallinity for both zeolites A and Y, and ∼5 nm regions of crystallinity could be identified in zeolite Y. Upon adding the mother liquor to nutrient solutions of aluminates and silicates, it was found that the mother liquor could direct formation of the corresponding framework, thereby manifesting a memory effect. Dynamic light scattering studies showed that there were units present in the mother liquors that grew into crystals at a faster rate than the parent compositions used to generate the mother liquors. We propose that the mother liquors recovered after crystallization contain primary structural units having memory of the zeolite formed and that these units can assemble to form viable nuclei if provided with a source of nutrients.
Crystal structures and temperature-induced phase transitions of , and of its transformation to
Journal of Molecular Structure, 2009
We present a new effective method for synthesizing Sr 2 MWO 6 double perovskite oxides: the coprecipitation route at 1220 K in nitrogen environment. Using conventional X-ray diffraction methods, we have confirmed the room-temperature space group of Sr 2 Mn 2+ WO 6 to be P2 1 =n: Z = 2; a ¼ 5:6764ð1ÞÅ; b ¼ 5:6752ð1ÞÅ; c ¼ 8:0144ð1ÞÅ; b ¼ 90:12ð1Þ and V ¼ 258:18ð1ÞÅ 3 . We show that the compound presents the following temperature induced phase-transition sequence: P2 1 =n ! I4=m ! Fm 3m. After a thermal treatment, 24 h at 870 K in air, the Sr 2 Mn 2þ WO 6 compound transforms irreversibly to Sr 2 Mn 3þ WO 6þd . This transformation has been confirmed by EPR and XANES measurements. Using conventional X-ray diffraction methods, we have shown the room-temperature space group of Sr 2 Mn 3þ WO 6þd to be I4=m: Z = 2; a ¼ 5:6353ð1Þ Å; c ¼ 8:0149ð1Þ Å and V ¼ 254:53ð1Þ Å 3 . We show that the compound presents the following temperature induced phase-transition sequence: I4=mð! I4=mmmÞ ! Fm 3m. The tetragonal-to-tetragonal phase transition is suggested to be present, it is not observed as it is very weak; it is attributed to the presence of the Jahn-Teller active Mn 3+ cation.
Crystallization of Soft Crystals
Langmuir, 2009
The crystallization of micelles formed by surfactant F127 solvated by 20% in water was investigated in the vicinity of a hydrophilic interface. Upon entering the crystalline phase from low temperature, a large correlation length develops without preferential texture. Upon heating, the correlation length decreases and Oswald ripening is observed with crystallites orienting with respect to each other while retaining long-range and textured correlation.
Angewandte Chemie International Edition, 2009
Among switchable molecular materials, Fe II spin-crossover (SC) complexes have been widely studied over the last decades. Their reversible low-spin (LS)Ðhigh-spin (HS) switching triggered by a change in temperature or pressure, or by light irradiation, has attracted much interest for both basic scientific understanding and potential technological applications in information storage or visual displays. In these materials, the coexistence of short-and long-range interactions between molecules yields cooperative effects such as hysteresis and/or two-step transitions. Usually, the SC phenomenon is isostructural, but in a few cases symmetry breaking occurs in the LS phase, alongside intermolecular reorganization. Few examples of mononuclear molecular materials that undergo two-step SC associated with intermolecular reorganization in the broken-symmetry phase, the so-called intermediate (INT) phase, involving fractional population of the HS state, have been reported. To date, the INT phase has been fully described only in very few cases by diffraction techniques, which evidenced HS-LS or LS-HS-LS long-or short-range ordering. Over the last ten years, we have investigated supramolecular Fe II SC materials including imidazolyl groups. In view of the first-order SC evidenced in [Fe II H 2 L 2Me ](ClO 4 ) 2 , where H 2 L 2Me denotes the acyclic hexadentate N 6 Schiff base bis[N-(2-methylimidazol-4-yl)methylidene-3-aminopropyl]ethylenediamine, the new SC material [Fe II H 2 L 2Me ]-(PF 6 ) 2 , 1 has been synthesized. Here we report on its two rare types of behavior: long-range LS-HS-HS-LS ordering in the INT phase, and structural symmetry breaking in the LS phase. In addition, another symmetry-breaking process occurs on generating the photoinduced HS phase (PIHS): in the emerging field of photoinduced phase transitions, this result opens a new subject of debate, that is, the possibility of reaching different types of false ground states through light irradiation. shows the thermal variation of the c M T product of 1 (c M is the molar magnetic susceptibility), in the cooling and warming modes, evidencing a two-step SC process. The . Temperature dependence of c M T in the 10-300 K range for 1 measured first on cooling (!)and then on warming mode (~), at 1 K min À1 sweeping rate; (~) indicates the temperature dependence of c M T at the same sweep rate after irradiating the sample at 10 K with a 532 nm laser.
Journal of the …, 2009
The development of functional materials with physical properties that can be controlled on the molecular level is an important goal for the realization of nanoscale devices. 1,2 To this end, spin crossover (SCO) materials, which show dramatic switching responses (including with bistability) to external perturbations (e.g., temperature, pressure, magnetic field, light, and guest/chemical environment), have been actively investigated. 2-4 While the SCO phenomenon itself has been known for more than 70 years and extensive understandings of the process developed, 5 rational materials design in this area remains elusive due to the myriad solid state effects that influence SCO behavior. In an attempt to deconvolute these effects, extensive efforts have been devoted toward exploring the local influence of anion species, ligand functionality, and included guest molecules on SCO. 3,6-8 While some useful structure-property correlations have emerged, this approach has largely been frustrated by difficulties associated with preparing a broad series of analogous materials in which the crystal packing is not significantly altered. The recent development of nanoporous spin crossover frameworks (SCOFs) provides a novel route to circumvent this problem, since the structural geometries of these materials are often only weakly perturbed by extraframework species, which, in the case of neutral guests, may be conveniently exchanged in situ through desorption/sorption. In exploiting this approach, we have recently shown that guest size dramatically influences the SCO properties of a small-pore (ca. 4 Å) pillared-Hofmann material, [Fe(pz)Ni(CN) 4 ] · x(guest) (pz ) pyrazine), through a steric "internal pressure" mechanism in which host-guest attraction/repulsion between the pore walls strongly perturbs the crystal packing and therefore SCO energetics. In an effort to explore the local electronic influence of sorbed guests, we turn our attention here to a much larger pore system, SCOF-2(guest) ; where SCOF-2 is [Fe(NCS) 2 (bpbd) 2 ] and bpbd ) 2,3-bis(4′-pyridyl)-2,3-butanediol), in which bulk steric influences are expected to have considerably less influence on the SCO properties due to the comparatively very loose packing of guests in the 1-D channels of this material.
Template-induced Crystal Growth
2000
The process of "mineralisation" in biology leads to a diversity of inorganic structures based on silica or calcium carbonate. Some of these are composite and, at the same time, highly crystalline. In all cases a molecular or self assembled "template" species has been identified as the promoter for the crystallisation of the new structure. In biology these "templates" are the end step in the conveyance of genetic information to the inorganic synthesis and an understanding of how they work is the key to mimicking biomineralisation in the laboratory. The lecture will describe how modem scattering methods, using x-rays and neutrons, have revealed the very first steps in the process from the first association of the inorganic with the "template" in zeolite and mesoporous silicate syntheses in the bulk and at interfaces. We now have some control of the phase diagram at surfactant interfaces and novel nanoscale structures have been produced and quantitative thermodynamic information on the kinetics of growth between 20A and I W A will be discussed.
Pure and Applied Chemistry, 2002
We describe various molecular switching processes occurring in several types of inorganic solids: spin cross-over (SC) compounds, photomagnetic Prussian blue analogs (PBAs), and valence-tautomeric system. Their thermo-, photo-, piezo-, and magneto-chromic properties are illustrated by recent examples. A common description of their static properties by a two-level model is given.