Pure Crystalline Material Research Articles

Measurement of the Quantum Tunneling Gap in a Dysprosocenium Single-Molecule Magnet.

We perform magnetization sweeps on the high-performing single-molecule magnet [Dy(Cpttt)2][B(C6F5)4] (Cpttt = C5H2tBu3-1,2,4; tBu = C(CH3)3) to determine the quantum tunneling gap of the ground-state avoided crossing at zero-field, finding a value on the order of 10-7 cm-1. In addition to the pure crystalline material, we also measure the tunnel splitting of [Dy(Cpttt)2][B(C6F5)4] dissolved in dichloromethane (DCM) and 1,2-difluorobenzene (DFB). We find that concentrations of 200 or 100 mM [Dy(Cpttt)2][B(C6F5)4] in these solvents increases the size of the tunneling gap compared to the pure sample, despite a similarity in the strength of the dipolar fields, indicating that either a structural or vibrational change due to the environment increases quantum tunneling rates.

In Situ Synthesis of Surface-Mounted Novel Nickel(II) Trimer-Based MOF on Nickel Oxide Hydroxide Heterostructures for Enhanced Methanol Electro-Oxidation.

Engineering the heterogeneous interface fusing MOFs and inorganic active component is an effective strategy to improve the electrochemical performance. Herein, we report a new Ni3-based MOF (denoted as CTGU-24) with an infrequent two-fold interpenetrating 3D (3,8)-connected network constructed from Ni(II) trimer and mixed tripodal tectonics for the electrocatalytic methanol oxidation reaction (MOR). In order to improve its stability and activities, the heterogeneous hybrid CTGU-24@NiOOH has been fabricated successfully via the first preparation of the NiOOH nanosphere and then in situ formation of CTGU-24 decorated on the NiOOH surface. Moreover, the integration of CTGU-24@NiOOH and different additives [acetylene black (AB) and ketjen black (KB)], resulting in the optimized hybrid sample AB&CTGU-24@NiOOH (4:4). It attains better MOR performance with an area-specific peak current density of 34.53 mA·cm−2 than pure CTGU-24 (14.99 mA·cm−2) and improved durability in an alkali medium. The new findings indicate that the CTGU-24@NiOOH heterostructure formed in situ and the integration of moderate additives are critical to optimizing and improving electrocatalytic activity of pure MOF crystalline material.

Behavior of copper under high pressure: Experimental and theoretical analyses

The physical properties of high-purity copper under high pressure were investigated with X-ray diffraction(XRD) using the 3rd generation synchrotron radiation and a diamond anvil cell(DAC) and First-principles calculation using ab-initio simulation program. And they differ 15 % from those reported in the past. The previously reported experimental isothermal bulk moduli for polycrystalline copper and single crystalline copper are 140.2 ± 3.9 GP and 137.6 ± 0.2 GPa respectively, and the theoretical isothermal bulk modulus of copper is 134.6 GPa [1–20]. However, the recently measured bulk moduli of copper are 120.8 ± 4.4 GPa for polycrystal and 120.7 ± 2.1 GPa for single crystal respectively. The difference might mainly come from the purity of copper owing to the development of scientific technology, and the 3-dimensional effect of defects in nearly pure(perfect) crystalline materials was first observed by using DAC and XRD.

Understanding the Electrochemical Performance of Hybrid Na(2-x)LixFeP2O7 (x= 0, 0.6) Cathode Materials

The need for green energy is increasing every year, and renewable energy and efficient storage require large-scale lithium-ion batteries (LIBs). The use of LIBs has resulted in declining lithium (Li) reserves, which effectively increases the cost of current LIBs. Na ion batteries (NIBs) have been proposed as an alternative to the LIBs as it displays similar properties to them. However, Na ions (Na+), possessing higher ionic radii, and lower energy density than Li ion (Li+), the NIBs have limited commercialization potential. One proposed solution is the development of hybrid cathodes, where the cathode has both Li+ and Na+ in the structure and can be active in both Li and Na cells. The current work describes the development of hybrid cathode material in which the substitution of Li+ for Na+ in the configuration of Na(2-x)LixFeP2O7 (x=0,0,6) is considered to form Na1.4Li0.6FeP2O7 cathodes. The solid-state technique was used for the synthesis of Na(2-x)LixFeP2O7 (x=0.6) cathode. Structural analysis indicates the formation of phase pure crystalline materials with non-uniform and sub-micron particles. It is also noticed that the original triclinic structure of Na2FeP2O7 is preserved with the substitution of Li+. It is also revealed that Na1.4Li0.6FeP2O7 shows improved thermal stability up to 550°C when compared to Na2FeP2O7. The electrochemical performance of Na2FeP2O7 and Na1.4Li0.6FeP2O7 is investigated using various electrochemical characterizations. Both Li and Na half cells show electrochemical activity for Na1.4Li0.6FeP2O7 with decent cyclability. However, Na1.4Li0.6FeP2O7, suffers from lower electrochemical efficiency when compared to Na2FeP2O7. This could mainly be due to the lattice distortion upon substituting larger Na+ ions with smaller Li+ ions. Nevertheless, Na1.4Li0.6FeP2O7 hybrid cathode material can be used as a reference to synthesize new cathode materials with improved efficiency.

Adsorption behavior of mercury over hydrated lime: Experimental investigation and adsorption process characteristic study

This study reports the application of hydrated lime for the effective adsorption of the heavy mercury metal from the aqueous phase solutions. Initially, hydrated lime was subjected to structural characterization and thermal stability analysis. The FT-IR spectrum analysis revealed that the existence of the O–H bonds as a confirmation of hydrated lime formation. Subsequently, the XRD powder-based analysis demonstrated that most of the hydrated lime is pure crystalline material known as Portlandite while a small amount of calcite is also present in the structure of the hydrated lime. The thermal stability analysis revealed that the hydrated lime is highly thermally stable under harsh conditions without decomposing at higher temperatures up to 500 °C. Furthermore, the hydrated lime was subjected to the selective adsorption of heavy metal mercury to investigate the potential influence of the adsorbent particle size and loading on adsorption capacity. The results demonstrated that the decrease in the adsorbent particle size leads to the improvement in the mercury adsorption attributing to the rise in specific surface area. The enhancement in the loading of the adsorbent resulted in a reduction in mercury adsorption directing to the fact that already adsorbed metal ions onto the adsorbent surface lead to hindrance for the adsorption of other ions of heavy metal. These results lead to a significant impact on modern in inventing different adsorbents with promising water treatment efficiency for more industrial applications and the related recovery of mercury.

Calcium oxide(CaO) nanomaterial (Kukutanda twak Bhasma) from egg shell: Green synthesis, physical properties and antimicrobial behaviour

Bhasma is a calcined form of traditional biomaterials as nanomedicine, which are produced by treating with herbal juices and by different cycles of heat treatment. Bhasma are being used in the treatment of various diseases in the Indian subcontinent since 1000 years ago. In this present research, Calcium based Indian origin Ayurvedic medicine, Kukkutandatawak Bhasma (KB)prepared using low-cost eco-friendly approach from Hen’s eggshell. Lemon juice was used as an important ingredient in the preparation of these materials. Physical properties were measured using modern state of the art techniques such as X-ray powder diffraction (XRD), Fourier Transform infra-red spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and photoluminescence spectrometer (PL). Total 4 calcinations cycles required to convert eggshell powder into a pure phase of superfine powder in nanometric scale. The vibrating sample magnetometer (VSM) of pure crystalline materials shows ferromagnetic behaviour at room temperature. XRD analysis determined its average size 43 nm. Photoluminescence behaviour shows an emission spectrum in the UV range and at around 405 nm shows blue region confirmation. The antimicrobial evaluation revealed that Kukutandatwak Bhasma (CaO) as nanomedicine and is more effectual antifungal agent than antibacterial.

From Mechanical Effects to Mechanochemistry: Softening and Depression of the Melting Point of Deformed Plastic Crystals.

The melting of any pure crystalline material at constant pressure is one of its most fundamental properties, and it has been used to identify organic compounds or to verify their chemical or phase purity since the early times of chemistry. Here, we report that a mechanical deformation of plastic organic single crystals such as bending results in a small yet significant decrease in their melting point of about 0.3-0.4 K. The bent section of the crystal was found to be mechanically softer relative to the straight sections, and the softening temperature preceding the melting was also lower on the convex (outer) side of the bent crystal. Melting of the bent crystal starts at the kink and often appears as splitting of the respective endothermic peak in its thermal (DSC) fingerprint, while unilateral compression of the crystal results in multiple peaks. These thermomechanical effects become more pronounced with heavier mechanical damage due to an increased concentration of defects and ultimately result in a large temperature spread of the associated phase change in addition to melting-point depression in deformed or damaged crystals relative to their pristine counterparts. Within a broader context, the results show that mechanical treatment during sample preparation has a profound effect on the melting of a pure substance, and this could be critically important where the exact melting point is used as a means for polymorph identification.

Studying the kinetics of extraction treatment of rice husk when obtaining silicon carbide

Silicon carbide is characterized by a wide range of beneficial electrophysical, anti-corrosion, and strength properties. A promising raw material for the synthesis of silicon carbide is the waste of rice production, which includes compounds of silicon and carbon-containing organic substances. The cheapness and availability of such raw materials necessitate the development of technologies to obtain silicon carbide from it. An important direction in silicon carbide synthesis technology is to obtain a high purity product. To remove impurities from rice husks, it is necessary to carry out its pre-extraction treatment. It has been established that the extraction treatment of rice husks with acid solution makes it possible to clean the raw materials from metal compounds and the excess amount of carbon-containing components. To remove impurities of metal compounds and the excess amount of carbon-containing compounds from rice husks, it has been proposed to perform the extraction with an aqueous solution of the mixture of 10 % sulfur and 15 % acetic acids. We have derived the time dependences of the degree of extraction of cellulose from rice husks. Two temporal sections of the process have been identified. It is shown that the extraction of cellulose from rice husks obeys a pseudo first-order reaction. We have calculated the constants of speed and activation energy in the course of extraction for the two time sections of the process. The activation energy of extraction over a first period is 10.75 kJ/mol; over a second period, the activation energy value is 26.10 kJ/mol. It has been established that an increase in the extraction temperature from 20 to 100 °C leads to a two-fold improvement in the process efficiency. It is shown that silicon carbide, synthesized from rice husk after its extraction treatment, is a pure crystalline material whose particles’ size is from 1 to 20 micrometers

Study on the Melting Mechanism of Maleic Anhydride

Background: Melting of a pure crystalline material is generally treated thermodynamically which disregards the dynamic aspects of the melting process. According to the kinetic phenomenon, any process should be characterized by activation energy and preexponential factor where these kinetic parameters are derivable from the temperature dependence of the process rate. Study on such dependence in case of melting of a pure crystalline solid gives rise to a challenge as such melting occurs at a particular temperature only. The temperature region of melting of pure crystalline solid cannot be extended beyond this temperature making it difficult to explore the temperature dependence of the melting rate and consequently the derivation of the related kinetic parameters. Objective: The present study aims to explore the mechanism of the melting process of maleic anhydride in the framework of phase transition models. Taking this process as just another first-order phase transition, occurring through the formation of nuclei of new phase and their growth, particular focus is on the nucleation and growth models. Methods: Non-isothermal thermogravimetry, as well as differential scanning calorimetry studies, has been performed. Using isoconversional kinetic analysis, temperature dependence of the activation energy of melting has been obtained. Nucleation and growth models have been utilized to obtain the theoretical temperature dependencies for the activation energy of melting and these dependencies are then compared with the experimentally estimated ones. Conclusion: The thermogravimetry study indicates that melting is followed by concomitant evaporation, whereas the differential scanning calorimetry study shows that the two processes appear in two different temperature regions, and these differences observed may be due to the applied experimental conditions. From the statistical analysis, the growth model seems more suitable than the nucleation model for the interpretation of the melting mechanism of the maleic anhydride crystals.

Effect of stress on vacancy formation and migration in body-centered-cubic metals

Vacancy formation and migration control self-diffusion in pure crystalline materials, whereas irradiation produces high concentrations of vacancy and self-interstitial atom defects, exceeding by many orders of magnitude the thermal equilibrium concentrations. The defects themselves, and the extended dislocation microstructure formed under irradiation, generate strongly spatially fluctuating strain and stress fields. These fields alter the local formation and migration enthalpies of defects, and give rise to the anisotropy of diffusion even if in the absence of stress the diffusion tensor is isotropic. We have performed ab initio calculations of formation and migration energies of vacancies in all the commonly occurring body-centered-cubic (bcc) metals, including alkaline, alkaline-earth and transition metals, and computed elastic dipole and relaxation volume tensors of vacancies at the equilibrium lattice positions and along the vacancy migration pathways. We find that in all the bcc metals the dipole tensor of a migrating vacancy at a saddle point exhibits an anticrowdion character. Applied external stresses or the local stresses generated by dislocations may enhance or suppress anisotropic diffusion by altering the energy barriers with respect to the direction of migration of a defect.

Tuning the electro-optic and viscoelastic properties of ferroelectric liquid crystalline materials

This work deals with determination of the viscoelasticity coefficient in chiral smectic liquid crystals possessing the helical structure and is the continuation of the work, in which the elasticity coefficient was presented [Phase Transitions 89 (2016) 368]. The measurements have been performed using optical detection in the small deformation limit. The viscosity coefficient was measured on two commercially available pure chiral materials, namely, 4-(n-hexyloxy phenyl)-1-(2-fuethyl butyl) biphenyl-4-carboxylate and 4-(2-methylbutyl) phenyl-4-n-octylbiphenyl-4-carboxylate, and on resulting binary mixture composed from those materials in 50:50 weight ratio. All three liquid crystalline materials exhibit a tilted ferroelectric phase over a reasonably broad temperature range. Each of the two pure liquid crystalline materials have its own disadvantages. However, by design of the binary mixture in definite weight concentration, we tried to improve the behavior and to tune the properties; specifically, the effect of the viscoelastic properties on the mixture composition has been established.

Sodium intercalation/de-intercalation mechanism in Na4MnV(PO4)3 cathode materials

Na4MnV(PO4)3 is a sodium ion conducting material with a NASICON type crystal structure. This phase is not much known as an electrode material. The present work focuses on the sodium ion intercalation/de-intercalation mechanism and charge/discharge behavior of the material. The Na4MnV(PO4)3 is synthesized through a sol-gel process and characterized by XRD, SEM, and XPS. The structural analysis confirms the formation of a phase pure crystalline material with nanometric particle size which adopts a trigonal crystal structure. Galvanostatic intermittent titration technique (GITT) measurements indicate that Na4MnV(PO4)3 is electrochemically active having slanting voltage plateaus. Ex-situ and In-situ XRD analysis, as a function of sodium concentration, indicate that the intercalation/de-intercalation of sodium is associated with a single-phase reaction rather than a biphasic reaction when cycled between 1.5 and 4.5 V. The electrochemical measurements on composite electrodes, Na4MnV(PO4)3/CNTS (1 & 3 wt.%), show promising charge/discharge capacity (∼140 mAh/g), good cyclability (100% capacity retention after 40 cycles) and reasonable rate capability. The cyclic voltammetry (CV) and X-ray Photoelectron Spectroscopy (XPS) analyses indicate that the main contributions towards the activity of Na4MnV(PO4)3 can be attributed to the active of Mn2+/Mn3+ and V3+/V4+ redox couple with partial activity of V4+/V5+. The obtained results suggest that Na4MnV(PO4)3 is a promising electrode material which can be achieved better rate performance with long cycling stability and battery performance through engineering of the particle morphology and microstructure.

On the Relationship Between Scintillation Anisotropy and Crystal Structure in Pure Crystalline Organic Scintillator Materials

The scintillation anisotropy effect for proton recoil events has been investigated in five pure organic crystalline materials: anthracene, trans-stilbene, p-terphenyl, bibenzyl, and diphenylacetylene. These measurements include characterization of the scintillation response for one hemisphere of proton recoil directions in each crystal. In addition to standard measurements of the total light output and pulse shape at each angle, the prompt and delayed light anisotropies are analyzed, allowing for investigation of the singlet and triplet molecular excitation behaviors independently. This work provides new quantitative and qualitative observations that make progress toward understanding the physical mechanisms behind the scintillation anisotropy. These measurements show that the relationship between the prompt and delayed light anisotropies is correlated with crystal structure, as it changes between the pi-stacked crystal structure materials (anthracene and p-terphenyl) and the herringbone crystal structure materials (stilbene, bibenzyl, and diphenylacetylene). The observations are consistent with a model in which there are preferred directions of kinetic processes for the molecular excitations. These processes and the impact of their directional dependencies on the scintillation anisotropy are discussed.

Value adding red mud waste: High performance iron oxide adsorbent for removal of fluoride

A novel method for the synthesis of iron oxide based sorbents from bauxite residue (red mud) was developed by way of a sequential digestion and selective precipitation process. The red mud was consecutively digested with phosphoric acid and hydrochloric acid, precipitated by sodium hydroxide addition, and aged for 72h at pH 3–3.5. This process allowed the production of a relatively pure crystalline material, akaganeite (β-FeOOH), comprised of high surface area (223m2/g). The performance of the synthesised material as a fluoride sorbent was compared with a commercial adsorbent (granular ferric hydroxide). Equilibrium isotherms revealed that both sorbents reduced the amount of fluoride in solution to <1.5mg/L. Significantly, the red mud derived akaganeite had a higher maximum adsorption capacity than the commercial granular ferric hydroxide (11.40 and 9.23g/kg, respectively). Performance differences were suggested to relate to the presence of active sites which comprised of iron and aluminium and/or titanium species.

Laser triggered phase transition in photothermal liquid crystals.

Reversible high temperature phase transitions were easily induced under laser irradiation in pure thermotropic liquid crystals built around photothermal nickel-bis(dithiolene) cores. The strong photothermal activity of nickel-bis(dithiolene) liquid crystalline thin films allows reaching a temperature as high as 250 °C directly from room temperature in a few seconds with high spatial control.

Dynamic Exchange During Triplet Transport in Nanocrystalline TIPS-Pentacene Films.

The multiplication of excitons in organic semiconductors via singlet fission offers the potential for photovoltaic cells that exceed the Shockley-Quiesser limit for single-junction devices. To fully utilize the potential of singlet fission sensitizers in devices, it is necessary to understand and control the diffusion of the resultant triplet excitons. In this work, a new processing method is reported to systematically tune the intermolecular order and crystalline structure in films of a model singlet fission chromophore, 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-Pn), without the need for chemical modifications. A combination of transient absorption spectroscopy and quantitative materials characterization enabled a detailed examination of the distance- and time-dependence of triplet exciton diffusion following singlet fission in these nanocrystalline TIPS-Pn films. Triplet-triplet annihilation rate constants were found to be representative of the weighted average of crystalline and amorphous phases in TIPS-Pn films comprising a mixture of phases. Adopting a diffusion model used to describe triplet-triplet annihilation, the triplet diffusion lengths for nanocrystalline and amorphous films of TIPS-Pn were estimated to be ∼75 and ∼14 nm, respectively. Importantly, the presence of even a small fraction (<10%) of the amorphous phase in the TIPS-Pn films greatly decreased the ultimate triplet diffusion length, suggesting that pure crystalline materials may be essential to efficiently harvest multiplied triplets even when singlet fission occurs on ultrafast time scales.

Finite element implementation of dislocation-density-based crystal plasticity model and its application to pure aluminum crystalline materials

A new time-integration algorithm is presented for a dislocation-density-based crystal plasticity model. This includes a monolithic iterative scheme in which stresses were solved simultaneously with dislocation densities based on the fully backward Euler method for the integration of the constitutive model. Furthermore, the heuristic convergence criterion based on the slip resistance, instead of dislocation densities, together with the stresses is employed to circumvent stability issues. A closed form of the consistent tangent moduli is also derived. The constitutive models and time-integration procedures have been implemented as a user-subroutine UMAT of a finite element program Abaqus. Representative comparisons between the numerical predictions and experimental data are then given to verify the robustness and stability of the current implementation of the dislocation-density-based crystal plasticity model. It is demonstrated that finite element calculations reproduce well the anisotropic hardening response of differently oriented pure aluminum single crystals under tension and the variation of pile-up patterns according to different initial crystallographic orientations during nanoindentation. Furthermore, the numerical procedure was used to predict the deformation response of the aluminum multicrystalline specimen under simple shear. Non-uniform deformation fields by the digital image correlation method and surface profiles by the shadow Moiré method were well reproduced by numerical predictions. In addition, the effect of the initial crystallographic orientation and the interaction effects among different crystals on the deformation response of the multicrystal are addressed.

Microwave-Assisted Synthesis of Defects Metal-Imidazolate-Amide-Imidate Frameworks and Improved CO2 Capture.

In this work, we report three isostructural 3D frameworks, named IFP-11 (R = Cl), IFP-12 (R = Br), and IFP-13 (R = Et) (IFP = Imidazolate Framework Potsdam) based on a cobalt(II) center and the chelating linker 2-substituted imidazolate-4-amide-5-imidate. These chelating ligands were generated in situ by partial hydrolysis of 2-substituted 4,5-dicyanoimidazoles under microwave (MW)-assisted conditions in DMF. Structure determination of these IFPs was investigated by IR spectroscopy and a combination of powder X-ray diffraction (PXRD) with structure modeling. The structural models were initially built up from the single-crystal X-ray structure determination of IFP-5 (a cobalt center and 2-methylimidazolate-4-amide-5-imidate linker based framework) and were optimized by using density functional theory calculations. Substitution on position 2 of the linker (R = Cl, Br, and Et) in the isostructural IFP-11, -12, and -13 allowed variation of the potential pore window in 1D hexagonal channels (3.8 to 1.7 Å). The potential of the materials to undergo specific interactions with CO2 was measured by the isosteric heat of adsorption. Further, we resynthesized zinc based IFPs, namely IFP-1 (R = Me), IFP-2 (R = Cl), IFP-3 (R = Br), and IFP-4 (R = Et), and cobalt based IFP-5 under MW-assisted conditions with higher yield. The transition from a nucleation phase to the pure crystalline material of IFP-1 in MW-assisted synthesis depends on reaction time. IFP-1, -3, and -5, which are synthesized by MW-assisted conditions, showed an enhancement of N2 and CO2, compared to the analogous conventional electrical (CE) heating method based materials due to crystal defects.

Physical stability of the amorphous anticholesterol agent (ezetimibe): the role of molecular mobility.

The purpose of this paper is to examine the role of molecular mobility in the recrystallization process from the amorphous state of the anticholesterol drug ezetimibe. Both the molecular dynamics and crystallization kinetics have been studied using various experimental techniques, such as broadband dielectric spectroscopy (BDS), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). Our investigations have shown that ezetimibe easily recrystallizes from the disordered state, both below and above its glass transition temperature (Tg = 336 K). Moreover, we found that an only slightly elevated pressure (5 MPa) significantly accelerates the recrystallization process at T > Tg. We predict that the structural relaxation time of amorphous ezetimibe at 293 K (storage temperature) and ambient pressure is only 22 days. This result corresponds to the characteristic time, determined from XRD measurements, for amorphous ezetimibe to recrystallize during storage at Troom = 298 K. It leads to the conclusion that the molecular mobility reflected in structural relaxation of ezetimibe is mainly responsible for devitrification of this drug. Finally, we determined a relatively easy way to improve the physical stability of the drug by preparing a binary amorphous ezetimibe-Soluplus mixture. Ezetimibe in an amorphous mixture with 20 wt % Soluplus has a much better (over six times) solubility than the pure crystalline material.

Koordinationspolymere mit Tris(4‐carboxyphenyl)‐phosphanoxid als Ligand – Synthese, Kristallstrukturen und topologische Untersuchungen

AbstractThe solvothermal reaction of MnCl2·4H2O or CoCl2·6H2O with tris(4‐carboxyphenyl)‐phosphine oxide (H3TPO), in DMF orDMA resulted in the four coordination polymers [M3(tpo)2(dmf)(H2O)2](1: M = Mn; 2: M = Co), (NMe2H2)[Mn3Cl(HCO2)(htpo)(tpo)(H2O)] (3) and (NMe2H2)[Mn3(tpo)2(OAc)] (4). Structural characterization by X‐ray crystallography revealed that 1–4 form 3‐periodical infinite networks; after synthesis solvent molecules occupy the framework pores. The topologies of the networks in 1, 2 and 3 are unprecedented in literature and are systematically characterized. Furthermore, these topologies could be derived from hexagonal close packing (1, 2) and cubic close packing (3), respectively.Compounds 1, 2 and 4 were synthesized as pure crystalline materials, their thermal behaviour was examined by TG/DTA measurements and temperature dependent PXRD. 1, 2 and 4 show remarkable thermal stability with decomposition temperatures between 450 and 500 °C. Temperature dependent PXRD measurements of compounds 1 and 2 reveal a structural transition at 260 °C, framework 4 loses its crystallinity at 210 °C.