Search

Crystallization of DNL-6, a silicoaluminophosphate (SAPO) based molecular sieve with the RHO topology, was investigated under both the hydrothermal synthesis (HTS) and dry-gel conversion (DGC) conditions. Crystallization of DNL-6 under the HTS conditions is rather fast. But a combination of crystallization under the DGC conditions and reducing reaction temperature slow down the reactions, allowing for intermediates to be captured. Under the DGC conditions, DNL-6 crystallizes through a semi-crystalline layered phase. The nature of this intermediate is aluminophosphate (AlPO) rather than SAPO with most P atoms having a local environment of P(–O–Al)3(OH). The surfactant (cetyltrimethylammonium chloride) used for synthesis appears to be part of the layered intermediate. Si is directly incorporated in the DNL-6 framework via SM II mechanism when the semi-crystalline AlPO phase is transforming to DNL-6 with the assistance of a very small amount of water. Both the structure directing agent and the surfactant play a role in the formation of DNL-6, as they were found within the final synthesized products. SEM data show that hydrothermal synthesis produces a much more crystalline product. The facts that the semi-crystalline layered phase was also observed in the powder X-ray diffraction patterns of the solid samples obtained under the HTS conditions and that the evolution of the local structure around P and Al in the intermediate phases are similar imply that under the reaction conditions employed in the present study, the formation pathways of DNL-6 under the HTS and DGC conditions appear to have some similarities.

Crystallization of zeolite ZSM-39 (MTN), a clathrate and silicate analogue of the 17 Å cubic gas hydrate, was examined in a solvent system involving a tetramethylammonium chloride – 1,6-hexanediol deep eutectic mixture and significant amount of water. The crystallization process was followed by powder X-ray diffraction (PXRD), and solid-state nuclear magnetic resonance (SSNMR) techniques involving several nuclei such as 19F, 29Si, and 13C. The results indicate that the crystallization starts from the arrangement of amorphous Si–O–Si species around the tetramethylammonium ions and subsequent formation of the cages in the precursors similar to [51264] cages in the MTN topology. The larger [51264] cages are then connected via the smaller [512] cages containing the fluoride ions to form the final MTN structure. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses show that the crystal growth rates along and directions are roughly the same, suggesting that the (100) and (111) planes have similar stability under the crystallization conditions used. AFM study also shows that the freshly born nuclei on the (100) face are of a height of 2 nm, suggesting a layer by layer growth of the polyhedral crystal.

This paper presents the first example of high-silica and siliceous zeolite synthesis in the urea/choline chloride mixture as a deep eutectic solvent (DES) using F– as the mineralizing agent. A urea/choline chloride mixture was previously used as solvent to prepare AlPO4-based microporous materials SIZ-2 and AlPO-CJ2. However, generating these materials depends on the formation of ammonium ion as a structure-directing agent (SDA) that is the side product of urea decomposition. In the present study, we show that several highly siliceous zeolites with targeted topologies (MFI, BEA, MEL, and MTN) can be purposely synthesized by adding SDAs of choice rather than relying on solvent decomposition. The Si atoms in zeolite Beta synthesized in a urea/choline chloride mixture exhibit exceptionally high local ordering as shown in a 29Si MAS NMR spectrum. The synthesis of ZSM-11 using eutectic solvents or ionic liquid has not been reported. The major challenge in ZSM-11 synthesis is the intergrown structure formed with ZSM-5 due to the high similarity in their topologies. The present work shows that preparation of pure ZSM-11 can be achieved in urea/choline chloride DES using either DPHMII or DECDMPI as SDA. Using a urea/choline chloride mixture rather than alcohol-based traditional nonaqueous solvents is the key for the success of preparing phase-pure ZSM-11 free of any MFI intergrowths. This is because some alcohols can serve as SDA for MFI. The use of urea/choline chloride based DES eliminates the potential templateing effect of solvent for MFI formation. For MTN zeolite, morphology may be controlled in urea/choline chloride by choosing different SDAs. The disadvantage of this system is the long reaction times.

Metal-organic frameworks (MOFs) are versatile materials that incorporate metal centers along with organic linkers in highly ordered, intricate structures. MIL-53 is a MOF that exhibits a “breathing effect,” where the pore size and MOF topology are profoundly influenced by the identity and binding mechanism of guest molecules. This phenomenon renders MIL-53 a promising candidate for sensing applications. In this report, the adsorption of various organic compounds within MIL-53 is investigated using a combination of complementary techniques. Thermal gravimetric analysis experiments confirm loading of the guest molecules and yield insight into adsorption interactions and strengths. Significant guest-induced changes in the crystal structure of MIL-53 are revealed by powder X-ray diffraction experiments; specific unique phases of MIL-53 are related to the identity of the guest molecule and its binding mechanism to the framework. 27Al and 13C solid-state NMR experiments probe the interaction between guest molecules and MIL-53. The relationship between the nature of the guest, the structure of MIL-53, and 27Al NMR parameters is explored. 27Al NMR parameters are sensitive to the host-guest binding mechanism (i.e., hydrogen-bonding or π–π stacking interactions) and yield valuable information regarding the influence of the adsorbates on the local aluminum environment. This combination of physical characterization techniques is a useful probe of guest adsorption and the breathing effect within MIL-53 and should prove useful for investigation of related MOFs.

Mixed-chalcogen metal chalcogenide nanoparticles (MSexS1-x; M = Zn, Cd) have been synthesized using Me3Si-SeS-SiMe3 as a delivery source of Se2– and S2– to the metal core. This method demonstrates the ease with which mixed-chalcogen particles can be fabricated at low temperature using colloidal techniques. Reaction with Me3Si-SeS-SiMe3 occurs via a redox pathway resulting in Se–S bond cleavage and ultimately contributing to the nonequivalent Se:S ratio observed in the isolated particles. Subsequent thermolysis of ZnSe0.57S0.43 and CdSe0.28S0.72 in hexadecylamine gives rise to controlled particle growth while maintaining the observed stoichiometry. Particles are characterized by EDX, TEM, and powder X-ray diffraction analysis in conjunction with UV–vis absorption and photoluminescence (PL) spectroscopy.Key words: nanoparticles, semiconductors, mixed-chalcogen, quantum confinement, Group 12.

Pressure-induced structural changes in di-iron nonacarbonyl [Fe2(CO)9] were examined by in situ Raman spectroscopy with the aid of a diamond anvil cell. Our results indicate that Fe2(CO)9 undergoes a pressure-induced phase transformation at about 0.9 GPa. Upon further compression, another structural transformation is identified at 7 GPa. In the low-pressure phase below 0.9 GPa, the π back-bonding between metal and carbonyl increases with increasing pressure. In the high-pressure phase above 7 GPa, the combination of high-pressure and laser irradiation induces a change in structure from Fe2(CO)9 to Fe2(CO)8. Fe2(CO)8 appears to adopt a structure with C2v rather than D3d or D2h symmetry. The metal–metal bond is gradually weakened under high pressures, and Fe2(CO)8 eventually decomposes by breaking the Fe–Fe bond when compressed up to 17.7 GPa.Key words: metal carbonyl, Raman spectroscopy, high pressure, diamond anvil cell.

The copper tellurolate cluster [(Cu6(TePh)6(PEtPh2)5] (1) has been loaded into the pores of a trimethylsilylated MCM-41 (TMS–MCM-41) framework. Solutions of 1 in tetrahydrofuran lead to good impregnation weight % (~10 wt%, 1). The resulting material was analysed by powder X-ray diffraction (PXRD), nitrogen sorption isotherms, thermogravimetric analysis (TGA), energy dispersive X-ray (EDX) analysis, 31P CP MAS NMR spectroscopy, and transmission electron microscopy (TEM). It was observed that the loading process proceeds with the intact cluster 1 being present within the hexagonal architecture. The intact nature of 1 makes it an ideal candidate for condensation by photochemical or thermal means. Both of these condensation treatments increase the Cu:Te ratio of 1 to approach that observed in binary semiconductor Cu2Te. The condensation process was analysed by GC–MS spectrometry and characterization of the condensed, isolated composites was performed by TGA, EDX analysis, 31P CP MAS NMR spectroscopy, nitrogen adsorption, and TEM measurements. Thermal condensation results in the formation of Cu2Te particles, whereas photochemical condensation yields larger copper-tellurolate nanoclusters.Key words: copper, tellurium, cluster, MCM-41, trimethylsilylated, photolysis, thermolysis, Cu2Te, composite, mesoporous material.

This work describes the thermal decomposition of Re2(CO)10 in zeolite Y, which generates the zeolite-supported complex Re0(CO)3(O-Z)3, where (O-Z) represents a framework oxygen. The adsorption and thermal decomposition of Re2(CO)10 was performed on dehydrated and hydrated zeolite NaY. The conversion to Re0(CO)3(O-Z)3 was not significantly affected by the presence of water within the supercages as the supported complex formed at around 200 °C no matter what the initial water content of the zeolite was. However, when the zeolite sample was treated at ≥200 °C for long periods, the adsorbed H2O became involved in the reactivity, playing a role as an oxidant. The subcarbonyl complex Re0(CO)3(O-Z)3 was oxidized, generating isolated Re2O7 or HReO4, or a mixture of both, which was dispersed inside the zeolite host. This result suggests that thermal decomposition of Re2(CO)10 on a hydrated zeolite under mild conditions can be a convenient route for preparation of zeolite-supported Re2O7 catalysts. Re0(CO)3(O-Z)3 was also formed in siliceous zeolite Y (SiY) upon heating. But it quickly decomposes into metal Re at around 200 °C, suggesting that the tricarbonyl species is destabilized in the almost natural zeolite framework. The present study also shows that FT-Raman spectroscopy is a useful technique for monitoring the behavior of the metal carbonyl species in zeolitic hosts.Key words: Raman spectroscopy, zeolite Y, rhenium carbonyl, rhenium oxide.

The IR and Raman spectra of two singly layered silicates, silinaite and makatite, have been investigated. The vibrational spectra were assigned based on previous studies of various silicates. The correlation between vibrational modes and the structural properties of silicates under investigation has been made. The IR and Raman spectra of silinaite are in good agreement with the known structure. However, the observed vibrational data of makatite are not completely consistent with those predicted by a factor group analysis based on the published single-crystal data.Key words: layered silicates, silinaite, makatite, vibrational spectroscopy.

The order–disorder behaviour of 1-chloroadamantane (1-C10H15Cl) has been investigated by differential scanning calorimetry, and variable-temperature vibrational and 13C NMR spectroscopy. The factor group splittings in the vibrational spectra are in accord with the known crystal structures of the two phases. The 13C spin-lattice relaxation times and dipolar dephasing measurements have been analysed to give the barriers to rotation in both phases and to determine the nature of the rotations in each phase. In the ordered phase, the motion is limited to rotation about the molecular axis. In the disordered phase, additional motions occur about axes through the tertiary carbon atoms.