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Until now, the comprehensive structural analysis of single crystals of zeolite ECR-1, an aluminosilicate with the EON topology, has been hindered owing to the submicron dimensions of the obtained crystals. Additionally, this zeolite, which is characterized by a topology comprising alternating periodic building units of MAZ and MOR layers, exhibits stacking faults that impede accurate refinement through the Rietveld method. In this report, we present, for the first time, the structure of ECR-1 elucidated by studying a nanocrystal with a significantly reduced number of stacking faults. The sample used was synthesized hydrothermally using trioxane as the organic structure-directing agent. The structure determination was conducted using precession electron diffraction (PED) at 103 K. Partial dehydration occurred owing to the high vacuum conditions in the TEM sample chamber. From the dynamical refinement (Robs = 0.097), 8.16 Na+ compensating cations were localized on six distinct crystallographic sites, along with approximately four water molecules per unit cell. Furthermore, a canonical Monte Carlo computational study was conducted to compare the experimental cationic distribution and location of water molecules with the simulation. [ABSTRACT FROM AUTHOR]

An organic cation lacking specificity in its structure-directing action offers the possibility, through the screening of other structure-directing parameters, to synthesize a variety of zeolites. In this work we show that the organic structure-directing agent 2-isopropyl-1,3-dimethylimidazolium (2iPr13DMI) can produce up to seven different zeolite phases depending on water concentration, the presence of inorganic impurities, crystallization temperature and time, and germanium molar fraction. The obtained phases are very different in terms of pore system, connectivity of the zeolite structure and structural units. At the pure SiO2 side, ZSM-12 and SSZ-35 dominate, with ZSM-12 being favored by the presence of potassium impurities and by less concentrated conditions. The introduction of Ge at low levels favors SSZ-35 over ZSM-12 and as the Ge fraction increases it successively affords CSV, -CLO and two distinct UOS zeolites, HPM-11 and HPM-6. These two zeolites have the same topology but distinct chemical compositions and display powder X-ray diffraction patterns that are much different from each other and from that of as-synthesized IM-16 (UOS reference material). They also show different symmetry at 96 K. Rietveld refinements of the three as-made UOS materials mentioned are provided. HPM-6 and HPM-11 are produced in distinct, non-adjacent crystallization fields. The frequent cocrystallization of the chiral STW zeolite, however, did not afford its synthesis as a pure phase. Molecular mechanics simulations of the location of the organic cation and host–guest interactions fail to explain the observed trends, but also considering the intrinsic stability of the zeolites and the effect of germanium help to rationalize the results. The study is completed by DFT calculations of the NMR chemical shifts of 13C in UOS (helping to understand splittings in the spectrum) and 19F in CSV (supporting the location of fluoride inside the new [4452], which is an incomplete double 4-ring). [ABSTRACT FROM AUTHOR]

The ESR spectrum of a non-Kekule polynuclear aromatic compound is presented. The compound comes from triangulene which is a pi biradical. Pi biradicals present difficulty in writing structures wherein each pi electron is paired with one on a neighboring carbon. It was shown that triangulene has a pair of nondisjoint degenerate nonbonding molecular orbitals and as such should have a triplet ground state.

IM-20, a microporous germanosilicate with a zeolitic structure, is prepared by the fluoride route with 3-butyl-1-methyl-3H-imidazol-1-ium as the organic structure-direction agent and its structure is solved by using synchrotron powder X-ray diffraction data. Two types of d4r composite building units are present in IM-20 and the pure silica or silica-rich units are shown to be fluoride-free in this material.

Water intrusion-extrusion isotherms performed at room temperature on hydrophobic pure silica chabazite have shown that the water-Si-CHA system exhibit real spring behavior. The studies have shown that Si-OH clusters have behaved like a real water trap at the origin of two water populations, where a first layer of water has strongly hydrogen bonded with the silanols of the framework and a subsequent layer of liquidlike physisorbed water molecules in interaction with the first layer.

The structure determined from molecular modeling and Rietveld analysis on synchroton data of AlPo4-SOD dehydrated under vacuum at 100 degree Celsius together with some solid state NMR experiments of the rehydrated product is presented. The dehydration/rehydration of AlPo4-SOD, however, is a reversible but very slow process.