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A new two-dimensional zeolitic imidazolate framework (named as ZIF-L) was synthesized in zinc salt and 2-methylimidazole (Hmim) aqueous solution at room temperature. ZIF-L (Zn(mim)2·(Hmim)1/2·(H2O)3/2 or C10H16N5O3/2Zn) has unique cushion-shaped cavities and leaf-like crystal morphology, and exhibits excellent CO2 adsorption properties.

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The synthesis of pure silica MWW type zeolite ITQ-1 using trimethyladamantammonium (TMAda+) is described. The reproducibility of the synthesis, as well as the quality of the materials obtained, is greatly improved if the synthesis is assisted by hexamethyleneimine (HMI) as a second organic additive. As TMAda+ is too large to fit into the sinusoidal 10 MR channel (i.e., the channel delimited by a ring of 10 tetrahedra), the stabilization of this channel seems to require the presence of additional organic moieties. In the absence of HMI, these probably come from either the partial degradation of TMAda+ or from organics adsorbed on the PTFE liners in previous syntheses. The use of TMAda+ and HMI and Na+ cations allows a fast and highly reproducible synthesis of pure silica ITQ-1. The material obtained shows an improved crystallinity in both the as-made and the calcined form. The structure of calcined ITQ-1 has been refined in space group P6/mmm (a = 14.2081(1) Å, c = 24.945(2) Å, R exp = 0.103, R wp = 0.159, R f = 0.065), using synchrotron powder diffraction data, and the topology previously proposed for the aluminosilicate MCM-22 zeolite has been confirmed. Comparison of the highly resolved 29Si MAS NMR spectra of as-made and calcined ITQ-1 show that in the as-made form there is a high concentration of Si−OH defect groups, which are annealed upon calcination and which arise from a lack of connectivity between specific Si sites.

Dedicated to Professor Hans Paulsen on the occasion of his 75th birthday (23.XII. 1996) The solid-state structures of three stereoisomers, 1-3, of the cyclic tetramer of 3-aminobutanoic acid are presented. These cyclo-p-peptides were found to be highly insoluble materials, and it proved to be impossible to grow crystals of suficient quality for X-ray single-crystal analysis. The samples of 1-3 were, however, suitable candidates for structure determination from powder diffraction data (Fig. Z), and the application of this method is described. All three isomers have been found to adopt tubular structures (Figs. 2-4) in a fashion similar to those already observed for certain cyclo-a-peptides. The stacks of 16-membered rings are held together by four nonlinear C=O ...H-N H-bonds between pairs of molecules (Fig. 5 ) .

Despite substantial advances in crystal structure determination methodology for polycrystalline materials, some problems have remained intractable. A case in point is the zeolite catalyst IM-5, whose structure has eluded determination for almost 10 years. Here we present a charge-flipping structure-solution algorithm, extended to facilitate the combined use of powder diffraction and electron microscopy data. With this algorithm, we have elucidated the complex structure of IM-5, with 24 topologically distinct silicon atoms and an unusual two-dimensional medium-pore channel system. This powerful approach to structure solution can be applied without modification to any type of polycrystalline material (e.g., catalysts, ceramics, pharmaceuticals, complex metal alloys) and is therefore pertinent to a diverse range of scientific disciplines.

Physico-chemical characterization of the high-silica zeolite catalyst SSZ-74 (ref. 1) suggested that it, like the related materials TNU-9 (ref. 2) and IM-5 (ref. 3), has a multidimensional 10-ring channel system. Such pore systems are ideal for many petrochemical applications, and indeed SSZ-74 has been shown to be a good catalyst for a wide variety of reactions. The elucidation of its framework structure, however, proved to be difficult. Comparable problems were encountered with TNU-9 and IM-5, which were synthesized with related structure-directing agents. Their framework structures, which are the two most complex ones known, both have 24 Si atoms in the asymmetric unit, and were finally solved by combining high-resolution powder diffraction data with information derived from high-resolution electron microscopy images. Therefore, a similar approach, using the powder charge-flipping algorithm to combine the two types of data and molecular modelling to help to locate the structure-directing agent, was applied to SSZ-74. This procedure eventually revealed a most unusual 23-Si-atom framework structure (|(C(16)H(34)N(2))(4)&Si(92)(4)O(184)(OH)(8)]) with ordered Si vacancies.