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Two different quaternary ammonium cations, methyltriethyl- (MTEA) and tetraethylammonium cations (TEA) were used as templates in the synthesis of pure-silica as well as aluminosilicate ZSM-12 (MTW-type) frameworks. The distribution of the template cations in the 12-membered rings channels in the 1-dimensional framework topology was studied; thus the as-prepared products were characterized by means of X-ray powder diffraction, Raman, transmission FTIR, solid-state NMR spectroscopy, thermogravimetric and elemental analyses and SEM. It was shown that in pure-silica (PS) ZSM-12, TEA cations are well ordered - a superstructure with three-times longer b edge (in comparison to unit cell of empty framework) along the channel is formed, which can be seen by virtue of a few additional peaks in the X-ray powder pattern. Herein we describe that its aluminosilicate counterpart with TEA also contains ordered TEA cations and is isostructural to PS-ZSM-12. Conversely, in both pure-silica and aluminosilicate ZSM-12 frameworks with MTEA, the cations are disordered and no superstructure is formed.

Pure-silica ZSM-12, containing tetraethylammonium cations (TEA) was synthesized using a ‘two-silica’ source strategy and its structure was determined from laboratory X-ray powder diffraction data. This is the first known zeolite structure in which the positions of the TEA cations have been established. The ordered arrangement of TEA cations in the straight nonintersecting channels of the host material, which is reflected in several weak superstructural diffraction peaks, was determined by using the combination of simulated annealing and Rietveld refinement. In accordance with Raman spectroscopy, the calculations confirmed the presence of a tt . tt form of the TEA cations and the absence of the other stable form ( tg . tg ) which was also consistent with the dimensions and elliptical cross-section of the channels. Therefore in ZSM-12 structure pore (channels) geometry is directly connected with the conformation of TEA cations. The compound with a moiety formula C 16 H 40 N 2 O 84 Si 42 ( M r = 2784.28, Z = 4) crystallizes in the monoclinic Cc space group with unit cell parameters a = 25.2177(9), b = 15.1903(5), c = 24.4754(7) A, β = 108.516(2)°. The final structure, which resulted in a good agreement between calculated and observed powder diffraction pattern ( R wp = 10.17%), was additionally confirmed by results from thermogravimetric measurements and FTIR spectroscopy.

A Cr 3+ -modified natural zeolite sample from the deposit of Donje Jesenje (Croatia) was structurally studied using X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXS), inductively coupled plasma mass spectrometry (ICP-MS), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The analyses revealed the presence of up to 0.4 wt% of chromium in the clinoptilolite crystals. The X-ray photoelectron spectroscopy depth analysis suggested a uniform distribution of chromium from the surface of the crystallites to the depth of 50(3) nm. The study of local environment of chromium by XANES (X-ray absorption near edge structure) showed that chromium cations in the sample were predominantly in the 3+ oxidation state. EXAFS (extended X-ray absorption fine structure) analysis revealed that Cr 3+ cations bond to six oxygen atoms at the distance of 1.97(2) A and two chromium atoms at the distance of 2.54(2) A suggesting that Cr 3+ cations most probably arrange in the zeolite pores in the form of small clusters of CrO 6 octahedra. The chromium could not be completely desorbed from the sample after post-treatment with NaCl or HCl solutions thus indicating mostly irreversible sorption of chromium in the zeolite.

The crystal structure of a novel Ni-containing precursor to the molecular sieve AlPO4-34 (CHA framework type) has been determined in its as-synthesized form using high-resolution synchrotron powder diffraction data. One [Ni(1,2-diaminoethane)(2)O-2](2-) complex is found per chabazite-like cage in the triclinic unit cell Of C4H18N4NiAl6P6O26 (a = 9.0854(9) Angstrom, b = 9.3327(3) Angstrom, c = 8,936(1) Angstrom, alpha = 86.27(6)degrees, beta = 101.26(6)degrees, gamma = 92.72(5)degrees, P (1) over bar). Although the connectivity of the aluminophosphate framework is related to that of AlPO4-34, it is not identical because some P-O-Al bridges are broken. The Al atoms associated with this disruption of the connectivity form double Al-O-Al bridges and are five-coordinate, while the P atoms interact strongly with the Ni(II) complex ion to form an unusual P-O-Ni-O-P bridge across the chabazite cage. The triclinic deformation associated with these structural features disappears upon calcination, when the Ni(II) complex decomposes and the fully connected CHA framework type forms.

The large-pore molecular sieve MnAPO-50 of pure, greenish yellow crystals up to 100×100×300 μm was synthesized hydrothermally in the presence of di-n-propylamine. The product is thermally stable up to 250°C in air and up to 430°C in vacuum. It transforms into the dense phases Mn2P2O7 and AlPO4-tridymite at 550°C in air and at 650°C in vacuum. The single-crystal X-ray structure analysis of the as-synthesized MnAPO-50 (trigonal, P3, a=12.746(1) A, c=9.140(1) A) served as direct evidence of the very high degree of incorporation of Mn into the tetrahedral framework. The presence of Mn and Al on both of the two non-phosphorus framework tetrahedral sites was revealed: the T sites on the general position and on the threefold axis were occupied by 86% of Al, 14% of Mn and 3% of Al, 97% of Mn, respectively. Thirty-five per cent of the non-phosphorus tetrahedral framework sites were thus occupied by Mn, which is in reasonable agreement with the formula (Mn0.186(6)Al0.309(9)P0.504(2))O2, calculated on the basis of the elemental analysis.