Tetrahedral frameworks, octahedral

Diffraction patterns and FTIR spectra of skeletal vibrations of the ZSM-5 and ferrierite zeolites indicated high crystallinity of the analyzed samples. The strong band with a chemical shift of about 55 ppm in the 27Al MAS NMR spectra of hydrated zeolites indicated the presence of more than 97 % Al in the framework in tetrahedral coordination the very low intensity of the peak at 0 ppm indicated less than 3 % rel. of Al in octahedral coordination. 

The past nearly six decades have seen a chronological progression in molecular sieve materials from the aluminosilicate zeolites to microporous silica polymorphs, microporous aluminophosphate-based polymorphs, metallosilicate and metaHo-phosphate compositions, octahedral-tetrahedral frameworks, mesoporous molecular sieves and most recently hybrid metal organic frameworks (MOFs). A brief discussion of the historical progression is reviewed here. For a more detailed description prior to 2001 the reader is referred to [1]. The robustness of the field is evident from the fact that publications and patents are steadily increasing each year. 

Early to mid-1990s Metallophosphates Mesoporous molecular sieves Octahedral-tetrahedral frameworks... 

Two major new classes of molecular sieve type materials were reported in the 1990s (i) microporous frameworks based on mixed octahedral-tetrahedral frameworks in contrast to the previously described tetrahedral frameworks and (ii) mesoporous molecular sieves with pore sizes ranging from about 2 nm to greater than 10 nm. 

Octahedral-Tetrahedral Frameworks The microporous materials described heretofore were all based on tetrahedral frameworks. Microporous titanosihcate materials with mixed octahedral-tetrahedral frameworks were reported in the 1990s. 

Zeolites. A1 n.m.r. has been used to discriminate between framework (tetrahederally co-ordinated) and extra-framework (octahedrally co-ordinated) A1 in a number of natural and synthetic zeolites with different framework structures.65,72 7S 78 94 95 It appears that signal intensities can be used quantitatively to determine the relative amounts of the two forms of A1 present, but some caution must be exercised for non-ordered materials.78 Heat treatment of zeolites tends to remove the tetrahedrally co-ordinated A1 from the framework and deposit it in the zeolite pores as the octahedrally coordinated form A1(H20)63 +. This process has been monitored by 27A1 n.m.r.75... 

During the course of hydrothermal dealumination (ultrastabilisation) of zeolite Y quadrupole nutation NMR detects four kinds of aluminium sites. In addition to signals from the framework (F), non-framework tetrahedral (NFT) and non-framework octahedral (NFO) aluminium there is a signal which we attribute to distorted framework (DFT) aluminium bonded to hydroxyl nests formed during dealumination. 

The recent descriptions of the ALPO-n, SAPO-n and MeAPO-n families of microporous materials illustrate that hydrothermal syntheses can afford a wide and diverse range of four-coordinate framework structures based on nearregular tetrahedra [1,2]. As building blocks, octahedra and tetrahedra can also be combined, in various proportions, into a variety of structure types [3,4]. Reflecting the conditions used for conventional synthesis [3,4], most of these structures are condensed, with little accessible pore volume. There are, however, examples of both synthetic [5-7] and natural materials [8-11] that have microporous crystalline structures. Further, the formation chemistry of silicates and aluminosilicates [12,13] illustrates that the more open structures are generally produced under relatively mild conditions. Open octahedral-tetrahedral structures with large pore systems might therefore also be accessible under appropriate low temperature hydrothermal conditions. 

Insertion electrodes — insertion electrodes the electrochemical activity of which relates to insertion processes. Insertion involves two types of materials host materials and guest materials. Host materials provide a framework (lattice) of atoms/molecules, with specific sites such octahedral, tetrahedral, trigonal, or prismatic sites. The guest atoms or ions are inserted electrochemically (by applying an electrical field) and occupy these sites. Insertion can be in most cases reversible, thus leaving most host materials invariant in their physical and chemical properties after an insertion-deinsertion cycle. 

Solids with octahedral, tetrahedral, square planar, and linear metal coordination geometries, including many different types of polyhedra connectivity modes, are amenable to dimensional reduction. Tulsky and Long compiled an enormous database of over 300 different allowed combinations of M and X and over 10,000 combinations of A, M, and X. The formalism may be extendable to quaternary phases as well. However, frameworks containing anion-anion linkages, anions other than halides, oxide, or chalcogenides, nonstoichiometric phases, and mixed-valence compounds were excluded from their initial study. 

Rocha J. and Anderson M. W., Microporous titanosilicates and other novel mued octahedral-tetrahedral framework oxides, Eur. J. Inor. Chem. (2000) pp. 801-818. 

Figure 1 shows the A1 NMR spectra of dealuminated H-mordenite samples. The framework tetrahedral aluminium at 54 ppm decreases and the extra-framework octahedral aluminium at ca. 0 ppm increases as a function of increasing temperature of dealumination. In the final sample dealuminated at 973 K (e), the rather broad NMR lines for both tetrahedral and octahedral aluminium show the presence of extra-framework aluminosilicate and alumina species [14]. 

S.S. Dhingra and R.C. Haushalter, Hydrothermal Synthesis and Crystal Structure of H3NCH2CH2NH3[In2(HPO 4)4]. A Novel Octahedral-Tetrahedral Framework Indium Phosphate with Occluded Organic Cations. J. Chem. Soc., Chem. Commun., 1993, 1665-1667. 

Using Al MAS and Al MQ MAS NMR, dealumination of zeolite H- 3 has been observed at specific T-positions in the framework. " Al MQ MAS NMR was able to resolve aluminium in the Ti and Tj positions from the other (T3-T9) positions in the framework. A quantitative analysis of the Al MQ MAS NMR spectra has shown that aluminium atoms in positions Ti and T3 resist dealumination and do not adopt an octahedral coordination. It has also been shown that a heat treatment of NH4-P gives a single type of fairly symmetric framework octahedral aluminium, which can be reconverted into framework tetrahedral aluminium by ammonia treatment. 

There are now four major classes of materials in which organic components exert a significant structural role in controlling the inorganic oxide microstructure zeolites, mesoporous oxides of the MCM-41 class, biomineralized materials, and microporous octahedral-tetrahedral or square pyramidal-tetrahedral transition metal phosphate frameworks (TMPO) with entrained organic cations. ... 

Haushaulter, R.C. Mundi, L.A., Reduced Molybdenum Phosphates - Octahedral Tetrahedral Framework... 

Rocha J, Anderson MW. Microporous titanosUicates and other novel mixed octahedral-tetrahedral framework oxides. EurJ Inorg Chem 2000 5 801-818. 

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