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In an attempt to incorporate tin (Sn) into high-entropy alloys composed of refractory metals Hf, Nb, Ti and Zr with the addition of 3d transition metals Cu, Fe, and Ni, we synthesized a series of alloys in the system HfTiZrSnM (M = Cu, Fe, Nb, Ni). The alloys were characterized crystallographically, microstructurally, and compositionally, and their physical properties were determined, with the emphasis on superconductivity. All Sn-containing alloys are multi-phase mixtures of intermetallic compounds (in most cases four). A common feature of the alloys is a microstructure of large crystalline grains of a hexagonal (Hf, Ti, Zr)5Sn3 partially ordered phase embedded in a matrix that also contains many small inclusions. In the HfTiZrSnCu alloy, some Cu is also incorporated into the grains. Based on the electrical resistivity, specific heat, and magnetization measurements, a superconducting (SC) state was observed in the HfTiZr, HfTiZrSn, HfTiZrSnNi, and HfTiZrSnNb alloys. The HfTiZrSnFe alloy shows a partial SC transition, whereas the HfTiZrSnCu alloy is non-superconducting. All SC alloys are type II superconductors and belong to the Anderson class of “dirty” superconductors.

In this study, we investigate the scandium-containing Sc-Hf-Nb-Ta-Ti-Zr system of refractory high-entropy alloys (HEAs). Using the arc-melting method, we synthesized nine equimolar alloys (five 4-, three 5- and one 6-component), with all of them containing Sc. The alloys were characterized by XRD, electron microscopy and EDS, while superconductivity was investigated via electrical resistivity, specific heat and the Meissner effect. The results were compared to the parent Hf-Nb-Ta-Ti-Zr refractory HEAs, forming a single-phase body-centered cubic (bcc) structure and quite homogeneous microstructure. The addition of Sc produces a two-phase structure in the Sc-Hf-Nb-Ta-Ti-Zr alloys, with one phase being bcc and the other hexagonal close-packed (hcp). The hcp phase absorbs practically all Sc, whereas the Sc-poor bcc phase is identical to the bcc phase in the Hf-Nb-Ta-Ti-Zr parent system. Upon the Sc addition, the microstructure becomes very inhomogeneous. Large bcc dendrites (10–100 µm) are homogeneous in the central parts, but become a fine dispersion of sub-micron precipitates of the bcc and hcp phases close to the edges. The interdendritic regions are also a fine dispersion of the two phases. Superconductivity of the Sc-Hf-Nb-Ta-Ti-Zr alloys originates from the bcc phase fraction, which demonstrates identical superconducting parameters as the bcc Hf-Nb-Ta-Ti-Zr parent alloys, while the Sc-containing hcp phase fraction is non-superconducting.

Mo$_8$O$_{23}$ is a low-dimensional chemically robust transition metal oxide coming from a prospective family of functional materials, MoO$_{3-x}$, ranging from a wide gap insulator $(x=0)$ to a metal $(x=1)$. The large number of stoichometric compounds with intermediate $x$ have widely different properties. In Mo$_8$O$_{23}$, an unusual charge density wave transition has been suggested to occur above room temperature, but its low temperature behaviour is particularly enigmatic. We present a comprehensive experimental study of the electronic structure associated with various ordering phenomena in this compound, complemented by theory. Density-functional theory (DFT) calculations reveal a cross-over from a semi-metal with vanishing band overlap to narrow-gap semiconductor behaviour with decreasing temperature. A buried Dirac crossing at the zone boundary is confirmed by angle-resolved photoemission spectroscopy (ARPES). Tunnelling spectroscopy (STS) reveals a gradual gap opening corresponding to a metal-to-insulator transition at 343 K in resistivity, consistent with CDW formation and DFT results, but with large non-thermal smearing of the spectra implying strong carrier scattering. At low temperatures, the CDW picture is negated by the observation of a metallic Hall contribution, a non-trivial gap structure in STS below $\sim 170$ K and ARPES spectra, that together represent evidence for the onset of the correlated state at $70$ K and the rapid increase of gap size below $\sim 30$ K. The intricate interplay between electronic correlations and the presence of multiple narrow bands near the Fermi level set the stage for metastability and suggest suitability for memristor applications., Comment: 13 pages, 6 figures, pre-print of an article published in Scientific Reports. The final authenticated version is available online at http://dx.doi.org/10.1038/s41598-019-52231-4

The CoCrFeMnNi high-entropy alloy (HEA) is a magnetically concentrated crystalline system with all lattice sites magnetic, containing randomness (five different types of spins are randomly positioned on the lattice) and frustration (a consequence of mixed ferromagnetic and antiferromagnetic interactions). The sample material was prepared as a non-equiatomic, fully random solid solution of the five magnetic elements and we have studied experimentally the nature of the magnetic state. Upon cooling, no long-range magnetic ordering takes place, but the spin system undergoes a kinetic freezing transition to a spin glass phase, where below the spin freezing temperature T f ≈ 20 K, ergodicity of the system is broken. The observed broken-ergodicity phenomena include zero-field-cooled – field-cooled magnetization splitting in low magnetic fields, a frequency-dependent cusp in the ac susceptibility, an ultraslow time-decay of the thermoremanent magnetization and the memory effect, where the state of the spin system reached upon isothermal aging at a certain temperature can be retrieved after a reverse temperature cycle. All these phenomena are associated with the out-of-equilibrium dynamics of a nonergodic, frustrated system of coupled spins that approach thermal equilibrium, but can never reach it on a finite experimental time scale, so that we are observing only transient effects of partial equilibration within localized spin domains.

We address the nature of the collective magnetic state in an ideal high-entropy alloy (HEA), representing a magnetically concentrated system with all lattice sites occupied by localized magnetic moments and containing randomness and frustration due to chemical disorder. Being a “metallic glass on a topologically ordered lattice”, HEAs possess simultaneously the properties of an ordered crystal and an amorphous glass. The influence of this crystal-glass duality on the collective magnetic state was studied experimentally on a hexagonal Tb-Dy-Ho-Er-Tm (TDHET) HEA, composed of rare-earth (RE) elements with zero pair mixing enthalpies that assure completely random mixing of the elements and very similar atomic radii that minimize lattice distortions, representing a prototype of an ideal HEA. The TDHET HEA is characterized by probability distributions of the atomic moments P ( μ ) , the exchange interactions P ( J ) , the magnetocrystalline anisotropy P ( D ) , and the dipolar interactions P ( H d ) . Based on the measurements of the static and dynamic magnetization, the magnetization M ( H ) curves, the thermoremanent magnetization, the specific heat and the magnetoresistance, we found that the collective magnetic state of the TDHET is temperature-dependent, forming a speromagnetic (SPM) state in the temperature range between about 140 and 30 K and an asperomagnetic (ASPM) state below 20 K. In the intermediate temperature range between 30 and 20 K, a spin glass (SG) state is formed, representing a transition state between the speromagnetic and asperomagnetic states. The observed temperature evolution of the magnetic ground state in the TDHET HEA upon cooling in the sequence SPM→SG→ASPM is a result of temperature-dependent, competing magnetic interactions. The distribution of the exchange interactions P ( J ) shifts continuously on the J axis from the high-temperature SPM-type with the average interaction biased towards a net negative value, J ‾ 0 , through the SG-type with J ‾ = 0 , to the low-temperature ASPM-type with J ‾ > 0 . This shift is a band-structure effect, closely linked with the crystallinity of the spin system, which the TDHET HEA shares with the topologically ordered crystals. The probability distributions P ( μ ) , P ( J ) , P ( D ) and P ( H d ) are, on the other hand, a consequence of chemical disorder, a property that the TDHET HEA shares with the amorphous magnets. Both features, the topologically ordered lattice and the amorphous-type chemical disorder essentially determine the magnetic state of an ideal, RE-based HEA.

Reversible colour change of leuco dye-based composites is in general closely related to their phase change, thus the two phenomena should occur at around the same temperature and should be influenced similarly. However, spatial confinement of the analysed sample affects the change in colour differently compared to its phase transition and the most pronounced effects can be observed during cooling. The bulk composite is coloured while still liquid and the colour hysteresis does not exhibit a loop. In an open-porous medium the colouration coincides well with the crystallization and the colour hysteresis widens to about 4 °C. Microencapsulated composite exhibits two crystallization processes, one of them taking place at the bulk crystallization temperature and the other one at about 20 °C lower. Under such conditions the composite is coloured just before the onset of the second crystallization, i.e. about 15 °C below crystallization in the bulk, and the corresponding colour hysteresis widens to 18 °C. The two crystallization forms are thermally independent and have the same crystalline structure. These effects should be taken into account when designing future applications where the phase-changing materials are implemented.

Dinuclear ferrocene-based conjugates comprising a small homochiral sequence of two aminoacids (FcCO-Pro-Ala-NHFc) were prepared using stepwise solution-phase coupling techniques. The propensity of these bioorganometallics to form tight turns that resemble those in natural peptides was investigated by means of spectroscopy and the crystal structure was determined by X-ray diffraction analysis. The experimental data were corroborated by DFT calculations. The intramolecular NHFc⋯OCFc hydrogen bond keeps the molecule in the β-turn conformation. Molecules are further organized into bilayers with the inner region containing amino acid parts with relatively strong NHAla⋯OCAla hydrogen bonds, and the outer region linked by relatively weaker ferrocene⋯ferrocene interactions. The current research again confirms the robustness of the β-turn and its persistence in solution and in the solid state of small dinuclear ferrocene peptidomimetics.

A precise X-ray crystal structure determination of systems that exist in a polycrystalline form often poses a challenge due to several factors that limit the resolution of the diffraction measurement. The location of atoms is usually determined at significantly lower precision than the unit cell parameters, rendering the complete characterization of the structure difficult. This is particularly pronounced when precise location of hydrogen atoms is required, for instance in ionizable biomolecules or in hydrogen bonds. In such cases periodic quantum (DFT) calculations may crucially assist structure determination, because they can reliably predict the location of atoms, provided that the unit cell parameters, the space group and tentative atomic positions are known. In this work we present DFT-assisted structure determination of pentadecafluorooctanoic acid hydrate, a benchmark system featuring short hydrogen bonds (RO...O ≈ 2.5 Å) between acid and water molecules. While Rietveld refinement based solely on powder diffraction data cannot reliably resolve the location of crystal water molecules and even less so the position of hydrogen atoms in the network of hydrogen bonds, periodic DFT optimization yields several minimum energy structures suitable for further refinement. Due to the low experimental resolution and similarity, comparison between model and experimental powder diffraction pattern can barely distinguish between certain structure candidates provided by DFT calculations, but it can rule out those featuring larger misfits. The proposed structure solution is delivered from a tandem application of structure determination from powder diffraction data and DFT optimization, the former providing the unit cell parameters and estimated atomic positions that are finely tuned by DFT. The present strategy can in principle be generalized to other examples of structure determination at relatively low resolution, such as is often the case with biological macromolecules. This work is licensed under a Creative Commons Attribution 4.0 International License.

Four novel ruthenium organometallic complexes: [(η$^6$-p-cymene)Ru(4,4,4-trifluoro-1-(4-bromophenyl)-1,3-butanedione)Cl] (1), [(η$^6$-p-cymene)Ru(4,4,4-trifluoro-1-(4-bromophenyl)-1,3-butanedione)pta]PF$_6$ (2), [(η$^6$-p-cymene)Ru(4,4,4-trifluoro-1-(4-iodophenyl)-1,3-butanedione)Cl] (3) and [(η$^6$-p-cymene)Ru(4,4,4-trifluoro-1-(4-iodophenyl)-1,3-butanedione)pta]PF$_6$ (4) were synthesized and characterized by elemental analysis, infrared (IR), UV-Vis, NMR and mass spectroscopy and single-crystal X-ray diffraction. The crystal structures and spectroscopic data were compared to the previously published complexes [(η$^6$-p-cymene)Ru(4,4,4-trifluoro-1-(4-chloro-phenyl)-1,3-butanedione)Cl] (5) and [(η$^6$-p-cymene)Ru(4,4,4-trifluoro-1-(4-chlorophenyl)-1,3-butanedione)pta]PF$_6$ (6). The pairs of complexes 1 and 3 as well as 2 and 4 are isostructural, with the former crystallizing in triclinic P-1 and the latter in monoclinic P2$_1$/c. The ruthenium(II) ion is found in a pseudo-octahedral “piano-stool” geometry in all compounds. Bond lengths and angles are consistent with other complexes of this type. Complexes 2 and 4 exhibit some moderate dynamic disorder. The lack of hydrogen bonding and major π-π interactions means that most of intramolecular interactions are fairly weak and involve halogen atoms present. This was further confirmed by $^1$H-NMR spectra, where a significant difference is observed only on the ligand near the halogen atom, following an expected trend. The combined data show that the difference in any activity depends substantially on the type of the ligand′s substituted halogen atom.

Due to daily increase in energy demand it is a great task to explore and use a sustainable and carbon-free energy systems. Hydrogen, as clean and easily productive (from water and renewable energy) is possible future energy carrier. Problem of its safe and efficient storage can be solved by solid state storage-through chemical bonding in crystalline compounds or by physical adsorption in porous materials[1]. Metal-hydride organic frameworks (HOF) are a novel hybrid materials designed by combining molecular building blocks of light-weight complex hydrides with organic linkers developed for coordination frameworks. They will be based on crystal engineering principles of coordination frameworks and have new properties (guest-host interactions, dehydrogenation properties) defined by the nature of the unique complex-hydride ligands. HOFs present new type of frameworks due to coordination than usually available in coordination frameworks. Also, directional anionic ligands other than hydrides can be used. We used imidazoles or its derivatives because the metal-imidazolate-metal angle of 145° is very similar to metal- borohydride-metal angle observed in Mg(BH4)2[2]. We will present first results on mono- and bi-metallic mixed anion (borohydride and imidazolate) frameworks based on Zn2+ node and light alkali metal cations (Li+, Na+). For synthesis we used ball-milling procedure under inert atmosphere, solvent free and liquid- assisted grinding with different solvents (DMF, DMSO, THF, acetonitrile).

The synthesis and conformational analysis of a series of the monosubstituted aminoferrocene-based peptides bearing homo- and heterochiral Pro-Ala sequences are described. A change of the Pro amino acid chirality can affect the secondary structure. A homochiral derivatives of t-BuCO-AA2-AA1-NHFc favour β-turns, and a disruption of the secondary structure is observed in their heterochiral analogues in solution. A detailed computational study suggested formation of γ-turns in their heterochiral derivatives. The X-ray determined crystal structures of heterochiral compounds show preference for β-turns. The calculated interaction energies pointed out the significance of the intermolecular hydrogen bonds favourable enough to overcome rearangement of a single molecule from the most stable conformer to the one adopted in the solid state. The current research pointed out the potential of the investigated compounds for the fine tuning of their conformational properties by variation of the chirality of constituted amino acids.

The system Li–A–Y–BH4 (A=K Rb Cs) is found to contain five new compounds and four further ones known from previous work on the homoleptic borohydrides. Crystal structures have been solved and refined from synchrotron X ray powder diffraction thermal stability of new compounds have been investigated and ionic conductivity measured for selected samples. Significant coordination flexibility for Y3+ is revealed which allows the formation of both octahedral frameworks and tetrahedral complex anions with the tetrahydroborate anion \{BH4\} both as a linker and terminal ligand. Bi and trimetallic cubic double perovskites c A3Y(BH4)6 or c A2LiY(BH4)6 (A=Rb Cs) form in all the investigated systems with the exception of the Li–K–Y system. The compounds with the stoichiometry AY(BH4)4 crystallize in all investigated systems with a great variety of structure types which find their analog amongst metal oxides. In situ formation of a new borohydride – closo borane is observed during decomposition of all double perovskites.

Recently, preparation and preliminary testing of Li2FeSiO4, a representative of a new class of Li storage materials, has been reported [A. Nyten, A. Abouimrane, M. Armand, T. Gustaffson, J.O. Thomas, Electrochem. Commun. 7 (2005) 156]. In the present paper, we report preparation of another material from this class: Li2MnSiO4. To the best of our knowledge, the existence of this compound has not been reported so far. Similarly as in the case of the LiMPO4 materials family (M = Fe, Mn), the Mn analogue shows considerably poorer electrochemical performance. Quite unexpectedly, however, the Mn analogue shows a better stability, especially under harsh conditions. This property appears to be crucial for determination of detailed structural features of this class of materials. The obtained structure reveals partial occupation of alternate tetrahedral sites by Li and Mn, thus implying a high ionic conductivity of these materials. The poor electrochemical performance is most likely due to poor electron wiring. Keywords: Lithium-ion battery, Manganese silicate, Iron silicate, Cathode material, Crystal structure

Reaction of (Z)-2-Benzoylamino-4-dimethylamino-2-oxo-3-butene 1 with amidines 2a–e afforded pyrimidines 3a–e. Acid-catalysed treatment of 1 with potassium cyanide gave (E)-3benzoylamino-4-cyano-2-oxo-3-butene 4. 1,3-Dipolar cycloadditions of nitrile imines and 2,4,6trimethoxybenzonitrile oxide 7a to compound 4 afforded the corresponding pyrazole derivatives 6a–d and the isoxazole-4-carbonitrile 8a. In the reaction of 4 with 2,4,6-trimethylbenzonitrile oxide 7b, bis-cycloadduct 9 was formed and its structure was also determined by X-Ray analysis.

This work studied the phases in the Al corner of the Al–Mn–Be phase diagram in the as-cast state and heat-treated conditions. Metallographic investigations, X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy were used for identifying the phases. The Be contents in the identified phases were precisely determined using Auger electron spectroscopy. The results indicated that Al6Mn does not dissolve Be, whilst λ-Al4Mn dissolves up to 7 at.% Be. The average composition of the T phase, which is normally designated as Al15Mn3Be2, was 72 at.% Al, 19 at.% Mn, and 9 at.% Be. The phase with the nominal composition Be4AlMn contained more Al than Mn. The atomic ratio Al:Mn was between 1.3:1 and 2:1. The hexagonal Be-rich phase did not dissolve any Al and Mn. The icosahedral quasicrystalline (IQC) phase contained up to 45 at.% Be. The compositions of T phase, λ–Al4Mn, IQC, and Be4AlMn may vary, however, the ratio (Al + Be):Mn remained constant, and was close either to four or six indicating substitution of Al atoms with Be atoms in these phases.

The unique electronic and structural characteristics of 1,4-beilzoquinones with possibilities for numerous interactions such as coordination, hydrogen bonding accompanied by proton and/or electron transfer, pi-interactions, and redox activity, are used by nature to perform important biological reactions. In spite of their wide use in supramolecular chemistry for construction of functional materials, the intercorrelation of their versatile interactions has not been completely evaluated. The impacts of hydrogen bonding and cations on interactions of quinoid skeleton are studied on the prepared series of alkali (Li(+), Na(+), K(+), NH(4)(+), and Rb(+)) chloranilate hydrates, and anhydrous caesium homologue. The pi center dot center dot center dot pi stacking interactions of chloranilate dianions observed in the structures of sodium chloranilate dihydrate and caesium sodium chloranilate monohydrate [with centroid separation distances of 3.662(1) and 3.740(2) angstrom and shifts of 1.698 and 1.358 angstrom. respectively] are tuned by hydrogen bonding involving water Molecules. The crystal structures of potassium and rubidium chloranilate monohydrates are isostructural whereas their ammonium homologue, due to the presence of cation with pronounced proton-donor activity, exhibits completely different hydrogen bonding network. In the six of seven structures studied chloranilate dianion reveals the crystallographic symmetry C(i).

By a selective exchange of ligand Br by Cl, a series of nonstoichiometric bromo-chloro-pyridine- molybdenum(III) octahedral compounds of the type (cat)[MoBraCl(4-a)py2] (cat = pyH, a = 3–1 (1, 4, 7)); cat = [(C2H5)3NH], a = 2.744 (2); cat = Rb, a = 2.278 (5); cat =[(C6H5)4)As], a = 1.258 (8) and [MoBraCl(3–a)py3] (a = 2–1 (3, 6)) have been prepared and characterized. Owing to great similarity of the powder diffraction patterns and IR spectra of compounds mer- [MoBraCl(3-a)py3] (a = 3–0) with the known monoclinic modification in the space group P21/c and compounds [MoBraCl(3-a)py3] (a = 2-1 (3, 6)), the same type of crystal lattice was confirmed. Isostructurality was observed also for the orthorhombic trans-(pyH)[MoBr4py2]](Pnma) and compounds 1 and 4, while compound 7 is isostructural to trans-(pyH)[MoCl4py2]. X-ray crystallographic analyses of 2, 5 and 8, obtained by recrystallization of (pyH)[MoBraCl(4-a)py2] (a = 3–1) with different cations, were performed. In these compounds, MoIII is octahedrally coordinated with four halogenido ions at distances 2.4953(6)–2.5920(10) Å and two pyridine molecules at distances 2.195(4)-2.220(4) Å. Trans oriented pyridine rings in compounds 5 and 8 are co-planar, while deviation from co-planarity was noticed for compound 2 (8.9(3)°). The stoichiometry of four coordinated Br and Cl atoms in these compounds is not ideal, since the structure analysis results for 2, 5 and 8 show a mixed occupancy of crystallographic sites; thus, refined population parameters for both atoms (Br and Cl) were calculated., Selektivnom zamjenom bromovoga liganda klorovim dobijena je i karakterizirana serija nestehiometrijskih bromo-kloro-piridin-MoIII kompleksa tipa (cat)[MoBraCl(4–a)py2] (cat = pyH, a = 3–1 (1, 4, 7); cat = [(C2H5)3NH], a = 2.744 (2); cat = Rb, a = 2.278 (5); cat = [(C6H5)4As], a = 1.258 (8)) i [MoBraCl(3–a)py3] (a = 2–1 (3, 6)). Uslijed velike sličnosti difraktograma praha i IR spektara spojeva mer-[MoBraCl(3–a)py3] (a = 3–0) poznate monoklinske modifikacije u prostornoj grupi P21/c i spojeva [MoBraCl(3–a)py3] (a = 2–1 (3, 6)), potvr|en je isti tip kristalne re{etke. Opa`ena je izostrukturnost rompskoga trans-(pyH)[MoBr4py2] (Pnma) i spojeva 1 i 4, dok je spoj 7 izostrukturiran s trans-(pyH)[MoCl4py2]. Načinjena je rentgenska strukturna analiza spojeva 2, 5 i 8 dobijenih prekristalizacijom (pyH)[MoBraCl(4–a)py2] (a = 3–1) s različitim kationima. U tim je spojevima MoIII oktaedarski koordiniran s četiri halogenidna iona na udaljenostima 2.4953(6)–2.5920(10) Å i dvije molekule piridina na udaljenostima 2.195(4)–2.220(4) Å. Trans orijentirani piridinski prstenovi u spojevima 5 i 8 su koplanarni dok je kod spoja 2 ustanovljena devijacija od koplanarnosti (8.9(3)°). Strukturnom analizom utočnjeni su faktori zauzetosti četiri koordinirana atoma (Br, Cl) u spojevima 2, 5 i 8. Na|eno je da su navedeni kristalografski položaji zauzeti atomima Cl i Br u nestehiometrijskome omjeru.

Methods for the crystal structure determination from powder diffraction data are reviewed with special emphasis on the application to technical ceramics. Experimental techniques using other than laboratory X-ray, such as synchrotron radiation, neutron and electron beams, are also described. As an illustrative example, the crystal structure determinations of compounds LaNbTiO6, La0.462Nb0.614Ti0.386O3 and La0.37Nb0.889Ti0.111O3 in the ternary system of La2O3–Nb2O5–TiO2 are reported.

The triclinic form of AlPO4-34, a microporous aluminophosphate with the chabazite (CHA) topology, adopts a rhombohedral symmetry upon calcination. The framework structure of this phase remains intact under ambient conditions, but it distorts dramatically, though reversibly, in the presence of water. Following these structural changes in situ by X-ray diffraction revealed that there are actually two stable rehydrated phases, which differ from each other by one water molecule in the channel. Both of these phases have triclinic unit cells that are closely related to that of the calcined rhombohedral phase. The structure of the low-temperature (10 °C), fully rehydrated phase (phase B) was elucidated by combining high-resolution synchrotron powder diffraction with solid-state NMR techniques. Coordination of three of the six Al atoms to water molecules causes the deformation of the framework and the reduction of the symmetry. Rietveld refinement of the structure of phase B in the triclinic space group P1 (a = 9.026, b = 9.338, c = 9.508 Å, α = 95.1°, β = 104.1°, and γ = 96.6°) converged with RF = 0.079 and RWP = 0.176 (Rexp = 0.087). Framework connectivities derived from the structure were used to assign 31P NMR lines as well as part of the 27Al NMR signal.

An overview of contemporary methods of crystal structure solution from powder diffraction data is given. Methods are compared with respect to their advantages and disadvantages. A choice of an appropriate method is discussed in the light of understanding the structural problem to be solved. The need of the variety of methods for the variety of problems is illustrated by examples. Some directions of possible future development are discussed.

The tris(1,2-diaminoethane)nickel(II) complex was found to be a novel structure-directing agent for the preparation of the chabazite-like AlPO 4 -34 molecular sieve. During crystallization the complex undergoes a ligand exchange, thus helping stabilization of the AlPO 4 's chabazite structure by hydroxyls that have exchanged one 1,2-diaminoethane (en) molecule from the Ni(II) coordination sphere. The exchanged complex, [Ni(en) 2 (OH) 2 ], remains in the chabazite host causing a triclinic deformation of the rhombohedral chabazite framework. Upon calcination the triclinic phase completely transforms into the rhombohedral chabazite-like AlPO 4 -34 as evidenced from the in situ XRD pattern.

Zinc, manganese and cobalt containing aluminophosphates with the chabazite (CHA) structure type (MeAPO-34, MeZn, Mn and Co) have been synthesized hydrothermally in the presence of tetraethylammonium hydroxide. All samples showed a very high crystallinity without impurity phases, as evidenced by X-ray diffraction and scanning electron microscopy. The results of EXAFS spectroscopy on as-synthesized samples show that the metals possess 4 oxygen atoms in the first coordination shell which is an indication for a tetrahedral coordination in the lattice. The decrease of the EXAFS amplitude for some samples upon calcination is in agreement with the presence of Lewis acid sites, as previously reported. 31P NMR confirmed the incorporation of metals in the AlPO4-34 structure. For Zn and Mn, the 31P NMR spectra show various lines attributed to different P(nAl, 4-nMe) units and the calculation of the fraction of metal in the samples after deconvolution of the spectra is in very good agreement with elemental analysis. Comparison of the relative intensities of the lines with those obtained by a binomial theorem showed that metals randomly substitute Al in the AlPO4-34 framework. Incorporation of Co in the samples was suggested by a strong decrease in both T1 and T2 relaxation times with respect to SAPO-34 or ZnAPO-34, thus confirming EXAFS data.