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The structure and stoichiometry of a new metal-free and ammonium-free compound [dabcoH2]2+H3O+Br− 3 (where [dabcoH2]2+ = 1,4-diazabicyclo[2.2.2]octane dication) correspond to the general formula ABX 3 characteristic of perovskites. In enantiomorphic trigonal polymorph α of [dabcoH2]2+H3O+Br− 3, the corner-sharing [H3O]Br6 octahedra combine into a 3D framework embedding [dabcoH2]2+ dications in pseudo-cubic cages. In the more dense polymorph β, the face-sharing [H3O]Br6 octahedra form 1D polyanionic columns separated by [dabcoH2]2+ dications. These different topologies correlate with different crystal fields around the cations and their different disorder types: orientational disorders of [dabcoH2]2+ dications and H3O+ cations in polymorph α and positional disorder of [H3O]+ cations in polymorph β. The orientational disorder increases the lengths of OH...Br hydrogen bonds in polymorph α, but NH...Br distances of ordered dabcoH2 dications are longer in polymorph β. The presence of polar [H3O]+ cations in [dabcoH2]2+H3O+Br− 3 polymorphs offers additional polarizability of the centres compared with analogous metal-free [dabcoH2]2+[NH4]+Br− 3 perovskite.

The structure and stoichiometry of a new metal-free and ammonium-free compound [dabcoH

Short contacts F···F and their triangular motifs F3 are the eminent features in the new high-pressure perfluorobenzene (C6F6) phase II formed above 0.89 GPa. Fluorine atoms are strongly electronega...

Synthetic chemistry and drug design through different software is becoming more and more important nowadays. In this modern era each person is suffering from many diseases due to various factors such as financial, environmental, food etc. Proposed thiocarbamates of various diamines were synthesized hypothetically and they were docked with AChE (Acetylcholine esterase) and BChE (Butyrylcholine esterase) using MOE (Molecular Operating Environment). From results of MOE, most active (KR-25 and KR-26) were synthesized using reported methods and their structures were confirmed with Fourier-transform infrared spectroscopy, mass spectrometry and XRD (X-ray powder diffraction). Later on in-vitro enzyme inhibition studies against both targeted enzymes were screened out which also supported the docking results. The DFT (Density Functional Theory) studies were carried out for all proposed structures in the form of optimization and HOMO-LUMO calculation. ADMET (absorption, distribution, metabolism, excretion and toxicity) studies were applied on compounds in order to check their different parameters. It was concluded from docking, in-vitro enzyme inhibition and ADMET that KR-25 and KR-26 are more potent for AChE and BChE.

Background: Atropisomers are very interesting stereoisomers having axial chirality resulting from restricted rotation around single bonds and are found in various classes of compounds. ortho-Substituted arylpyridines are an important group of them. A regio- and atropselective Suzuki–Miyaura cross-coupling reaction on 3,4,5-tribromo-2,6-dimethylpyridine was studied.Results: Reactions with various amounts of ortho-substituted phenylboronic acids with 3,4,5-tribromo-2,6-dimethylpyridine gave a series of mono- di- and triarylpyridine derivatives which allowed to draw conclusions about the order of substitution. Also, the observed selectivity in the case of ortho-methoxyphenylboronic acid suggested an additional metal O-chelation effect in the transition state, apparently not present in the ortho-chloro analogues. The rotational barrier in selected atropisomers was determined on the basis of HT NMR and thermal epimerisation experiments. The structure of most presented atropisomeric derivatives of 2,6-dimethylpyridine was confirmed by single-crystal X-ray analysis. Racemic chiral, differently substituted atropisomers were also examined by 1H NMR spectroscopy in the presence of a chiral solvating agent.Conclusion: This regio- and atropselectivity may be generally applicable to other arylpyridine systems. A regio- and atropselective Suzuki–Miyaura cross-coupling process has been observed, giving an efficient access to a class of atropisomeric compounds. An opposite selectivity using a differently ortho-substituted phenylbornic acid was observed.

Holmium-doped monoclinic KGd(WO4)2 nanoparticles were synthesized by the mechano-chemical method. The structure and morphology of KGW:Ho 10 at.% nanopowders were investigated with the use of X-ray Powder Diffraction, Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). Emission and excitation spectra of KGW nanocrystals were also measured using a fluorometer with a xenon lamp and OPO laser source. The influence of nanoparticles of KGW doped with 10 at.% of holmium on the viability of J774.1 mouse BALB/c monocyte macrophage cells was tested by the WST8 assay. Preliminary immunity cell studies demonstrated a high viability of KGW:Ho 10 at%. Hence, these nanoparticles are promising for imaging applications. To characterize and quantify the physical stability of the nanoparticles of KGW:Ho 10 at.% suitable for biomedical applications, nanoparticles of KGW:Ho in the range of 80–200 nm were prepared.

Racemic ketoprofen (KP) and β-cyclodextrin (β-CD) powder samples from co-precipitation (1), evaporation (2), and heating-under-reflux (3) were analysed using X-ray techniques and nuclear magnetic resonance (NMR) spectroscopy. On the basis of NMR studies carried out in an aqueous solution, it was found that in the samples obtained by methods 1 and 2, there were large excesses of β-CD in relation to KP, 10 and 75 times, respectively, while the sample obtained by method 3 contained equimolar amounts of β-CD and KP. NMR results indicated that KP/β-CD inclusion complexes were formed and the estimated binding constants were approximately 2400 M−1, showing that KP is quite strongly associated with β-CD. On the other hand, the X-ray single-crystal technique in the solid state revealed that the (S)-KP/β-CD inclusion complex with a stoichiometry of 2:2 was obtained as a result of heating-under-reflux, for which the crystal and molecular structure were examined. Among the methods used for the preparation of the KP/β-CD complex, only method 3 is suitable.

During the attempted photochemical cyclization of 2,3-bisbenzylidene-γ-hydroxybutyric acid cyclic amide ester, it was observed that a γ-butyrolactone ring was formed, which was concurrent with the release of the amine fragment from the amide. The process occurs with high yield giving rise to the formation of β-apopicropodophyllin and its regioisomer. Additional experiments confirmed the photochemical nature of this transformation, and that it is independent from the photocyclization of the benzylidene groups – a typical reactivity for the members of the fulgide family. In contrast to the latter UV-driven cyclization, the photochemical cleavage of the amide was proven to proceed under irradiation with visible light.

The first synthesis of sterically demanding, stable at room temperature atropisomeric derivatives of penta-(ortho-substituted phenyl)pyridines is described. The Suzuki-Miyaura cross-coupling reaction of pentabromopyridine and selected meta- and ortho-tolylboronic acids afforded a series of pentaarylpyridine derivatives. The structures of two room temperature stable atropisomeric derivatives of penta-(o-tolyl)pyridines were confirmed by single-crystal X-ray analysis. Racemic atropisomers were examined by 1H NMR spectroscopy with a chiral solvating agent in order to visualize the presence of individual enantiomers.

The Suzuki–Miyaura cross-coupling reaction of 3,5-dibromo-2,4,6-collidine and bromo derivatives of 2,6- and 2,4-lutidine with several ortho-substituted boronic acids produced a library of arylated pyridines. The reaction conditions were carefully optimized to allow high yield of the desired products. In several cases the presence of stable atropisomers were detected, even at elevated temperature during GC–MS analysis. Some of the diastereomers were isolated and characterized by spectroscopic methods and X-ray crystallography. Racemic forms of selected samples were tested by 1H NMR spectroscopy in the presence of chiral solvating agents in order to visualize the presence of individual enantiomers.

The Suzuki–Miyaura reaction of 4-amino-3,5-dibromo-2,6-lutidine with various ortho-substituted phenylboronic acids resulted in the formation of a series of mono- and diarylated lutidines in the form of atropisomers. The absolute stereochemistry of the chiral compounds was established, in some cases, by X-ray crystal structure analysis and HPLC-ECD (ECD = electronic circular dichroism) in combination with time-dependent density functional theory (TDDFT) calculations.

The present study was designed to check enzyme (esterase and α-glucosidase) inhibition potential of newly synthesized thiazolidinones. Two precursors from ethylene diamine were prepared and further condensed with different aromatic aldehydes yielded fourteen different compounds. The synthesized compound ‘a’ was characterized with single crystal X-Ray diffraction (SC-XRD) technique, while the structures of all others were determined with FTIR and NMR (1H and 13C) spectroscopy. The compounds were further theoretically optimized through Gaussian 9 software and calculated their different parameters and energy gap between HOMO and LUMO. In-vitro enzyme inhibition studies were carried out spectrophotometrically which depicted that these molecules may be good therapeutic for targeted enzymes and their related diseases. Docking results of the synthetic thiazolidinone also advocated experimental out comes of the under studied compounds.

A combined experimental–theoretical study of silver(I) and silver(II) fluorides under high pressure is reported. For AgI, the CsCl-type structure is stable to at least 39 GPa; the overtone of the IR-active mode is seen in the Raman spectrum. Its AgIIF2 sibling is a unique compound in many ways: it is more covalent than other known difluorides, crystallizes in a layered structure, and is enormously reactive. Using X-ray diffraction and guided by theoretical calculations (density functional theory), we have been able to elucidate crystal structures of high-pressure polymorphs of AgF2. The transition from ambient pressure to an unprecedented nanotubular structure takes place via an intermediate orthorhombic layered structure, which lacks an inversion center. The observed phase transitions are discussed within the broader framework of the fluorite → cotunnite → Ni2In series, which has been seen for other metal difluorides.

The syntheses and characterizations of mixed-cation fluorosulfates containing AgII ions are reported and add to the moderately well-known chemistry of AgII compounds. The compounds synthesized mostly show different structures and compositions. The mixed sodium–silver fluorosulfate is isostructural with Ag3(SO3F)4 (monoclinic P21/c, a = 5.2812 A, b = 13.0473 A, c = 19.3557 A, and β = 100.970°) and has the composition (Ag0.05Na0.95)(Ag0.65Na0.35)AgII(SO3F)4. The mixed potassium–silver fluorosulfate does not correspond to KI2AgII(SO3F)4 but rather to KAgI2AgII(SO3F)5 [orthorhombic P2221, a = 6.4736(3) A, b = 7.3915(4) A, and c = 17.7736(10) A]. Two rubidium–silver fluorosulfates form as a mixture, one corresponds to RbAgI2AgII(SO3F)5 [orthorhombic P2221, a = 6.4828(6) A, b = 7.3551(7) A, c = 18.0262(17) A], and the other corresponds to RbAgII(SO3F)3 [monoclinic P21/m, a = 15.8152(14) A, b = 15.4861(13) A, c = 17.0211(14) A, and β = 101.513(5)°]. The cesium fluorosulfate/silver(II) fluorosulfate phase diagram is exemplified by the CsAgII(SO3F)3 salt [triclinic P, a = 14.9241(5) A, b = 9.7046(3) A, c = 17.8465(7) A, α = 109.116(2)°, β = 84.655(3)°, and γ = 119.171(3)°]. The IR and Raman spectra of the compounds were measured, and their thermal stability and magnetic properties have been determined. The MAgI2AgII(SO3F)5 systems show antiferromagnetic behavior with absolute superexchange constants of up to 19.1 meV for M = K, and ferromagnetism can be observed below 20–40 K for the MAg(SO3F)3 derivatives (M = Rb, Cs).

Exceptionally rich diagram of ten phases, I–X, has been revealed for ferroelectric 1,4-diazabicyclo[2.2.2]octane perchlorate, [C6H13N2]+ClO4–, dabcoHClO4. Pressure- and temperature-induced transformations of this NH+···N hydrogen bonded structure have been characterized by single-crystal X-ray diffraction, calorimetric, and dielectric measurements. At high pressure the single crystals were in situ grown in a diamond-anvil cell at isochoric conditions. There are nine phases of dabcoHClO4 between 400 and 11 K at ambient pressure, whereas phase X is formed at 1.5 GPa and 296 K. Tetragonal phase I space group P4/mmm transforms to orthorhombic phases II (Pm21n), III (Pc21n), IV (Pc2a), and V (orthorhombic-modulated) on decreasing temperature. Phase II is stable up to 0.22 GPa, at 0.6 GPa phase III is formed, and above 1.50 GPa a new phase X (Pc21a) has been obtained. At normal conditions dabcoHClO4 is isostructural with the ferroelectric crystal of dabcoHBF4; however, their phase diagrams are very different. A...

Here we redetermine the crystal structure of Ag(II)SO4, an unusual d9 system, at 1 atm from powder X-ray data and we report hydrostatic pressure X-ray diffraction experiments on Ag(II)SO4 inside the diamond anvil cell. AgSO4 crystallizes in the monoclinic C2/c cell, with a = 12.8476(2) A, b = 13.6690(4) A, c = 9.36678(19) A, β = 47.5653(13)°, and V = 1214.04(5) A3 (Z = 16). AgSO4 exhibits bulk modulus, B0, of 36.9 GPa, and undergoes sluggish decomposition at ∼23 GPa yielding a high-pressure phase of Ag2S2O7 (K2S2O7-type), with the substrate and product coexisting at 30 GPa. Theoretical calculations within Density Functional Theory for the C2/c cell nicely reproduce the observed trend for lattice constants as well as the B0 values of AgSO4, and suggest that the rigidity of the infinite [Ag(SO4)] chains as well as the Jahn–Teller effect for the Ag(II) cation persist even at 30 GPa.

Valence (redox) isomerism based on electron exchange between a metal and a ligand is immensely rare in purely inorganic systems, with only one documented case, that of PbS

Anhydrous fluorosulfates of sodium(I) and thallium(I) have been structurally characterized for the first time; structure of a novel polymorphic form of rubidium(I) fluorosulfate is also reported. NaSO3F is hexagonal (P63/mmc, a = b = 5.4812(2) A, c = 6.5172(3) A, Z = 2), while RbSO3F and TlSO3F are orthorhombic an both adopt the Pnma space group, but despite similar ionic radii of metal cations they are not isostructural with each other (Rb: a = 8.7812(7) A, b = 6.0318(6) A, c = 7.5108(6) A, Z = 4; Tl: a = 5.2205(3) A, b = 5.5141(2) A, c = 13.4378(7) A, Z = 4). The three fluorosulfates studied here complete the list of fluorosulfates of monovalent metals, for which the crystal structures have been determined.

Trifluoromethansulfonate of silver(I), AgSO(3)CF(3) (abbreviated AgOTf), extensively used in organic chemistry, and its fluorosulfate homologue, AgSO(3)F, have been structurally characterized for the first time. The crystal structures of both homologues differ substantially from each other. AgOTf crystallizes in a hexagonal system (R3 space group, No.148) with a = b = 5.312(3) Å and c = 32.66(2) Å, while AgSO(3)F crystallizes in a monoclinic system in the centrosymmetric P2(1)/m space group (No.11) with a = 5.4128(10) Å, b = 8.1739(14) Å, c = 7.5436(17) Å, and β = 94.599(18)°, adopting a unique structure type (100 K data). There are two types of fluorosulfate anions in the structure; in one type the F atom is engaged in chemical bonding to Ag(I) and in the other type the F atom is terminal; accordingly, two resonances are seen in the (19)F NMR spectrum of AgSO(3)F. Theoretical analysis of the electronic band structure and electronic density of states, as well as assignment of the mid- and far-infrared absorption and Raman scattering spectra for both compounds, have been performed based on the periodic DFT calculations. AgSO(3)F exhibits an unusually low melting temperature of 156 °C and anomalously low value of melting heat (ca. 1 kJ mol(-1)), which we associate with (i) disorder of its anionic sublattice and (ii) the presence of 2D sheets in the crystal structure, which are weakly bonded with each other via long Ag-O(F) contacts. AgSO(3)F decomposes thermally above 250 °C, yielding mostly Ag(2)SO(4) and liberating SO(2)F(2). AgOTf is much more thermally stable than AgSO(3)F; it undergoes two consecutive crystallographic phase transitions at 284 °C and 326 °C followed by melting at 383 °C; its thermal decomposition commences above 400 °C leading at 500 °C to crystalline Ag(2)SO(4) and an unidentified phase as major products of decomposition in the solid state.

“It could be said that among the coinage metals (Cu, Ag, Au), only silver is normal . (...) gold is anomalous due to large relativistic effects. Copper is anomalous as it has a nodeless and therefore very compact d shell, with strong electron–electron repulsion (...)”. The “normality” of elemental silver, is reflected in the prevalence of its monovalent oxidation state, +1 (as expected for a Group 11 element), which also has severe consequences for its second oxidation state—it renders Ag an extremely powerful oxidizer. The standard redox potential for the Ag/Ag redox pair equals +1.98 V versus NHE and it is surpassed only by those of FC/F , F2/2F , ClC/Cl and OHC/OH . Thus Ag is stabilized in connections with fluoride ligands, whereas its oxo and aza compounds are rare and are quite unstable thermodynamically and thermally. Here we investigate in detail the thermal decomposition of recently synthesized Ag sulfate, AgSO4. [4] The activation energy for decomposition turns out to be substantial ( 127 kJmol ) rendering this compound metastable at ambient (p, T) conditions. We show, based on literature about thermal decomposition for over 50 different sulfates and oxo-sulfates (see the Supporting Information), that solely AgSO4 s low-temperature thermal decomposition is associated with the reduction of a metal cation (“reductive decomposition”). We consider the reaction pathway for decomposition and we point out structural links between AgSO4 and crystalline product of its decomposition, AgSO3.5 Ag2S2O7. Ag sulfate was reported to decompose thermally in a single step while yielding Ag disulfate and releasing O2 [Eq. (1)]

Two polymorphs (α, β) of pyrazinium hydrogen sulfate (pyzH+HSO_4^-, abbreviated as PHS) with distinctly different hydrogen-bond types and topologies but close electronic energies have been synthesized and characterized for the first time. The α-polymorph (P212121) forms distinct blocks in which the pyzH+and HSO_4^- ions are interconnected through a network of NH...O and OH...O hydrogen bonds. The β-form (P\bar 1) consists of infinite chains of alternating pyzH+and HSO_4^- ions connected by NH...O and OH...N hydrogen bonds. Density functional theory (DFT) calculations indicate the possible existence of a hypothetical polarP1 form of the β-polymorph with an unusually high dipole moment.

We report the crystal structure and magnetic properties of a novel β polymorph of K 2 AgF 4 . β-K 2 AgF 4 is paramagnetic above 20 K and exhibits a low Curie temperature (0 < 5 K). Solid state DFT (GGA and GGA+U) calculations were performed to analyze the electronic and magnetic structure of β-K 2 AgF 4 at 0 K/0 GPa, reproducing correctly the ferromagnetic (FM) semiconductor ground state with the band gap at the Fermi level of approximately 1.65 eV. Furthermore, we show that the novel β form is thermodynamically favoured over the previously reported two-dimensional α form and can be formed either by slow spontaneous exothermic α to β phase transition occurring on heating or direct synthesis from KF and AgF 2 at 300 °C. The relative stability of the α and β phases is rationalized in terms of the size of the M + cation in the M 2 M'F 4 series (M = Na, K, Cs, M' = Cu, Ag) and the mismatch between [MF] and [M'F 4/2 ] sublattices in the layered perovskite α form.

Molecular arrangements have been determined at the lowest limits of pressure ranges of benzene phase I, at 0.15 GPa, and phase II at 0.91 and 0.97 GPa, all at 295 K. All intermolecular contacts both in phase I and phase II to about 1.0 GPa exceed the sums of van der Waals radii; however, the transition between phases I and II does not affect the pattern of CH···π(arene) hydrogen bonds. In phase I the molecules are CH···π bonded approximately perpendicular into sheets, and there are substantial voids between the molecules within the sheets. The mechanism of transition to phase II involves a collapse of the voids, simultaneous with a shift of the CH···π bonded sheets. The thickness of sheets increases, which partly compensates the volume reduction due to the voids collapse; hence, the transition exhibits a large hysteresis of two GPa and a sluggish character at 295 K. No other phases of benzene have been observed between 0.15 and 5.0 GPa.

Alkali and alkaline-earth metal amidoboranes constitute a new class of inorganic hydrogen storage materials containing distinct [NH2BH3]− units. Here we have attempted synthesis of one of the lightest among M(III) amidoboranes, Y(NH2BH3)3, with its high nominal hydrogen content of 8.4 wt.%, using few different routes. Polycrystalline Y(NH2BH3)3, successfully obtained via mechanochemical synthesis utilizing LiNH2BH3 and YCl3, has been subject to structural and spectroscopic investigations as well as studies of thermal decomposition. Y(NH2BH3)3 crystallizes monoclinic (C2/c) with a = 13.18902(63) A, b = 7.82233(38) A, c = 14.874274(68) A, β = 92.42620(40)° (Z = 8, V = 1533.19(13) A3). The title compound is quite unstable at ambient conditions and it spontaneously decomposes within several days. When heated up in argon, it exothermally emits hydrogen contaminated with significant amount of ammonia, in the 50–250 °C temperature range.

Crystalline phases obtained by reactions of MSO3F (M: Na, K, Rb, Cs), AgSO3F, and (SO3F)2 (77 K room temp., 2—5 d) are characterized by powder XRD, Raman spectroscopy, and magnetic measurements.

1,2-Diaminoethane has been in-situ pressure- and temperature-frozen; apart from two known low-temperature phases, Iα and II, three new phases, Iβ, Iγ and III, have been observed and their structures determined by X-ray diffraction. The measurements at 0.1 MPa were carried out at 274, 243 and 224 K, and 296 K measurements were made at 0.15 GPa (phase Iα), at 0.3 and 1.1 GPa (phase Iβ), at 1.5 GPa (phase Iγ), and at 0.2, 0.3 and 0.5 GPa (phase III). All these phases are monoclinic, space group P21/c, but the unit-cell dimension of phases Iα and III are very different at 296 K: a Iα = 5.078 (5), b Iα = 7.204 (8), c Iα = 5.528 (20) Å, β Iα = 115.2 (2)° at 0.15 GPa, and a III = 5.10 (3), b III = 5.212 (2), c III = 7.262 (12) Å, β III = 111.6 (4)° at 0.2 GPa, respectively; in both phases Z = 2. An ambient-pressure low-temperature phase II has been observed below 189 K. Discontinuities in the unit-cell dimensions and in the N...N distance mark the isostructural transition between phases Iα and Iβ at 0.2 GPa, which can be attributed to a damping process of the NH2 group rotations. In phase Iγ the unit-cell parameter a doubles and Z increases to 4. The molecule has inversion symmetry in all the structures determined. 1,2-Diaminoethane can be considered as a simple structural ice analogue, but with NH...N hydrogen bonds and with the H-atom donors (four in one molecule) in excess over H-atom acceptors (two per molecule). Thus, the transformations of 1,2-diaminoethane phases involving the conformational dynamics affect the hydrogen-bonding geometry and molecular association in the crystal. The 1,2-diaminoethane:1,2-dihydroxyethane mixture has been separated by pressure-freezing, and a solid 1,2-diaminoethane crystal in liquid 1,2-dihyroxyethane has been obtained.

The crystal structure of benzene, C6H6, in situ pressure-frozen in phase I, has been determined by X-ray diffraction at 0.30, 0.70 and 1.10 GPa, and 296 K. The molecular aggregation within phase I is consistent with van der Waals contacts and electrostatic attraction of the positive net atomic charges at the H atoms with the negative net charges of the C atoms. The C—H...aromatic ring centre contacts are the most prominent feature of the two experimentaly determined benzene crystal structures in phases I and III, whereas no stacking of the molecules has been observed. This specific crystal packing is a likely reason for the exceptionally high polymerization pressure of benzene. The changes of molecular arrangement within phase I on elevating the pressure and lowering the temperature are analogous.

The crystalline form of magnetic spherules, retrieved from the Pleistocene and Holocene mineral and organic surface sediments at the Northern foreland of Morasko meteorite-impact site, have been determined. While the magnetite (Fe 3 O 4 ) composition of the spherules prevails, also hematite, maghemite and plagioclase crystalline inclusions have been observed. The magnetite form varies from amorphous, through fine powder, rough powder, holocrystalline to single crystals, as well as mixed forms, such as powder and holocrystalline, or amorphous and holocrystalline. The relieves on the surface of the spherules reflect the size and shape of the crystallites. The morphology of the spherules, their chemical composition and structure have been characterized and discussed in relation to the Morasko-Meteorite fall, and possible other cosmic, geological or anthropogenic origins.

The single crystal of 1,2-dichloroethane, C2H4Cl2wasin-situcrystallized in a Merrill-Bassett diamond-anvil cell, and its structure determined at 0.7 GPa and 280 K. The crystals are monoclinic, space groupP21/c. The C2H4Cl2molecules in thes-transconformation are located at the inversion centers. The —H2C—CH2—ethylene group is disordered in two sites, with equal occupancies, one rotated by 180° to the other about the Cl⋯Cl axis of the molecule. The crystal cohesion forces have been attributed mainly to Cl⋯Cl intermolecular interactions, and their role in the mechanism of the phase transition at 177 K has been analysed. It was found that the order-disorder phase transition in the structure of 1,2-dichloroethane is associated with the breaking of the Cl⋯Cl intermolecular interactions in the disordered phase. The crystal amorphization under non-homogeneous strain and subsequent transition to a new pressure-induced polymorph at 1.5 GPa has been observed.

Conformational disorder and inversions of the lactone ring induce structural transformations in the crystals of 6-hydroxy-4,4,5,7,8-pentamethyl-3,4-dihydrocoumarin, C14H18O3. The onset of ordering of the lactone ring at 300 K proceeds continuously, changes the space group from P21/m to P21/c and doubles the unit cell; the abrupt inversion of the lactone rings at 225 K changes the crystal translational symmetry in the (010) plane. The mechanism combining the molecular conformation and dynamics with the crystal structure, its symmetry, and phase transitions is presented.

High purity samples of a [Ag(pyrazine)(2)]S(2)O(8) complex were obtained using modified synthetic pathways. Di(pyrazine)silver(II) peroxydisulfate is sensitive to moisture forming [Ag(pyrazine)(2)](S(2)O(8))(H(2)O) hydrate which degrades over time yielding HSO(4)(-) derivatives and releasing oxygen. One polymorphic form of pyrazinium hydrogensulfate, β-(pyrazineH(+))(HSO(4)(-)), is found among the products of chemical decomposition together with unique [Ag(i)(pyrazine)](5)(H(2)O)(2)(HSO(4))(2)[H(SO(4))(2)]. Chemical degradation of [Ag(pyrazine)(2)]S(2)O(8) in the presence of trace amounts of moisture can explain the very low yield of wet synthesis (11-15%). Attempts have failed to obtain a mixed valence Ag(II)/Ag(I) pyrazine complex via partial chemical reduction of the [Ag(pyrazine)(2)]S(2)O(8) precursor with a variety of inorganic and organic reducing agents, or via controlled thermal decomposition. Thermal degradation of [Ag(pyrazine)(2)]S(2)O(8) containing occluded water proceeds at T90 °C via evolution of O(2); simultaneous release of pyrazine and SO(3) is observed during the next stages of thermal decomposition (120-285 °C), while Ag(2)SO(4) and Ag are obtained upon heating to 400-450 °C.

We describe the successful synthesis of the first mixed-cation (pseudoternary) amidoborane, Na[Li(NH(2)BH(3))(2)], with theoretical hydrogen capacity of 11.1 wt%. Na[Li(NH(2)BH(3))(2)] crystallizes triclinic (P1) with a = 5.0197(4) Å, b = 7.1203(7) Å, c = 8.9198(9) Å, α = 103.003(6)°, β = 102.200(5)°, γ = 103.575(5)°, and V = 289.98(5) Å(3) (Z = 2), as additionally confirmed by Density Functional Theory calculations. Its crystal structure is topologically different from those of its orthorhombic LiNH(2)BH(3) and NaNH(2)BH(3) constituents, with distinctly different coordination spheres of Li (3 N atoms and 1 hydride anion) and Na (6 hydride anions). Na[Li(NH(2)BH(3))(2)], which may be viewed as a product of a Lewis acid (LiNH(2)BH(3))/Lewis base (NaNH(2)BH(3)) reaction, is an important candidate for a novel lightweight hydrogen storage material. The title material decomposes at low temperature (with onset at 75 °C, 6.0% mass loss up to 110 °C, and an additional 3.0% up to 200 °C) while evolving hydrogen contaminated with ammonia.

At normal conditions 1,4-diazabicyclo[2.2.2]octane hydrobromide [C(6)H(13)N(2)](+.)Br(-) forms centrosymmetric crystals, space group Pm2, NH(+)...N hydrogen-bonded linear polycationic chains with disordered protons in the structure. As in H(2)O ice Ih, the protons in [C(6)H(13)N(2)](+.)Br(-) crystals remain disordered at low temperatures. Above 0.4 GPa the [C(6)H(13)N(2)](+.)Br(-) crystals transform into a new polar NH(+)...Br(-) hydrogen bonded complex, space group Cmc2. It has been crystallized in-situ in a diamond anvil cell and its structure determined by X-rays. The low-pressure triggering of this transformation indicates that it is a possible source of defects in the real structure at normal conditions, where, along with disproportionation defects, they can be responsible for anomalous dielectric properties, including relaxor-like behavior of NH...N hydrogen-bonded compounds.

As nowadays CCD detectors have become routine tools for X-ray diffraction structure determinations, they are increasingly available in X-ray laboratories and are also more often applied in high-pressure studies. For high-pressure experiments, when the sample crystal is enclosed in the diamond-anvil cell (DAC), the diffractometers equipped with CCD detectors have certain advantages and also some disadvantages, when compared to the diffractometers with point detectors. CCD-detectors are convenient, because they allow data collections to be carried out without prior determinations of the crystal orientation matrix (UB matrix). When a diffractometer with a point detector is used, the UB matrix must be determined before the data collection [1]. The determination of the UB matrix is often troublesome from a set of few reflections located with a point detector, while the CCD detector considerably facilitates this task: in most cases the reflections from the diamond anvils and of the DAC beryllium discs can be sorted out and then the unit cell of the sample crystal can be immediately found automatically from large data sets or by using procedures for visualizing the nodes of the reciprocal lattice; these procedures and 3dimmesional reflection profiles available from 2-D detectors are also very efficient for accessing the quality of the sample. Another advantage of CCD detectors is the speed of data collection, which is much quicker than the procedures of point-detector diffractometers measuring reflections one by one. CCD detectors also record all the reciprocal-space “volume”, not only the reflections. This information is indispensable for investigating phase transitions, structural disorder (diffused scattering), and for the inspection of background.

As part of an investigation into Ni(macrocycle) complexes as a new class of complex hydride hydrogen store catalysts, two isomers of the unusually stable nickel borohydride, Ni(cyclam)(BH4)2 (cyclam = 1,4,8,11-tetraazacyclotetradecane), have been isolated and characterised by means of single crystal X-ray diffraction, infrared spectroscopy, thermogravimetry and calorimetry. trans-Ni(cyclam)(BH4)2 crystallizes monoclinic (P21/c, a = 7.1397(5) A, b = 12.8109(7) A, c = 8.7041(5) A, β = 109.948(6)°, V = 748.36(8) A3, Z = 2); cis-Ni(cyclam)(BH4)2 crystallizes orthorhombic (Pnma, a = 14.4512(7) A, b = 9.4625(6) A, c = 11.7824(7) A, V = 1611.18(16) A3, Z = 4, with static disorder). The compounds were found to be considerably more thermally stable than the unchelated relative, Ni(BH4)2, with the onset of decomposition for the trans isomer at 170 °C, thus nearly 200 °C higher than the decomposition temperature of Ni(BH4)2. This spectacular stabilisation holds promise for related macrocycle complexes of late transition metals to be used as hydrogenation catalysts on an equal footing with their unligated early transition metal counterparts.

In the paper by Budzianowski & Katrusiak (2002) Acta Cryst. (2002), B58, 125–133 Figs. 5 and 8 on pages 131 and 132 were transposed while adjusting colour details indicated by the authors in the proof. Revised PDF versions of these pages are available in the online version of this erratum, which is available through Crystallography Journals Online.