Metal-free enantiomorphic perovskite [dabcoH2]2+[H3O]+Br- 3 and its one-dimensional polar polymorph.

The structure and stoichiometry of a new metal-free and ammonium-free compound [dabcoH2]2+H3O+Br- 3 (where [dabcoH2]2+ = 1,4-di-aza-bicyclo-[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 ß, 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 ß. 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 ß. 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.

Comprehensive Characterisation of the Ketoprofen-ß-Cyclodextrin Inclusion Complex Using X-ray Techniques and NMR Spectroscopy.

Racemic ketoprofen (KP) and ß-cyclodextrin (ß-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 ß-CD in relation to KP, 10 and 75 times, respectively, while the sample obtained by method 3 contained equimolar amounts of ß-CD and KP. NMR results indicated that KP/ß-CD inclusion complexes were formed and the estimated binding constants were approximately 2400 M-1, showing that KP is quite strongly associated with ß-CD. On the other hand, the X-ray single-crystal technique in the solid state revealed that the (S)-KP/ß-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/ß-CD complex, only method 3 is suitable.

"Clicking" fragment leads to novel dual-binding cholinesterase inhibitors.

Cholinesterase inhibitors are potent therapeutics in the treatment of Alzheimer's disease. Among them, dual binding ligands have recently gained a lot of attention. We discovered novel dual-binding cholinesterase inhibitors, using "clickable" fragments, which bind to either catalytic active site (CAS) or peripheral anionic site (PAS) of the enzyme. Copper(I)-catalyzed azide-alkyne cycloaddition allowed to effectively synthesize a series of final heterodimers, and modeling and kinetic studies confirmed their ability to bind to both CAS and PAS. A potent acetylcholinesterase inhibitor with IC50 = 18 nM (compound 23g) was discovered. A target-guided approach to link fragments by the enzyme itself was tested using butyrylcholinesterase.

Some mechanistic aspects regarding the Suzuki-Miyaura reaction between selected ortho-substituted phenylboronic acids and 3,4,5-tribromo-2,6-dimethylpyridine.

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.

High-Pressure Behavior of Silver Fluorides up to 40 GPa.

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.

Ag2S2O8 meets AgSO4: the second example of metal-ligand redox isomerism among inorganic systems.

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 PbS2 which adopts two polymorphic forms corresponding to Pb(iv)(S2-)2 and Pb(ii)(S22-). Here we have taken advantage of metathetic reactions using salts of weakly coordinating anions and we have prepared for the first time Ag(i)2S2O8, silver(i) peroxydisulphate. The title compound crystallizes in the non-centrosymmetric Cc space group with partial disorder of the anionic sublattice. Ag(i)2S2O8 is a highly thermally unstable diamagnetic and colourless valence isomer of the antiferromagnetic and black Ag(ii)SO4, described by us in the past.

Thermal and chemical decomposition of di(pyrazine)silver(II) peroxydisulfate and unusual crystal structure of a Ag(I) by-product.

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, ß-(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 T > 90 °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.

Crystal and electronic structure, lattice dynamics and thermal properties of Ag(I)(SO3)R (R = F, CF3) Lewis acids in the solid state.

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 ß = 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.

Na[Li(NH2BH3)2]--the first mixed-cation amidoborane with unusual crystal structure.

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)°, ß = 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.

Structural polymorphism of pyrazinium hydrogen sulfate: extending chemistry of the pyrazinium salts with small anions.

Two polymorphs (alpha, beta) 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 alpha-polymorph (P2(1)2(1)2(1)) 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 beta-form (P1) 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 polar P1 form of the beta-polymorph with an unusually high dipole moment.

Anomalous protonic-glass evolution from ordered phase in NH...N hydrogen-bonded dabcoHBF4 ferroelectric.

Dielectric properties, spontaneous polarization, and phase transitions of the NH+...N bonded ferroelectric dabcoHBF4 (i.e., 1,4-diazabicyclo[2.2.2]octane tetrafluoroborate, [C6H13N2]+ BF4-) have been related to one-dimensional arrangement of the cations and to their conformational properties. The onset of conformational transformation lowering the symmetry of the cations, rearrangement of the anions, and proton disordering in NH+...N hydrogen bonds, linking the cations into linear chains, lead to a ferroelectric-ferroelectric phase transition at T23 = 153 K. A weak coupling between the protonic and anionic sites in dabcoHBF4 results in the formation of distinct phase-diagram regions: the high-temperature paraelectric phase with disordered protons, the intermediate ferroelectric phase with the protons ordered, and the low-temperature ferroelectric phase where the protons become disordered again. The lowest temperature phase remains ferroelectric owing to the ionic displacements, while the protons assume the glass state. In this phase the H+ transfers involve local formation of neutral, monocationic, and dicationic species. Such an anomalous formation of protonic glass state from the ordered phase depends on the subtle structural features pertaining to the proton transfers in bistable hydrogen bonds. In paraelectric phase I, between the mp and T12 = 374 K, the anions are orientationally disordered, the protons are disordered in the hydrogen bonds and the cations rotate about the [z] direction; in ferroelectric phase II below T12, the protons and cations order, the dabco cations assume a planar conformation of ethylene bridges, and the anions exhibit a residual temperature-dependent gradual ordering (two 80:20 occupied sites of the anion are still observed at 332 K); and in ferroelectric phase III below T23, the cations assume left- and right-twisted propeller conformations and the anions are ordered but the protons become disordered in the hydrogen bonds.

Competing hydrogen-bonding patterns and phase transitions of 1,2-diaminoethane at varied temperature and pressure.

1,2-diaminoethane has been in-situ pressure- and temperature-frozen; apart from two known low-temperature phases, Ialpha and II, three new phases, Ibeta, Igamma 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 Ialpha), at 0.3 and 1.1 GPa (phase Ibeta), at 1.5 GPa (phase Igamma), and at 0.2, 0.3 and 0.5 GPa (phase III). All these phases are monoclinic, space group P2(1)/c, but the unit-cell dimension of phases Ialpha and III are very different at 296 K: aIalpha=5.078 (5), bIalpha=7.204 (8), cIalpha=5.528 (20) A, betaIalpha=115.2 (2) degrees at 0.15 GPa, and aIII=5.10 (3), bIII=5.212 (2), cIII=7.262 (12) A, betaIII=111.6 (4) degrees 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 Ialpha and Ibeta at 0.2 GPa, which can be attributed to a damping process of the NH2 group rotations. In phase Igamma 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.

Pressure tuning between NH...N hydrogen-bonded ice analogue and NH...Br polar dabcoHBr complexes.

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.

Pressure-frozen benzene I revisited.

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 experimentally 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.

Coupling of the lactone-ring conformation with crystal symmetry in 6-hydroxy-4,4,5,7,8-pentamethyl-3,4-dihydrocoumarin.

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 P2(1)/m to P2(1)/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.