Hydrogen‐bonded sheet structures in neutral,anionic and hydrated 6‐amino‐2‐(morpholin‐4‐yl)‐5‐nitrosopyrimidines

In each of 6‐amino‐3‐methyl‐2‐(morpholin‐4‐yl)‐5‐nitrosopyrimidin‐4(3H)‐one, C₉H₁₃N₅O₃, (I), morpholin‐4‐ium 4‐amino‐2‐(morpholin‐4‐yl)‐5‐nitroso‐6‐oxo‐1,6‐dihydropyrimidin‐1‐ide, C₄H₁₀NO⁺·C₈H₁₀N₅O₃⁻, (II), and 6‐amino‐2‐(morpholin‐4‐yl)‐5‐nitrosopyrimidin‐4(3H)‐one hemihydrate, C₈H₁₁N₅O₃·0.5H₂O, (III), the bond distances within the pyrimidine components are consistent with significant electronic polarization, which is most marked in (II) and least marked in (I). Despite the high level of substitution, the pyrimidine rings are all effectively planar, and in each of the pyrimidine components, there are intramolecular N—H...O hydrogen bonds. In each compound, the organic components are linked by multiple N—H...O hydrogen bonds to form sheets of widely differing construction, and in compound (III) adjacent sheets are linked by the water molecules, so forming a three‐dimensional hydrogen‐bonded framework. This study also contains the first direct geometric comparison between the electronic polarization in a neutral aminonitrosopyrimidine and that in its ring‐deprotonated conjugate anion in a metal‐free environment.     

Dynamics of the dispersion interaction in an energy transfer system

On the propagation of resonant radiation through an optically dense system, photon capture is commonly followed by one or more near-field transfers of the resulting optical excitation. The process invokes secondary changes to the local electronic environment, shifting the electromagnetic interactions between participant chromophores and producing modified intermolecular forces. From the theory it emerges that energy transfer, when it occurs between chromophores with electronically dissimilar properties, can itself generate significant changes in the intermolecular potentials. This report highlights specific effects that can be anticipated when laser light propagates across an interface between differentially absorbing components in a model energy transfer system.     

Study of tin amalgam mirrors by 119Sn Mössbauer spectroscopy and other analytical methods

From the beginning of the 16 ^th until the end of the 19 ^th century the most widely used mirrors consisted of a pane of glass backed with a reflecting layer of tin-mercury amalgam. They were made by sliding the glass pane over a tin foil covered with liquid mercury. After removal of the superfluous mercury, tin amalgam formed slowly at ambient temperature and yielded a reflecting layer adhering to the surface of the glass. Such mirrors often deteriorate in the course of time by oxidation of the tin in the amalgam to stannous or stannic oxide. ¹¹⁹Sn Mössbauer spectroscopy, scanning electron microscopy, micro-XRF and X-ray diffraction have been used to study this deterioration process. The studied specimens were a modern mirror made for the reconstruction of the Green Vault in Dresden in the early 2000s, two rather well preserved German mirrors from the 17 ^th and 19 ^th centuries and several strongly deteriorated specimens of Baroque mirrors from the south of Spain. The modern mirror consists mainly of a Sn_0.9Hg_0.1 amalgam with only 2 % of SnO₂. The older German mirrors showed more pronounced oxidation, containing 12 and 15 % of SnO₂, which did not noticeably impair their reflectivity. In the samples from the Spanish mirrors at best a few percent of metallic phase was left. The majority of the tin had oxidised to SnO₂, but between 8 and 20 % of the tin was present as SnO. X-ray diffraction yielded similar results and micro-XRF mapping using synchrotron radiation for excitation gave information on the distribution of Sn and Hg in the reflecting layer of the mirrors.     

Regioselective synthesis of novel polyfunctionally substituted pyrazolo[1,5-a]pyrimidines under solvent-free conditions

A series of 2-(pyrazolo[1,5-a]pyrimidin-5-yl)benzoic acids 5 has been prepared by a novel protocol that uses the fusion method between 5-amino-1H-pyrazoles 4 and 3-(3-oxo-2-benzofuran-1(3H)-ylidene)pentane-2,4-dione 3. The use of this novel protocol renders good to excellent yields along with short reaction times. In addition, this solvent-free cyclocondensation proceeds in a regiospecific fashion by intramolecular ring opening of the furane ring in a Michael-type reaction.     

2‐Amino‐4‐(4‐chlorophenyl)‐7,7‐dimethyl‐5‐oxo‐5,6,7,8‐tetrahydro‐4H‐chromene‐3‐carbonitrile

The supramolecular structure of the title compound, C₁₈H₁₇ClN₂O₂, is determined by the intersection of two chains formed by N—H⋯O and N—H⋯N hydrogen bonds, forming a two‐dimensional sheet.     

2‐Amino­benzimidazolium O‐ethyl malonate: eight independent N—H⋯O hydrogen bonds generate sheets

The title compound, C₇H₈N₃⁺·C₅H₇O₄⁻, crystallizes with Z′ = 2 in space group P2₁/c; eight independent N—H⋯O hydrogen bonds [H⋯O = 1.75–1.88 Å, N⋯O = 2.699 (2)–2.829 (2) Å and N—H⋯O = 147–179°] link the four inde­pendent ions into sheets.     

Study by grazing incident diffraction and surface spectroscopy of amalgams from ancient mirrors

Characterization of four amalgam surfaces, with different alteration degrees from Andalusia historical mirrors, has been carried out by grazing-incidence X-ray diffraction (GIXRD), and other spectroscopic techniques (SEM/EDX, XPS, and REELS). The combination of all these techniques allows determining the corrosion state of the amalgams. The results show that the amalgams are composed in all cases of a binary alloy of tin and mercury. As mercury has high vapour pressure at RT, it slowly segregates and eventually evaporates, it leaves finely divided particles of tin that easily can be oxidize, forming tin monoxide (SnO) and tin dioxide (SnO₂). In one of the samples, most of the amalgam remains unoxidized, since Hg_0.1Sn_0.9 and metallic Sn phases are the major components; in two other samples, Hg_0.1Sn_0.9 and Sn phases are not detected while SnO₂ and SnO phases appear. Finally, in the last studied sample, only SnO₂ phase is detected. The surface analyses of these samples by XPS show that, for most of them an unique chemical species (Sn⁴⁺) is found.      

2‐{2‐[2‐(4‐Methoxybenzoyl)ethylamino]‐4‐nitroanilino}ethyl acetate: complex sheets built from five independent hydrogen bonds

The molecules of the title compound, C₂₀H₂₃N₃O₆, are almost completely planar, apart from the H atoms bonded to tetrahedral C atoms. A combination of five hydrogen bonds, one of the N—H...O type and two each of the C—H...O and C—H...π(arene) types, links the molecules into complex sheets.     

Four differently substituted 2‐aryl‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepines: hydrogen‐bonded structures in one,two and three dimensions

In (2RS,4SR)‐7‐chloro‐2‐exo‐(2‐chloro‐6‐fluorophenyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C₁₆H₁₂Cl₂FNO, (I), molecules are linked into chains by a single C—H...π(arene) hydrogen bond. (2RS,4SR)‐2‐exo‐(2‐Chloro‐6‐fluorophenyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C₁₆H₁₃ClFNO, (II), is isomorphous with compound (I) but not strictly isostructural with it, as the hydrogen‐bonded chains in (II) are linked into sheets by an aromatic π–π stacking interaction. The molecules of (2RS,4SR)‐7‐methyl‐2‐exo‐(4‐methylphenyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C₁₈H₁₉NO, (III), are linked into sheets by a combination of C—H...N and C—H...π(arene) hydrogen bonds. (2S,4R)‐2‐exo‐(2‐Chlorophenyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C₁₆H₁₄ClNO, (IV), crystallizes as a single enantiomer and the molecules are linked into a three‐dimensional framework structure by a combination of one C—H...O hydrogen bond and three C—H...π(arene) hydrogen bonds.