2‐Amino‐4‐chloro‐6‐[N‐methyl‐N‐(4‐methylphenyl)amino]pyrimidine: formation versus fragmentation of hydrogen‐bonded chains of edge‐fused R22(8) rings in 4,6‐disubstituted 2‐aminopyrimidines

Molecules of the title compound, C₁₂H₁₃ClN₄, are linked by two independent N—H...N hydrogen bonds into a chain of edge‐fused R₂²(8) rings. The significance of this study lies in its attempt to rationalize the patterns of supramolecular aggregation in the title compound and in a range of analogous 4,6‐disubstituted 2‐aminopyrimidines.     

Thermal decomposition of sodium nitrite and sodium nitrate pre-adsorbed on TiO2 surfaces

The thermal decomposition of sodium nitrite or nitrate pre-adsorbed upon TiO₂ surfaces has been investigated by employing several techniques as infrared spectroscopy (IR) and temperature programmed desorption in conjunction with mass spectrometry analysis (TPD-MS) to study the features observed during these thermal decompositions. Differential thermal analysis (DTA) in combination with X-ray diffraction analysis (XRD) were used to investigate the possibility of a solid state chemical reaction between the solid products originated from the thermal decomposition of the pre-adsorbed species and the TiO₂. On the basis of our results, various characteristic features of these thermal decomposition reactions will be discussed.This work was supported by JUNTA DE ANDALUCIA (financial support for research groups/1990).     

Methyl 2‐methyl‐6‐methyl­thio‐1,3‐dioxo‐4‐[(2,3,4,6‐tetra‐O‐acetyl‐β‐d‐gluco­pyran­osyl)­amino]‐2,3‐di­hydro‐1H‐pyrrolo­[3,4‐c]­pyridine‐7‐carboxyl­ate

The title compound, C₂₅H₂₉N₃O₁₃S, has peripheral acetyl and carbo­methoxy groups which show disorder. The absolute structure, although known from the starting materials, was confirmed by the analysis. There are no intermolecular hydrogen bonds. This structure is of importance because it elucidates the pathway for hetero‐Diels–Alder reactions between di­methyl acetyl­enedi­carboxyl­ate and 6‐amino­pyridin‐4(3H)‐one derivatives catalyzed by tri­fluoro­acetic acid.     

Synthesis and Structure Elucidation of New Regioisomeric 2‐Alkylamino‐6‐aryl‐8,9‐dihydropyrimido[4,5‐b][1,4]diazepin‐4(7H)‐ones

Novel 2‐Alkylamino‐6‐aryl‐8,9‐dihydropyrimido[4,5‐b][1,4]diazepin‐4(7H)‐ones 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i , 5j , 5k , 5l , 5m , 5n , 5o were prepared regioselectively by the reaction of 2‐alkylamino‐5,6‐diaminopyrimidin‐4(3H)‐ones 3a , 3b , 3c and dimethylamino propiophenones (Mannich bases) 4a , 4b , 4c , 4d , 4e , 4f . The combination of conventional heating and microwave irradiation approaches provided the possibility of working with both stable and sensitive diaminopyrimidines by controlling parameters such as reaction rates, temperature, and power of irradiation. All products were fully characterized by detailed NMR measurements.     

Ring conformations and intermolecular interactions in two fused dibenzoazocines

5‐Acetyl‐2‐chloro‐8,11‐dimethyl‐5,6,11,12‐tetrahydrodibenzo[b,f]azocine, C₁₉H₂₀ClNO, (I), crystallizes as a single fully ordered isomer, but 14‐acetyl‐8,11‐dimethyl‐7,8,13,14‐tetrahydrobenzo[f]naphtho[1,2‐b]azocine–14‐acetyl‐8,9‐dimethyl‐7,8,13,14‐tetrahydrobenzo[f]naphtho[1,2‐b]azocine (74/26), C₂₃H₂₃NO, (II), exhibits threefold whole‐molecule disorder involving both configurational and structural isomers. In (I) and in the predominant form of (II), the azocine rings adopt very similar conformations, forming boat‐shaped rings having approximate twofold rotational symmetry. There are no direction‐specific intermolecular interactions in the crystal structure of (I), but the molecules of (II) are weakly linked into chains by an aromatic π–π stacking interaction. The compounds were made under green conditions using an acid‐catalysed cyclization process having very high atom utilization.     

Multiple dot-in-rod PbS/CdS heterostructures with high photoluminescence quantum yield in the near-infrared

Pb cations in PbS quantum rods made from CdS quantum rods by successive complete cationic exchange reactions are partially re-exchanged for Cd cations. Using STEM-HAADF, we show that this leads to the formation of unique multiple dot-in-rod PbS/CdS heteronanostructures, with a photoluminescence quantum yield of 45-55%. We argue that the formation of multiple dot-in-rods is related to the initial polycrystallinity of the PbS quantum rods, where each PbS crystallite transforms in a separate PbS/CdS dot-in-dot. Effective mass modeling indicates that electronic coupling between the different PbS conduction band states is feasible for the multiple dot-in-rod geometries obtained, while the hole states remain largely uncoupled.     

5‐Methyl‐N‐[2‐nitro‐4‐(trifluoromethyl)phenyl]‐1H‐pyrazole‐3‐amine: a chain of hydrogen‐bonded R22(6) and R22(16) rings

The molecular skeleton of the title compound, C₁₁H₉F₃N₄O₂, is almost planar and exhibits a polarized (charge‐separated) electronic structure in the nitroaniline portion. Molecules are linked by N—H...N and C—H...O hydrogen bonds to form a chain in which centrosymmetric R₂²(6) and R₂²(16) rings alternate.     

A chain of π‐stacked molecules in 4‐(2‐chlorophenyl)pyrrolo[1,2‐a]quinoxaline and a hydrogen‐bonded sheet in (4RS)‐4‐(1,3‐1,3‐benzodioxol‐6‐yl)‐4,5‐dihydropyrrolo[1,2‐a]quinoxaline

In the molecule of 4‐(2‐chlorophenyl)pyrrolo[1,2‐a]quinoxaline, C₁₇H₁₁ClN₂, (I), the bond lengths are consistent with electron delocalization in the two outer rings of the fused tricyclic system, with a localized double bond in the central ring. The molecules of (I) are linked into chains by a π–π stacking interaction. In (4RS)‐4‐(1,3‐benzodioxol‐6‐yl)‐4,5‐dihydropyrrolo[1,2‐a]quinoxaline, C₁₈H₁₄N₂O₂, (II), the central ring of the fused tricyclic system adopts a conformation intermediate between screw‐boat and half‐chair forms. A combination of N—H...O and C—H...π(arene) hydrogen bonds links the molecules of (II) into a sheet. Comparisons are made with related compounds.     

Dibenzylammonium hydrogen maleate and a redetermination at 120 K of bis(dibenzylamino)methane

In dibenzylammonium hydrogen maleate [or dibenzylammonium (2Z)‐3‐carboxyprop‐2‐enoate], C₁₄H₁₆N⁺·C₄H₃O₄⁻, (I), the anion contains a fairly short and nearly linear O—H...O hydrogen bond, with an O...·O distance of 2.4603 (16) Å, but with the H atom clearly offset from the mid‐point of the O...O vector. The counter‐ions in (I) are linked by two N—H...O hydrogen bonds to form C₂²(6) chains and these chains are weakly linked into sheets by a C—H...O hydrogen bond. Bis(dibenzylamino)methane, C₂₉H₃₀N₂, (II), crystallizes with two independent molecules lying across twofold rotation axes in the space group C2/c, and the molecules are conformationally chiral; there are no direction‐specific intermolecular interactions in the crystal structure of (II).