Preparation,characterization and luminescence‐sensing properties of two ZnII MOFs with mixed 5‐amino‐2,4,6‐tribromoisophthalic acid and bipyridyl‐type ligands

The bromo‐substituted aromatic dicarboxylic acid 5‐amino‐2,4,6‐tribromoisophthalic acid (H₂ATBIP), in the presence of the N‐donor flexible bipyridyl‐type ligands 1,3‐bis(pyridin‐4‐yl)propane (bpp) and N,N′‐bis(pyridin‐4‐ylmethyl)oxalamide (4‐bpme) and Zn^II ions, was used as an O‐donor ligand to assemble two novel luminescent metal–organic frameworks (MOFs), namely poly[[(μ‐5‐amino‐2,4,6‐tribromoisophthalato‐κ²O¹:O³)[μ‐1,3‐bis(pyridin‐4‐yl)propane‐κ²N:N′]zinc(II)] dimethylformamide monosolvate], {[Zn(C₈H₂Br₃NO₄)(C₁₃H₁₄N₂)]·C₃H₇NO}_n, ( 1 ), and poly[[(μ‐5‐amino‐2,4,6‐tribromoisophthalato‐κ²O¹:O³)diaqua[μ‐N,N′‐bis(pyridin‐4‐ylmethyl)oxalamide‐κ²N:N′]zinc(II)] monohydrate], {[Zn(C₈H₂Br₃NO₄)(C₁₄H₁₄N₄O₂)(H₂O)₂]·H₂O}_n, ( 2 ), using the solution evaporation method. Both ( 1 ) and ( 2 ) were characterized by FT–IR spectroscopy, elemental analysis (EA), solid‐state diffuse‐reflectance UV–Vis spectroscopy, and powder and single‐crystal X‐ray diffraction analysis. Complex ( 1 ) shows a two‐dimensional (2D) corrugated layer simplified as a 2D (4,4) topological network. The supramolecular interactions (π–π stacking, hydrogen bonding and C—Br…Br halogen bonding) play significant roles in the formation of an extended three‐dimensional (3D) supramolecular network of ( 1 ). Complex ( 2 ) crystallizes in the chiral space group P2₁2₁2₁ and exhibits a novel 3D homochiral framework, showing a diamond‐like topology with Schläfli symbol 6⁶. The homochirality of ( 2 ) is further confirmed by the solid‐state circular dichroism (CD) spectrum. The second harmonic generation (SHG) property of ( 2 ) was also investigated. The hydrogen and C—Br…Br/O halogen bonding further stabilize the framework of ( 2 ). The central Zn^II ions in ( 1 ) and ( 2 ) show tetrahedral and octahedral coordination geometries, respectively. The coordinated and uncoordinated water molecules in ( 2 ) could be removed selectively upon heating. Most importantly, ( 1 ) and ( 2 ) show rapid and highly sensitive sensing for a large pool of nitroaromatic explosives (NAEs).     

Two new CoII coordination polymers with multifunctional 5‐amino‐2,4,6‐tribromoisophthalic acid and flexible isomeric bis(imidazole) ligands: preparation,crystal structure and characterization

Two new Co^II coordination polymers (CPs), namely, catena‐poly[[[(5‐amino‐2,4,6‐tribromobenzene‐1,3‐dicarboxylato‐κO)aquacobalt(II)]‐bis[μ‐1,3‐bis(imidazol‐1‐ylmethyl)benzene‐κ²N:N′]] 4.75‐hydrate], {[Co(C₈H₂Br₃NO₄)(C₁₄H₁₄N₄)₂(H₂O)]·4.75H₂O}_n, (1), and poly[(μ‐5‐amino‐2,4,6‐tribromobenzene‐1,3‐dicarboxylato‐κ²O¹:O³)[μ‐1,2‐bis(imidazol‐1‐ylmethyl)benzene‐κ²N:N′]cobalt(II)], [Co(C₈H₂Br₃NO₄)(C₁₄H₁₄N₄)]_n, (2), have been synthesized successfully by the assembly of multifunctional 5‐amino‐2,4,6‐tribromoisophthalic acid (H₂ATBIP) and Co^II ions in the presence of the flexible isomeric bis(imidazole) ligands 1,3‐bis(imidazol‐1‐ylmethyl)benzene (mbix) and 1,2‐bis(imidazol‐1‐ylmethyl)benzene (obix). The isomeric mbix and obix ligands have a big influence on the structures of CPs (1) and (2). CP (1) is composed of chains of nanometre‐sized elliptical rings, in which the Co^II atom exhibits a distorted octahedral coordination geometry and ATBIP²⁻ acts as a monodentate ligand. Two adjacent chains are interlinked by π–π stacking interactions and hydrogen bonds, resulting in a supramolecular double chain. Hydrogen‐bonded R₈⁶(16) rings extend adjacent supramolecular double chains into a two‐dimensional supramolecular layer. Halogen bonding and a hydrogen‐bonded R₄²(8) ring further link the two‐dimensional supramolecular layers, leading to the formation of a three‐dimensional supramolecular network. The Co^II ion in CP (2) is tetracoordinated, exhibiting a distorted tetrahedral configuration. The ATBIP²⁻ ligand exhibits a bis(monodentate) coordination bridging mode, linking adjacent Co^II ions into zigzag chains, which are further bridged by the auxiliary bridging obix ligand, resulting in a two‐dimensional (4,4) topological network. Interlayer hydrogen and halogen–halogen bonding further extend the two‐dimensional layers into a three‐dimensional supramolecular network. A detailed analysis of the solid‐state UV–Vis–NIR diffuse‐reflectance spectra of (1) and (2) indicates that a wide optical band gap exists in both (1) and (2). CP (1) exhibits an irreversible dehydration–rehydration behaviour.     

Synthesis and characterization of two one‐dimensional CdII coordination polymers (CPs) with 5‐amino‐2,4,6‐tribromoisophthalic acid and flexible N‐donor bipyridyl ligands

The bromo‐substituted aromatic dicarboxylic acid 5‐amino‐2,4,6‐tribromoisophthalic acid (H₂ATBIP) was used to assemble with Cd^II ions in the presence of the N‐donor flexible bipyridyl ligands 3,3′‐(diazene‐1,2‐diyl)dipyridine (mzpy) and 1,3‐bis(pyridin‐3‐ylmethyl)urea (3bpmu), leading to the formation of two chain coordination polymers by adopting solution methods, namely, catena‐poly[[[triaqua(5‐amino‐2,4,6‐tribromoisophthalato‐κO)cadmium(II)]‐μ‐3,3′‐(diazene‐1,2‐diyl)dipyridine‐κ²N¹:N^1′] dihydrate], {[Cd(C₈H₂Br₃NO₄)(C₁₀H₈N₄)(H₂O)₃]·2H₂O}_n or {[Cd(ATBIP)(mzpy)(H₂O)₃]·2H₂O}_n, ( 1 ), and catena‐poly[[[tetraaquacadmium(II)]‐μ‐1,3‐bis(pyridin‐3‐ylmethyl)urea‐κ²N¹:N^1′‐[diaquabis(5‐amino‐2,4,6‐tribromoisophthalato‐κO)cadmium(II)]‐μ‐1,3‐bis(pyridin‐3‐ylmethyl)urea‐κ²N¹:N^1′] octahydrate], {[Cd(C₈H₂Br₃NO₄)(C₁₂H₁₂N₄O)(H₂O)₃]·4H₂O}_n or {[Cd(ATBIP)(3bpmu)(H₂O)₃]·4H₂O}_n, ( 2 ). Both complexes were characterized by FT–IR spectroscopic analysis, thermogravimetric analysis (TGA), solid‐state diffuse reflectance UV–Vis spectroscopic analysis, and single‐crystal and powder X‐ray diffraction analysis (PXRD). The mzpy and 3bpmu ligands bridge the Cd^II metal centres in ( 1 ) and ( 2 ) into one‐dimensional chains, and the ATBIP²⁻ ligands show a monodentate coordination to the Cd^II centres in both coordination polymers. A discrete water tetramer exists in ( 1 ). Within the chains of ( 1 ) and ( 2 ), there are halogen bonds between adjacent ATBIP²⁻ and mzpy or 3bpmu ligands, as well as hydrogen bonds between the ATBIP²⁻ ligands and the coordinated water molecules. With the aid of weak interactions, the structures of ( 1 ) and ( 2 ) are further extended into three‐dimensional supramolecular networks. An analysis of the solid‐state diffuse reflectance UV–Vis spectra of ( 1 ) and ( 2 ) indicates that a wide indirect band gap exists in both complexes. Complexes ( 1 ) and ( 2 ) exhibit irreversible and reversible dehydration–rehydration behaviours, respectively, and the solid‐state fluorescence properties of both complexes have been studied.     

Reaction of Amidrazones with Diaminomaleonitrile: Synthesis of 4‐Amino‐5‐Iminopyrazoles

Diaminomaleonitrile and N‐arylbenzamidrazones reacted together to give 4‐amino‐5‐iminopyrazoles. A probable reaction mechanism involves firstly removal of ammonia, followed by addition and cylization of the hydrazino‐N ² of amidrazone to the nitrile group in diaminomaleonitrile. The structure of the obtained products was proved by IR, mass, NMR spectra and elemental analyses.     

2‐Amino‐5‐iodopyridinium bromide hemihydrate and 2‐amino‐5‐iodopyridinium chloride monohydrate

The hydrobromide and hydrochloride salts of 2‐amino‐5‐iodopyridine were prepared from aqueous solutions. The hydrobromide salt, C₅H₆IN₂⁺·Br⁻·0.5H₂O, crystallizes as a hemihydrate, and exhibits hydrogen bonding and π‐stacking which stabilize the crystal structure. The hydrochloride salt, C₅H₆IN₂⁺·Cl⁻·H₂O·0.375HCl, crystallized as the hydrate and exhibits similar hydrogen bonding and π‐stacking in the lattice. The most interesting feature of the hydrochloride salt is the presence of an additional fractional HCl molecule which introduces disorder in the location of the water molecule. The additional proton from the fractional HCl molecule is accounted for by the presence of a partial hydronium ion on one of the water sites.     

Synthesis of 5‐Acyl‐2‐Amino‐3‐Cyanothiophenes: Chemistry and Fluorescent Properties

Independent of the substrate structure and reaction conditions, 3‐amino‐2‐cyanothioacrylamides, which contain two active electrophilic centers, were shown to interact with various active halo methylene compounds under mild conditions to afford 5‐acyl‐2‐amino‐3‐cyanothiophenes as the only products. A series of new polyfunctional thiophene derivatives with a rare combination of functionalities were synthesized, and their photophysical properties were experimentally and computationally investigated. The calculated electronic characteristics of the ground and excited states were compared to the experimental results, which provided a good understanding of the relationship between the optoelectronic properties and the molecular structures. After absorption of light quanta, the systems populate an intramolecular charge‐transfer (ICT) Franck–Condon state, and emission occurs from a twisted ICT minimum.     

2‐Amino‐5‐(2‐pyridyl)‐thiadiazole as Bidentate Ligand

The amino substituted bidentate chelating ligand 2‐amino‐5‐(2‐pyridyl)‐1,3,4‐thiadiazole (H₂ L ) was used to prepare 3:1‐type coordination compounds of iron(II), cobalt(II) and nickel(II). In the iron(II) perchlorate complex [Fe^II(H₂ L )₃](ClO₄)₂·0.6MeOH·0.9H₂O a 1:1 mixture of mer and fac isomers is present whereas [Fe^II(H₂ L )₃](BF₄)₂·MeOH·H₂O, [Co^II(H₂ L )₃](ClO₄)₂·2H₂O and [Ni^II(H₂ L )₃](ClO₄)₂·MeOH·H₂O feature merely mer derivatives. Moessbauer spectroscopy and variable temperature magnetic measurements revealed the [Fe^II(H₂ L )₃]²⁺ complex core to exist in the low‐spin state, whereas the [Co^II(H₂ L )₃]²⁺ complex core resides in its high‐spin state, even at very low temperatures.     

3‐Amino‐1,2,4‐triazine

In the crystal structure of 3‐amino‐1,2,4‐triazine, C₃H₄N₄, the mol­ecules form hydrogen‐bonded chains that are almost parallel to the b axis (3.2°), and which are inclined to the a and c axes by ～21 and ～69°, respectively. The distortion of the 1,2,4‐triazine ring in the crystal is compared with gas‐phase ab initio molecular‐orbital calculations.     

Selenium-assisted nucleic acid crystallography: use of phosphoroselenoates for MAD phasing of a DNA structure

The combination of synchrotron radiation and a variety of atoms or ions (either covalently attached to the biomolecule prior to crystallization or soaked into crystals) that serve as anomalous scatterers constitutes a powerful tool in the X-ray crystallographer's repertoire of structure determination techniques. Phosphoroselenoates in which one of the nonbridging phosphate oxygens in the backbone is replaced by selenium offer a simplified means for introducing an anomalous scatterer into oligonucleotides by conventional solid-phase synthesis. Unlike other methods that are used to derivatize DNA or RNA by covalent attachment of a heavy atom (i.e., bromine at the C5 position of pyrimidines), tedious synthesis of specialized nucleosides is not required. Introduction of selenium is readily accomplished in solid-phase oligonucleotide synthesis by replacing the standard oxidation agent with a solution of potassium selenocyanide. This results in a diastereomeric mixture of phosphoroselenoates that can be separated by strong anion-exchange HPLC. As a test case, all 10 DNA hexamers of the sequence CGCGCG containing a single phosphoroselenoate linkage (PSe) were prepared. Crystals were grown for a subset of them, and the structure of [d(C(PSe)GCGCG)](2) was determined by the multiwavelength anomalous dispersion technique and refined to 1.1 A resolution.     

5‐Amido‐ and 5‐Amino‐Substituted Epoxyisoindolo[2,1‐a]tetrahydroquinolines and 10‐Carboxylic Acids: Their Synthesis and Reactivity

The interactions between 4‐R‐substituted 2‐furyl‐1,2,3,4‐tetrahydroquinolines (synthesized by the Povarov reaction) and a number of alkenes have been investigated. Maleic, dibromomaleic, dichloromaleic, and citraconic anhydrides, as well as acryloyl, methacryloyl, crotonyl, and cynnamoyl chlorides were used as alkene components. It was shown that the initial N‐acylation of the tetrahydroquinolines was followed by a spontaneous [4+2]‐cycloaddition of an N‐acryloyl substituent to the furan ring. It was established that the intramolecular Diels–Alder reaction of furans is reversible, occurs stereoselectively as exo‐addition, and led to target epoxyisoindolo[2,1‐a]tetrahydroquinolines with moderate yields. Oxidation and aromatization of the synthesized products were carried out.     

2,4,6‐Trifluorobenzonitrile

The title compound, C₇H₂F₃N, contains three crystallographically independent molecules in the crystal structure; two of these molecules have symmetry m and the third has symmetry mm. Each independent molecule forms a planar or approximately planar layer with its own kind. There are three different types of interlayer contacts, two of which are similar to each other, while the third is distinctly different. The packing within the layers is similar to that found in 2,5‐ and 3,6‐difluorobenzonitrile, with weak C—H...N interactions holding the molecules in the layers. The remarkable feature of this structure is the presence of more than one type of interlayer interaction.     

2‐Amino‐5‐methyl­pyridinium (2‐amino‐5‐methyl­pyridine)trichloro­zincate(II)

The title compound, (C₆H₉N₂)[ZnCl₃(C₆H₈N₂)], consists of one 2‐amino‐5‐methyl­pyridinium cation and one (2‐amino‐5‐methyl­pyridine)trichloro­zincate(II) anion, which are held together by N—H·Cl hydrogen bonds and π–π inter­actions. The cation and the pyridine ligand show similar geometric features, except for the N—C bond lengths. Mol­ecules of the title compound are connected by N—H·Cl hydrogen bonds to form chiral chains; these chains are associated further by C—H·Cl hydrogen bonds to form layers, which are in turn linked by π–π inter­actions.     

2‐Amino‐5‐(3,4‐dimethoxybenzylidene)‐1‐methylimidazol‐4(5H)‐one N,N‐dimethylformamide monosolvate

The crystal structure of the title compound, C₁₃H₁₅N₃O₃·C₃H₇NO, was determined as part of a larger project focusing on creatinine derivatives as potential pharmaceuticals. The molecule is essentially planar, in part because of intramolecular hydrogen bonding. Inversion‐related pairs of molecules result from intermolecular hydrogen bonding. The π systems of 2‐amino‐5‐(3,4‐dimethoxybenzylidene)‐1‐methylimidazol‐4(5H)‐one and an inversion‐related molecule overlap slightly, indicating a small amount of π–π stacking. Bond lengths, angles and torsion angles are consistent with similar structures, except in the imidazolone ring near the doubly bonded C atom, where significant differences occur.     

The Synthesis of 3‐Amino‐pyrazine‐2‐carbohydrazide and 3‐Amino‐N′‐methylpyrazine‐2‐carbohydrazide Derivatives

In research of new biologically active compounds, the reactions of amino‐pyrazin‐2‐hydrazide and methylhydrazide with isothiocyanates, aromatic aldehydes, ketones, CS₂, and formic acid were made. New thiosemicarbazides, 1,3,4‐thiadiazoles, 1,3,4‐oxadiazoles, and 1,2,4‐triazoles were obtained. New 4‐oxopteridine derivative 26 was also synthesized.     

2‐Amino‐4‐(4‐pyridyl)­pyrimidine and the 1:1 adduct with 4‐amino­benzoic acid

The structure of the title compound, C₉H₈N₄, comprises non‐planar mol­ecules that associate via pyrimidine N—H?N dimer R(8) hydrogen‐bonding associations [N?N 3.1870 (17) Å] and form linear hydrogen‐bonded chains via a pyrimidine N—H?N(pyridyl) interaction [N?N 3.0295 (19) Å]. The dihedral angle between the two rings is 24.57 (5)°. The structure of the 1:1 adduct with 4‐amino­benzoic acid, C₉H₈N₄·C₇H₇NO₂, exhibits a hydrogen‐bond­ing network involving COOH?N(pyridyl) [O?N 2.6406 (17) Å], pyrimidine N—H?N [N?N 3.0737 (19) and 3.1755 (18) Å] and acid N—H?O interactions [N?O 3.0609 (17) and 2.981 (2) Å]. The dihedral angle between the two linked rings of the base is 38.49 (6)° and the carboxyl­ic acid group binds to the stronger base group in contrast to the (less basic) complementary hydrogen‐bonding site.