Photoisomerization of trans‐2‐[4′‐(Dimethylamino)styryl]benzothiazole

Photoreaction of trans‐2‐[4′‐(dimethylamino)styryl]benzothiazole (t‐DMASBT) under direct irradiation has been investigated in dioxane, chloroform, methanol and glycerol to understand the mechanism of photoisomerization. Contrary to an earlier report, isomerization takes place in all these solvents including glycerol. The results show that restriction on photoisomerization leads to the increase in fluorescence quantum yield in glycerol. The results are consistent with the theoretically simulated potential energy surface reported earlier using time‐dependent density functional theory (TDDFT) calculations. DFT calculations on cis isomers under isolated condition have suggested that cis‐B conformer is more stable than cis‐A conformer due to hydrogen‐bonding interaction. In the ground state, cis‐DMASBT is predominantly present as cis‐B. The fluorescence spectra of the irradiated t‐DMASBT suggested that photoisomerization follows not the adiabatic path as proposed by Saha et al., but the nonadiabatic path.     

A tetranuclear copper(II) cluster: bis(μ‐4‐chlorobenzoato‐κ2O:O′)(4‐chlorobenzoato‐κ2O,O′)(4‐chlorobenzoato‐κO)tetrakis(μ3‐2‐pyridylmethanolato‐κ4N,O:O:O)tetracopper(II)

The title compound, [Cu₄(C₇H₄ClO₂)₄(C₆H₆NO)₄], consists of isolated tetranuclear clusters, where the Cu²⁺ cations are five‐ and sixfold coordinated by O atoms from the 4‐chlorobenzoate anions and by pyridine N and methanolate O atoms from bidentate 2‐pyridylmethanolate ligands. While three Cu atoms are six‐coordinated by an NO₅ donor set forming distorted octahedra, the fourth Cu atom is five‐coordinated by an NO₄ donor set forming a distorted tetragonal–pyramidal coordination around the Cu atom. The nucleus is a deformed cubane‐like Cu₄O₄ structure, with Cu...Cu distances in the range 3.0266 (11)–3.5144 (13) Å.     

A novel dinuclear bismuth(III) coordination compound: bis(μ‐pyridine‐2,6‐dicarboxylato)‐κ4O2,N,O6:O6′;κ4O2:O2′,N,O6‐bis[(azido‐κN)(1,10‐phenanthroline‐κ2N,N′)bismuth(III)] tetrahydrate

A novel dinuclear bismuth(III) coordination compound, [Bi₂(C₇H₃NO₄)₂(N₃)₂(C₁₂H₈N₂)₂]·4H₂O, has been synthesized by an ionothermal method and characterized by elemental analysis, energy‐dispersive X‐ray spectroscopy, IR, X‐ray photoelectron spectroscopy and single‐crystal X‐ray diffraction. The molecular structure consists of one centrosymmetric dinuclear neutral fragment and four water molecules. Within the dinuclear fragment, each Bi^III centre is seven‐coordinated by three O atoms and four N atoms. The coordination geometry of each Bi^III atom is distorted pentagonal–bipyramidal (BiO₃N₄), with one azide N atom and one bridging carboxylate O atom located in axial positions. The carboxylate O atoms and water molecules are assembled via O—H...O hydrogen bonds, resulting in the formation of a three‐dimensional supramolecular structure. Two types of π–π stacking interactions are found, with centroid‐to‐centroid distances of 3.461 (4) and 3.641 (4) Å.     

Diaquabis(4‐fluorobenzoato‐κO)bis(nicotinamide‐κN)cobalt(II)

The title compound, [Co(C₇H₄FO₂)₂(C₆H₆N₂O)₂(H₂O)₂], is a three‐dimensional hydrogen‐bonded supramolecular complex. The Co^II ion resides on a centre of symmetry and is in an octahedral coordination environment comprising two pyridyl N atoms, two carboxylate O atoms and two O atoms from water molecules. Intermolecular N—H...O and O—H...O hydrogen bonds produce R₃²(6), R₂²(12) and R₂²(16) rings, which lead to two‐dimensional chains. An extensive three‐dimensional network of C—H...F, N—H...O and O—H...O hydrogen bonds and π–π interactions are responsible for crystal stabilization.     

(Z)‐5‐[4‐(Dimethylamino)benzylidene]‐2‐(piperidin‐1‐yl)‐1,3‐thiazolidin‐4(5H)‐one

The molecules of the title compound, C₁₇H₂₁N₃OS, are characterized by a wide C—C—C angle at the methine C atom linking the aryl and thiazolidine rings, associated with a short repulsive intramolecular S...H contact between atoms in these two rings. A single piperidine–arene C—H...π hydrogen bond links pairs of molecules into centrosymmetric dimers.     

Alkylations of N4‐(4‐Pyridyl)‐3,5‐di(2‐pyridyl)‐1,2,4‐triazole: First Observation of Room‐Temperature Rearrangement of an N4‐Substituted Triazole to the N1 Analogue

Attempts to use alkylation to introduce a positive charge at the nitrogen atom of the 4‐pyridyl ring in the bis(bidentate) triazole ligand N⁴‐(4‐pyridyl)‐3,5‐di(2‐pyridyl)‐1,2,4‐triazole ( pydpt ) were made to ascertain what effect a strongly electron‐withdrawing group would have on the magnetic properties of any subsequent iron(II) complexes. Alkylation of pydpt under relatively mild conditions led in some cases to unexpected rearrangement products. Specifically, when benzyl bromide is used as the alkylating agent, and the reaction is carried out in refluxing acetonitrile, the N⁴ substituent moves to the N¹ position. However, when the same reaction is performed in dichloromethane at room temperature, the rearrangement does not occur and the desired product containing an alkylated N⁴ substituent is obtained. Heating a pure sample of N⁴‐Bzpydpt?Br to reflux in MeCN resulted in clean conversion to N1Bzpydpt.Br . This is consistent with N4‐Bzpydpt.Br being the kinetic product whereas N1Bzpydpt.Br is the thermodynamic product. When methyl iodide is used as the alkylating agent, the N⁴ to N¹ rearrangement occurs even at room temperature, and at reflux pydpt is doubly alkylated. The observation of the lowest reported temperatures for an N⁴ to N¹ rearrangement is due to this particular rearrangement involving nucleophilic aromatic substitution: a possible mechanism for this transformation is suggested.     

Di‐μ‐acesulfamato‐κ3N,O:O;κ3O:N,O‐bis[(acesulfamato‐κ2N,O)bis(3‐methylpyridine)cadmium(II)]

In the structure of the title compound, [Cd₂(C₄H₄NO₄S)₂(C₆H₇N)₂], the dinuclear Cd^II complex is located on a twofold axis with two Cd²⁺ ions bridged by two oxide O atoms. Each Cd²⁺ ion is additionally coordinated in an equatorial plane by two N and three O atoms of the acesulfamate ligands and axially by two N atoms of the 3‐methylpyridine ligands, resulting in a distorted pentagonal bipyramidal coordination. We present here an example of a supramolecular assembly based on hydrogen bonds in a mixed‐ligand metal complex; intermolecular C—H...O hydrogen bonds give rise to R₄⁴(40) rings, which lead to one‐dimensional chains.     

Polymeric diaqua(μ2‐2,2′‐bipyrimidinyl‐κ4N1,N1′:N3,N3′)‐di‐μ3‐hydroxy‐bis(μ5‐benzene‐1,3,5‐tricarboxylato‐κ5O1:O2:O3:O3:O5)tetracobalt(II) dihydrate

The structure of the title compound, [Co₄(C₉H₃O₆)₂(OH)₂(C₈H₆N₄)(H₂O)₂]·2H₂O, contains three separate species, namely the μ₅‐bridging C₉H₃O₆^3? anion, the doubly chelating and therefore μ₂‐bridging C₈H₆N₄ ligand (bi­pyrimidine, BPM), and the dihydrated di­aqua­di­hydroxy tetranuclear cationic cluster, [Co₄(OH^?)₂(H₂O)₂]⁶⁺·2H₂O, which lies on a crystallographic centre of symmetry, as does the BPM ligand with, in this case, the centre of symmetry coincident with the midpoint of the C—C bond joining the six‐membered rings. Within the cation cluster, the Co atoms of one pair are five‐coordinate and those of the other six‐coordinate.     

{N‐[2‐(η5‐Cyclopentadienyl)ethyl]‐4‐toluenesulfonamido‐N,O}(tetrahydrofuran‐O)bis(trifluoromethanesulfonato‐O)titanium(II)

The title compound, [Ti(CF₃O₃S)₂(C₁₄H₁₅NO₂S)(C₄H₈O)], contains a unique ligand system in which the Ti ion is bound to the N and O atoms of a 2‐p‐toluene­sulfon­amide ligand, which is linked by an ethyl group to a coordinated cyclo­penta­diene moiety. The distorted octahedral geometry about the Ti ion is completed by two tri­fluoro­methane­sulfonate ligands and a tetra­hydro­furan mol­ecule. Comparison with related compounds shows that both the Ti—N and Ti—O bonds of the sulfon­amide, although longer than normal values, indicate significant bonding interactions.     

Bis(μ‐4‐chloro­benzoato‐κ2O:O)bis[(2‐aminopyridine‐κN)silver(I)]

The title compound, [Ag₂(C₇H₄ClO₂)₂(C₅H₆N₂)₂], lies about an inversion centre and the Ag atom is three‐coordinated by two O atoms and one N atom from three different ligands. The 4‐chloro­benzoate anion acts as a monodonor ligand, bridging two inversion‐related Ag atoms of the compound into a dimer. There are weak intermolecular N—H⋯O hydrogen bonds in the structure.     

The 4‐(Dimethylamino) benzaldehyde‐4‐ethylthiosemicarbazone as Ionophore for Mercury(II) Solid State Selective Electrode

Hg(II) has formed a soluble complex with 4‐(dimethylamino) benzaldehyde‐4‐ethylthiosemicarbazone (DMABET) in methanol with a molar ratio of mercury(II):DMABET of 1 : 4. The formation constant (K_f) and Gibbs free energy (?G) of the complex showed that the formation of the complex was favorable. The DMABET was investigated as ionophore for Hg(II)‐ion selective electrode (ISE). At optimum pH 1–5 the proposed Hg(II)‐ISE showed an almost Nernstian slope at 27.8±1 mV, with linear regression coefficient, R²=0.995 and a detection limit of 5×10^?6 M. There was no serious interference from silver(I) with selectivity coefficient 5.69×10^?3. The electrode life span was more than 3 months. It has been applied for real water sample analysis and the results were in good agreement with the standard method.     

A Fluorescent Blue Phosphazene Dye: Synthesis,Structure and Optical Properties of 1,6‐Bis(Dimethylamino)‐2,5,7,10‐Tetraazo‐1,6λ5‐Diphosphapyrene

Herein we report on the synthesis, structure, and optical properties of the fluorescent blue phosphazene dye 1,6‐bis(dimethylamino)‐2,5,7,10‐tetraazo‐1,6λ⁵‐diphosphapyrene, which was isolated as the unexpected product of the reaction between 1,4,5,8‐(tetraamino)naphthalene and [P(NMe₂)₃Br]Br. This dye, which turned out to be soluble in water and a range of organic solvents (including hexane, tetrahydrofuran / petroleum ether, acetonitrile, and ethanol), was structurally characterized by XRD. Its absorption as well as emission spectra and their sensitivity to pH variations were analyzed. The experimental work is complemented by quantum chemical calculations on the possible intermediate on the way to the isolated product and on its pK_a value.     

Tetrakis(μ‐benzoato‐κ2O:O)bis{[4‐(dimethylamino)pyridine‐κN1]copper(II)}

The title compound, [Cu₂(C₇H₅O₂)₄(C₇H₁₀N₂)₂], is a crystallographically centrosymmetric binuclear complex, with Cu atoms [Cu...Cu = 2.6982 (4) Å] bridged by four benzoate ligands. Each of the Cu atoms in this bunuclear copper(II) acetate hydrate analogue is present in an approximately square‐pyramidal environment, with four O atoms in a plane and the pyridine N atom at the apical site. Selected geometric parameters are compared with values for related tetrabenzoate complexes of copper(II).     

Two polymorphs of N1,N4‐bis(5‐hydroxypenta‐1,3‐diynyl)‐N1,N4‐diphenylbenzene‐1,4‐diamine

The title compound, C₂₈H₂₀N₂O₂, forms two conformational polymorphs, (I) and (II), where the molecular structures are similar except for the orientation of the two hydroxy groups. In (I), which was obtained by slow evaporation from chloroform, the two hydroxy groups have an anti conformation. The molecules form a sheet structure within the ac plane, where the hydroxy groups form zigzag hydrogen bonds. In (II), which was obtained by slow evaporation from acetonitrile, the two hydroxy groups have a syn conformation. The molecules form a double‐sheet structure within the ab plane, where the hydroxy groups form 4‐helix hydrogen bonds.     

catena‐Poly­[[di­aqua­cadmium(II)]‐μ‐5‐carboxyimidazole‐4‐carboxylato‐κ4N1,O5:O4,N3]

A new cadmium coordination polymer, [Cd(C₅H₂N₂O₄)(H₂O)₂]_n, possesses a one‐dimensional zigzag chain structure built from Cd^II centers bridged sequentially by pairs of O and N atoms of the 5‐carboxyimidazole‐4‐carboxylate ligand. The Cd^II center is in a distorted octahedral geometry, being coordinated by two O atoms from two coordinated water mol­ecules [Cd—O = 2.322 (7) and 2.364 (7) Å], and by two N atoms [Cd—N = 2.222 (6) and 2.232 (6) Å] and two carboxyl O atoms [Cd—O = 2.383 (6) and 2.414 (6) Å] from two 5‐carboxyimidazole‐4‐carboxylate ligands.     

{4‐[(Carbamimidoylhydrazono)methyl‐κ2N1,N4]‐5‐hydroxymethyl‐2‐methylpyridinium‐3‐olate‐κO}(methanol‐κO)copper(II) dinitrate

The title compound, [Cu(C₉H₁₃N₅O₂)(CH₄O)](NO₃)₂, consists of square‐planar cationic complex units where the Cu^II centre is coordinated by an N,N′,O‐tridentate pyridoxal–aminoguanidine Schiff base adduct and a methanol molecule. The tridentate ligand is a zwitterion exhibiting an almost planar conformation. The dihedral angles between the mean planes of the pyridoxal ring and the six‐ and five‐membered chelate rings are all less than 2.0°. The charge on the complex cation is neutralized by two nitrate counter‐ions. Extensive N—H...O and C—H...O hydrogen bonding connects these ionic species and leads to the formation of layers. The pyridoxal hydroxy groups are the only fragments that deviate significantly from the flat layer structure; these groups are involved in O—H...O hydrogen bonding, connecting the layers into a three‐dimensional crystal structure.     

catena‐Poly­[[(pyridin‐4‐ol‐κN)silver(I)]‐μ‐pyridin‐4‐olato‐κ2N:O]

The title complex, [Ag(C₅H₄NO)(C₅H₅NO)]_n, consists of a polymeric neutral chain involving both a neutral pyridin‐4‐ol ligand and a deprotonated pyridin‐4‐olate monoanion. The Ag^I atom shows a T‐shaped coordination geometry, defined by one N atom of the pyridin‐4‐ol and one O and one N atom of two independent pyridin‐4‐olate bridges; the N—Ag—N moiety is approximately linear. The polymeric chains are connected via strong O—H⋯O hydrogen bonds and offset π–π interactions into a three‐dimensional network.     

Bis(5‐hydroxy‐2‐hydroxy­methyl‐4‐pyrone‐κ2O4,O5)bis(2‐hydroxy­methyl‐5‐oxido‐4‐pyrone‐κ2O4,O5)­calcium(II) tetrahydrate

In the title compound, [Ca(C₆H₅O₄)₂(C₆H₆O₄)₂]·4H₂O, which is a kojic acid–Ca²⁺ complex, the Ca atom is on a twofold axis and is octacoordinated by O atoms from four pyrone ligand mol­ecules. The hydroxyl and ketone O atoms of each ligand form a five‐membered chelate ring with the Ca atom. The crystal structure is stabilized by partial stacking and O—H?O hydrogen bonds.