Synthesis of some new Pyridine‐based Heterocyclic Compounds with Anticipated Antitumor Activity

A novel class of 5‐amino‐N′‐(1‐(pyridin‐4‐yl)ethylidene)‐1H‐pyrazole‐4‐carbohydrazides and 8‐(pyridin‐4‐yl)pyrido[2,3‐d][1,2,4]triazolo[4,3‐a]pyrimidin‐5(1H)‐ones was synthesized from reaction of 2‐cyano‐N′‐(1‐(pyridin‐4‐yl)ethylidene)‐acetohydrazide and 7‐(pyridin‐4‐yl)‐2‐thioxo‐2,3‐dihydropyrido[2,3‐d]pyrimidin‐4(1H)‐one with the appropriate hydrazonoyl halides. Moreover, 2‐cyano‐N′‐(1‐(pyridin‐4‐yl)‐ethylidene)‐acetohydrazide was used for the synthesis of 2‐cyano‐N′‐(1‐(pyridin‐4‐yl)ethylidene)‐acrylohydrazides and 2‐oxo‐2‐(2‐(1‐(pyridin‐4‐yl)ethylidene)‐hydrazinyl)‐acetohydrazonoyl cyanides. The structures of the newly prepared compounds were confirmed by both elemental and spectral analyses as well as by alternate synthesis. The anticancer activities of the prepared compounds were screened against the hepatocellular carcinoma (HepG2) cell line, and the results showed that most of the compounds exhibit considerable activities.     

Three novel topologically different metal–organic frameworks built from 3‐nitro‐4‐(pyridin‐4‐yl)benzoic acid

The design and synthesis of metal–organic frameworks (MOFs) have attracted much interest due to the intriguing diversity of their architectures and topologies. However, building MOFs with different topological structures from the same ligand is still a challenge. Using 3‐nitro‐4‐(pyridin‐4‐yl)benzoic acid (HL) as a new ligand, three novel MOFs, namely poly[[(N,N‐dimethylformamide‐κO)bis[μ₂‐3‐nitro‐4‐(pyridin‐4‐yl)benzoato‐κ³O,O′:N]cadmium(II)] N,N‐dimethylformamide monosolvate methanol monosolvate], {[Cd(C₁₂H₇N₂O₄)₂(C₃H₇NO)]·C₃H₇NO·CH₃OH}_n, ( 1 ), poly[[(μ₂‐acetato‐κ²O:O′)[μ₃‐3‐nitro‐4‐(pyridin‐4‐yl)benzoato‐κ³O:O′:N]bis[μ₃‐3‐nitro‐4‐(pyridin‐4‐yl)benzoato‐κ⁴O,O′:O′:N]dicadmium(II)] N,N‐dimethylacetamide disolvate monohydrate], {[Cd₂(C₁₂H₇N₂O₄)₃(CH₃CO₂)]·2C₄H₉NO·H₂O}_n, ( 2 ), and catena‐poly[[[diaquanickel(II)]‐bis[μ₂‐3‐nitro‐4‐(pyridin‐4‐yl)benzoato‐κ²O:N]] N,N‐dimethylacetamide disolvate], {[Ni(C₁₂H₇N₂O₄)₂(H₂O)₂]·2C₄H₉NO}_n, ( 3 ), have been prepared. Single‐crystal structure analysis shows that the Cd^II atom in MOF ( 1 ) has a distorted pentagonal bipyramidal [CdN₂O₅] coordination geometry. The [CdN₂O₅] units as 4‐connected nodes are interconnected by L^? ligands to form a fourfold interpenetrating three‐dimensional (3D) framework with a dia topology. In MOF ( 2 ), there are two crystallographically different Cd^II ions showing a distorted pentagonal bipyramidal [CdNO₆] and a distorted octahedral [CdN₂O₄] coordination geometry, respectively. Two Cd^II ions are connected by three carboxylate groups to form a binuclear [Cd₂(COO)₃] cluster. Each binuclear cluster as a 6‐connected node is further linked by acetate groups and L^? ligands to produce a non‐interpenetrating 3D framework with a pcu topology. MOF ( 3 ) contains two crystallographically distinct Ni^II ions on special positions. Each Ni^II ion adopts an elongated octahedral [NiN₂O₄] geometry. Each Ni^II ion as a 4‐connected node is linked by L^? ligands to generate a two‐dimensional network with an sql topology, which is further stabilized by two types of intermolecular OW—HW…O hydrogen bonds to form a 3D supramolecular framework. MOFs ( 1 )–( 3 ) were also characterized by powder X‐ray diffraction, IR spectroscopy and thermogravimetic analysis. Furthermore, the solid‐state photoluminescence of HL and MOFs ( 1 ) and ( 2 ) have been investigated. The photoluminescence of MOFs ( 1 ) and ( 2 ) are enhanced and red‐shifted with respect to free HL. The gas adsorption investigation of MOF ( 2 ) indicates a good separation selectivity (71) of CO₂/N₂ at 273 K (i.e. the amount of CO₂ adsorption is 71 times higher than N₂ at the same pressure).     

Three AgI,CuI and CdII coordination polymers based on the new asymmetrical ligand 2‐{4‐[(1H‐imidazol‐1‐yl)methyl]phenyl}‐5‐(pyridin‐4‐yl)‐1,3,4‐oxadiazole: syntheses,characterization and emission properties

The new asymmetrical organic ligand 2‐{4‐[(1H‐imidazol‐1‐yl)methyl]phenyl}‐5‐(pyridin‐4‐yl)‐1,3,4‐oxadiazole ( L , C₁₇H₁₃N₅O), containing pyridine and imidazole terminal groups, as well as potential oxdiazole coordination sites, was designed and synthesized. The coordination chemistry of L with soft Ag^I, Cu^I and Cd^II metal ions was investigated and three new coordination polymers (CPs), namely, catena‐poly[[silver(I)‐μ‐2‐{4‐[(1H‐imidazol‐1‐yl)methyl]phenyl}‐5‐(pyridin‐4‐yl)‐1,3,4‐oxadiazole] hexafluoridophosphate], {[Ag( L )]PF₆}_n, catena‐poly[[copper(I)‐di‐μ‐iodido‐copper(I)‐bis(μ‐2‐{4‐[(1H‐imidazol‐1‐yl)methyl]phenyl}‐5‐(pyridin‐4‐yl)‐1,3,4‐oxadiazole)] 1,4‐dioxane monosolvate], {[Cu₂I₂( L )₂]·C₄H₈O₂}_n, and catena‐poly[[[dinitratocopper(II)]‐bis(μ‐2‐{4‐[(1H‐imidazol‐1‐yl)methyl]phenyl}‐5‐(pyridin‐4‐yl)‐1,3,4‐oxadiazole)]–methanol–water (1/1/0.65)], {[Cd( L )₂(NO₃)₂]·2CH₄O·0.65H₂O}_n, were obtained. The experimental results show that ligand L coordinates easily with linear Ag^I, tetrahedral Cu^I and octahedral Cd^II metal atoms to form one‐dimensional polymeric structures. The intermediate oxadiazole ring does not participate in the coordination interactions with the metal ions. In all three CPs, weak π–π interactions between the nearly coplanar pyridine, oxadiazole and benzene rings play an important role in the packing of the polymeric chains.     

Structural comparison of group 7 tricarbonyl complexes of 2‐{[2‐(1H‐imidazol‐4‐yl)ethyl]iminomethyl}‐5‐methylphenolate

Two tricarbonyl complexes of rhenium(I) and manganese(I) coordinated by the ligand 2‐{[2‐(1H‐imidazol‐4‐yl)ethyl]iminomethyl}‐5‐methylphenolate are reported, viz. fac‐tricarbonyl(2‐{[2‐(1H‐imidazol‐4‐yl‐κN³)ethyl]iminomethyl‐κN}‐5‐methylphenolato‐κO)rhenium(I) methanol monosolvate, [Re(C₁₆H₁₄N₃O₄)(CO)₃]·CH₃OH, (I), and fac‐tricarbonyl(2‐{[2‐(1H‐imidazol‐4‐yl‐κN³)ethyl]iminomethyl‐κN}‐5‐methylphenolato‐κO)manganese(I), fac‐[Mn(C₁₆H₁₄N₃O₄)(CO)₃], (II), display facial coordination in a distorted octahedral environment. The crystal structure of (I) is stabilized by O—H...O, N—H...O and C—H...O hydrogen‐bond interactions, while that of (II) is stabilized by N—H...O hydrogen‐bond interactions only. These interactions result in two‐dimensional networks and π–π stacking for both structures.     

Synthesis and characterization of a cadmium(II)–organic supramolecular coordination compound based on the multifunctional 2‐amino‐5‐sulfobenzoic acid ligand

Much attention has been paid by chemists to the construction of supramolecular coordination compounds based on the multifunctional ligand 5‐sulfosalicylic acid (H₃SSA) due to the structural and biological interest of these compounds. However, no coordination compounds have been reported for the multifunctional amino‐substituted sulfobenzoate ligand 2‐amino‐5‐sulfobenzoic acid (H₂asba). We expected that H₂asba could be a suitable building block for the assembly of supramolecular networks due to its interesting structural characteristics. The reaction of cadmium(II) nitrate with H₂asba in the presence of the auxiliary flexible dipyridylamide ligand N,N′‐bis[(pyridin‐4‐yl)methyl]oxamide (4bpme) under ambient conditions formed a new mixed‐ligand coordination compound, namely bis(3‐amino‐4‐carboxybenzenesulfonato‐κO¹)diaquabis{N,N′‐bis[(pyridin‐4‐yl)methyl]oxamide‐κN}cadmium(II)–N,N′‐bis[(pyridin‐4‐yl)methyl]oxamide–water (1/1/4), [Cd(C₇H₆NO₅S)₂(C₁₄H₁₄N₄O₂)₂(H₂O)₂]·C₁₄H₁₄N₄O₂·4H₂O, (1), which was characterized by single‐crystal and powder X‐ray diffraction analysis (PXRD), FT–IR spectroscopy, thermogravimetric analysis (TG), and UV–Vis and photoluminescence spectroscopic analyses in the solid state. The central Cd^II atom in (1) occupies a special position on a centre of inversion and exhibits a slightly distorted octahedral geometry, being coordinated by two N atoms from two monodentate 4bpme ligands, four O atoms from two monodentate 4‐amino‐3‐carboxybenzenesulfonate (Hasba⁻) ligands and two coordinated water molecules. Interestingly, complex (1) further extends into a threefold polycatenated 0D→2D (0D is zero‐dimensional and 2D is two‐dimensional) interpenetrated supramolecular two‐dimensional (4,4) layer through intermolecular hydrogen bonding. The interlayer hydrogen bonding further links adjacent threefold polycatenated two‐dimensional layers into a three‐dimensional network. The optical properties of complex (1) indicate that it may be used as a potential indirect band gap semiconductor material. Complex (1) exhibits an irreversible dehydration–rehydration behaviour. The fluorescence properties have also been investigated in the solid state at room temperature.     

Controllable assembly of a three‐dimensional metal–organic supramolecular framework displaying hydrogen‐bonding and π–π stacking interactions

The complex poly[[aqua(μ₂‐phthalato‐κ²O¹:O²){μ₃‐2‐[3‐(pyridin‐2‐yl)‐1H‐pyrazol‐1‐yl]acetato‐κ⁴N²,N³:O:O′}{μ₂‐2‐[3‐(pyridin‐2‐yl)‐1H‐pyrazol‐1‐yl]acetato‐κ³N²,N³:O}dizinc(II)] dihydrate], {[Zn₂(C₁₀H₈N₃O₂)₂(C₈H₄O₄)(H₂O)]·2H₂O}_n, has been prepared by solvothermal reaction of 2‐[3‐(pyridin‐2‐yl)‐1H‐pyrazol‐1‐yl]acetonitrile (PPAN) with zinc(II). Under hydrothermal conditions, PPAN is hydrolyzed to 2‐[3‐(pyridin‐2‐yl)‐1H‐pyrazol‐1‐yl]acetate (PPAA⁻). The structure determination reveals that the complex is a one‐dimensional double chain containing cationic [Zn₄(PPAA)₄]⁴⁺ structural units, which are further extended by bridging phthalate ligands. The one‐dimensional chains are extended into a three‐dimensional supramolecular architecture via hydrogen‐bonding and π–π stacking interactions.     

A one‐dimensional lead(II) coordination polymer with terminal and bridging 5‐carboxy‐2‐(pyridin‐3‐yl)‐1H‐imidazole‐4‐carboxylate ligands

In the coordination polymer catena‐poly[[[diaqua[5‐carboxy‐2‐(pyridin‐3‐yl)‐1H‐imidazole‐4‐carboxylato‐κ²N³,O⁴]lead(II)]‐μ‐5‐carboxy‐2‐(pyridin‐3‐yl)‐1H‐imidazole‐4‐carboxylato‐κ³N³,O⁴:N²] dihydrate], {[Pb(C₁₀H₆N₃O₄)(H₂O)₂]·2H₂O}_n, the two 5‐carboxy‐2‐(pyridin‐3‐yl)‐1H‐imidazole‐4‐carboxylate ligands have different coordination modes, one being terminal and the other bridging. The bridging ligand links Pb^II cations into one‐dimensional coordination polymer chains. The structure is also stabilized by intra‐ and interchain π–π stacking interactions between the pyridine rings, resulting in the formation of a two‐dimensional network. Extensive hydrogen‐bonding interactions lead to the formation of a three‐dimensional supramolecular network.     

Two isomorphous ZnII/CoII complexes with tri‐tert‐butoxysilanethiol and histamine,and (4‐hydroxymethyl‐1H‐imidazole‐κN)bis(tri‐tert‐butoxysilanethiolato‐κ2O,S)zinc(II)

The complexes [2‐(1H‐imidazol‐4‐yl‐κN³)ethylamine‐κN]bis(tri‐tert‐butoxysilanethiolato‐κS)cobalt(II), [Co(C₁₂H₂₇O₃SSi)₂(C₅H₉N₃)], and [2‐(1H‐imidazol‐4‐yl‐κN³)ethylamine‐κN]bis(tri‐tert‐butoxysilanethiolato‐κS)zinc(II), [Zn(C₁₂H₂₇O₃SSi)₂(C₅H₉N₃)], are isomorphous. The central Zn^II/Co^II ions are surrounded by two S atoms from the tri‐tert‐butoxysilanethiolate ligand and by two N atoms from the chelating histamine ligand in a distorted tetrahedral geometry, with two intramolecular N—H...O hydrogen‐bonding interactions between the histamine NH₂ groups and tert‐butoxy O atoms. Molecules of the complexes are joined into dimers via two intermolecular bifurcated N—H...(S,O) hydrogen bonds. The Zn^II atom in [(1H‐imidazol‐4‐yl‐κN³)methanol]bis(tri‐tert‐butoxysilanethiolato‐κ²O,S)zinc(II), [Zn(C₁₂H₂₇O₃SSi)₂(C₄H₆N₂O)], is five‐coordinated by two O and two S atoms from the O,S‐chelating silanethiolate ligand and by one N atom from (1H‐imidazol‐4‐yl)methanol; the hydroxy group forms an intramolecular hydrogen bond with sulfur. Molecules of this complex pack as zigzag chains linked by N—H...O hydrogen bonds. These structures provide reference details for cysteine‐ and histidine‐ligated metal centers in proteins.     

CdII and CoII coordination polymers constructed from benzene‐1,4‐dicarboxylic acid and 2‐(pyridin‐3‐yl)‐1H‐benzimidazole ligands

In poly[aqua(μ₃‐benzene‐1,4‐dicarboxylato‐κ⁵O¹,O^1′:O¹:O⁴,O^4′)[2‐(pyridin‐3‐yl‐κN)‐1H‐benzimidazole]cadmium(II)], [Cd(C₈H₄O₄)(C₁₂H₉N₃)(H₂O)]_n, (I), each Cd^II ion is seven‐coordinated by the pyridine N atom from a 2‐(pyridin‐3‐yl)benzimidazole (3‐PyBIm) ligand, five O atoms from three benzene‐1,4‐dicarboxylate (1,4‐bdc) ligands and one O atom from a coordinated water molecule. The complex forms an extended two‐dimensional carboxylate layer structure, which is further extended into a three‐dimensional network by hydrogen‐bonding interactions. In catena‐poly[[diaquabis[2‐(pyridin‐3‐yl‐κN)‐1H‐benzimidazole]cobalt(II)]‐μ₂‐benzene‐1,4‐dicarboxylato‐κ²O¹:O⁴], [Co(C₈H₄O₄)(C₁₂H₉N₃)₂(H₂O)₂]_n, (II), each Co^II ion is six‐coordinated by two pyridine N atoms from two 3‐PyBIm ligands, two O atoms from two 1,4‐bdc ligands and two O atoms from two coordinated water molecules. The complex forms a one‐dimensional chain‐like coordination polymer and is further assembled by hydrogen‐bonding interactions to form a three‐dimensional network.     

Oxidative degradation of the organometallic iron(II) complex [Fe{bis[3‐(pyridin‐2‐yl)‐1H‐imidazol‐1‐yl]methane}(MeCN)(PMe3)](PF6)2: structure of the ligand decomposition product trapped via coordination to iron(II)

Iron is of interest as a catalyst because of its established use in the Haber–Bosch process and because of its high abundance and low toxicity. Nitrogen‐heterocyclic carbenes (NHC) are important ligands in homogeneous catalysis and iron–NHC complexes have attracted increasing attention in recent years but still face problems in terms of stability under oxidative conditions. The structure of the iron(II) complex [1,1′‐bis(pyridin‐2‐yl)‐2,2‐bi(1H‐imidazole)‐κN³][3,3′‐bis(pyridin‐2‐yl‐κN)‐1,1′‐methanediylbi(1H‐imidazol‐2‐yl‐κC²)](trimethylphosphane‐κP)iron(II) bis(hexafluoridophosphate), [Fe(C₁₇H₁₄N₆)(C₁₆H₁₂N₆)(C₃H₉P)](PF₆)₂, features coordination by an organic decomposition product of a tetradentate NHC ligand in an axial position. The decomposition product, a C—C‐coupled biimidazole, is trapped by coordination to still‐intact iron(II) complexes. Insights into the structural features of the organic decomposition products might help to improve the stability of oxidation catalysts under harsh conditions.     

Two cobalt(II) supramolecular isomers based on N,N′‐bis(pyridin‐3‐yl)oxalamide induced by the molecular orientation of lattice DMF molecules

Supramolecular isomerism for coordination networks refers to the existence of different architectures having the same building blocks and identical stoichiometries. For a given building block, different arrangements can lead to the formation of a series of supramolecular isomers. Two one‐dimensional Co^II coordination polymers based on N,N′‐bis(pyridin‐3‐yl)oxalamide (BPO), both catena‐poly[[[dichloridocobalt(II)]‐bis[μ‐N,N′‐bis(pyridin‐3‐yl)oxalamide‐κ²N:N′]] dimethylformamide disolvate], {[CoCl₂(C₁₂H₁₀N₄O₂)₂]·2C₃H₇NO}_n, have been assembled by the solvothermal method. Single‐crystal X‐ray diffraction analyses reveal that the two compounds are supramolecular isomers, the isomerism being induced by the orientation of the dimethylformamide (DMF) molecules in the crystal lattice.     

Polymorphism of 3‐(5‐phenyl‐1,3,4‐oxadiazol‐2‐yl)‐ and 3‐[5‐(pyridin‐4‐yl)‐1,3,4‐oxadiazol‐2‐yl]‐2H‐chromen‐2‐ones

This study of 3‐(5‐phenyl‐1,3,4‐oxadiazol‐2‐yl)‐2H‐chromen‐2‐one, C₁₇H₁₀N₂O₃, 1 , and 3‐[5‐(pyridin‐4‐yl)‐1,3,4‐oxadiazol‐2‐yl]‐2H‐chromen‐2‐one, C₁₆H₉N₃O₃, 2 , was performed on the assumption of the potential anticancer activity of the compounds. Three polymorphic structures for 1 and two polymorphic structures for 2 have been studied thoroughly. The strongest intermolecular interaction is stacking of the `head‐to‐head' type in all the studied crystals. The polymorphic structures of 1 differ with respect to the intermolecular interactions between stacked columns. Two of the polymorphs have a columnar or double columnar type of crystal organization, while the third polymorphic structure can be classified as columnar‐layered. The difference between the two structures of 2 is less pronounced. Both crystals can be considered as having very similar arrangements of neighbouring columns. The formation of polymorphic modifications is caused by a subtle balance of very weak intermolecular interactions and packing differences can be identified only using an analysis based on a study of the pairwise interaction energies.     

Structural studies of (prop‐2‐en‐1‐yl)bis[(pyridin‐2‐yl)methylidene]amine hetero‐scorpionate copper complexes

The structures of five compounds consisting of (prop‐2‐en‐1‐yl)bis[(pyridin‐2‐yl)methylidene]amine complexed with copper in both the Cu^I and Cu^II oxidation states are presented, namely chlorido{(prop‐2‐en‐1‐yl)bis[(pyridin‐2‐yl)methylidene]amine‐κ³N,N′,N′′}copper(I) 0.18‐hydrate, [CuCl(C₁₅H₁₇N₃)]·0.18H₂O, (1), catena‐poly[[copper(I)‐μ₂‐(prop‐2‐en‐1‐yl)bis[(pyridin‐2‐yl)methylidene]amine‐κ⁵N,N′,N′′:C²,C³] perchlorate acetonitrile monosolvate], {[Cu(C₁₅H₁₇N₃)]ClO₄·CH₃CN}_n, (2), dichlorido{(prop‐2‐en‐1‐yl)bis[(pyridin‐2‐yl)methylidene]amine‐κ³N,N′,N′′}copper(II) dichloromethane monosolvate, [CuCl₂(C₁₅H₁₇N₃)]·CH₂Cl₂, (3), chlorido{(prop‐2‐en‐1‐yl)bis[(pyridin‐2‐yl)methylidene]amine‐κ³N,N′,N′′}copper(II) perchlorate, [CuCl(C₁₅H₁₇N₃)]ClO₄, (4), and di‐μ‐chlorido‐bis({(prop‐2‐en‐1‐yl)bis[(pyridin‐2‐yl)methylidene]amine‐κ³N,N′,N′′}copper(II)) bis(tetraphenylborate), [Cu₂Cl₂(C₁₅H₁₇N₃)₂][(C₆H₅)₄B]₂, (5). Systematic variation of the anion from a coordinating chloride to a noncoordinating perchlorate for two Cu^I complexes results in either a discrete molecular species, as in (1), or a one‐dimensional chain structure, as in (2). In complex (1), there are two crystallographically independent molecules in the asymmetric unit. Complex (2) consists of the Cu^I atom coordinated by the amine and pyridyl N atoms of one ligand and by the vinyl moiety of another unit related by the crystallographic screw axis, yielding a one‐dimensional chain parallel to the crystallographic b axis. Three complexes with Cu^II show that varying the anion composition from two chlorides, to a chloride and a perchlorate to a chloride and a tetraphenylborate results in discrete molecular species, as in (3) and (4), or a bridged bis‐μ‐chlorido complex, as in (5). Complex (3) shows two strongly bound Cl atoms, while complex (4) has one strongly bound Cl atom and a weaker coordination by one perchlorate O atom. The large noncoordinating tetraphenylborate anion in complex (5) results in the core‐bridged Cu₂Cl₂ moiety.     

Mononuclear and three‐dimensional metal complexes based on a multidentate hydrazone ligand

A potentially pentadentate hydrazone ligand, N′‐[1‐(pyrazin‐2‐yl)ethylidene]nicotinohydrazide (HL), was prepared from the condensation reaction of nicotinohydrazide and acetylpyrazine. Reactions of HL with MnCl₂, Mn(CH₃COO)₂ and Cd(CH₃COO)₂ afforded three metal complexes, namely dichlorido{N′‐[1‐(pyrazin‐2‐yl‐κN¹)ethylidene]nicotinohydrazide‐κ²N′,O}manganese(II), [MnCl₂(C₁₂H₁₁N₅O)], (I), bis{N′‐[1‐(pyrazin‐2‐yl‐κN¹)ethylidene]nicotinohydrazidato‐κ²N′,O]manganese(II), [Mn(C₁₂H₁₀N₅O)₂], (II), and poly[[(acetato‐κ²O,O′){μ₃‐N′‐[1‐(pyrazin‐2‐yl‐κ²N¹:N⁴)ethylidene]nicotinohydrazidato‐κ³N′,O:N¹}cadmium(II)] chloroform disolvate], {[Cd(C₁₂H₁₀N₅O)(CH₃COO)]·2CHCl₃}_n, (III), respectively. Complex (I) has a mononuclear structure, the Mn^II centre adopting a distorted square‐pyramidal coordination. Complex (II) also has a mononuclear structure, with the Mn^II centre occupying a special position (C₂ symmetry) and adopting a distorted octahedral coordination environment, which is defined by two O atoms and four N atoms from two N′‐[1‐(pyrazin‐2‐yl)ethylidene]nicotinohydrazidate (L⁻) ligands related via a crystallographic twofold axis. Complex (III) features a unique three‐dimensional network with rectangular channels, and the L⁻ ligand also serves as a counter‐anion. The coordination geometry of the Cd^II centre is pentagonal bipyramidal. This study demonstrates that HL, which can act as either a neutral or a mono‐anionic ligand, is useful in the construction of interesting metal–organic compounds.     

Two nickel(II) bis[(pyridin‐2‐yl)methyl]amine complexes with homophthalic and benzene‐1,2,4,5‐tetracarboxylic acids

Two new Ni^II complexes involving the ancillary ligand bis[(pyridin‐2‐yl)methyl]amine (bpma) and two different carboxylate ligands, i.e. homophthalate [hph; systematic name: 2‐(2‐carboxylatophenyl)acetate] and benzene‐1,2,4,5‐tetracarboxylate (btc), namely catena‐poly[[aqua{bis[(pyridin‐2‐yl)methyl]amine‐κ³N,N′,N′′}nickel(II)]‐μ‐2‐(2‐carboxylatophenyl)aceteto‐κ²O:O′], [Ni(C₉H₆O₄)(C₁₂H₁₃N₃)(H₂O)]_n, and (μ‐benzene‐1,2,4,5‐tetracarboxylato‐κ⁴O¹,O²:O⁴,O⁵)bis(aqua{bis[(pyridin‐2‐yl)methyl]amine‐κ³N,N′,N′′}nickel(II)) bis(triaqua{bis[(pyridin‐2‐yl)methyl]amine‐κ³N,N′,N′′}nickel(II)) benzene‐1,2,4,5‐tetracarboxylate hexahydrate, [Ni₂(C₁₀H₂O₈)(C₁₂H₁₃N₃)₂(H₂O)₂]·[Ni(C₁₂H₁₃N₃)(H₂O)₃]₂(C₁₀H₂O₈)·6H₂O, (II), are presented. Compound (I) is a one‐dimensional polymer with hph acting as a bridging ligand and with the chains linked by weak C—H...O interactions. The structure of compound (II) is much more complex, with two independent Ni^II centres having different environments, one of them as part of centrosymmetric [Ni(bpma)(H₂O)]₂(btc) dinuclear complexes and the other in mononuclear [Ni(bpma)(H₂O)₃]²⁺ cations which (in a 2:1 ratio) provide charge balance for btc⁴⁻ anions. A profuse hydrogen‐bonding scheme, where both coordinated and crystal water molecules play a crucial role, provides the supramolecular linkage of the different groups.     

Novel one‐ and two‐dimensional ZnII coordination polymers based on a versatile 3,6‐bis(pyridin‐4‐yl)phenanthrene‐9,10‐dione ligand

Two new Zn^II coordination polymers, namely, catena‐poly[[dibromidozinc(II)]‐μ‐[3,6‐bis(pyridin‐4‐yl)phenanthrene‐9,10‐dione‐κ²N:N′]], [ZnBr₂(C₂₄H₁₄N₂O₂)]_n, (1), and poly[[bromido[μ₃‐10‐hydroxy‐3,6‐bis(pyridin‐4‐yl)phenanthren‐9‐olato‐κ³N:N′:O⁹]zinc(II)] hemihydrate], {[ZnBr(C₂₄H₁₅N₂O₂)]·0.5H₂O}_n, (2), have been synthesized through hydrothermal reaction of ZnBr₂ and a 60° angular phenanthrenedione‐based linker, i.e. 3,6‐bis(pyridin‐4‐yl)phenanthrene‐9,10‐dione, in different solvent systems. Single‐crystal analysis reveals that polymer (1) features one‐dimensional zigzag chains connected by weak C—H...π and π–π interactions to form a two‐dimensional network. The two‐dimensional networks are further stacked in an ABAB fashion along the a axis through C—H...O hydrogen bonds. Layers A and B comprise left‐ and right‐handed helical chains, respectively. Coordination polymer (2) displays a wave‐like two‐dimensional layered structure with helical chains. In this compound, there are two opposite helical –Zn–HL– chains [HL is 10‐hydroxy‐3,6‐bis(pyridin‐4‐yl)phenanthren‐9‐olate] in adjacent layers. The layers are packed in an ABAB sequence and are further connected through O—H...Br and O—H...O hydrogen‐bond interactions to form a three‐dimensional framework. In (1) and (2), the mutidentate L and HL ligands exhibits different coordination modes.     

A novel two‐dimensional metal–organic supramolecular framework including π–π stacking and hydrogen‐bond interactions

[μ‐N,N′‐Bis(pyridin‐3‐yl)benzene‐1,4‐dicarboxamide‐<!?show [forcelb]><!?tlsb=0.12pt>1:2κ²N:N′]bis{[N,N′‐bis(pyridin‐3‐yl)benzene‐1,4‐dicarboxamide‐κN]diiodidomercury(II)}, [Hg₂I₄(C₁₈H₁₄N₄O₂)₃], is an S‐shaped dinuclear molecule, composed of two HgI₂ units and three N,N′‐bis(pyridin‐3‐yl)benzene‐1,4‐dicarboxamide (L) ligands. The central L ligand is centrosymmetric and coordinated to two Hg^II cations via two pyridine N atoms, in a syn–syn conformation. The two terminal L ligands are monodentate, with one uncoordinated pyridine N atom, and each adopts a syn–anti conformation. The HgI₂ units show highly distorted tetrahedral (sawhorse) geometry, as the Hg^II centres lie only 0.34 (2) or 0.32 (2) Å from the planes defined by the I and pyridine N atoms. Supramolecular interactions, thermal stability and solid‐state luminescence properties were also measured.     

2,6‐Bis(azaindole)pyridine: reactivity with iron(III) and copper(II) salts

1‐[6‐(1H‐Pyrrolo[2,3‐b]pyridin‐1‐yl)pyridin‐2‐yl]‐1H‐pyrrolo[2,3‐b]pyridin‐7‐ium tetrachloridoferrate(III), (C₁₉H₁₄N₅)[FeCl₄], (II), and [2,6‐bis(1H‐pyrrolo[2,3‐b]pyridin‐1‐yl‐κN⁷)pyridine‐κN]bis(nitrato‐κO)copper(II), [Cu(NO₃)₂(C₁₉H₁₃N₅)], (III), were prepared by self‐assembly from FeCl₃·6H₂O or Cu(NO₃)₂·3H₂O and 2,6‐bis(1H‐pyrrolo[2,3‐b]pyridin‐1‐yl)pyridine [commonly called 2,6‐bis(azaindole)pyridine, bap], C₁₉H₁₃N₅, (I). Compound (I) crystallizes with Z′ = 2 in the P space group, with both independent molecules adopting a trans–trans conformation. Compound (II) is a salt complex with weak C—H...Cl interactions giving rise to a zigzag network with π‐stacking down the a axis. Complex (III) lies across a twofold rotation axis in the C2/c space group. The Cu^II center in (III) has an N₃O₂ trigonal–bipyramidal environment. The nitrate ligand coordinates in a monodentate fashion, while the bap ligand adopts a twisted tridentate binding mode. C—H...O interactions give rise to a ribbon motif.     

Four NiII complexes with the new cyclam–methylimidazole ligand 1‐[(1‐methyl‐1H‐imidazol‐2‐yl)methyl]‐1,4,8,11‐tetraazacyclotetradecane

Although it has not proved possible to crystallize the newly prepared cyclam–methylimidazole ligand 1‐[(1‐methyl‐1H‐imidazol‐2‐yl)methyl]‐1,4,8,11‐tetraazacyclotetradecane (L^Im1), the trans and cis isomers of an Ni^II complex, namely trans‐aqua{1‐[(1‐methyl‐1H‐imidazol‐2‐yl)methyl]‐1,4,8,11‐tetraazacyclotetradecane}nickel(II) bis(perchlorate) monohydrate, [Ni(C₁₅H₃₀N₆)(H₂O)](ClO₄)₂·H₂O, (1), and cis‐aqua{1‐[(1‐methyl‐1H‐imidazol‐2‐yl)methyl]‐1,4,8,11‐tetraazacyclotetradecane}nickel(II) bis(perchlorate), [Ni(C₁₅H₃₀N₆)(H₂O)](ClO₄)₂, (2), have been prepared and structurally characterized. At different stages of the crystallization and thermal treatment from which (1) and (2) were obtained, a further two compounds were isolated in crystalline form and their structures also analysed, namely trans‐{1‐[(1‐methyl‐1H‐imidazol‐2‐yl)methyl]‐1,4,8,11‐tetraazacyclotetradecane}(perchlorato)nickel(II) perchlorate, [Ni(ClO₄)(C₁₅H₃₀N₆)]ClO₄, (3), and cis‐{1,8‐bis[(1‐methyl‐1H‐imidazol‐2‐yl)methyl]‐1,4,8,11‐tetraazacyclotetradecane}nickel(II) bis(perchlorate) 0.24‐hydrate, [Ni(C₂₀H₃₆N₆)](ClO₄)₂·0.24H₂O, (4); the 1,8‐bis[(1‐methyl‐1H‐imidazol‐2‐yl)methyl]‐1,4,8,11‐tetraazacyclotetradecane ligand is a minor side product, probably formed in trace amounts in the synthesis of L^Im1. The configurations of the cyclam macrocycles in the complexes have been analysed and the structures are compared with analogues from the literature.     

Design and synthesis of methyl 2‐{[4‐phenyl‐5‐(pyridin‐2‐yl)‐4H‐1,2,4‐triazol‐3‐yl]sulfanyl}acetate (phpy2NS) as a ligand for complexes of Group 12 elements: structural assessment and hydrogen‐bonded supramolecular assembly analysis

The reaction of 2‐cyanopyridine with N‐phenylthiosemicarbazide afforded 2‐[amino(pyridin‐2‐yl)methylidene]‐N‐phenylhydrazine‐1‐carbothioamide (Ham4ph) and crystals of 4‐phenyl‐5‐(pyridin‐2‐yl)‐2,4‐dihydro‐3H‐1,2,4‐triazole‐3‐thione (pyph3NS, 1 , C₁₃H₁₀N₄S). Crystals of methyl 2‐{[4‐phenyl‐5‐(pyridin‐2‐yl)‐4H‐1,2,4‐triazol‐3‐yl]sulfanyl}acetate (phpy2NS, 2 , C₁₆H₁₄N₄O₂S), derived from 1 , were obtained by the reaction of Ham4ph with chloroacetic acid, followed by the acid‐catalyzed esterification of the carboxylic acid with methyl alcohol. Crystals of bis(methanol‐κO)bis(methyl 2‐{[4‐phenyl‐5‐(pyridin‐2‐yl)‐4H‐1,2,4‐triazol‐3‐yl‐κ²N¹,N⁵]sulfanyl}acetato)zinc(II)/cadmium(II) hexabromidocadmate(II), [Zn_0.76Cd_0.24(C₁₆H₁₄N₄O₂S)₂(CH₃OH)₂][Cd₂Br₆] or [Zn_0.76Cd_0.24(phpy2NS)₂(MeOH)₂][Cd₂Br₆], 3 , and dichlorido(methyl 2‐{[4‐phenyl‐5‐(pyridin‐2‐yl)‐4H‐1,2,4‐triazol‐3‐yl‐κ²N¹,N⁵]sulfanyl}acetato)mercury(II), [HgCl₂(C₁₆H₁₄N₄O₂S)] or [Hg(phpy2NS)Cl₂], 4 , were synthesized using ligand 2 and CdBr₂ or HgCl₂, respectively. The molecular and supramolecular structures of the compounds were studied by X‐ray diffractometry. The asymmetric unit of 3 is formed from CdBr₃ and M(phpy2NS)(MeOH) units, where the metal centre M has a 76% occupancy of Zn^II and 24% of Cd^II. The M²⁺ centre of the cation, located on a crystallographic inversion centre, is hexacoordinated and appears as a slightly distorted octahedral [MN₄O₂]²⁺ cation. The Cd centre of the anion is coordinated by two terminal bromide ligands and two bridging bromide ligands that generate [Cd₂Br₆]^2? cadmium–bromide clusters. These clusters display crystallographic inversion symmetry forming two edge‐shared tetrahedra and serve as agents that direct the structure in the formation of supramolecular assemblies. In mononuclear complex 4 , the coordination geometry around the Hg²⁺ ion is distorted tetrahedral and comprises two chloride ligands and two N‐atom donors from the phpy2NS ligand, viz. one pyridine N atom and the other from triazole. In the crystal packing, all four compounds exhibit weak intermolecular interactions, which facilitate the formation of three‐dimensional architectures. Along with the noncovalent interactions, the structural diversity in the complexes can be attributed to the metal centre and to the coordination geometry, as well as to its ionic or neutral character.