Synthesis and characterization of two novel bimetallic macrocyclic complexes generated from 1,2,4‐triazole‐containing semi‐rigid ligands and M(NO3)2 units (M = Ni and Zn)

Bimetallic macrocyclic complexes have attracted the attention of chemists and various organic ligands have been used as molecular building blocks, but supramolecular complexes based on semi‐rigid organic ligands containing 1,2,4‐triazole have remained rare until recently. It is easier to obtain novel topologies by making use of asymmetric semi‐rigid ligands in the self‐assembly process than by making use of rigid ligands. A new semi‐rigid ligand, 3‐[(pyridin‐4‐ylmethyl)sulfanyl]‐5‐(quinolin‐2‐yl)‐4H‐1,2,4‐triazol‐4‐amine (L), has been synthesized and used to generate two novel bimetallic macrocycle complexes, namely bis{μ‐3‐[(pyridin‐4‐ylmethyl)sulfanyl]‐5‐(quinolin‐2‐yl)‐4H‐1,2,4‐triazol‐4‐amine}bis[(methanol‐κO)(nitrato‐κ²O,O′)nickel(II)] dinitrate, [Ni₂(NO₃)₂(C₁₇H₁₄N₆S)₂(CH₃OH)₂](NO₃)₂, (I), and bis{μ‐3‐[(pyridin‐4‐ylmethyl)sulfanyl]‐5‐(quinolin‐2‐yl)‐4H‐1,2,4‐triazol‐4‐amine}bis[(methanol‐κO)(nitrato‐κ²O,O′)zinc(II)] dinitrate, [Zn₂(NO₃)₂(C₁₇H₁₄N₆S)₂(CH₃OH)₂](NO₃)₂, (II), by solution reactions with the inorganic salts M(NO₃)₂ (M = Ni and Zn, respectively) in mixed solvents. In (I), two Ni^II cations with the same coordination environment are linked by L ligands through Ni—N bonds to form a bimetallic ring. Compound (I) is extended into a two‐dimensional network in the crystallographic ac plane via N—H…O, O—H…N and O—H…O hydrogen bonds, and neighbouring two‐dimensional planes are parallel and form a three‐dimensional structure via π–π stacking. Compound (II) contains two bimetallic rings with the same coordination environment of the Zn^II cations. The Zn^II cations are bridged by L ligands through Zn—N bonds to form the bimetallic rings. One type of bimetallic ring constructs a one‐dimensional nanotube via O—H…O and N—H…O hydrogen bonds along the crystallographic a direction, and the other constructs zero‐dimensional molecular cages via O—H…O and N—H…O hydrogen bonds. They are interlinked into a two‐dimensional network in the ac plane through extensive N—H…O hydrogen bonds, and a three‐dimensional supramolecular architecture is formed via π–π interactions between the centroids of the benzene rings of the quinoline ring systems.     

Structure determination of three furan‐substituted benzimidazoles and calculation of π–π and C—H...π interaction energies

The synthesis and structural characterization of 2‐(furan‐2‐yl)‐1‐(furan‐2‐ylmethyl)‐1H‐benzimidazole [C₁₆H₁₂N₂O₂, (I)], 2‐(furan‐2‐yl)‐1‐(furan‐2‐ylmethyl)‐1H‐benzimidazol‐3‐ium chloride monohydrate [C₁₆H₁₃N₂O₂⁺·Cl⁻·H₂O, (II)] and the hydrobromide salt 5,6‐dimethyl‐2‐(furan‐2‐yl)‐1‐(furan‐2‐ylmethyl)‐1H‐benzimidazol‐3‐ium bromide [C₁₈H₁₇N₂O₂⁺·Br⁻, (III)] are described. Benzimidazole (I) displays two sets of aromatic interactions, each of which involves pairs of molecules in a head‐to‐tail arrangement. The first, denoted set (Ia), exhibits both intermolecular C—H...π interactions between the 2‐(furan‐2‐yl) (abbreviated as Fn) and 1‐(furan‐2‐ylmethyl) (abbreviated as MeFn) substituents, and π–π interactions involving the Fn substituents between inversion‐center‐related molecules. The second, denoted set (Ib), involves π–π interactions involving both the benzene ring (Bz) and the imidazole ring (Im) of benzimidazole. Hydrated salt (II) exhibits N—H...OH₂...Cl hydrogen bonding that results in chains of molecules parallel to the a axis. There is also a head‐to‐head aromatic stacking of the protonated benzimidazole cations in which the Bz and Im rings of one molecule interact with the Im and Fn rings of adjacent molecules in the chain. Salt (III) displays N—H...Br hydrogen bonding and π–π interactions involving inversion‐center‐related benzimidazole rings in a head‐to‐tail arrangement. In all of the π–π interactions observed, the interacting moieties are shifted with respect to each other along the major molecular axis. Basis set superposition energy‐corrected (counterpoise method) interaction energies were calculated for each interaction [DFT, M06‐2X/6‐31+G(d)] employing atomic coordinates obtained in the crystallographic analyses for heavy atoms and optimized H‐atom coordinates. The calculated interaction energies are −43.0, −39.8, −48.5, and −55.0 kJ mol⁻¹ for (Ia), (Ib), (II), and (III), respectively. For (Ia), the analysis was used to partition the interaction energies into the C—H...π and π–π components, which are 9.4 and 24.1 kJ mol⁻¹, respectively. Energy‐minimized structures were used to determine the optimal interplanar spacing, the slip distance along the major molecular axis, and the slip distance along the minor molecular axis for 2‐(furan‐2‐yl)‐1H‐benzimidazole.     

Structural and spectroscopic characterization of two new blue luminescent pyridylbenzimidazole zinc(II) complexes

Luminescent metal complexes are used in photooptical devices. Zinc(II) complexes are of interest because of the ability to tune their color, their high thermal stability and their favorable carrier transport character. In particular, some zinc(II) complexes with aryl diimine and/or heterocyclic ligands have been shown to emit brightly in the blue region of the spectrum. Zinc(II) complexes bearing derivatized imidazoles have been explored for possible optoelectronic applications. The structures of two zinc(II) complexes of 5,6‐dimethyl‐2‐(pyridin‐2‐yl)‐1‐[(pyridin‐2‐yl)methyl]‐1H‐benzimidazole (L), namely dichlorido(dimethylformamide‐κO){5,6‐dimethyl‐2‐(pyridin‐2‐yl‐κN)‐1‐[(pyridin‐2‐yl)methyl]‐1H‐benzimidazole‐κN³}zinc(II) dimethylformamide monosolvate, [ZnCl₂(C₂₀H₁₈N₄)(C₃H₇NO)]·C₃H₇NO, (I), and bis(acetato‐κ²O,O′){5,6‐dimethyl‐2‐(pyridin‐2‐yl‐κN)‐1‐[(pyridin‐2‐yl)methyl]‐1H‐benzimidazole‐κN³}zinc(II) ethanol monosolvate, [Zn(C₂H₃O₂)₂(C₂₀H₁₈N₄)]·C₂H₅OH, (II), are reported. Complex (I) crystallized as a dimethylformamide solvate and exhibits a distorted trigonal bipyramidal coordination geometry. The coordination sphere consists of a bidentate L ligand spanning axial to equatorial sites, two chloride ligands in equatorial sites, and an O‐bound dimethylformamide ligand in the remaining axial site. The other complex, (II), crystallized as an ethanol solvate. The Zn^II atom has a distorted trigonal prismatic coordination geometry, with two bidentate acetate ligands occupying two edges and a bidentate L ligand occupying the third edge of the prism. Complexes (I) and (II) emit in the blue region of the spectrum. The results of density functional theory (DFT) calculations suggest that the luminescence of L results from π*←π transitions and that the luminescence of the complexes results from interligand charge‐transfer transitions. The orientation of the 2‐(pyridin‐2‐yl) substituent with respect to the benzimidazole system was found to have an impact on the calculated HOMO–LUMO gap (HOMO is highest occupied molecular orbital and LUMO is lowest unoccupied molecular orbital).     

A one‐dimensional silver(I) coordination polymer based on the 2‐[2‐(pyridin‐4‐yl)‐1H‐benzimidazol‐1‐ylmethyl]phenol ligand exhibiting photoluminescence

A one‐dimensional Ag^I coordination complex, catena‐poly[[silver(I)‐μ‐{2‐[2‐(pyridin‐4‐yl)‐1H‐benzimidazol‐1‐ylmethyl]phenol‐κ²N²:N³}] perchlorate monohydrate], {[Ag(C₁₉H₁₅N₃O)]ClO₄·H₂O}_n, was synthesized by the reaction of 2‐[2‐(pyridin‐4‐yl)‐1H‐benzimidazol‐1‐ylmethyl]phenol (L) with silver perchlorate. In the complex, the L ligands are arranged alternately and link Ag^I cations through one benzimidazole N atom and the N atom of the pyridine ring, leading to an extended zigzag chain structure. In addition, the one‐dimensional chains are extended into a three‐dimensional supramolecular architecture via O—H...O hydrogen‐bond interactions and π–π stacking interactions. The complex exhibits photoluminescence in acetonitrile solution, with an emission maximum at 390 nm, and investigation of the thermal stability reveals that the network structure is stable up to 650 K.     

1,2‐Bis[(pyridin‐2‐ylmethyl)sulfanyl]ethane and its dimorphic hydrochloride salt

Although having been described as a liquid in the literature for 41 years, 1,2‐bis[(pyridin‐2‐ylmethyl)sulfanyl]ethane, C₁₄H₁₆N₂S₂, (I), has now been obtained as monoclinic crystals via a new and convenient method of purification. Molecules of (I) are located on crystallographic inversion centres and are held together by C—H...N and C—H...S interactions, resulting in the formation of a three‐dimensional network structure. In addition, two polymorphs of the corresponding hydrochloride salt, 2‐[({2‐[(pyridin‐1‐ium‐2‐ylmethyl)sulfanyl]ethyl}sulfanyl)methyl]pyridin‐1‐ium dichloride, C₁₄H₁₈N₂S₂²⁺·2Cl⁻, (II) and (III), have been isolated. Molecules of (II) and (III) have similar conformations and are located on inversion centres. Both polymorphs form three‐dimensional networks through N—H...Cl, C—H...Cl and C—H...S interactions. The structure of (III) displays voids of 35 ų.     

Synthesis and characterization of a novel long‐alkyl‐chain ester‐substituted benzimidazole gelator and its octan‐1‐ol solvate

The synthesis of a novel benzimidazole derivative with a long‐chain‐ester substituent, namely methyl 8‐[4‐(1H‐benzimidazol‐2‐yl)phenoxy]octanoate, (3), is reported. Ester (3) shows evidence of aggregation in solution and weak gelation ability with toluene. The octan‐1‐ol solvate, methyl 8‐[4‐(1H‐benzimidazol‐2‐yl)phenoxy]octanoate octan‐1‐ol monosolvate, C₂₂H₂₆N₂O₃·C₈H₁₈O, (4), exhibits a four‐molecule hydrogen‐bonded motif in the solid state, with N—H…O hydrogen bonds between benzimidazole molecules and O—H…N hydrogen bonds between the octan‐1‐ol solvent molecules and the benzimidazole unit. The alkyl chains of the ester and the octan‐1‐ol molecules are in unfolded conformations. The phenylene ring is canted by 10.27 (6)° from the plane of the benzimidazole ring system. H…C contacts make up 20.7% of the Hirshfeld surface coverage. Weak C—H…π interactions involving the benzimidazole alkyl chain and three aromatic rings are observed.     

A concise and efficient synthesis of amino‐substituted (1H‐benzo[d]imidazol‐1‐yl)pyrimidine hybrids: synthetic sequence and the molecular and supramolecular structures of six examples

A concise and efficient synthesis of a series of amino‐substituted benzimidazole–pyrimidine hybrids has been developed, starting from the readily available N⁴‐(2‐aminophenyl)‐6‐methoxy‐5‐nitrosopyrimidine‐2,4‐diamine. In each of N⁵‐benzyl‐6‐methoxy‐4‐(2‐phenyl‐1H‐benzo[d]imidazol‐1‐yl)pyrimidine‐2,5‐diamine, C₂₅H₂₂N₆O, (I), 6‐methoxy‐N⁵‐(4‐methoxybenzyl)‐4‐[2‐(4‐methoxyphenyl)‐1H‐benzo[d]imidazol‐1‐yl]pyrimidine‐2,5‐diamine, C₂₇H₂₆N₆O₃, (III), 6‐methoxy‐N⁵‐(4‐nitrobenzyl)‐4‐[2‐(4‐nitrophenyl)‐1H‐benzo[d]imidazol‐1‐yl]pyrimidine‐2,5‐diamine, C₂₅H₂₀N₈O₅, (IV), the molecules are linked into three‐dimensional framework structures, using different combinations of N—H…N, N—H…O, C—H…O, C—H…N and C—H…π hydrogen bonds in each case. Oxidative cleavage of 6‐methoxy‐N⁵‐(4‐methylbenzyl)‐4‐[2‐(4‐methylphenyl)‐1H‐benzo[d]imidazol‐1‐yl]pyrimidine‐2,5‐diamine, (II), with diiodine gave 6‐methoxy‐4‐[2‐(4‐methylphenyl)‐1H‐benzo[d]imidazol‐1‐yl]pyrimidine‐2,5‐diamine, which crystallized as a monohydrate, C₁₉H₁₈N₆O·H₂O, (V), and reaction of (V) with trifluoroacetic acid gave two isomeric products, namely N‐{5‐amino‐6‐methoxy‐6‐[2‐(4‐methylphenyl)‐1H‐benzo[d]imidazol‐1‐yl]pyrimidin‐2‐yl}‐2,2,2‐trifluoroacetamide, which crystallized as an ethyl acetate monosolvate, C₂₁H₁₇F₃N₆O₂·C₄H₈O₂, (VI), and N‐{2‐amino‐6‐methoxy‐4‐[2‐(4‐methylphenyl)‐1H‐benzo[d]imidazol‐1‐yl]pyrimidin‐5‐yl}‐2,2,2‐trifluoroacetamide, which crystallized as a methanol monosolvate, C₂₁H₁₇F₃N₆O₂·CH₄O, (VIIa). For each of (V), (VI) and (VIIa), the supramolecular assembly is two‐dimensional, based on different combinations of O—H…N, N—H…O, N—H…N, C—H…O and C—H…π hydrogen bonds in each case. Comparisons are made with some related structures.     

Exo conformers of N‐(pyridin‐2‐yl)‐ and N‐(pyridin‐3‐yl)norbornene‐5,6‐dicarboximide crystals

Two isomeric pyridine‐substituted norbornenedicarboximide derivatives, namely N‐(pyridin‐2‐yl)‐exo‐norbornene‐5,6‐dicarboximide, (I), and N‐(pyridin‐3‐yl)‐exo‐norbornene‐5,6‐dicarboximide, (II), both C₁₄H₁₂N₂O₄, have been crystallized and their structures unequivocally determined by single‐crystal X‐ray diffraction. The molecules consist of norbornene moieties fused to a dicarboximide ring substituted at the N atom by either pyridin‐2‐yl or pyridin‐3‐yl in an anti configuration with respect to the double bond, thus affording exo isomers. In both compounds, the asymmetric unit consists of two independent molecules (Z′ = 2). In compound (I), the pyridine rings of the two independent molecules adopt different conformations, i.e. syn and anti, with respect to the methylene bridge. The intermolecular contacts of (I) are dominated by C—H...O interactions. In contrast, in compound (II), the pyridine rings of both molecules have an anti conformation and the two independent molecules are linked by carbonyl–carbonyl interactions, as well as by C—H...O and C—H...N contacts.     

Hydrogen bonding and π–π interactions in the cocrystal salt [Fe(bpe)2(H2O)4](TCEP)2·2(bpe) [bpe is trans‐1,2‐bis(pyridin‐4‐yl)ethene and TCEP is 1,1,3,3‐tetracyano‐2‐ethoxypropenide]

The cocrystal salt tetraaquabis[trans‐1,2‐bis(pyridin‐4‐yl)ethene‐κN]iron(II) bis(1,1,3,3‐tetracyano‐2‐ethoxypropenide)–trans‐1,2‐bis(pyridin‐4‐yl)ethene (1/2), [Fe(C₁₂H₁₀N₂)₂(H₂O)₄](C₉H₅N₄O)₂·2C₁₂H₁₀N₂, is a rare example of a mononuclear Fe^II compound with trans‐1,2‐bis(pyridin‐4‐yl)ethane (bpe) ligands. The complex cation resides on a crystallographically imposed inversion center and exhibits a tetragonally distorted octahedral coordination geometry. Both the symmetry‐independent bpe ligand and the cocrystallized bpe molecule are essentially planar. The 1,1,3,3‐tetracyano‐2‐ethoxypropenide counter‐ion is nonplanar and the bond lengths are consistant with significant electron delocalization. The extended structure exhibits an extensive O—H…N hydrogen‐bonding network with layers of complex cations joined by the cocrystallized bpe. Both the coordinated and the cocrystallized bpe are involved in π–π interactions. Hirshfeld and fingerprint plots reveal the important intermolecular interactions. Density functional theory was used to estimate the strengths of the hydrogen‐bonding and π–π interactions, and suggest that the O—H…N hydrogen bonds enhance the strength of the π‐interactions by increasing the polarization of the pyridine rings.     

π–π Dimerization of a mono(pyridyl–imine) platinum(II) chelate

The cation of the title complex salt, chlorido{2,2‐dimethyl‐N‐[(E)‐1‐(pyridin‐2‐yl)ethylidene]propane‐1,3‐diamine}platinum(II) tetrafluoridoborate, [PtCl(C₁₂H₁₉N₃)]BF₄, exhibits a nominally square‐planar Pt^II ion coordinated to a chloride ion [Pt—Cl = 2.3046 (9) Å] and three unique N‐atom types, viz. pyridine, imine and amine, of the tridentate Schiff base ligand formed by the 1:1 condensation of 1‐(pyridin‐2‐yl)ethanone and 2,2‐dimethylpropane‐1,3‐diamine. The cations are π‐stacked in inversion‐related pairs (dimers), with a mean plane separation of 3.426 Å, an intradimer Pt...Pt separation of 5.0785 (6) Å and a lateral shift of 3.676 Å. The centroid (Cg) of the pyridine ring is positioned approximately over the Pt^II ion of the neighbouring cation (Pt...Cg = 3.503 Å).     

Supramolecular structures of rhenium(I) complexes mediated by ligand planarity via the interplay of substituents

The crystal and molecular structures of two Re^I tricarbonyl complexes, namely fac‐tricarbonylchlorido[1‐(4‐fluorocinnamoyl)‐3‐(pyridin‐2‐yl‐κN)pyrazole‐κN²]rhenium(I), [ReCl(C₁₇H₁₂FN₃O)(CO)₃], (I), and fac‐tricarbonylchlorido[1‐(4‐nitrocinnamoyl)‐3‐(pyridin‐2‐yl‐κN)pyrazole‐κN²]rhenium(I) acetone monosolvate, [ReCl(C₁₇H₁₂ClN₄O₃)(CO)₃]·C₃H₆O, (II), are reported. The complexes form centrosymmetric dimers that are linked into one‐dimensional columns by C—H…Cl and N—O…H interactions in (I) and (II), respectively. C—H…Cl interactions in (II) generate two R₂¹(7) loops that merge into a single R₂¹(10) loop. These interactions involve the alkene, pyrazole and benzene rings, hence restricting the ligand rotation and giving rise to a planar conformation. Unlike (II), complex (I) exhibits a twisted conformation of the ligand and a pair of molecules forms a centrosymmetric dimer with an R₂²(10) loop via C—H…O interactions. The unique supramolecular structures of (I) and (II) are determined by their planarity and weak interactions. The planar conformation of (II) provides a base for appreciable π–π stacking interactions compared to (I). In addition, an N—O…π interaction stabilizes the supramolecular structure of (II). We report herein the first n→π* interactions of Re^I tricarbonyl complexes, which account for 0.33 kJ mol⁻¹. Intermolecular C—H…Cl and C—H…O interactions are present in both complexes, with (II) showing a greater preference for these interactions compared to (I), with cumulative contributions of 48.7 and 41.5%, respectively. The influence of inductive (fluoro) and/or resonance (nitro) effects on the π‐stacking ability was further supported by LOLIPOP (localized orbital locator‐integrated π over plane) analysis. The benzene ring of (II) demonstrated a higher π‐stacking ability compared to that of (I), which is supported by the intrinsic planar geometry. The HOMA (harmonic oscillator model of aromaticity) index of (I) revealed more aromaticity with respect to (II), suggesting that NO₂ greatly perturbed the aromaticity. The Hirshfeld fingerprint (FP) plots revealed the preference of (II) over (I) for π–π contacts, with contributions of 6.8 and 4.4%, respectively.     

Three structures containing (E)‐1,2‐bis­(benzimidazol‐2‐yl)ethene groups

Two of the title compounds, namely (E)‐1,2‐bis­(1‐methyl­benzimidazol‐2‐yl)ethene, C₁₈H₁₆N₄, (Ib), and (E)‐1,2‐bis­(1‐ethyl­benzimidazol‐2‐yl)ethene, C₂₀H₂₀N₄, (Ic), consist of centrosymmetric trans‐bis­(1‐alkyl­benzimidazol‐2‐yl)ethene mol­ecules, while 3‐eth­yl‐2‐[(E)‐2‐(1‐ethyl­benzimidazol‐2‐yl)­ethen­yl]benzimidazol‐1‐ium perchlorate, C₂₀H₂₁N₄⁺·ClO₄⁻, (II), contains the monoprotonated analogue of compound (Ic). In the three structures, the benzimidazole and benzimidazolium moieties are essentially planar; the geometric parameters for the ethene linkages and their bonds to the aromatic groups are consistent with double and single bonds, respectively, implying little, if any, conjugation of the central C=C bonds with the nitro­gen‐containing rings. The C—N bond lengths in the N=C—N part of the benzimidazole groups differ and are consistent with localized imine C=N and amine C—N linkages in (Ib) and (Ic); in contrast, the corresponding distances in the benzimidazolium cation are equal in (II), consistent with electron delocalization resulting from protonation of the amine N atom. Crystals of (Ib) and (Ic) contain columns of parallel mol­ecules, which are linked by edge‐over‐edge C—H⋯π overlap. The columns are linked to one another by C—H⋯π inter­actions and, in the case of (Ib), C—H⋯N hydrogen bonds. Crystals of (II) contain layers of monocations linked by π–π inter­actions and separated by both perchlorate anions and the protruding eth­yl groups; the cations and anions are linked by N—H⋯O hydrogen bonds.     

Two different one‐dimensional supramolecular chains formed from the reaction of 2‐[1‐(pyridin‐4‐ylmethyl)‐1H‐benzimidazol‐2‐yl]quinoline with two different precursors,Co(NO3)2 and CoCl2

Two different one‐dimensional supramolecular chains with Co^II cations have been synthesized based on the semi‐rigid ligand 2‐[1‐(pyridin‐4‐ylmethyl)‐1H‐benzimidazol‐2‐yl]quinoline (L), obtained by condensation of 2‐(1H‐benzimidazol‐2‐yl)quinoline and 4‐(chloromethyl)pyridine hydrochloride. Starting from different Co^II salts, two new compounds have been obtained, viz. catena‐poly[[[dinitratocobalt(II)]‐μ‐2‐[1‐(pyridin‐4‐ylmethyl)‐1H‐benzimidazol‐2‐yl]quinoline] dichloromethane monosolvate acetonitrile monosolvate], {[Co(NO₃)₂(C₂₂H₁₆N₄)]·CH₂Cl₂·CH₃CN}_n, (I) and catena‐poly[[[dichloridocobalt(II)]‐μ‐2‐[1‐(pyridin‐4‐ylmethyl)‐1H‐benzimidazol‐2‐yl]quinoline] methanol disolvate], {[CoCl₂(C₂₂H₁₆N₄)]·2CH₃OH}_n, (II). In (I), the Co^II centres lie in a distorted octahedral [CoN₃O₃] coordination environment. {Co(NO₃)₂L}_n units form one‐dimensional helical chains, where the L ligand has different directions of twist. The helical chains stack together via interchain π–π interactions to form a two‐dimensional sheet, and another type of π–π interaction further connects neighbouring sheets into a three‐dimensional framework with hexagonal channels, in which the acetonitrile molecules and disordered dichloromethane molecules are located. In (II), the Co^II centres lie in a distorted trigonal–bipyramidal [CoCl₂N₃] coordination environment. {CoCl₂L}_n units form one‐dimensional chains. The chains interact via C—H...π and C—H...Cl interactions. The result is that two‐dimensional sheets are generated, which are further linked into a three‐dimensional framework via interlayer C—H...Cl interactions. When viewed down the crystallographic b axis, the methanol solvent molecules are located in an orderly manner in wave‐like channels.     

Three zinc(II) and cadmium(II) complexes containing 4‐amino‐3,5‐bis(pyridin‐2‐yl)‐1,2,4‐triazole and polynitrile ligands: synthesis,molecular and supramolecular structures,and photoluminescence properties

Three photoluminescent complexes containing either Zn^II or Cd^II have been synthesized and their structures determined. Bis[4‐amino‐3,5‐bis(pyridin‐2‐yl)‐1,2,4‐triazole‐κ²N ¹,N ⁵]bis(dicyanamido‐κN ¹)zinc(II), [Zn(C₁₂H₁₀N₆)₂(C₂N₃)₂], (I), bis[4‐amino‐3,5‐bis(pyridin‐2‐yl)‐1,2,4‐triazole‐κ²N ¹,N ⁵]bis(dicyanamido‐κN ¹)cadmium(II), [Cd(C₁₂H₁₀N₆)₂(C₂N₃)₂], (II), and bis[4‐amino‐3,5‐bis(pyridin‐2‐yl)‐1,2,4‐triazole‐κ²N ¹,N ⁵]bis(tricyanomethanido‐κN ¹)cadmium(II), [Cd(C₁₂H₁₀N₆)₂(C₄N₃)₂], (III), all crystallize in the space group P , with the metal centres lying on centres of inversion, but neither analogues (I) and (II) nor Cd^II complexes (II) and (III) are isomorphous. A combination of N—H…N and C—H…N hydrogen bonds and π–π stacking interactions generates three‐dimensional framework structures in (I) and (II), and a sheet structure in (III). The photoluminescence spectra of (I)–(III) indicate that the energies of the π–π* transitions in the coordinated triazole ligand are modified by minor changes of the ligand geometry associated with coordination to the metal centres.     

Three isomorphous two‐dimensional coordination polymers generated from a benzimidazole bridging ligand and ZnX2 (X = Cl,Br and I)

A novel bridging asymmetric benzimidazole ligand, 4‐{2‐[3‐(pyridin‐4‐yl)phenyl]‐1H‐benzimidazol‐1‐ylmethyl}benzoic acid, was used to construct three isomorphous two‐dimensional coordination polymers, namely catena‐poly[chlorido(μ₃‐4‐{2‐[3‐(pyridin‐4‐yl)phenyl]‐1H‐benzimidazol‐1‐ylmethyl}benzoato)zinc(II)], [Zn(C₂₆H₁₈N₃O₂)Cl]_n, (I), and the bromide, (II), and iodide, (III), analogues. Neighbouring two‐dimensional networks are stacked into three‐dimensional frameworks via interlayer π–π interactions. The luminescent properties of (I)–(III) were investigated and they display an obvious red‐shift in the solid state at room temperature.     

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.     

The inner‐salt zwitterion,the dihydrochloride dihydrate and the dimethyl sulfoxide disolvate of 3,6‐bis(pyridin‐2‐yl)pyrazine‐2,5‐dicarboxylic acid

In the inner‐salt zwitterion of 3,6‐bis(pyridin‐2‐yl)pyrazine‐2,5‐dicarboxylic acid, (I), namely 5‐carboxy‐3‐(pyridin‐1‐ium‐2‐yl)‐6‐(pyridin‐2‐yl)pyrazine‐2‐carboxylate, [C₁₆H₁₀N₄O₄, (Ia)], the pyrazine ring has a twist–boat conformation. The opposing pyridine and pyridinium rings are almost perpendicular to one another, with a dihedral angle of 80.24 (18)°, and are inclined to the pyrazine mean plane by 36.83 (17) and 43.74 (17)°, respectively. The carboxy and carboxylate groups are inclined to the mean plane of the pyrazine ring by 43.60 (17) and 45.46 (17)°, respectively. In the crystal structure, the molecules are linked via N—H...O and O—H...O hydrogen bonds, leading to the formation of double‐stranded chains propagating in the [010] direction. On treating (Ia) with aqueous 1 M HCl, the diprotonated dihydrate form 2,2′‐(3,6‐dicarboxypyrazine‐2,5‐diyl)bis(pyridin‐1‐ium) dichloride dihydrate [C₁₆H₁₂N₄O₄²⁺·2Cl⁻·2H₂O, (Ib)] was obtained. The cation lies about an inversion centre. The pyridinium rings and carboxy groups are inclined to the planar pyrazine ring by 55.53 (9) and 19.8 (2)°, respectively. In the crystal structure, the molecules are involved in N—H...Cl, O—H...O_water and O_water—H...Cl hydrogen bonds, leading to the formation of chains propagating in the [010] direction. When (Ia) was recrystallized from dimethyl sulfoxide (DMSO), the DMSO disolvate 3,6‐bis(pyridin‐2‐yl)pyrazine‐2,5‐dicarboxylic acid dimethyl sulfoxide disolvate [C₁₆H₁₀N₄O₄·2C₂H₆OS, (Ic)] of (I) was obtained. Here, the molecule of (I) lies about an inversion centre and the pyridine rings are inclined to the planar pyrazine ring by only 23.59 (12)°. However, the carboxy groups are inclined to the pyrazine ring by 69.0 (3)°. In the crystal structure, the carboxy groups are linked to the DMSO molecules by O—H...O hydrogen bonds. In all three crystal structures, the presence of nonclassical hydrogen bonds gives rise to the formation of three‐dimensional supramolecular architectures.     

Synthesis and structures of photoactive manganese–carbonyl complexes derived from 2‐(pyridin‐2‐yl)‐1,3‐benzothiazole and 2‐(quinolin‐2‐yl)‐1,3‐benzothiazole

PhotoCORMs (photo‐active CO‐releasing molecules) have emerged as a class of CO donors where the CO release process can be triggered upon illumination with light of appropriate wavelength. We have recently reported an Mn‐based photoCORM, namely [MnBr(pbt)(CO)₃] [pbt is 2‐(pyridin‐2‐yl)‐1,3‐benzothiazole], where the CO release event can be tracked within cellular milieu by virtue of the emergence of strong blue fluorescence. In pursuit of developing more such trackable photoCORMs, we report herein the syntheses and structural characterization of two Mn^I–carbonyl complexes, namely fac‐tricarbonylchlorido[2‐(pyridin‐2‐yl)‐1,3‐benzothiazole‐κ²N ,N ′]manganese(I), [MnCl(C₁₂H₈N₂S)(CO)₃], (1), and fac‐tricarbonylchlorido[2‐(quinolin‐2‐yl)‐1,3‐benzothiazole‐κ²N ,N ′]manganese(I), [MnCl(C₁₆H₁₀N₂S)(CO)₃], (2). In both complexes, the Mn^I center resides in a distorted octahedral coordination environment. Weak intermolecular C—H…Cl contacts in complex (1) and Cl…S contacts in complex (2) consolidate their extended structures. These complexes also exhibit CO release upon exposure to low‐power broadband visible light. The apparent CO release rates for the two complexes have been measured to compare their CO donating capacity. The fluorogenic 2‐(pyridin‐2‐yl)‐1,3‐benzothiazole and 2‐(quinolin‐2‐yl)‐1,3‐benzothiazole ligands provide a convenient way to track the CO release event through the `turn‐ON' fluorescence which results upon de‐ligation of the ligands from their respective metal centers following CO photorelease.     

Adsorption behaviour of a CdII–triazole MOF for butan‐2‐one in a single‐crystal‐to‐single‐crystal (SCSC) fashion: the role of hydrogen bonding and C—H…π interactions

The adsorption behaviour of the Cd^II–MOF {[Cd(L)₂(ClO₄)₂]·H₂O ( 1 ), where L is 4‐amino‐3,5‐bis[3‐(pyridin‐4‐yl)phenyl]‐1,2,4‐triazole, for butan‐2‐one was investigated in a single‐crystal‐to‐single‐crystal (SCSC) fashion. A new host–guest system that encapsulated butan‐2‐one molecules, namely poly[[bis{μ₃‐4‐amino‐3,5‐bis[3‐(pyridin‐4‐yl)phenyl]‐1,2,4‐triazole}cadmium(II)] bis(perchlorate) butanone sesquisolvate], {[Cd(C₂₄H₁₈N₆)₂](ClO₄)₂·1.5C₄H₈O}_n, denoted C₄H₈O@Cd‐MOF ( 2 ), was obtained via an SCSC transformation. MOF 2 crystallizes in the tetragonal space group P4₃2₁2. The specific binding sites for butan‐2‐one in the host were determined by single‐crystal X‐ray diffraction studies. N—H…O and C—H…O hydrogen‐bonding interactions and C—H…π interactions between the framework, ClO₄^? anions and guest molecules co‐operatively bind 1.5 butan‐2‐one molecules within the channels. The adsorption behaviour was further evidenced by ¹H NMR, IR, TGA and powder X‐ray diffraction experiments, which are consistent with the single‐crystal X‐ray analysis. A ¹H NMR experiment demonstrates that the supramolecular interactions between the framework, ClO₄^? anions and guest molecules in MOF 2 lead to a high butan‐2‐one uptake in the channel.     

Planarity of heteroaryldithiocarbazic acid derivatives showing tuberculostatic activity: structure–activity relationships

The search for new tuberculostatics is an important issue due to the increasing resistance of Mycobacterium tuberculosis to existing agents and the resulting spread of the pathogen. Heteroaryldithiocarbazic acid derivatives have shown potential tuberculostatic activity and investigations of the structural aspects of these compounds are thus of interest. Three new examples have been synthesized. The structure of methyl 2‐[amino(pyridin‐3‐yl)methylidene]hydrazinecarbodithioate, C₈H₁₀N₄S₂, at 293 K has monoclinic (P2₁/n) symmetry. It is of interest with respect to antibacterial properties. The structure displays N—H…N and N—H…S hydrogen bonding. The structure of N′‐(pyrrolidine‐1‐carbonothioyl)picolinohydrazonamide, C₁₁H₁₅N₅S, at 100 K has monoclinic (P2₁/n) symmetry and is also of interest with respect to antibacterial properties. The structure displays N—H…S hydrogen bonding. The structure of (Z)‐methyl 2‐[amino(pyridin‐2‐yl)methylidene]‐1‐methylhydrazinecarbodithioate, C₉H₁₃N₄S₂, has triclinic (P) symmetry. The structure displays N—H…S hydrogen bonding.