Nitrogen Heterocyclic Ligands Research Articles

Silver(I) Complexes with Mefenamic Acid and Nitrogen Heterocyclic Ligands: Synthesis, Characterization, and Biological Evaluation.

Four Ag(I) complexes with mefenamato and nitrogen heterocyclic ligands, [Ag(2-apy)(mef)]2 (1), [Ag(3-apy)(mef)] (2), [Ag2(tmpyz)(mef)2] (3), and {[Ag(4,4'-bipy)(mef)]2(CH3CN)1.5(H2O)2}n (4), (mef = mefenamato, 2-apy = 2-aminopyridine, 3-apy = 3-aminopyridine, tmpyz = 2,3,5,6-tetramethylpyrazine, 4,4'-bipy = 4,4'-bipyridine), were synthesized and characterized. The interactions of these complexes with BSA were investigated by fluorescence spectroscopy, which indicated that these complexes quench the fluorescence of BSA by a static mechanism. The fluorescence data also indicated that the complexes showed good affinity for BSA, and one binding site on BSA was suitable for the complexes. The in vitro cytotoxicity of the four complexes against human cancer cell lines (MCF-7, HepG-2, A549, and MDA-MB-468) and one normal cell line (HTR-8) was evaluated by the MTT assay. Complex 1 displayed high cytotoxic activity against A549 cells. Further studies revealed that complex 1 could enhance the intracellular levels of ROS (reactive oxygen species) in A549 cells, cause cell cycle arrest in the G0/G1 phase, and induce apoptosis in A549 cells in a dose-dependent manner.

N-N-Bridged Polynuclear POM-Based Coordination Polymers Based on a V-Type Ligand: Proton Conduction and Magnetism.

The construction of polyoxometalate (POM)-based coordination polymers, in the presence of a nitrogen heterocyclic ligand, is intriguing due to the potential for obtaining diverse structures. These structures exhibit extensive application possibilities in the fields of proton conductivity and magnetism. Herein, four new POM-based polynuclear coordination polymers with the formulas of {[Fe2(btb)3(H2O)2(SiW12O40)]·3H2O}n (1), {[Cd2(btb)2(H2O)6(HPMoVI10MoV2O40)]·2H2O}n (2), {[Co3(OH)2(btb)2(H2O)5(HPMoVI10MoV2O40)]·7H2O}n (3), and {[Cu3(OH)(btb)2(H2O)(HP2Mo5O23)]·6H2O}n (4) have been prepared using the V-type 1,3-bis(4H-1,2,4-triazole-4-yl)benzene (btb) ligand. Compounds 1 and 2 feature similar two-dimensional (2D) structures, derived from the binuclear Fe2N6 and Cd2N4 subunits connected by tridentate btb ligands. Meanwhile, in compound 3, hexanuclear Co6(OH)4 units are bound by quadridentate btb ligands forming a 2D layer with the same 4-c sql topology simplification as compounds 1 and 2. In compound 1, Keggin-type polyoxoanions are monodentate-coordinated to metal ions and suspended on the 2D structure, while, in compounds 2 and 3, they act as discrete counterions residing in the interstitial spaces between two adjacent layers, thereby extending the 2D structures into 3D structures through hydrogen bonding interactions. In compound 4, trinuclear Cu3(OH) subunits are further constructed into a 3D framework through cooperation with four tridentate and quadridentate btb ligands as well as Strandberg-type anions. Furthermore, the proton conduction of the four compounds has been investigated. They display high proton conductivities at 358 K and 98% RH with powdered samples, which are 1.26 × 10-3, 1.24 × 10-3, 3.24 × 10-4, and 2.57 × 10-4 S cm-1, respectively. Interestingly, by mixing with Nafion, the composite membranes of compounds 2 and 4 exhibit enhanced proton conductivities, measuring at 4.87 × 10-2 and 1.28 × 10-2 S cm-1, respectively, at 358 K and 98% RH, which suggests excellent potential for applications. In addition, compounds 1, 3, and 4 display antiferromagnetic behaviors due to similar magnetic interactions. This work can provide research insights into the assembly of 2D POM-based coordination polymers with nitrogen heterocyclic ligands and Keggin-type POMs and further promote their research progress in proton conduction.

Three Keggin POMs-based coordination polymers constructed by linear N-heterocyclic ligand for proton conduction, photocatalytic activity and magnetic property

POMs-based coordination polymers are promising materials for their potential application in the fields of proton conduction, catalysis and magnetism. Three new coordination polymers namely, {[Co2(bib)3(H2O)2(H4W12O40)]·7H2O}n (1), {[Zn3(bib)8(H3ZnW12O40)2]·12H2O}n (2) and {[Ag5(bib)5(H3W12O40)]·5H2O}n (3) were synthesized under hydrothermal conditions based on linear nitrogen heterocyclic ligand 1,4-bis(1-imidazolyl)benzene (bib). In compound 1, CoII ions are linked with [H4W12O40]4– anions to form a planar network and can be simplified as kgd topology, which are further linked with bib ligands to form a 3D framework. Zn2 ions of compound 2 alternately connect with bib ligands and [H3ZnW12O40]3– anions to form 1D chain structure, while Zn1 ion forms isolated unit with three bib ligands and one [H3ZnW12O40]3– anion, and a 3D framework is finally constructed through π … π stacking interactions. In compound 3, the 3D structure is constructed from a number of 1D chains formed by AgI ions and bib ligands in different directions through π … π stacking interaction and Ag⋯O weak connection. The proton conductivity of 1–3 are 2.03 ​× ​10−5, 1.04 ​× ​10−6 and 1.87 ​× ​10−4 ​S ​cm−1 at 98% RH and 358 ​K, respectively. In addition, compounds 1–3 exhibit photocatalytic degradation capacity towards RhB and compound 1 displays antiferromagnetic behavior.

Synthesis and structure of vanadium (IV) single-stranded dihelicate involving multi-ring nitrogen-heterocyclic ligand

1 The single stranded-helicate Vanadium(IV) complex [V2O2Cl4(L)(H2O)2] (1) involving heterocyclic bis-bidentate ligand viz. 3,3/-dipyridine-2-yl-[1.1/]bi[imidazo[1,5-a]pyridineyl] (L) with biological relevance is prepared and characterized by X-ray diffraction analysis. The compound lacks molecular center of symmetry where coordination environments around V(1) and V(2) centres are distorted octahedral (V···V# separation of 5.827 Å). Structure of the compound in the solid state structure shows anion−π interactions, classical and Carene-H---anion non-classical H-bonding interactions. These interactions play significant roles in shaping the extended structure of this molecule.

Synthesis and Structure of Polymeric Copper(I) Compound with Single-Stranded Dihelicate Units involving Multiring Nitrogen-Heterocyclic Ligand

The polymeric copper(I) complex [Cu2(L)I2] (1) containing a new biologically relevant heterocyclic bis-bidentate ligand viz. 3,3′-dipyridine-2-yl-[1.1′]bi[imidazo[1,5-a]pyridineyl] (L) was synthesized and characterized by single-crystal X-ray diffraction analysis. The molecule lacks molecular center of symmetry where coordination environments around both Cu(1) and Cu(2) are distorted tetrahedral (Cu···Cu# separation of 3.5 Å). Compound in its solid-state structure shows π-π non-covalent interactions as well as Carene-H---anion non-classical hydrogen bonding interactions that play dominant roles in shaping the extended structure of the molecule.

Two isostructural Ni/Co(II) MOFs based on nitrogen heterocyclic ligands and their derived carbon materials for HER performance

Developing efficient, available, and low-cost electrocatalysts for the hydrogen evolution reaction (HER) is important for clean energy systems. Non-noble transition metals are the most promising candidates for the replacement of conventional Pt group catalysts for the HER. Herein, we constructed two isostructural Ni/Co(II) MOFs based on nitrogen heterocyclic ligands, that is, 4-(4-(5-(pyridin-4-yl)-4H-1,2,4-triazol-3-yl)phenyl)pyridine (PPPT), pyromellitic dianhydride (PMDA), and nickel nitrate or cobalt nitrate. After high-temperature calcination in a nitrogen atmosphere, Ni-MOF/NC-T (NC is nitrogen-doped carbon) and Co-MOF/NC-T were obtained. Ni-MOF/NC-800 shows a good HER performance. The overpotential of Ni-MOF/NC-800 was 369 mV at 10 mA·cm−2 current density. The Tafel slope was 127.1 mV dec−1 for Ni-MOF/NC-800, Meanwhile, the HER performance of Co-MOF/NC-700 is slightly worse than that of Ni-MOF/NC-800. This work provides an idea for the simple synthesis of HER catalysts with better performance.

Hemilabile N‐heterocyclic carbene and nitrogen ligands on Fe (II) catalyst for utilization of CO2 into cyclic carbonate

Six Fe (II) complexes were synthesized based on the concept of the hemilability of hybrid ligands, and their catalytic behaviors and performances were evaluated for the fixation of CO2 via the cycloaddition of epoxides. The catalytic potential of the Fe (II) complexes, in combination with bis(triphenylphosphoranylidene)ammonium chloride, have been proved to achieve the efficient conversion in some challenging substrates such as internal, disubstituted epoxides, oxetanes, and fatty acid‐derived epoxides for synthesis of cyclic carbonates under the mild reaction conditions. Ultraviolet–visible and in situ Fourier transform infrared spectroscopy experiments as well as our previous coordination of Ni complexes studies revealed that the origin of activity of Fe (II) complexes might be attributed to the trans effect between N‐heterocyclic carbene ligands and pyridine nitrogen donors.

A Trinuclear Cobalt-Organic Framework: Solvatochromic Sensor towards CH2 Cl2 , and its Derivative as an Anode of Lithium-Ion Batteries with High Performance.

Here, a porous cobalt-organic framework with pillared layer structures, namely [Co3 OBA3 PTD(H2 O)2 ⋅ 2 DMA⋅H2 O]n (1, H2 OBA=4,4'-oxybis(benzoic acid); PTD=6-(pyridin-4-yl)-1,3,5-triazine-2,4-diamine), was fabricated by using cobalt trinuclear nodes, low-cost carboxylic linker, and accessible nitrogen heterocyclic ligands. This compound exhibited a highly efficient solvatochromism towards CH2 Cl2 within one minute and can be used 200 times at least. The corresponding dropper detector was assembled as a practical sensor. Meanwhile, the porous Co3 O4 was obtained by a simple but effective annealing treatment. Electrochemical measurements confirm that this Co3 O4 material derived from compound 1 shows high and stable lithium storage capabilities (1081.75 mA h g-1 at 200 mA g-1 after 115 cycles) and excellent rate properties.

Spectrophotometric kinetic study of mercury(II)-catalyzed formation of [4-CNpyRu(CN)5]3− via ligand exchange reaction of hexacyanoruthenate(II) with 4-cyanopyridine: a mechanistic approach

The kinetics of the formation of yellow-colored complex [4-CNpy Ru(CN)5]3− via cyanide substitution from the coordination sphere of [Ru(CN)6]4− using Hg(II) as catalyst by nitrogen heterocyclic ligand 4-cyanopyridine (4-CNpy) has been studied spectrophotometrically in an aqueous medium by monitoring the increment in absorbance at 400 nm, the λmax of yellow-colored product [4-CNpy Ru(CN)5]3−. The reaction rate followed first-order kinetics in [4-CNpy] and was independent to [Ru(CN)64−]. The complex behavior in the reaction rate was observed with increasing [Hg2+]. Negative salt effect upon variation in ionic strength was noticed in the progressive course of the reaction. A suitable mechanistic scheme compatible with the experimental results has been suggested which is supported by activation parameters.

Synthesis, structures, magnetic and electric properties of four new coordination polymers constructed with heterocyclic nitrogen ligands and multidentate organic acid

Four new coordination polymers based on heterocyclic nitrogen and aromatic carboxylic acids, namely [Co(L1)(2,5-TDC)(H2O)]n (1), [Co(L1)(1,3-BDC)]n (2), [Cu(L2)(1,4-NDC)]n (3), and [Mn(L2)2(2-AIOC)(H2O)]n (4) [L1 = 3,6-bis(1H-imidazol-1-yl)pyridazine, L2 = 3,6-bis(1H-benzo[d]imidazol-1-yl) pyridazine, 1,2-H2TDC = 2,5-thiophenedicarboxylic acid, 1,3-H2BDC = benzenedicarboxylic acid, 1,4-H2NDC = 1,4-naphthalenedicarboxylic acid, 2-H2AIOC = 2-aminoterephthalic acid] have been hydro-/solvothermally prepared and further characterized. 1 and 2 show 2D plane structure which belong to typical sql and sp topological net, respectively. 3 is a six-connected 3D framework with a pcu topological net and 4 belongs to a 3D supramolecular structure constructed via hydrogen bonds. Magnetic tests revealed that 1–3 presence the antiferromagnetic behavior, while 4 displays a ferrimagnetic behavior. The electrochemical measurements explained that 3 possesses excellent cycling stability that it can retain about 91.1% of original capacitance after cycling 10,000 times at 3 A g−1 in 2 mol L−1 KOH aqueous electrolyte.

A Novel Supramolecular Silver Coordination Complex Based on a Triazole Carboxylate Ligand: Synthesis and Fluorescence Sensing of Colchicine and a Series of Nitro Explosives

AbstractA novel supramolecular coordination complex [Ag(HMCTCA)(H2MCTCA)] (1) was firstly synthesized by the reaction of a nitrogen heterocyclic organic ligand H2MCTCA (5‐Methyl‐1‐(4‐carboxylphenyl)‐1H‐1,2,3‐triazole‐4‐carboxylic Acid) with AgNO3. It was characterized in detail by some microanalysis means such as elemental analysis, IR, UV, TG and PXRD. Furthermore, the solid fluorescent behavior was explored at room temperature. The results indicated that coordination complex 1 exhibited excellent fluorescent properties. Based on this phenomenon, we discussed its application in fluorescence sensing. The results illustrated that the coordination complex 1 can be applied to detect colchicine and a series of nitro explosives. It is worth noting that coordination complex 1 showed preeminent sensitivity for detecting p‐nitroaniline (PNA), the detection limit was as low as 0.59 μM.

Crystal structures and luminescence properties of lanthanide complexes with 4-bromobenzoate and nitrogen heterocyclic ligands

Five crystals of lanthanide complexes with 4-bromobenzoate (p-BrBA), 2,4,6-tri(2-pyridyl)-1,3,5-trianzine (TPTZ) and 1,10-phenanthroline (Phen) ligands were synthesized. The structures of the complexes [Sm2(TPTZ-TPTZ)(p-BrBA)4] (1), [Eu2(TPTZ)2(p-BrBA)6] (2), [Tb(TPTZ)(p-BrBA)3(H2O)] (3), [Tb2(Phen)2(p-BrBA)2Ac4] (4) and [Dy2(Phen)2(p-BrBA)6] (5) were determined by single-crystal X-ray diffraction. The crystals 1, 5 belong to monoclinic crystal system, and the other three crystals belong to triclinic crystal system. The dinuclear compound [Sm2(TPTZ-TPTZ)(p-BrBA)4] possesses a coupled [TPTZ-TPTZ]2- ligand that coordinates with two Sm3+ ions in both tridentate and bidentate coordination modes. To investigate the luminescence properties of the complexes, six complexes with similar composition in the powder form were also synthesized, whose formulas are [Eu(TPTZ)(p-BrBA)3(H2O)2], [Tb(TPTZ)(p-BrBA)3(H2O)], [Eu2(Phen)(p-BrBA)3Ac3], [Tb(Phen)(p-BrBA)3], [Sm(TPTZ)(p-BrBA)3(H2O)] and [Dy(Phen)(p-BrBA)3]. The luminescence intensity, luminescence lifetime and quantum efficiency of Eu and Tb complexes with Phen ligand are remarkably superior to the corresponding TPTZ complexes. This difference may mainly result from the stronger structural rigidity of the Phen ligand, which reduces the non-radiative transition of the complexes.

Connecting Titanium-Oxo Clusters by Nitrogen Heterocyclic Ligands to Produce Multiple Cluster Series with Photocatalytic H2 Evolution Activities

We herein demonstrate the ability of nitrogen heterocyclic ligands in connecting polyoxotitanium complexes into crystalline multiple cluster series. Moreover, their bandgap and photocatalytic water-splitting behavior were studied. The highest H2 evolution activity reaches up to 42.80 μmol g–1 h–1 for PTC-46.

Synthesis, chemical nuclease activity, and in vitro cytotoxicity of benzimidazole-based Cu(II)/Co(II) complexes

In this study, novel mono/di-nuclear Cu(p-2-bmb)(OH)(ClO4) (1) and Co2(p‐2-bmb)2Cl4 (2) (p-2-bmb=1-((2-(pyridin-2-yl)-benzoimidazol-1-yl)methyl)-1H-benzotriazole) complexes with the nitrogen heterocyclic benzimidazole-based ligand were synthesized and characterized. The two complexes showed anti-proliferative effects in various carcinoma cell lines, especially complex 1 in the SMMC7721 tumor cell line. Complex 1 was also able to pass through the cell membrane and enter the nucleus and mitochondrion. An analysis of in vitro chemical nuclease activity revealed that complex 1 partially intercalated to calf thymus DNA and exhibited strong unwinding activity against pBR322 superhelical plasmid DNA. The comet assay and flow cytometry analysis confirmed that 1 caused extensive DNA damage and arrested SMMC7721 tumor cells at G2/M phase of the cell cycle, leading to loss of mitochondrial membrane potential and apoptosis. These results suggest that these benzimidazole-based metal complexes could be potential anti-cancer agents.

A new nitrogen heterocyclic carbene containing diiron complex as bio-inspired catalyst for proton reduction and benzene hydroxylation

A new diiron complex (μ-dmedt)[Fe2(CO)5IPr] (2, dmedt = 2,3-butanedithiol, IPr = 1,3-bis(2,6-diisopropylphenyl) imidazol-2-ylidene) was synthesized as analogue of the active site of [Fe-Fe]-H2ases. The sterically bulky nitrogen heterocyclic carbene ligand of IPr coordinated to the iron center was introduced via CO/L substitution reaction in mild conditions. The reactivity of electrocatalytic reduction of proton and catalytic hydroxylation of benzene were explored for the developed diiron complex. Complex 2 undergoes two irreversible reduction events at ca. -2.17 V and −2.50 V and acts as an efficient electrocatalyst for proton reduction to hydrogen with both HOAc and H2O as proton source. The catalytic hydroxylation of benzene by complex 2 achieved phenol yield of 32.4% with almost 100% selectivity. The enhanced catalytic activity compared to the all carbonyl precursor and related derivatives was attributed to the good electron donating ability of introduced IPr ligand.

Synthesis and photoluminescent properties of Eu (III) complexes with fluorinated β-diketone and nitrogen heterocyclic ligands

Two fluorinated β-diketones and their six europium (III) complexes using 2,2-dipyridine, 1,10-phenanthroline or 4′-phenyl-terpyridine as the secondary ligand were synthesized and characterized. The photoluminescence behavior for these complexes was investigated in solid state in detail. Based on the emission spectra and luminescence decay curves of these complexes in solid state, the Judd−Ofelt intensity parameters (Ωt), lifetime (τ) and luminescence quantum efficiency (η) were determined. The Ω2 values indicate that the europium (III) ion is in a highly polarizable chemical environment in these complexes. Europium (III) complexes with the secondary ligands 2,2-dipyridine or 1,10-phenanthroline exhibited much better photoluminescence properties than complexes with the secondary ligand 4′-phenyl-terpyridine. Especially, europium (III) complexes of 4,4,4-trifluoro-1-(4-fluorophenyl)-butane-1,3-dione containing the secondary ligands 2,2-dipyridine or 1,10-phenanthroline showed a longer lifetime (τ = 0.799 and 0.826 ms, respectively) and a higher luminescence quantum efficiency (η = 56.5 and 56.1, respectively) among these complexes.

Facile synthesis of novel blue light and large Stoke shift emitting tetradentate polyazines based on imidazo[1,5-a]pyridine

A facile double condensation procedure, through both standard and microwave heating, provides a versatile one step approach for the synthesis of multidentate nitrogen heterocyclic ligands containing the imidazo[1,5-a]pyridine moiety. The obtained compounds show interesting optical properties: blue fluorescent emissions, moderate quantum yields and large Stokes shifts, enabling their technological application.

Electrical conductivity and luminescence properties of two silver(I) coordination polymers with heterocyclic nitrogen ligands

The synthesis and X-ray structural characterization of two novel silver(I) coordination polymers, [Ag(NO3)(quin)]n (1) and [Ag8(HL)2(H2O)4(mpyz)]·3H2O (2) are reported, where quin=5,6,7,8-tetrahydroquinoxaline, H6L=cyclohexane-1,2,3,4,5,6-hexacarboxylic acid and mpyz=2-methyl pyrazine. The single crystal diffraction analyses showed that complex 1 is a 2D layered structure, while 2 presents a 3D polymeric architecture. In complex 2 the network is stabilized by argentophilic interactions and hydrogen bonding. Electrical conductivity of order 3×10−4Scm−1 (1) and 1.6×10−4Scm−1 (2) is measured on thin film specimen at room temperature. The photoluminescence and thermal properties of the complexes have also been studied.

Enhanced optoelectronics properties of europium(III) complexes with β-diketone and nitrogen heterocyclic ligands

Preparation and photoluminescence behavior of six new europium complexes with β-diketone 1-(2-hydroxy phenyl)-3-phenylpropane-1,3-dione (HPPP) and bathophenanthroline (batho), 2,2′-bipyridyl (bipy), 2,2′-biquinoline (biq), neocuproin (neo) and 1,10-phenanthroline (phen) are reported in solid state. The ligand (HPPP) and complexes Eu(HPPP)3·H2O (1), Eu(HPPP)3·phen (2), Eu(HPPP)3·batho (3), Eu(HPPP)3·bipy (4), Eu(HPPP)3·biq (5) and Eu(HPPP)3·neo (6) were characterized by means of elemental analysis, infrared spectroscopy, proton nuclear magnetic resonance (1H-NMR). The optical properties, thermal stability and crystalline nature were investigated by photoluminescence spectroscopy, thermogravimetric analysis and XRD respectively. The emission spectra show narrow intense emission band of central europium (III) metal ion that arise from the high intense 5D0 → 7F0 transition. The introduction of ancillary ligands like batho, bipy, biq, neo, phen enlarged the π-conjugation system in complexes as a result higher luminescence intensity, longer life time (τ) and higher quantum efficiency (η) observed in europium ternary complexes in comparison to Eu(HPPP)3·H2O (1). Based on the emission spectra, the luminescence decay curve was measured which indicated that the transfer of energy from HPPP ligand to the europium metal is more efficient in complexes 2–6 than complex 1.

Synthesis, Properties, and Structures of Chromium(VI) and Chromium(V) Complexes with Heterocyclic Nitrogen Ligands

AbstractThe reaction of CrO2Cl2 with 2, 2′‐bipyridyl or 1, 10‐phenanthroline (diimine) in CCl4 or anhydrous CH3CO2H solution, produces orange‐brown diamagnetic [CrO2Cl2(diimine)]. The X‐ray structure of [CrO2Cl2(2, 2′‐bipy)] shows a six‐coordinate central chromium(VI) atom with cis‐dioxo groups trans to the diimine. In contrast, the diimines react with CrO3 in CH3CO2H / conc. aqueous HCl to form bright red paramagnetic CrV complexes, [CrOCl3(diimine)]. The X‐ray structure of [CrOCl3(2, 2′‐bipy)] shows a six‐coordinate central chromium atom with mer‐chlorines and the diimine trans to O/Cl. The addition of [2, 2‐bipyH2]Cl2 to a solution of CrO3 in CH3CO2H saturated with HCl gas, produces the CrV anion [2, 2′‐bipyH2][CrOCl4]Cl, which loses HCl on heating in vacuo to form [CrOCl3(2, 2′‐bipy)]. IR, UV/Vis, and 1H NMR spectra (CrVI only) are reported for the new complexes. Attempts to extend these routes to oxygen donor ligands, including ethers and phosphine oxides, were unsuccessful. The diimine complexes are the first structurally autheticated adducts of chromium(VI) and (V) oxide‐chlorides with neutral ligands.