Pyridylpyrazole Ligands Research Articles

Dissociation of a tripodal pyridyl-pyrazole ligand and assortment of metal complex: Synthesis, structure, DFT, thermal stability, cytotoxicity, DNA cleavage, and molecular docking studies

A tripodal pyridyl-pyrazole based N,N,O donor ligand (L) has been designed, and it's copper(II) complex, [Cu(L1)Cl2]2.(dmpzH)2 (1) where dmpzH refers protonated dimethylpyrazole, and manganese(II) complex, [Mn(L)(Cl)2] (2)] have been synthesized and characterized by a combination of various spectroscopy, X-ray crystallography, electrochemical, thermogravimetric and density functional theory. The X-ray structure of 1 showed the copper(II) coordinated by the two sets of NO donors which had been assorted from the ligand (L) along with two bridging and one terminal chloride atoms. The distorted square-planar centrosymmetric structure of 1 is further stabilized by the hydrogen bonding with exogenous protonated pyrazole units that had been extracted from L. The title ligand retained its original structure when bound with Mn(II) giving a pseudo-octahedral geometry. The central Mn(II) was coordinated by two pyrazolyl nitrogen (N1, N7), one tertiary amine nitrogen (N3), one carbohydrazide oxygen atom O1, and two exogenous chloride ions in a cis disposition. Cytotoxicity experiments carried out in a series of human cell lines (IMR-32, HepG2 and HeLa) to confirm the apoptotic mechanism of cell death, predominantly in IMR-32. The DNA cleavage studies were then performed in the presence of the synthesized compounds to verify the influence of ligand structural features in their nuclease activity. Complex 2 was able to cause double-strand DNA scissions both in an oxidizing and reducing environment, whereas complex 1 broke the single-strand DNA in a reducing environment only, suggesting its potential anticancer therapeutics. To shed a better understanding of DNA-substrate interaction, a molecular docking study was performed.

Influence of reaction temperature and stoichiometry on the coordination mode of a multidentate pyridylpyrazole ligand in Co(ii) complexes: from a 0D mononuclear structure to 3D frameworks

Three Co(ii) coordination polymers with different dimensionality have been successfully constructed under controlled conditions by changing the reaction temperature and stoichiometry.

A Heterogeneous Ruthenium dmso Complex Supported onto Silica Particles as a Recyclable Catalyst for the Efficient Hydration of Nitriles in Aqueous Medium.

In the present work, we describe an efficient method for the covalent anchoring of a Ru-dmso complex onto two types of supports: mesoporous silica particles (SP) and silica coated magnetic particles (MSNP). First, we have prepared and characterized the molecular complexes containing the bidentate pyridylpyrazole ligands pypz-Me and pypz-CH2COOEt, with the formula [RuIICl2(pypz-R)(dmso)2] (R = Me, 1; CH2COOEt, 2). Complex 2 was anchored onto the silica supports, yielding the heterogeneous systems SP@2 and MSNP@2 which were fully characterized by IR, UV-vis, SEM, TEM, TGA, and XPS techniques. Hydration of representative nitriles has been tested with the molecular complexes and their SP@2 and MSNP@2 heterogeneous counterparts, in aqueous medium under neutral conditions. The heterogeneous catalysts display high yields and excellent selectivity values. Both systems can be reused throughout several cycles for benzonitrile and acrylonitrile substrates, without any significant loss in reactivity. The MSNP@2 material can be easily recovered by a magnet, facilitating its reusability.

Counteranion-Triggered and Excitation-Dependent Chemopalette Effect in a Supramolecular Dual-Emissive System Based on Cu3Pz3.

Three Cu3Pz3-based isostructural complexes (Cu3L3)2(CuX)2 (labeled as 1-ClO4, 1-NO3, and 1-Br, where X = ClO4-, NO3-, and Br-, respectively) were prepared by solvothermal reactions of an angular bifunctional pyridyl-pyrazole ligand, 4-(pyridin-4'-ylthio)-3,5-dimethyl-1 H-pyrazole ( HL), with Cu(ClO4)2, Cu(NO3)2, and CuBr, respectively. Pyrazolate (Pz) groups are highly specific to form planar trinuclear Cu3Pz3 units. Two Cu3L3 units are further connected by two CuX units through NPy-Cu-NPy (Py = 4-pyridyl) bonds to form an octanuclear chairlike molecule (Cu3L3)2(CuX)2, which then self-assembles through intertrimeric cuprophilicity to construct chainlike supraaggregates featuring two luminophores, [Cu3Pz3]2 and CuPy2X. With different counteranions (ClO4-, NO3-, and Br-), the complexes give off various emissions from red to green upon UV irradiation. 1-ClO4 and 1-NO3 show only low-energy (LE) orange (λemmax = 585 nm) and red (λemmax = 640 nm) emissions, while 1-Br exhibits excitation-dependent (260-360 nm) emissions from yellow to green due to variation in the relative intensities of two resolvable emissions, high energy (HE, λemmax = 520 nm) and LE (λemmax = 630 nm). The dual emissions are assigned to 3CC (LE states) based on excimeric [Cu3Pz3]2 units and 3XLCT/3MLCT (HE states) based on CuPy2X units. This work realizes a chemopalette effect through regulations of the counteranion and excitation energy in a dual-emissive system. It provides valuable insights into the nature of dual-emissive materials and the further investigation of the photophysical mechanism in such a system.

Theoretical Insights into Preorganized Pyridylpyrazole-Based Ligands toward the Separation of Am(III)/Eu(III).

Pyridylpyrazole ligands have shown excellent competence for partitioning actinides from lanthanides. As far as we know, the preorganization structure of the ligand has a great impact on the extraction separation ability. However, the mechanism that works well for some ligands but fails for others needs to be clearly elucidated. In this work, we designed three various pyridylpyrazole ligands, BPP, BPBP, and BPPhen, and further preorganized one or both side pyrazole rings of these ligands. The properties of these ligands and the coordination structures, bonding nature and thermodynamic behaviors of the related Am(III) and Eu(III) complexes have been systematically studied in a theoretical fashion. All analyses of geometries, charge transfer, QTAIM (quantum theory of atoms in molecules) and NBO (natural bond orbital) suggest that the Am-N bonds possess more covalence compared to that of Eu-N bonds. According to the thermodynamic results, increasing the rigidity of the bridging skeleton rather than the side chain can enhance the extraction ability and Am(III)/Eu(III) selectivity of the ligand. This work may identify the reasonability of a useful approach on achieving highly efficient Am(III)/Eu(III) separation through tuning the preorganization level of the ligand and further provide meaningful theoretical basis on the input of preorganization toward ligand design and screening.

Insight into the Extraction Mechanism of Americium(III) over Europium(III) with Pyridylpyrazole: A Relativistic Quantum Chemistry Study.

Separation of trivalent actinides (An(III)) and lanthanides (Ln(III)) is one of the most important steps in spent nuclear fuel reprocessing. However, it is very difficult and challenging to separate them due to their similar chemical properties. Recently the pyridylpyrazole ligand (PypzH) has been identified to show good separation ability toward Am(III) over Eu(III). In this work, to explore the Am(III)/Eu(III) separation mechanism of PypzH at the molecular level, the geometrical structures, bonding nature, and thermodynamic behaviors of the Am(III) and Eu(III) complexes with PypzH ligands modified by alkyl chains (Cn-PypzH, n = 2, 4, 8) have been systematically investigated using scalar relativistic density functional theory (DFT). According to the NBO (natural bonding orbital) and QTAIM (quantum theory of atoms in molecules) analyses, the M-N bonds exhibit a certain degree of covalent character, and more covalency appears in Am-N bonds compared to Eu-N bonds. Thermodynamic analyses suggest that the 1:1 extraction reaction, [M(NO3)(H2O)6]2+ + PypzH + 2NO3- → M(PypzH)(NO3)3(H2O) + 5H2O, is the most suitable for Am(III)/Eu(III) separation. Furthermore, the extraction ability and the Am(III)/Eu(III) selectivity of the ligand PypzH is indeed enhanced by adding alkyl-substituted chains in agreement with experimental observations. Besides this, the nitrogen atom of pyrazole ring plays a more significant role in the extraction reactions related to Am(III)/Eu(III) separation compared to that of pyridine ring. This work could identify the mechanism of the Am(III)/Eu(III) selectivity of the ligand PypzH and provide valuable theoretical information for achieving an efficient Am(III)/Eu(III) separation process for spent nuclear fuel reprocessing.

A Recoverable Ruthenium Aqua Complex Supported on Silica Particles: An Efficient Epoxidation Catalyst.

The preparation and characterization of complexes with a phosphonated terpyridine (trpy) ligand (trpy-P-Et) and a bidentate pyridylpyrazole (pypz-Me) ligand, with formula [RuII (trpy-P-Et)(pypz-Me)X]n+ (2: X=Cl, n=1; 3: X=H2 O, n=2), is described, together with the anchoring of 3 on two types of supports: mesoporous silica particles (SP) and silica-coated magnetic particles (MSP). Aqua complex 3 is easily obtained by heating 2 in refluxing water and exhibits a two-electron RuIV/II redox process. It was anchored on SP and MSP supports by two different synthetic strategies, yielding the heterogeneous systems SP@3 and MSP@3, which were fully characterized by IR and UV/Vis spectroscopy, SEM, cyclic voltammetry, and differential pulse voltammetry. Catalytic olefin epoxidation was tested with molecular complex 3 and its SP@3 and MSP@3 heterogeneous counterparts, including reuse of the heterogeneous systems. The MSP@3 material can be easily recovered by a magnet, which facilitates its reusability.

Selective Extraction of Americium(III) over Europium(III) Ions with Pyridylpyrazole Ligands: Structure–Property Relationships

To clarify the structure–property relationships of pyridylpyrazole ligands and provide guidance for the design of new and more efficient ligands for the selective extraction of actinides over lanthanides, a series of alkyl‐substituted pyridylpyrazole ligands with different branched chains at different positions of the pyrazole ring were synthesized. Extraction experiments showed that the pyridylpyrazole ligands exhibited good selective extraction abilities for AmIII ions, and the steric effects of the branched chain had a significant impact on the distribution ratios of AmIII and EuIII ions as well as the separation factor. Moreover, both slope analyses and UV/Vis spectrometry titrations indicated the formation of a 1:1 complex of 2‐(1‐octyl‐1H‐pyrazol‐3‐yl)pyridine (C8‐PypzH) with EuIII ions. The stability constant (log K) for this complex obtained from the UV/Vis titration was 4.45 ± 0.04. Single crystals of the complexes of 3‐(2‐pyridyl)pyrazole (PypzH) with Eu(NO3)3 and Sm(NO3)3 were obtained; PypzH acts as a bidentate ligand in the crystal structures, and the N atom with a bound H atom did not participate in the coordination. In general, this study revealed some interesting findings on the effects of the alkyl‐chain structure and the special complexation between pyridylpyrazole ligands and LnIII ions.

Pyridylpyrazole N^N ligands combined with sulfonyl-functionalised cyclometalating ligands for blue-emitting iridium(iii) complexes and solution-processable PhOLEDs.

A series of blue iridium(iii) complexes (12-15) comprising sulfonyl-functionalised phenylpyridyl cyclometalating ligands and pyridylpyrazole N^N ligands are reported, with an X-ray crystal structure obtained for 12. The complexes are highly emissive with photoluminescence quantum yields of 0.52-0.70 in dichloromethane solutions: two of the complexes (12 and 14) show emissions at λ 457 nm which is considerably blue-shifted compared to the archetypal blue emitter FIrpic (λmax 468 nm). The short excited state lifetimes (1.8-3.3 μs) and spectral profiles are consistent with phosphorescence from a mixture of ligand-centred and MLCT excited states. Density functional (DFT) and time dependent DFT (TD-DFT) calculations are in agreement with the electrochemical properties and the blue phosphorescence of the complexes. The additional mesityl substituent on the pyridylpyrazole ligand of 12 and 13 enhances the solubility of the complexes facilitating thin film formation by solution processing. Phosphorescent organic light-emitting diodes (PhOLEDs) have been fabricated using 12 or 13 in a solution-processed single-emitting layer using either poly(vinylcarbazole) (PVK) or 1,3-bis(N-carbazolyl)benzene (mCP) as host. The most blue-shifted electroluminescence (λ 460 nm, CIEx,y 0.15, 0.21) is obtained for an OLED containing complex 12 and mCP, with a brightness of 5400 cd m-2 at 10 V which is high for PhOLEDs with similar blue CIE coordinates using a solution-processed emitter layer.

Syntheses, characterizations and structures of cadmium(II) and zinc(II) pseudohalide complexes containing pyridylpyrazole ligand

Syntheses, characterizations and structures of cadmium(II) and zinc(II) pseudohalide complexes containing pyridylpyrazole ligand

Mononuclear, dinuclear and 1-D polymeric complexes of Cd(II) of a pyridyl pyrazole ligand: Syntheses, crystal structures and photoluminescence studies

The syntheses, crystal structures and photoluminescence properties of four new Cd(II) complexes are reported using strongly coordinating ligand 3,5-dimethyl-1-(2′-pyridyl) pyrazole (L) in presence of anionic ancillary bridging ligands as nitrite, chloride and dicyanamide. Among the complexes two (1 and 2) are monomeric, 3 is μ2 – chloro bridged dimer and the last one (4) is a mixed alternate chloro – end to end (EE) dicyanamide bridged 1D polymer. All the four complexes have been X-ray crystallographically characterized. The ligand L behaves as a potent bidentate neutral N, N donor. Geometrical diversity of Cd(II) complexes is due to no loss or gain of crystal field stability with the variation of geometry. Consequently the stability of a structure depends on steric requirements. The ligand L shows considerable fluorescence and all four complexes in methanol exhibit interesting photoluminescence properties with different emission intensities. The band maxima and fluorescence efficiency (in methanol) are found to be dependent on the coordination chromophore and structural rigidity induced by the incorporated Cd(II) ion. Among the synthesized complexes 1 exhibits the highest fluorescence intensity in methanol.

A Highly Active Ruthenium(II) Pyrazolyl–Pyridyl–Pyrazole Complex Catalyst for Transfer Hydrogenation of Ketones

Ruthenium(II) complexes bearing a pyrazolyl–pyridyl–pyrazole ligand were synthesized and exhibited exceptionally high catalytic activity in the transfer hydrogenation of ketones in refluxing isopro...

A binuclear chloride bridged copper(II) complex with a modified ligand structure and different coordination environment and mononuclear cobalt(II) complexes with a pyridylpyrazole ligand: Synthesis, structure and cytotoxic activity

One new binuclear chloride bridged copper(II) complex [L′(Cl)Cu-(μ-Cl)-Cu(pz)L′](PF6)2 (1) and two mononuclear cobalt(II) complexes [Co(Cl)L]BF4·1/2CH3OH (2) and [Co(Cl)L]PF6 (3) where L={N,N-bis(3,5-dimethylpyrazol-1-ylmethyl)}(2-aminomethyl)pyridine, L′={N-(3,5-dimethylpyrazol-1-ylmethyl)}(2-aminomethyl)pyridine and pz=3,5-dimethyl-pyrazole have been synthesized and characterized by physico-chemical methods and single crystal X-ray diffraction studies. The crystal structure of the binuclear copper(II) complex [L′(Cl)Cu-(μ-Cl)-Cu(pz)L′](PF6)2 shows that the two square plane copper(II) moieties are joined through a single chloride (μ-Cl) bridge and the coordination environment around the two copper atoms are different, whereas the cobalt ion in [Co(Cl)L]BF4·1/2CH3OH has a trigonal bipyramidal geometry. The cytotoxic activity of the ligand, and the copper and cobalt complexes 1 and 2 were measured in vitro against the human lymphocyte HL-60 and it shows that the metal complexes have different cytotoxic activities to the organic ligand.

Programmable self-assembly of homo- or hetero-metallomacrocycles using 4-(1H-pyrazolyl-4-yl)pyridine

The dimetallic [M(2)(bpy)(2)(NO(3))(2)](NO(3))(2) moieties (M = Pd(II) or Pt(II)) react preferentially at the pyrazolyl end of the pyridyl-pyrazole ligand, giving rise to dimetallic corners. Subsequently, the dimetallic corner building blocks featuring two pyridine donors are coordinated by monometallic [M(bpy)(NO(3))(2)] moieties (M = Pd(II) or Pt(II)) to form homo- or hetero-metallomacrocycles.

From Simple to Complex: Topological Evolution and Luminescence Variation in a Copper(I) Pyridylpyrazolate System Tuned via Second Ligating Spacers

By systematically varying the geometric length and electronic properties of the second ligating ligands of halogen (Cl(-), Br(-), and I(-)) and pseudohalogen (CN(-), SCN(-), and N(3)(-)) anions, we synthesized 11 isomeric/isostructural copper(I) complexes: [Cu(2)(L3-3)I](n) (1), [Cu(2)(L4-4)Br](n) (2-Br), [Cu(2)(L4-4)Cl](n) (2-Cl), [Cu(2)(L3-4)(CN)](n) (3), [Cu(2)(L3-3)(CN)](n) (4), [Cu(3)(L4-4)(CN)(2)](n) (5), {[Cu(2)(L4-4)Br](2)·CuBr}(n) (6-Br), {[Cu(2)(L4-4)Cl](2)·CuCl}(n) (6-Cl), [Cu(2)(L4-4)(SCN)](n) (7α-SCN), [Cu(2)(L4-4)(SCN)](n) (7β-SCN), and [Cu(2)(L4-4)(N(3))](n) (7α-N(3)). These structures are based on a series of isomeric pyridylpyrazole ligands, namely, 3,5-bis(3-pyridyl)-1H-pyrazole (HL3-3), 3-(3-pyridyl)-5-(4-pyridyl)-1H-pyrazole (HL3-4), and 3,5-bis(4-pyridyl)-1H-pyrazole (HL4-4), and their structural features range from 1-D (1), 2-D (2), and 3-D noninterpenetration (3), to 3-D 2-fold interpenetration (4 and 5), to 3-D self-catenation (6 and 7), exhibiting a trend from simple to complex with dimension expansion and an interpenetrating degree increase. The five most complex structures (6 and 7) with self-catenated networks are based on 2-fold interpenetrated networks linked via appropriate second ligating spacers (Cl(-), Br(-), SCN(-), and N(3)(-)), representing a strategy to construct self-catenated coordination polymers through cross-linking interpenetrated frameworks. Moreover, these complexes exhibit strong photoluminescence, which is mainly ascribed to Cu(I)-related charge transfers (MLCT, MC, and MMLCT) regulated by the electronic properties of halogen or pseudohalogen. The topological evolution and luminescence variation presented in this work open an avenue to understanding the luminescence origin and the structure-property relationship of luminescent coordination polymers.

Cyanato bridged binuclear nickel(II) and copper(II) complexes with pyridylpyrazole ligand: Synthesis, structure and magnetic properties

Binuclear cyanate bridged nickel(II) complex [Ni(L)(NCO)]2(PF6)2 (1) and copper(II) complex [Cu(L)(NCO)]2(PF6)2 (2), where L is N,N-bis(3,5-dimethylpyrazol-1-ylmethyl)aminomethylpyridine, a tetradentate N4-coordinated ligand have been synthesized and characterized by physicochemical method. The structures of complexes 1 and 2 have been studied by single crystal X-ray diffraction analysis. The structure analysis reveals that both nickel(II) and copper(II) center are coordinated in distorted octahedral fashion and coordination mode of cyanate ligand is end-to-end (μ-1,3) for complex 1 but it is double end-on (μ-1,1) mode for complex 2. The variable temperature magnetic susceptibility data, measured from 2 to 300K, show weak antiferromagnetic interaction with J value −6.2(1)cm−1 for complex 1, whereas complex 2 has very weak ferromagnetic interaction with J value +0.5(1)cm−1.

Syntheses, crystal structures and magnetic properties of two dicopper(II) complexes and a zigzag 1-D Cu(II) complex of a bidentate pyridyl-pyrazole ligand

Two new dinuclear copper compounds, [Cu2(pypz)2(N3)2(NO3)2] (1) and [Cu2(pypz)2(OH)2(NO3)2] (2), and one 1-D polymeric Cu(II) complex, [Cu(pypz)(dca)3]n (3) [‘pypz’=(3,5dimethyl-1-(2′-pyridyl)pyrazole) and dca=(dicyanamide)], have been synthesized and characterized crystallographically and spectroscopically. Complex 1 is pseudo-octahedral, adjacent Cu atoms are connected by a pair of μ(1,1) azido groups and the structure is stabilized by π–π interactions between two pyridyl moieties from two different neighboring complex molecules. Complexes 2 and 3 are square pyramidal. The hydroxo bridged complex 2 is further stabilized through H-bonding. The 1-D polymeric chain of 3 is bridged by an end-to-end dicyanamide bridge and it propagates along the crystallographic b axis, whilst the polymer chains are stacked one upon another along the crystallographic c axis. Low temperature magnetic measurement shows that complexes 1 and 2 are ferromagnetic (J values are 30.81 and 14.79cm−1, respectively), whereas due to larger Cu–Cu distances, complex 3 shows weak ferromagnetism.

Dinuclear metal phosphonates and -phosphates

The reaction of Cu(II) or Cd(II) salts with 2,4,6- iPr 3C 6H 2PO 3H 2, 2,4,6- iPr 3C 6H 2CH 2PO 3H 2 or 2,6- iPr 2C 6H 3OPO 3H 2 in the presence of strong chelating nitrogen ligands such as 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 2-pyridylpyrazole (pypz) or 3,5-dimethyl pyrazole (dmpz) as the ancillary ligands afforded dinuclear copper or cadmium complexes [Cu 2(2,4,6- iPr 3C 6H 2PO 3H) 4(bpy) 2] (4), [Cu 2(2,6- iPr 2C 6H 3OPO 3H) 2(bpy) 2(OAc) 2(CH 3OH) 2]·(CH 3OH) (5), [Cd 2(2,6- iPr 2C 6H 3OPO 3H) 4 (bpy) 2(CH 3OH) 2]·2(CH 3OH) (6), [Cd 2(2,6- iPr 2C 6H 3OPO 3H) 4(phen) 2] (7), [Cu 2(2,6- iPr 2C 6H 3OPO 3H) 2(PyPz) 2(CH 3OH) 2] (8) and [Cu 2(2,4,6- iPr 3C 6H 2CH 2PO 3H) 2(DMPz) 2Cl 2]·(CH 3OH) (9) The molecular structures of 4–7 are grossly similar. The common structural features in these complexes are that the two metal centers are bridged by two bidentate [RPO 2(OH)] − ligands generating a central eight-membered ring. Each of the metal centers also contains a chelating nitrogen ligand and a monodentate phosphonate or a phosphate ligand. In 5 and 6 other terminal ancillary ligands are also present. In compound 8, each of the two copper centers contains a monodentate [RPO 2(OH)] − ligand along with a molecule of methanol. The two coppers are bridged by two monoanionic pyridylpyrazole ligands. The molecular structure of 9 is similar to that of 4–7. However, in 9 each of the two copper centers contain only terminal monodentate ligands in the form of two chlorides and a pyrazole. Magnetic studies on all of these copper complexes reveal an anti-ferromagnetic behavior at low temperatures. In addition, these complexes were found to be artificial nucleases and can convert supercoiled pBR322 DNA form I into nick form II in 1 min in the presence of an external oxidant through a hydrolytic and/or an oxidative pathway.

Highly Efficient Pyridylpyrazole Ligands for the Heck Reaction. A Combined Experimental and Computational Study

Several [PdCl2(L)] complexes, where L is a pyridylpyrazole ligand, have been used as precatalysts in the Heck reactions between phenyl halides and tert-butyl acrylate. The used ligands differ from each other in the substitution at N1. The best results are obtained when this substituent is a hydroxyethyl group, and the corresponding complexes yield good results even for the reaction of chlorobenzene. Theoretical studies have shown that the presence of an OH group in the N1 substituent favors Pd−X dissociation, since it stabilizes the resulting cationic complex and the dissociation becomes thermodynamically favorable even in the absence of a coordinating solvent molecule.

C,N‐Pyridylpyrazole‐Based Ligands: Synthesis and Preliminary Use in Metal Ion Extraction

The synthesis of new N‐donor pyridylpyrazole ligands with a functionalized arm is described. The complexation capabilities of these compounds towards bivalent metal ions (Hg2+, Cd2+, Pb2+, Cu2+, and Zn2+) and alkali metal ions (K+, Na+, and Li+) were investigated using the liquid‐liquid extraction process. The percentage limits of extraction were determined by atomic absorption measurements.