Bipyridyl Ligands Research Articles

Two New NIR Luminescencent Er(III) Coordination Polymers with Potential Application Optical Amplification Devices

Two new Er(III)-cluster-based coordination compounds have been synthesized by hydrothermal technique using monosodium 2-sulfoterephthalate (2-stp) and 4,4′-bipyridyl (4,4′-bpy) ligands. Depending on synthetic procedure, monomeric and polymeric Er(III) products, isolated as {[Er(2-stp)2(H2O)6]0.2(4,4′-bipy)0.4(H2O)}, 1 and {[Er(2-stp)(4,4′-bipy)(H2O)](H2O)}n, 2. Both compounds have been characterized by elemental analysis, FT-IR, UV–visible and single-crystal X-ray diffraction and solid-state photoluminescence. The X-ray structure analyses show that Er atom is surrounded by two 2-stp ligands which have monodentate connection mode forming a monomeric structure in compound 1. However, in compound 2, Er atoms are coordinated by four bridging 2-stp ligands which adopt a hexadentate connection mode to form a central symmetrically dimeric building unit. The photoluminescence spectrums of the compounds have been exhibited intense blue emission for 1 and cyan-blue emission for 2. The band observed in NIR region at 1532 nm (for 1) and 1540 nm (for 2) are the typical ErIII emission. The excellent NIR luminescent properties, indicating their promising potential applications as gain medium materials in optical amplification devices.

Complexation of a guanidinium-modified calixarene with diverse dyes and investigation of the corresponding photophysical response.

We herein describe the comprehensive investigation of the complexation behavior of a guanidinium-modified calix[5]arene pentaisohexyl ether (GC5A) with a variety of typical luminescent dyes. Fluorescein, eosin Y, rose bengal, tetraphenylporphine sulfonate and sulfonated aluminum phthalocyanine were employed as classical aggregation-induced quenching dyes. 2-(p-Toluidinyl)naphthalene-6-sulfonic acid and 1-anilinonaphthalene-8-sulfonic acid were selected as representatives of intramolecular charge-transfer dyes. Phosphated tetraphenylethylene was involved as the classical aggregation-induced emission dye. Sulfonated acedan representing one example of two-photon fluorescent probes, was also investigated. A ruthenium(II) complex with carboxylated bipyridyl ligands was included as a representative candidate of luminescent transition-metal complexes. We determined the association constants of the GC5A–dye complexes by fluorescence titration and discuss the complexation-induced photophysical changes. In addition, a comparison of the complexation behavior of GC5A with that of other macrocycles and potential applications according to the diverse photophysical responses are provided.

Highly Active Ruthenium CNC Pincer Photocatalysts for Visible-Light-Driven Carbon Dioxide Reduction.

Five ruthenium catalysts described herein facilitate self-sensitized carbon dioxide reduction to form carbon monoxide with a ruthenium catalytic center. These catalysts include four new and one previously reported CNC pincer complexes featuring a pyridinol derived N-donor and N-heterocyclic carbene (NHC) C-donors derived from imidazole or benzimidazole. The complexes have been characterized fully by spectroscopic and analytic methods, including X-ray crystallography. Introduction of a 2,2'-bipyridine (bipy) coligand and phenyl groups on the NHC ligand was necessary for rapid catalysis. [(CNC)Ru(bipy)(CH3CN)](OTf)2 is among the most active and durable photocatalysts in the literature for CO2 reduction without an external photosensitizer. The role of the structure of this complex in catalysis is discussed, including the importance of the pincer's phenyl wingtips, the bipyridyl ligand, and a weakly coordinating monodentate ligand.

Molecular Design of pH-Sensitive Ru(II)-Polypyridyl Luminophores.

Three new [Ru(bpy)2X]+ complex ions, where bpy represents bipyridyl ligand and X denotes pyridyl diazolate or pyrazinyl diazolate coordination site, have been computationally designed and synthesized as pH-sensitive molecules. The choice of pyridyl and pyrazinyl moieties allows for the nitrogen content to vary, whereas the influence of the protonation site is quantified by using 1,2-diazolate and 1,3-diazolate derivatives. The absorption and emission properties of the deprotonated and protonated complex ions were characterized by UV-vis and photoluminescence spectroscopy as well as by time-dependent density functional theory. Protonation causes (1) a strong blue shift in the lowest energy 3MLCT → S0 emission wavelengths, (2) a substantial increase in the emission intensity, and (3) a change in the character of the corresponding 3MLCT emitting states. The blue shift in the emission wavelength becomes less pronounced when the nitrogen content in the X-ligand increases and when going from 1,2- to 1,3-diazolate derivatives. The contrast in the emission intensity of the protonated/deprotonated forms is the highest for the complex ion, containing a 2-pyridyl derivative of the 1,2-diazolate. The complex ions are suggested as potential pH-responsive materials based on change in the color and intensity of the emitted radiation. The broad impact of the research demonstrates that the modification of the nitrogen content and position within the protonable ligands is an effective approach for modulation of the pH-optosensing properties of Ru-polypyridyl complexes.

Optimisation of octahedral iron(II) and cobalt(II) spin-crossover metal complex for thermoelectric application

Four spin-crossover (SCO) complexes with general formulae, [M2(CH3COO)4(L)2] and [M(L)3](BF4)2, where M = Fe(II) and Co(II), containing extended π-conjugated bipyridyl ligand and N3-Schiff bases appended with linear C16 carbon chains at the N atoms were successfully synthesized and characterized. Correlation of its structural properties to thermoelectric behavior is investigated: (1)structure of complexes, (2)choice of metal centre and (3)choice of counter ions. It was found that the structure of the molecule, i.e. molecular versus ionic has the largest impact on the SCO behavior. We found that the molecular complexes with higher percentage of high-spin (73.4% HS for Fe-dinuc and 78% HS for Co-dinuc) have produced the highest Seebeck values in mV K−1 (−0.57 ± 0.01 for Fe-dinuc and −0.58 ± 0.01 for Co-dinuc) due to the weaker metal-to-ligand bonds resulting in the increase mobility of the I− during agglomeration formed, thus increased the entropy in the solution. Additionally, choice of metal centre also was a factor to determine the magnitude of Seebeck performance due to the spin state transition during electron transfer. For counter ion effect, it has the effect of determining the sign of the Seebeck value where I− is easier to oxidize/reduce process compared to CH3COO− and BF4− due to lower redox potential. These findings will assist in a systematic molecule design pathway for high potential SCO complexes for thermoelectric applications.

Phosphorogenic and spontaneous formation of tris(bipyridine)ruthenium in peptide scaffolds.

Redox-active ruthenium complexes have been widely used in various fields; however, the harsh conditions required for their synthesis are not always conducive to their subsequent use in biological applications. In this study, we demonstrate the spontaneous formation of a derivative of tris(bipyridine)ruthenium at 37°C through the coordination of three bipyridyl ligands incorporated into a peptide to a ruthenium ion. Specifically, we synthesized six bipyridyl-functionalized peptides with randomly chosen sequences. The six peptides bound to ruthenium ions and exhibited similar spectroscopic and electrochemical features to tris(bipyridine)ruthenium, indicating the formation of ruthenium complexes as we anticipated. The photo-excited triplet state of the ruthenium complex formed in the peptides exhibited an approximately 1.6-fold longer lifetime than that of tris(bipyridine)ruthenium. We also found that the photo-excited state of the ruthenium complexes was able to transfer an electron to methyl viologen, indicating that the ruthenium complexes formed in the peptides had the same ability to transfer charge as tris(bipyridine)ruthenium. We believe that this strategy of producing ruthenium complexes in peptides under mild conditions will pave the way for developing new metallopeptides and metalloproteins containing functional metal-complexes.

Mechanistic Study of Ruthenium-Catalyzed C-H Hydroxylation Reveals an Unexpected Pathway for Catalyst Arrest.

We have recently disclosed [(dtbpy)2RuCl2] as an effective precatalyst for chemoselective C-H hydroxylation of C(sp3)-H bonds and have noted a marked disparity in reaction performance between 4,4'-di- tert-butyl-2,2'-bipyridine (dtbpy)- and 2,2'-bipyridine (bpy)-derived complexes. A desire to understand the origin of this difference and to further advance this catalytic method has motivated the comprehensive mechanistic investigation described herein. Details of this reaction have been unveiled through evaluation of ligand structure-activity relationships, electrochemical and kinetic studies, and pressurized sample infusion high-resolution mass spectrometry (PSI-MS). Salient findings from this investigation include the identification of more than one active oxidant and three disparate mechanisms for catalyst decomposition/arrest. Catalyst efficiency, as measured by turnover number, has a strong inverse correlation with the rate and extent of ligand dissociation, which is dependent on the identity of bipyridyl 4,4'-substituent groups. Dissociated bipyridyl ligand is oxidized to mono- and bis- N-oxide species under the reaction conditions, the former of which is found to act as a potent catalyst poison, yielding a catalytically inactive tris-ligated [Ru(dtbpy)2(dtbpy N-oxide)]2+ complex. Insights gained through this work highlight the power of PSI-MS for studies of complex reaction processes and are guiding ongoing efforts to develop high-performance, next-generation catalyst systems for C-H hydroxylation.

The effects of extended π-conjugation in bipyridyl ligands on the tunable photophysics, triplet excited state and optical limiting properties of Pt(ii) naphthalimidyl acetylide complexes.

Pt(ii) complexes that exhibit long-lived triplet excited state lifetimes are promising for optical power limiting materials. The introduction of large π-conjugated substituents can switch the triplet excited state to a long-lived 3π,π* state. Herein, we report four Pt(ii) diimine complexes with high π-conjugation via inserting an aryl group on the diimine ligand. Their photophysical properties were investigated using spectroscopic techniques. All the complexes exhibit strong ground absorption bands in their UV-Vis absorption spectra (maximum peaks ranging from 370 to 530 nm) and long-lived emission and triplet excited states. The insertion of π-conjugated substituents induces a pronounced red-shift in the ground state absorption and longer emission lifetime. Broadband transient absorption spectra in the visible-NIR region and Z-scan properties under 532 nm were carried out on the Pt(ii) diimine complexes, resulting in a remarkably strong reverse saturable absorption at 532 nm for nanosecond laser pulses. Otherwise, the high π-conjugation in the bipyridyl ligand increases the reverse saturable absorption. Therefore, these Pt(ii) diimine complexes with high π-conjugation are excellent candidates for devices that require strong reverse saturable absorption.

Antibacterial activities of Cu-MOFs containing glutarates and bipyridyl ligands.

Metal-organic frameworks (MOFs) can be utilized as antibacterial agents due to their effective antibacterial activities. Four three-dimensional (3D) Cu-MOFs formulated as [Cu2(Glu)2(μ-L)]·x(H2O) (Glu is glutarate, and L is bpy = 4,4'-bipyridine (1), bpa = 1,2-bis(4-pyridyl)ethane (2), bpe = 1,2-bis(4-pyridyl)ethylene (3), and bpp = 1,2-bis(4-pyridyl)propane (4)) were synthesized by hydrothermal reactions or modified literature methods. Their solid-state structures were slightly modified to increase their hydrolytic stabilities in aqueous solution. Despite the seemingly sufficient void spaces in all the solvent-free MOFs, only the thermally activated form of MOF 2 displayed selective gas uptake ability for CO2 over N2 and H2. The antibacterial activities of the four Cu-MOFs, 1, 2, 3, and 4, were investigated by determining their minimal bactericidal concentration (MBC) values against five strains of bacteria, including E. coli, S. aureus, K. pneumonia, P. aeruginosa, and MRSA, which can be easily met in our daily surrounding environments. Although these Cu-MOFs were found to be structurally very stable in aqueous medium during antibacterial activity tests, they exhibited excellent antibacterial activities against all five kinds of bacteria, including Gram-positive bacteria (S. aureus and MRSA) and Gram-negative bacteria (E. coli, K. pneumonia, and P. aeruginosa), with very low MBCs. The robust 3D frameworks with surface active metal sites rather than the small amount of leached CuII ions may participate more strongly in inactivating various kinds of bacteria and reduce potential cytotoxicity mainly caused by leached metal ions.

Ruthenium(II) Complexes of Mixed Bipyridyl and Dithiolate Ligands: Synthesis, Characterization and Electrochemical Studies

Ruthenium(II) Complexes of Mixed Bipyridyl and Dithiolate Ligands: Synthesis, Characterization and Electrochemical Studies

Chemical and Electrochemical Properties of [Cp*Rh] Complexes Supported by a Hybrid Phosphine-Imine Ligand

A series of [Cp*Rh] complexes (Cp* = η5-pentamethylcyclopentadienyl) bearing the κ2-[P,N]-8-(diphenylphosphino)quinoline (PQN) ligand have been prepared and characterized. Chemical or electrochemical reduction of the rhodium(III) form generates an isolable rhodium(I) complex; this rhodium(I) complex reacts with a range of organic acids to yield a rhodium(III) hydride bearing [Cp*] in the η5 mode and [PQN] in the expected κ2 mode. Solid-state structures of these three compounds from X-ray diffraction studies reveal only small changes in the intraligand bond distances across the series, suggesting the redox events associated with interconversion of these compounds are primarily metal centered. Cyclic voltammetry data show that the rhodium(III) chloride complex undergoes a two-electron reduction at −1.19 V vs ferrocenium/ferrocene, whereas the analogous solvento rhodium(III) acetonitrile complex undergoes two sequential one-electron reductions. The rhodium(III) hydride undergoes an irreversible, ligand-centered reduction near −1.75 V vs ferrocenium/ferrocene. Carrying out this reduction alone or in the presence of added of triethylammonium as a source of protons results in only modest yields of H2, as shown by bulk electrolyses and chemical reduction experiments. These results are discussed in the context of recent work with [Cp*Rh] complexes bearing more symmetric 2,2′-bipyridyl and diphosphine ligands.

Single-Electron Redox Chemistry on the [Cp*Rh] Platform Enabled by a Nitrated Bipyridyl Ligand.

[Cp*Rh] complexes (Cp* = pentamethylcyclopentadienyl) are attracting renewed interest in coordination chemistry and catalysis, but these useful compounds often undergo net two-electron redox cycling that precludes observation of individual one-electron reduction events. Here, we show that a [Cp*Rh] complex bearing the 4,4′-dinitro-2,2′-bipyridyl ligand (dnbpy) (3) can access a distinctive manifold of five oxidation states in organic electrolytes, contrasting with prior work that found no accessible reductions in aqueous electrolyte. These states are readily generated from a newly isolated and fully characterized rhodium(III) precursor complex 3, formulated as [Cp*Rh(dnbpy)Cl]PF6. Single-crystal X-ray diffraction (XRD) data, previously unavailable for the dnbpy ligand bound to the [Cp*Rh] platform, confirm the presence of both [η5-Cp*] and [κ2-dnbpy]. Four individual one-electron reductions of 3 are observed, contrasting sharply with the single two-electron reductions of other [Cp*Rh] complexes. Chemical preparation and the study of the singly reduced species with electronic absorption and electron paramagnetic resonance spectroscopies indicate that the first reduction is predominantly centered on the dnbpy ligand. Comparative cyclic voltammetry studies with [NBu4][PF6] and [NBu4][Cl] as supporting electrolytes indicate that the chloride ligand can be lost from 3 by ligand exchange upon reduction. Spectroelectrochemical studies with ultraviolet (UV)-visible detection reveal isosbestic behavior, confirming the clean interconversion of the reduced forms of 3 inferred from the voltammetry with [NBu4][PF6] as supporting electrolyte. Electrochemical reduction in the presence of triethylammonium results in an irreversible response, but does not give rise to catalytic H2 evolution, contrasting with the reactivity patterns observed in [Cp*Rh] complexes bearing bipyridyl ligands with less electron-withdrawing substituents.

Controlling Reversible Expansion of Li2O2 Formation and Decomposition by Modifying Electrolyte in Li-O2 Batteries

Summary The aprotic lithium-oxygen (Li-O2) battery has attracted worldwide attention because of its ultrahigh theoretical energy density. However, its practical application is critically hindered by cathode passivation, large polarization, and severe parasitic reactions. Here, we demonstrate an originally designed Ru(II) polypyridyl complex (RuPC) though which the reversible expansion of Li2O2 formation and decomposition can be achieved in Li-O2 batteries. Experimental and theoretical results revealed that the RuPC can not only expand the formation of Li2O2 in electrolyte but also suppress the reactivity of LiO2 intermediate during discharge, thus alleviating the cathode passivation and parasitic reactions significantly. In addition, an initial delithiation pathway can be achieved when charging in turn; thus, the Li2O2 products can be decomposed reversibly with a low overpotential. Consequently, the RuPC-catalyzed Li-O2 batteries exhibited a high discharge capacity, a low charge overpotential, and an ultralong cycle life. This work provides an alternative way of designing the soluble organic catalysts for metal-O2 batteries.

Spin Crossover Behavior in a Homologous Series of Iron(II) Complexes Based on Functionalized Bipyridyl Ligands.

A series of bulky substituted bipyridine-related iron(II) complexes [Fe(H2Bpz2)2(L)] (pz = pyrazolyl) were prepared, where L = 5,5'-dimethyl-2,2'-bipyridine (bipy-CH3, 1), L = dimethyl-2,2'-bipyridyl-5,5'-dicarboxylate (MeObpydc, 2), L = diethyl-2,2'-bipyridyl-5,5'-dicarboxylate (EtObpydc, 3), or L = diisopropyl-2,2'-bipyridine-5,5'-dicarboxylate ( i-PrObpydc, 4). The crystal structures of five new iron(II) complexes were determined by X-ray diffraction: those of 1, 3, and 4 and two modifications of 3 (3B) and 4 (4B). Complexes 1 and 3B display incomplete spin crossover (SCO) behavior because of a freezing-in effect, whereas 3 and 4B undergo gradual and incomplete SCO behaviors. Complexes 2 and 4 show a completely gradual and steep SCO, respectively. Such different SCO behaviors can be attributed to an electronic substituent effect in the bipyridyl ligand conformation and a crystal packing effect. Importantly, the electronic substituent effect of the isopropyl acetate group and C-H···O supramolecular interactions in 4 contribute to a highly cooperative behavior, which leads to an abrupt thermally induced spin transition.

Half-sandwich Iridium(III) complexes with triphenylamine-substituted dipyridine frameworks and bioactivity applications

Nine half-sandwich IrIII complexes [(η5-Cpx)Ir(NˆN)Cl]PF6, where Cpx is Cp* or its phenyl Cpxph or biphenyl Cpxbiph derivative and NˆN is a triphenylamine (TPA)-substituted bipyridyl ligand, were synthesized and characterized. MTT assay revealed that the complexes show potent antitumor activity with IC50 values of 1.2–36.3 μM against A549 lung cancer cells. The IrIII complexes bound to BSA and oxidized NADH to NAD+, leading to production of H2O2 (maximum turnover number, 37.9), which plays an important role in regulating cell apoptosis. Confocal microscopy showed that the complexes could target lysosomes effectively in cells with a high Pearson's colocalization coefficient (∼0.5) and followed an energy-dependent cellular uptake mechanism.

Synthesis and characterization of two one-dimensional CdII coordination polymers (CPs) with 5-amino-2,4,6-tribromoisophthalic acid and flexible N-donor bipyridyl ligands.

The bromo-substituted aromatic dicarboxylic acid 5-amino-2,4,6-tribromoisophthalic acid (H2ATBIP) was used to assemble with CdII ions in the presence of the N-donor flexible bipyridyl ligands 3,3'-(diazene-1,2-diyl)dipyridine (mzpy) and 1,3-bis(pyridin-3-ylmethyl)urea (3bpmu), leading to the formation of two chain coordination polymers by adopting solution methods, namely, catena-poly[[[triaqua(5-amino-2,4,6-tribromoisophthalato-κO)cadmium(II)]-μ-3,3'-(diazene-1,2-diyl)dipyridine-κ2N1:N1'] dihydrate], {[Cd(C8H2Br3NO4)(C10H8N4)(H2O)3]·2H2O}n or {[Cd(ATBIP)(mzpy)(H2O)3]·2H2O}n, (1), and catena-poly[[[tetraaquacadmium(II)]-μ-1,3-bis(pyridin-3-ylmethyl)urea-κ2N1:N1'-[diaquabis(5-amino-2,4,6-tribromoisophthalato-κO)cadmium(II)]-μ-1,3-bis(pyridin-3-ylmethyl)urea-κ2N1:N1'] octahydrate], {[Cd(C8H2Br3NO4)(C12H12N4O)(H2O)3]·4H2O}n or {[Cd(ATBIP)(3bpmu)(H2O)3]·4H2O}n, (2). Both complexes were characterized by FT-IR spectroscopic analysis, thermogravimetric analysis (TGA), solid-state diffuse reflectance UV-Vis spectroscopic analysis, and single-crystal and powder X-ray diffraction analysis (PXRD). The mzpy and 3bpmu ligands bridge the CdII metal centres in (1) and (2) into one-dimensional chains, and the ATBIP2- ligands show a monodentate coordination to the CdII centres in both coordination polymers. A discrete water tetramer exists in (1). Within the chains of (1) and (2), there are halogen bonds between adjacent ATBIP2- and mzpy or 3bpmu ligands, as well as hydrogen bonds between the ATBIP2- ligands and the coordinated water molecules. With the aid of weak interactions, the structures of (1) and (2) are further extended into three-dimensional supramolecular networks. An analysis of the solid-state diffuse reflectance UV-Vis spectra of (1) and (2) indicates that a wide indirect band gap exists in both complexes. Complexes (1) and (2) exhibit irreversible and reversible dehydration-rehydration behaviours, respectively, and the solid-state fluorescence properties of both complexes have been studied.

Crystal Structures of 2,2′-Bipyridyl Palladium(II) Complexes: [Pd(PPh3)2{κ1-C10H6N2Br}(Br)] and [Pd(PPh3)2Br]2{μ,κ2-C10H6N2}

A reaction of Pd(PPh3)4 (complex 1) and 6,6′-dibromo-2,2′-bipyridyl C10H6N2Br2 in a 1:1 molar ratio or 2:1 produces a mononuclear [Pd(PPh3)2{κ1-C10H6N2Br}(Br)] complex (2) and a binuclear [Pd(PPh3)2Br]2{μ,κ2-C10H6N2}complex (3). In complex 3, the 2,2′-bipyridyl ligand is coordinated through two C and two metal (Pd) centers and bridges two Pd atoms to the trans-N of the 2,2′-bipyridyl ligand. The crystal characteristics are outlined as follows: space group P2(1)/n, Z = 2, a = 9.2008(4) A, b = 14.5268(6) A, c = 30.6609(13) A, α = 90, β = 91.3415(13), and γ = 90°. Complexes 2 and 3 are characterized through elemental analyses, fast atom bombardment mass spectrometry, 1H, 13C, and 31P nuclear magnetic resonance spectroscopy, and single crystal X-ray diffraction.

ZnO nanowire sensitization with Ru polypyridyl complexes: charge-transfer probed by spectral and relaxation photocurrent measurements

Dye-sensitized ZnO nanowire (NW) electrodes were fabricated using Ru polypyridyl complexes that use nitrile instead of carboxylic group as anchoring unit to the NW surfaces. The complexes formula is [Ru(bpy)3−x(Mebpy-CN)x]2+ (x = 1−3, bpy = 2,2′-bipyridine, Mebpy-CN = 4-methyl-2,2′-bipyridine-4′-carbonitrile). The ZnO NWs were grown by a vapor transport method on insulating SiO2/Si substrates. The sensitized ZnO NW electrodes were studied by electron microscopy, Raman and PL spectroscopies, and spectral and relaxation photocurrent measurements. The Raman spectra confirm that the complexes were effectively anchored to the ZnO NWs through one of the pendant nitrile groups of the bipyridyl ligands. The nanostructured morphology of the NW electrodes was maintained so that their light trapping characteristics were preserved. The Ru complexes were found to be excellent sensitizers of the ZnO NWs, improving by orders of magnitude their photocurrent in the visible region. The Fe-based complex of formula [Fe(Mebpy-CN)3](PF6)2 was also tested; however it did not show any sensitizing effect. An order of magnitude shortening of the persistent photocurrent relaxation times (after the illumination is interrupted) was found to occur upon successful sensitization of the ZnO NWs with the Ru complexes. This effect is interpreted in terms of hole traps at ∼1 eV above the ZnO valence band edge, which are lowered by ∼50–60 meV in the soaked samples due to screening of the trap centers provided by the extra photoexcited charge carriers transferred from the sensitizing complex to the NWs.

Anion-controlled geometrically different Cu(II) ion-based coordination polymers and green synthetic route for copper nanoparticles: a combined experimental and computational insight

The Cu(II) ion-based polymeric complexes [Cu(2,2′-bpy).(N3)2]n (I), [Cu2(2,2′-bpy)2.(N3)4]n (II), and monomeric complex [Cu(2,2′-bpy).(NO3)2].5H2O (III) have been synthesized with rigid (–N3) and aromatic (2,2′-bpy = 2,2′-bipyridyl) ligand. The rigid azide group is responsible for the formation of 1-D extended structures in complexes I and II where as in the case of complex III, a monomeric complex is formed due to lack of a bridging group like –N3, resulting in limitation in dimensionality. The thermal stability of the 1-D complexes is comparatively higher than monomeric complex III. Hirshfeld surface analysis has also been applied to investigate other weak interactions and compared with the results from single-crystal X-ray data. Due to the presence of paramagnetic metal centers and long metal···metal distances in complexes I and II and presence of lattice water molecules in complex III, decrease in luminescence intensities have been observed. To attain further insights into the aforementioned interesting species, some chemical concepts such as highest occupied molecular orbital–lowest unoccupied molecular orbital gap, electronic chemical potential, chemical hardness, and electrophilicity index, identified as a derivative of electronic energy, have also been emphasized employing the quantum chemical calculations in the framework of the density functional theory method using the M06-2X/ 6-31G** level of study. Further, these complexes have been used to synthesize copper nanoparticles by applying a green synthetic route.

Ruthenium(II) Complexes Having a Pincer‐Type Ligand with Two N‐Heterocyclic Carbene Moieties

Two novel RuII complexes, having 2,2′‐bipyridyl and a pincer‐type methylene‐bridged N‐heterocyclic carbene (NHC) ligand, were synthesized and characterized to evaluate the effects of structural features of the complexes on their redox and photochemical properties. The methylene‐bridged NHC ligand coordinated in a meridional manner and the isopropyl groups on the NHC rings exhibited intramolecular CH/π interaction with the 2,2′‐bipyridyl ligand, which played a role to strongly maintain the distorted ligand structure. In addition, the two Ru complexes exhibited reversible redox waves in the cyclic voltammograms and they were oxidized by an electron‐transfer oxidant to afford RuIII complexes, which were characterized by EPR spectroscopy and theoretical analyses.