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Synthesis, characterization, electronic structure, and redox reactions of a mononuclear {FeNO}7complex with a very high N–O stretching frequency in solution are presented. Nitrosylation of [(LKP)Fe(DMF)]2+(1) (LKP= tris((1-methyl-4,5-diphenyl-1H-imidazol-2-yl)methyl)amine) produced a five-coordinate {FeNO}7complex, [(LKP)Fe(NO)]2+(2). While complex 2could accommodate an additional water molecule to generate a six-coordinate {FeNO}7complex, [(LKP)Fe(NO)(H2O)]2+(3), the coordinated H2O in 3dissociates to generate 2in solution. The molecular structure of 2features a nearly linear Fe–N–O unit with an Fe–N distance of 1.744(4) Å, N–O distance of 1.162(5) Å, and

A series of mononuclear non-oxido vanadium(IV) complexes, [VIV(L1–4)2] (1–4), featuring tridentate bi-negative ONS chelating S-alkyl/aryl-substituted dithiocarbazate ligands H2L1–4, are reported. All the synthesized non-oxido VIVcompounds are characterized by elemental analysis, spectroscopy (IR, UV–vis, and EPR), ESI-MS, as well as electrochemical techniques (cyclic voltammetry). Single-crystal X-ray diffraction studies of 1–3reveal that the mononuclear non-oxido VIVcomplexes show distorted octahedral (1and 2) or trigonal prismatic (3) arrangement around the non-oxido VIVcenter. EPR and DFT data indicate the coexistence of merand facisomers in solution, and ESI-MS results suggest a partial oxidation of [VIV(L1–4)2] to [VV(L1–4)2]+and [VVO2(L1–4)]−; therefore, all these three complexes are plausible active species. Complexes 1–4interact with bovine serum albumin (BSA) with a moderate binding affinity, and docking calculations reveal non-covalent interactions with different regions of BSA, particularly with Tyr, Lys, Arg, and Thr residues. In vitrocytotoxic activity of all complexes is assayed against the HT-29 (colon cancer) and HeLa (cervical cancer) cells and compared with the NIH-3T3 (mouse embryonic fibroblast) normal cell line by MTT assay and DAPI staining. The results suggest that complexes 1–4are cytotoxic in nature and induce cell death in the cancer cell lines by apoptosis and that a mixture of VIV, VV, and VVO2species could be responsible for the biological activity.

Herein, we present an unprecedented formation of a heterodinuclear complex [{(ppy)2IrIII}(μ-phpy){RuII(tpy)}](ClO4)2{[1](ClO4)2} using terpyridyl/phenylpyridine as ancillary ligands and asymmetric phpy as a bridging ligand. The asymmetric binding mode (N∧N-∩-N∧N∧C–) of the phpy ligand in {[1](ClO4)2} is confirmed by 1H, 13C, 1H–1H correlated spectroscopy (COSY), high-resolution mass spectrum (HRMS), single-crystal X-ray crystallography techniques, and solution conductivity measurements. Theoretical investigation suggests that the highest occupied molecular orbital (HOMO) and the least unoccupied molecular orbital (LUMO) of [1]2+are located on iridium/ppy and phpy, respectively. The complex displays a broad low energy charge transfer (CT) band within 450–575 nm. The time-dependent density functional theory (TDDFT) analysis suggests this as a mixture of metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT), where both ruthenium, iridium, and ligands are involved. Complex {[1](ClO4)2} exhibits RuIIIrIII/RuIIIIrIII- and RuIIIIrIII/RuIIIIrIV-based oxidative couples at 0.83 and 1.39 V, respectively. The complex shows anticancer activity and selectivity toward human breast cancer cells (IC50; MCF-7: 9.3 ± 1.2 μM, and MDA-MB-231: 8.6 ± 1.2 μM) over normal breast cells (MCF 10A: IC50≈ 21 ± 1.3 μM). The Western blot analysis and fluorescence microscopy images suggest that combined apoptosis and autophagy are responsible for cancer cell death.

Four new oxidovanadium [VVOL1–4(ema)] complexes (1–4) have been synthesized using tridentate binegative ONO donor ligands H2L1–4[H2L1: (E)-N′-(2-hydroxybenzylidene)furan-2-carbohydrazide; H2L2: (E)-N′-(4-(diethylamino)-2-hydroxybenzylidene)thiophene-2-carbohydrazide; H2L3: (E)-2-(4-(diethylamino)-2-hydroxybenzylideneamino)-4-methylphenol; H2L4: (E)-2-(3-ethoxy-2-hydroxybenzylideneamino)-4-methylphenol] and ethyl maltol (Hema) as a bidentate uninegative coligand and characterized by CHNS analysis, IR, UV–vis, NMR, and HR–ESI–MS methods. The structures of 1, 3, and 4are confirmed by single-crystal X-ray analysis. The hydrophobicity and hydrolytic stability of the complexes are tested using NMR and HR–ESI–MS and correlated with their observed biological activities. It is observed that 1hydrolyzed into a penta-coordinated vanadium-hydroxyl species (VVOL1-OH) with the release of ethyl maltol, whereas 2–4are found quite stable under the investigated time period. The biomolecular interaction of 1–4with DNA and BSA was performed using absorbance, fluorescence, and circular dichroism techniques. The in vitrocytotoxicity activities of H2L1–4and 1–4were tested against A549, HT-29, and NIH-3T3 cell lines. Among complexes, 2with an IC50value of 4.4 ± 0.1 μM displayed maximum anticancer activity against the HT-29 cell line. Complexes induce cell cycle arrest at the G2/M phase and subsequently trigger dose-dependent cell apoptosis, which is obtained by the cell apoptosis analysis via flow cytometry and confocal microscopy assays. Being fluorescence active, 1–4were observed to target the mitochondria and exhibit disruption of the mitochondrial membrane potential, which consequently causes overproduction of intracellular reactive oxygen species and induced cell apoptosis.

With aromatic and aliphatic thiol-S donor Schiff base ligands, the copper–sulfur clusters, [(L1)8CuI6CuII2](ClO4)2·DMF·0.5CH3OH (1) and [(L2)12CuI5CuII11(μ4-S)(μ4-O)6](ClO4)·4H2O, respectively, have been reported (Chem. Commun.2017, 53, 3334); HL1/HL2 are 2-(((3-methylthiophen-2-yl)methylene)amino)benzene/ethanethiol). Complex 1comprises a wheel shaped Cu8S8framework, made up of interlinked Cu2{μ-S(R)}2units. To understand the properties with relevance to the CuAsite and to check whether self-assembly generates similar type clusters to 1, three complexes, [(L3)8CuI6CuII2](ClO4)2·(C2H5)2O·2.5H2O (2), [(L3Cl)8CuI6CuII2](ClO4)2·1.25(C2H5)2O·1.25CH3OH·2H2O (3), and [(L3CF3)8CuI6CuII2](ClO4)2·2(C2H5)2O·H2O (4) have been synthesized with supporting ligands HL3X(HL3 = 2-((furan-2-ylmethylene)amino)benzenethiol when X = −H; X = −Cl or −CF3parato thiol-S are HL3Cland HL3CF3ligands, respectively). The X-ray structures of 3and 4feature a similar Cu8S8architecture to 1. The spectroscopic properties and the X-ray structures revealed that 2–4are fully spin delocalized mixed valence (MV) of class-IIItype clusters. The structural parameters of the N2Cu2{μ-S(R)}2units of 3and 4closely resemble those of the MV binuclear CuAsite. With the aid of UV–vis-NIR, EPR, and spectroelectrochemical studies, the electronic properties of these complexes have been described in comparison with the MV model complexes and CuAsite.

Water-soluble ruthenium complexes [(η6-arene)Ru(κ2-L)]n+(n= 0,1) ([Ru]-1–[Ru]-9) ligated with pyridine-based ligands are synthesized, and the molecular structure of the representative complex [Ru]-2is confirmed by X-ray crystallography. The studied complexes are employed for the catalytic dehydrogenation of formic acid in water. Screening of these complexes inferred that [Ru]-1[(η6-C10H14)Ru(κ2-NpyOH-L1)Cl]+(L1= pyridine-2-ylmethanol) outperformed others with an initial turnover frequency of 1548 h–1. Complex [Ru]-1also exhibited high stability in water and can be recycled up to seven times with a total turnover number of 6050. In addition to formic acid dehydrogenation, [Ru]-1also catalyzed the conversion of formaldehyde to hydrogen gas in water under base-free conditions. The effects of temperature, pH, formic acid, and catalyst concentration on the reaction kinetics are investigated in detail. Mass and NMR based mechanistic investigations inferred the presence of several important intermediate species, such as ruthenium-formate species [Ru]-1Band ruthenium-hydride species [Ru]-1C, involved in the catalytic dehydrogenation reaction. Moreover, the molecular structure of a diruthenium species [Ru]-1A′is also authenticated by single-crystal X-ray crystallography.

The magnetic and electronic properties of trilayer La4Ni3O8, similar to hole-doped cuprates, are investigated by performing full-potential linearized augmented plane wave method-based spin-polarized calculations with LDA and GGA functionals including Hubbard Uparameters to account for strong correlation effects. On the basis of these calculations, we found that La4Ni3O8is a C-type anti-ferromagnetic (C-AFM) Mott insulator in agreement with previous experimental and theoretical observations. Our calculations suggest that the two crystallographically nonequivalent nickel atoms Ni1 and Ni2 are found to be in high-spin state with an average valency of +1.33. Intermediate band-gap states are originated from dz2electrons of both types of Ni ions after including the strong correlation effects. To understand the role of hole doping on electronic structure, phase stability, and magnetic properties of La4Ni3O8, similar calculations were performed for La4–xSrxNi3O8as a function of x, using the supercell approach. We found that the hole doping brings insulator-to-metal transition without changing the C-AFM ordering, though the magnetic moment is enhanced at both Ni sites. Moreover, these Ni atoms are always in an average valence state irrespective of hole doping or volume change. So the electronic properties of hole-doped La4Ni3O8cannot be compared with hole-doped cuprates that are high-TCsuperconductors.

Bis-azoaromatic electron traps, viz. 2-(2-pyridylazo)azoarene 1, have been synthesized by colligating electron-deficient pyridine and azoarene moieties, and they act as apposite proradical templates for the formation of stable open-shell diradical complexes [(1•–)RhIII(1•–)]+([2]+), starting from the low-valent electron reservoir [RhI]. The less stable monoradical [RhIII(1•–)Cl2(PPh3)3] (3) has also been isolated as a minor product. These π-radical complexes are multiredox systems, and the electron transfer processes occur exclusively within the pincer-type NNN ligand backbone 1. Molecular and electronic structures of the diradicals and monoradicals have been ascertained with the aid of X-ray diffraction, electrochemical, spectroelectrochemical, and spectral (electronic, IR, NMR, and EPR) studies. In the diradicals [2]+, the orthogonal disposition of two ligand π orbitals linked via a closed-shell metal center (t26) impedes significant coupling between the radicals. Indeed, the observed magnetic moment of [2a]+lies near ∼2.3 μBover the temperature range 50–300 K. A very weak antiferromagnetic (AF) intramolecular spin–spin interaction between two ligand π arrays in [(1•–)RhIII(1•–)]+have been found experimentally (J≈ −5 cm–1), and this is further substantiated by density functional theory (DFT) calculations at the (U)B3LYP/6-31G(d,p) level.

A Ru(II) complex (Ru-1) of a substituted pyridyl-1,2,3-triazole ligand (BtPT) for highly selective “light-up” detection of hypochlorous acid is presented. An unusual anti-Markovnikov HOCl addition to the C═C bond of 1,2,3-triazole and a highly specific C(sp2)–H hydroxylation over epoxidation made Ru-1a highly selective luminescent HOCl probe. The abnormal regio- and stereoselective HOCl addition and subsequent hydroxylation mechanism in detail is supported by the combination of ESI-MS, 1H/13C NMR spectroscopy, and 1H NMR titration. The hydroxylation at the C5 center in 1,2,3-triazole increases the electron density and makes BtPTa better σ-donor as well as π-donor, which in turn increases the 3MC–3MLCT energy gap and inhibits the nonradiative decay from the excited state of Ru-1and is the key reason for luminescence light-up. Most importantly, the exogenous and endogenous HOCl imaging in the living HEK293T cells is also demonstrated. The probe showed low cytotoxicity and efficiently permeated the cell membrane. The cell-imaging experiments revealed rapid staining of the extranuclear region of HEK293T cells which clearly indicates the presence of cytoplasmic HOCl. The endogenous HOCl generation and imaging, stimulated by lipopolysaccharides (LPS) and paraquat in the HEK293T cells, is also demonstrated.

Pristine and Eu3+-doped BaZrO3were synthesized via a solid-state reaction method, and the synthesized samples were systematically characterized. X-ray diffraction confirmed the formation of single and pure phases of cubic-structured BaZrO3. Extended X-ray absorption fine structure (EXAFS) spectroscopy revealed the site occupancy of Eu3+and coordination environment around the different atomic sites. Photoluminescence (PL) excitation and emission spectra revealed the dominant absorption at 275 nm and a broad emission centered at 400 nm due to oxygen vacancies below the conduction band (CB). The PL emission intensity at 597 nm increased with increasing Eu3+doping concentration; simultaneously, emission from the defect level decreased. This confirmed the efficient energy transfer from oxygen vacancies to Eu3+. Density functional theory was employed to calculate the density of states (DOS) to explain the mechanisms of the PL phenomenon. DOS also showed the presence of impurity states due to Eu3+doping within the band-gap region. The coincidence of the oxygen vacancy state with Eu f state at the bottom of the CB confirmed the PL energy-transfer mechanisms from the oxygen vacancy to europium. The excited-state lifetime values of the 5D0state decreased with increasing doping concentration due to the increase of the nonradiative transition rate. The internal quantum efficiency, small excited-state lifetime, and photometric parameters indicated that 3 mol % Eu3+-doped BaZrO3can be a suitable candidate for the red-light-emitting device applications.

Aliphatic thiolato-S-bridged tri- and binuclear nickel(II) complexes have been synthesized and characterized as models for the Nipsite of the A cluster of acetyl coenzyme A synthase (ACS)/carbon monooxide (CO) dehydrogenase. Reaction of the in situ formed N2Sthioldonor ligands with [Ni(H2O)6](ClO4)2afforded the trinuclear complexes [Ni{(LMe(S))2Ni}2](ClO4)2·CH3CN (1·CH3CN) and [Ni{(LBr(S))2Ni}2](ClO4)2·5H2O (2·5H2O) following self-assembly. Complexes 1and 2react with [Ni(dppe)Cl2] and dppe [dppe = 1,2-bis(diphenylphosphino)ethane] to afford the binuclear [Ni(dppe)Ni(LMe(S))2](ClO4)2·2H2O (3·2H2O) and [Ni(dppe)Ni(LBr(S))2](ClO4)2·0.75O(C2H5)2[4·0.75O(C2H5)2], respectively. The X-ray crystal structures of 1–4revealed a central NiIIS4moiety in 1and 2and a NiIIP2S2moiety in 3and 4; both moieties have a square-planar environment around Ni and may mimic the properties of the Nipsite of ACS. The electrochemical reduction of both terminal NiIIions of 1and 2occurs simultaneously, which is further confirmed by the isolation of [Ni{(LMe(S))2Ni(NO)}2](ClO4)2(5) and [Ni{(LBr(S))2Ni(NO)}2](ClO4)2(6) following reductive nitrosylation of 1and 2. Complexes 5and 6exhibit νNOat 1773 and 1789 cm–1, respectively. In the presence of O2, both 5and 6transform to nitrite-bound monomers [(LMe(S–S))Ni(NO2)](ClO4) (7) and [(LBr(S–S))Ni(NO2)](ClO4)2(8). The nature of the ligand modification is evident from the X-ray crystal structure of 7. To understand the origin of multiple reductive responses of 1–4, complex [(LMe(SMe))2Ni](ClO4)2(9) is considered. The central NiS4part of 1is labile like the Nipsite of ACS and can be replaced by phenanthroline. The treatment of CO to reduce 3generates a 3red-(CO)2species, as confirmed by Fourier transform infrared (νCO= 1997 and 2068 cm–1) and electron paramagnetic resonance (g1= 2.18, g2= 2.13, g3= 1.95, and AP= 30–80 G) spectroscopy. The CO binding to NiIof 3redis relevant to the ACS activity.

The proton-coupled reduction of CuII-bound nitrite (NO2–) to nitric oxide (NO2–+ 2H++ e–→ NO(g) + H2O), such as occurs in the enzyme copper nitrite reductase, is investigated in this work. Our studies focus on the copper(II/I) model complexes [(L2)Cu(H2O)Cl] (1), [(L2)Cu(ONO)] (2), [(L2)Cu(CH3CO2)] (3), and [Co(Cp)2][(L2)Cu(NO2)(CH3CN] (4), where HL2 = N-[2-(methylthio)ethyl]-2′-pyridinecarboxamide. Complex 1readily reacts with a NO2–anion to form the nitrito-O-bound copper(II) complex 2. Electrochemical reduction of CuII→ CuIindicates coordination isomerization from asymmetric nitrito-κ2-O,O to nitro-κ1-N. Isolation and spectroscopic characterization of 4support this notion of nitrite coordination isomerization (νCu–N∼ 460 cm–1). A reduction of 2, followed by reaction with acetic acid, causes evolution of stoichiometric NO via the transient copper(II) nitrosyl species and subsequent formation of the acetate-bound complex 3. The probable copper nitrosyl intermediate [(L2)Cu(NO)(CH3CN)]+of the {CuNO}10type is evident from low-temperature UV–vis absorption (λmax= 722 nm) and electron paramagnetic resonance spectroscopy. A density functional theory (DFT)-optimized model of [(L2)Cu(NO)(CH3CN)]+shows end-on NO binding to Cu with Cu–N(NO) and N–O distances of 1.989 and 1.140 Å, respectively, and a Cu–N–O angle of 119.25°, consistent with the formulation of CuII-NO•. A spin-state change that triggers NO release is observed. Considering singlet- and triplet-state electronic configurations of this model, DFT-calculated νNOvalues of 1802 and 1904 cm–1, respectively, are obtained. We present here important mechanistic aspects of the copper-mediated nitrite reduction pathway with the use of model complexes employing the ligand HL2 and an analogous phenyl-based ligand, N-[2-(methylthio)phenyl]-2′-pyridinecarboxamide (HL1).

Herein, we report the uranyl sensitization of Sm3+emissions in uranium-codoped Li2B4O7:Sm3+phosphor. The uranyl speciation in codoped [Sm, U] LTB samples was determined by synchrotron-based extended X-ray absorption fine structure (EXAFS) spectroscopy that revealed two coordination shells for U(VI) ions with bond distances of U–Oax(∼1.81 Å) and U–Oeq(∼2.30 Å). EXAFS fitting suggested that the uranyl moiety is present as pentagonal bipyramids (UO7) and hexagonal bipyramids (UO8) with five and six equatorial oxygen ligands, respectively. The alteration of the local structure of Sm3+from [SmO4] to [SmO7] polyhedra and the changes in the coordination number of equatorial oxygen for uranyl were observed with different codoping concentrations of Sm3+and uranium. Density functional theory (DFT) calculations suggested the lowering of defect formation energy for Li vacancies on codoping of Sm and U. Hence, we proposed the increase of the equatorial coordination number of UO22+on the increase in the lithium vacancies in LTB. In addition, DFT supported the feasibility of efficient energy transfer (ET) due to the overlap of uranium and Sm3+excited state levels. The influence of the same on the spectral features and UO22+→ Sm3+energy transfer was investigated by time-resolved photoluminescence (PL) studies. The ET efficiency from the UO22+to Sm3+was 70.5% in 0.5 mol % codoped [Sm, U] LTB samples. The correlation of EXAFS and luminescence properties indicated a red shift in vibronic features of uranyl emission with increase in the equatorial coordination of the uranyl moiety from five to six. Additionally, a higher probability of ET was observed for uranyl speciation as UO8hexagonal bipyramids. Temperature-dependent emissions and decay profiles were collected under uranyl excitation to investigate the thermal dependence of ET. A high energy barrier (Ea∼ 4027 cm–1) was evaluated for the thermal quenching of Sm3+emissions. This work provides insights into the modulation of luminescence and ET efficiency via structural changes in uranyl and Sm local environment in LTB phosphor.