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We report a series of structurally relevant copper phenanthroline complexes as pre-catalysts for highly selective electrocatalytic reduction of CO2 to C2 products using inexpensive carbon paper electrodes. The Cu complexes with non-substituted phenanthroline promote the production of ethylene with a high faradaic efficiency of 71.2%, while the one with pyridinium-functionalized ligands is more selective for ethanol. The C2 selectivity can be effectively tuned by increasing the number of coordinated phenanthrolines and remains high at a wide range of potentials. [ABSTRACT FROM AUTHOR]

The combination of electron-deficient viologen ligands with electron-rich POMs is a typical acceptor–donor system that has recently received much attention. Under solvothermal and hydrothermal conditions, by introducing three symmetric viologen ligands into POM-based hybrid materials, we successfully constructed four POMs–viologen inorganic–organic hybrid compounds, namely (1,3-bcbpy)2·(δ-Mo8O26) (1) (1,3-bcbpy·2Cl = 1,1′-bis(3-carboxybenzyl)-4,4′-bipyridine dichloride), {CoII(1,4-bcbpy)2(H2O)2[H2(β-Mo8O26)]}·2H2O·2CH2O (2), (1,4-bcbpy)2·(δ-Mo8O26)·2H2O (3) (1,4-bcbpy·2Cl = 1,1′-bis(4-carboxybenzyl)-4,4′-bipyridine dichloride, CH2O = formaldehyde), and {CuII(1,1-pmbby)2(H2O)[H2(β-Mo8O26)2]}·5H2O·C2H7N (4) (1,1-pmbby·2Cl = 1,1′-[1,4-phenylbis(methylene)]bis-(4,4′-bipyridine)dichloride, C2H7N = dimethylamine). These four compounds exhibit different fascinating structures, especially compound 4 is a typical metal–organic framework. Compounds 1–4 exhibit good discoloration behaviors under various external stimuli. For example, compounds 1–4 showed a positive response to the irradiation from a 300 W Xe lamp. When a positive voltage was applied to the ECD based on compounds 1–4, 1/2/3/4-ECD underwent a significant color conversion. What's more, compound 4 also showed obvious discoloration results after heating. In a word, 1–4 are multifunctional discoloration materials under different external stimuli. In addition, the coated filter paper prepared based on compound 3 can be used as a new printing material medium and can be successfully applied in erasable inkless printing and dual anti-counterfeiting. [ABSTRACT FROM AUTHOR]

Antimicrobial photodynamic therapy offers significant benefits over standard antibiotic therapy in terms of rapid sterilization and resistance reduction. In this paper, a series of ruthenium complexes were designed and synthesized for antibacterial studies. [Ru(tpy)(dppz-R)Cl][PF6] (tpy = 2,2′:6′,2′′-terpyridine; dppz = dipyrido [3,2-a:2′,3′-c] phenazine; R = H, CH3, C(CH3)3, F, CF3, NO2, NH2 or CN), Ru1–Ru8 all showed superior in vitro antimicrobial effects under blue light irradiation. Ru2 has the best antimicrobial activity, with its inherent dark toxicity and photodynamic inactivation rapidly killing S. aureus without developing drug tolerance. Binding and damaging DNA as well as generating ROS may be its potential antimicrobial targets. Ru2 lacks a hemolytic effect on rabbit erythrocytes and has low phototoxicity against G. mellonella Larvae. In addition, Ru2 has been successfully used to treat skin wounds in mice infected with S. aureus. Therefore, Ru2 has shown great potential as a photodynamic antimicrobial agent against the threat of S. aureus infection. [ABSTRACT FROM AUTHOR]

In this paper, we report the synthesis and characterization of a mononuclear zinc complex (1) containing a redox-active bis(4-antipyrinyl) derivative of the 3-cyanoformazanate ligand. Complex 1 was readily obtained by refluxing zinc acetate with 3-cyano-1,5-(4-antipyrinyl)formazan (LH) in a methanolic solution. Single-crystal X-ray diffraction analysis of complex 1 shows that the formazanate ligands bind to the zinc center in a five-member chelate "open" form via the 1- and 4-positions of the 1,2,4,5-tetraazapentadienyl formazanate backbone leading to the formation of the mononuclear bis(formazanate) zinc complex exhibiting a distorted octahedral geometry. We also report the study of resistive-switching random access memory application of this solution-processable bis(formazanate) Zn(II) complex to facilitate the practical implementation of transition metal complex-based molecular memory devices. The complex demonstrated high conductance switching with a large ON–OFF ratio, good stability, and a long retention time. A trap-controlled space charge limited current mechanism is proposed for the observed resistive switching behavior of the device, wherein the role played by the [ZnIIL2] complex that comprises the extended redox-active conjugated ligand backbone is revealed by corroborating electrochemical studies, spectrochemical experiments, and DFT calculations. In addition to providing significant insights into the molecular design of transition metal complexes for memory applications, this study also presents the utilization of ZnIIL2 towards the realization of non-volatile resistive random access memory (RRAM) devices with inorganic/organic hybrid active layers that are highly cost-effective and sustainable. These devices exhibited multilevel switching and low current operation, both of which are desirable for advanced memory applications. [ABSTRACT FROM AUTHOR]

The diversity of catalytic activities and antioxidant properties of cerium oxide nanoparticles (CeO2 NPs) makes them promising materials for the theranostics of various diseases, especially those caused by disturbances in free radical homeostasis in living systems. Despite the fact that the functionalisation of nanoparticles' surface plays a critical role in nanomedicine applications, the effect of different coatings on their enzyme-like behaviour and antioxidant properties is still poorly understood, which limits the biomedical application of CeO2 NPs. This paper reports on the effect of low and high molecular weight biocompatible ligands on the SOD-like activity and radical scavenging properties of CeO2 NPs, which was analysed using a phosphate-rich medium resembling a natural environment. The results obtained show that these ligands modulate the SOD-like properties of CeO2 NPs as follows. Citrate and polysaccharide (maltodextrin and dextran) surface coatings increase the SOD-like activity of CeO2 NPs by an average of 2.2 times, and the protein corona (γ-globulin, γ-IgG) increases this activity by an average of 1.8 times. Citrate-coated CeO2 NPs and CeO2 nanoparticles modified with polysaccharide molecules are more effective SOD mimetics than CeO2@γ-IgG NPs. The SOD-like activity of phosphatidylcholine-coated CeO2 and CeO2@γ-IgG NPs is due to the combined action of nanoscale CeO2 and ligands. The antioxidant activity of CeO2 NPs after their modification with different ligands with respect to alkyl peroxyl radicals is multidirectional. Unexpectedly, citrate-, maltodextrin- and dextran-coated CeO2 NPs are more effective antioxidants than bare CeO2 NPs. CeO2 NPs modified with phosphatidylcholine or γ-IgG exhibited less radical-scavenging ability than bare CeO2 nanoparticles. Thus, common biocompatible ligands are able to regulate the biochemical activity of CeO2 NPs. [ABSTRACT FROM AUTHOR]

The π⋯π interactions in spin crossover (SCO) complexes can be used as an important means to fine-tune the spin transition behaviors. In this paper, three novel isostructural 2D Hofmann-type frameworks, [Fe(ppo)2M(CN)4] (1, M = Pt2+; 2, M = Pd2+; 3, M = Ni2+) have been successfully synthesized by judiciously choosing a large conjugated molecule, 2-(2-pyridyl)-5-(4-pyridyl)-1,3,4-oxadiazole (ppo) as the axial ligand. Single crystal X-ray crystallography analysis showed that there are different π⋯π interactions between the axial ppo ligands in 1–3. Variable temperature magnetic susceptibility studies revealed that 1 and 3 displayed incomplete and gradual SCO behaviors with T1/2 = 94 and 78 K, respectively, while 2 stayed in a high-spin state in the measured temperature range. The stronger π⋯π interactions between the conjugated ppo ligands observed in 1 and 3 than those in 2 may result in their different magnetic behaviors. [ABSTRACT FROM AUTHOR]

In this study, we synthesized two unsymmetrical and dipodal Schiff–Mannich combo ligands, namely benzoic acid (3-benzoimidazol-1-ylmethyl-2-hydroxy-5-methyl-benzylidene)-hydrazide (H2BBH) and the hydroxyl analogue 2-hydroxy-benzoic acid (3-benzoimidazol-1-ylmethyl-2-hydroxy-5-methyl-benzylidene)-hydrazide (H3BSH), for the selective detection of Zn2+ in semi-aqueous media. Both the probes selectively depict a turn-on response to Zn2+ as a result of the combined effect of chelation-induced enhanced fluorescence (CHEF) and photo-induced electron transfer (PET). Detailed experimental studies reveal that H2BBH and H3BSH can detect Zn2+ in solutions with limit of detections of 27 nM and 46 nM, respectively. The structures of probe-Zn2+ ensembles were proposed as [(HBBH)2Zn] and [(H2BSH)2Zn] by ESI-MS, FT-IR spectroscopy, 1H NMR titration and DFT/TD-DFT methods. Moreover, both the probes were successfully employed in the detection of Zn2+ in HuH-7 cells, seedlings of chickpea and mung beans, and paper strips. [ABSTRACT FROM AUTHOR]

[MoV2 O2S2]2+-based thiosemicarbazone complexes appear as very promising molecules for biological applications due to the intrinsic properties of their components. This paper deals with the synthesis and characterization of six coordination complexes obtained by the reaction of [MoV2 O2S2]2+ clusters with bisthiosemicarbazone ligands that contain flexible or rigid spacers between the two thiosemicarbazone units. Interestingly, structural characterization by single-crystal X-ray diffraction, MALDI-TOF MS technique and NMR spectroscopy revealed that the nuclearity of the complex is controlled by the nature of the spacer between the thiosemicarbazone units. Binuclear complexes, namely [MoV2 O2S2(L1-3)], are isolated with flexible spacers while tetranuclear complexes [(MoV² O2S2)2(L4-6)2] are formed when the bisthiosemicarbazone ligands are built on rigid spacers. [ABSTRACT FROM AUTHOR]

This paper presents the synthesis and structural characterization of a series of new ruthenium(II) complexes 1–7, with the general formula mer-[RuL3(N–N)Cl]Cl, where L is 2,2′:6′,2′′-terpyridine (tpy) or 4′-(4-chlorophenyl)-2,2′:6′,2′′-terpyridine (Cl-Ph-tpy) and N–N is o-benzoquinonediimine (o-bqdi), 2,3-naphthoquinonediimine (nqdi), 4,4′-dimethyl-2,2′-bipyridine (dmbpy) or 2,2′-bipyridine-4,4′-dicarboxylic acid (dcbpy). The kinetic results showed that the ligand substitution reactions of new Ru(II)-polypyridyl complexes with biomolecules were affected by different substituents and the aromaticity of meridional tridentate and bidentate spectator ligands as well as by the nature of the entering nucleophile. The reactivity of the complexes increases in the order: dmbpy < dcbipy < nqdi < o-bqdi. In addition, quantum chemical calculations were performed to support the interpretation and discussion of the experimental data. Furthermore, combining ethidium bromide (EB) and Hoechst 33258 (2-(4-hydroxyphenyl)-5-[5-(4-methylpiperazine-1-yl)benzimidazo-2-yl]-benzimidazole) fluorescence assay results implied that 1–7 might interact with calf thymus DNA through partial intercalation and/or minor groove binding. The human serum albumin (HAS)-fluorescence binding studies involving the site markers, eosin Y, as a marker for site I of subdomain IIA, and ibuprofen, as a marker for site II of subdomain IIIA, showed that Ru(II) compounds bind to both sites with moderately strong affinity (Kb = 104–106 M−1). Moreover, these DNA/HSA experimental results were confirmed by molecular docking. Complexes 2, 5 and 6 exerted good to strong and highly selective cytotoxic activity against breast adenocarcinoma (MDA-MB 231), colorectal carcinoma (HCT116) and cervix adenocarcinoma (HeLa). Depending on their structure and cell line, the complexes acted differently in terms of their influence on autophagy, the cell cycle and the engaged apoptotic pathway. [ABSTRACT FROM AUTHOR]

Earth-abundant, cheap and non-toxic zinc-based coordination compounds are drawing research attention as promising candidates for various applications, such as photoluminescent materials and anticancer agents. In this paper we report six zinc complexes (1–3-NO3 and 1–3-Cl) with pyridyl-based thiazolyl–hydrazone ligands, which differ in the nature of substituents at the ligands' periphery, anion type, and geometry around the metal ion. The complexes were characterized by single-crystal and powder X-ray diffraction analysis, as well as IR and NMR spectroscopy. The symmetrical complexes 2-Cl and 3-Cl, where zinc atoms are located at a two-fold axis, do not exhibit photophysical properties, unlike their asymmetrical analogs 2-NO3 and 3-NO3 with the same complex cation. Asymmetrical pentacoordinated 1-Cl and hexacoordinated 1-NO3 complexes exhibit photophysical properties. An admixture of allowed intra-ligand (1IL) and chloro (X)-to-ligand charge-transfer (1XLCT) electronic transitions is responsible for the fluorescence of the 1-Cl complex. The origin of the emission of the 1-NO3 complex is ascribed to an admixture of 3IL and ligand-to-ligand charge-transfer (3LLCT) forbidden electronic transitions, while for 3-NO3 most electronic excitations are of LLCT character. The thermal stability of the complexes is in accord with the strength of respective intermolecular interactions. The antiproliferative activity of the complexes was in the nanomolar range on some of the investigated cancer cell lines. Contrary to the increase of antiproliferative activity of the complexes in comparison to the free ligands in cancer cell lines, an acute toxicity determined in the brine shrimp assay follows the opposite trend. The overall results suggest that Zn(II) thiazoyl–hydrazone complexes have considerable potential as multifunctional materials. [ABSTRACT FROM AUTHOR]

The palladium-catalyzed oxidative homocoupling reactions of aryl boronic acids using a solvent-free and ligand-free ball-milling method have been reported. These reactions allow simple, fast, and efficient synthesis of a series of biphenyl-derived organic fluorescent materials in modest and good yields without the use of ligands in air. The new organic fluorescent material N-[4-(4-{phenyl[4-(triphenylvinyl)phenyl]amino}phenyl)-phenyl]-N-[4-(triphenylvinyl)phenyl]aniline (B6) shows typical aggregation-induced emission features and reversible mechanical force responsive fluorescent properties. [ABSTRACT FROM AUTHOR]

Three silyl [PSiP] pincer cobalt(II) chlorides 1–3 [(2-Ph2PC6H4)2MeSiCo(Cl)(PMe3)] (1), [(2-iPr2PC6H4)2MeSiCo(Cl)(PMe3)] (2) and [(2-Ph2PC6H4)2MeSiCo(Cl)(LSi:)] (LSi: = {PhC(NtBu)2}SiCl) (3) were synthesized and used as catalysts and their catalytic activity for dinitrogen silylation was studied. Among the three complexes complex 3 was new and was synthesized via the reaction of [PSiP] pincer preligand L1 with CoCl2 in the presence of chlorosilylene via Si–H bond cleavage. The molecular structure of 3 was determined by single crystal X-ray diffraction analysis. Compared to complex 1, complex 2 is the more effective catalyst for dinitrogen silylation and 363 equiv. of N(SiMe3)3 could be reached per Co atom. Further study indicates that using the silylene ligand in complex 3 instead of the PMe3 ligand in complex 1, the catalytic activity of 3 is lower than that of 1. The catalytic mechanism for this catalytic system is proposed with the support of experimental evidence. The [PSiP] pincer cobalt(I) dinitrogen complex was proposed as the active catalyst for dinitrogen silylation. [ABSTRACT FROM AUTHOR]

As phenanthroline (phen) possesses great coordination ability with various ions, the development of new chiral phen ligands is in great demand in asymmetric catalysis. Herein, we rationally designed and developed an entirely new class of C2-symmetric rigid-featured chiral phen ligands that provide the N,N,O,O-tetradentate coordination of the phen moiety and two additional N,N-dioxides. The chiral ligands, termed Phen-2NO ligands, incorporate the advantages of both the phen skeleton and the pyrroloimidazolone-based N-oxide moiety, and their electronic and steric properties can be readily tuned through the incorporation of substituents in the aromatic rings of the amide group. These ligands presented a superior performance in the Ni(II)-catalyzed asymmetric Michael-type Friedel–Crafts alkylation reaction of indoles with β,γ-unsaturated α-ketoesters. Excellent yields (up to 93%) and high enantioselectivities (up to 99% ee) are obtained for a wide range of substrates under mild conditions. These results demonstrated the promising potential of the Phen-2NO ligand as an efficient chiral phen ligand. [ABSTRACT FROM AUTHOR]

A series of metallophthalocyanine (PcM) complexes with axial N-heterocyclic carbene ligands (NHC; 1,3-diisopropylimidazol-2-ylidene (DIP) and 1,3-dimethylbenzimidazol-2-ylidene (DMB)) were prepared and structurally characterized. PcCoII(DIP), PcZnII(DIP), and PcZnII(DMB) are five-coordinate complexes with mild dome-type Pc-ring distortions, while PcFeII(DIP)2 is six-coordinate and has a very large ruffle-type ring-distortion with respect to typical PcM(L)2 systems. The distortion is induced by the highly steric axial DIP ligands. The distortions were quantified and classified by their bond lengths and torsion angles, and according to the normal-coordinate structural decomposition (NSD) analysis. Upon ligation of the NHC, the insoluble PcM materials were solublized in common organic solvents, with typical UV-visible Q-band maxima observable between 658 and 677 nm; the increased solubility is rationalized in terms of the reduced solid-state aggregation of the complexes, attributable to the axial ligation. [ABSTRACT FROM AUTHOR]

Ruthenium arene-based complexes have attracted growing interest in overcoming the lack of efficiency of platinum-based chemotherapeutic drugs. Herein, we prepared two pyrazolyl-pyridine type bidentate ligands using 2-acetyl pyridine with biphenyl-4-carbaldehyde and 1-pyrene carbaldehyde. The isolated ligands were utilized to prepare two new Ru(p-cymene) complexes, [Ru(η6-p-cymene)(bpy)Cl]PF6 (Ru-bpy(1)) and [Ru(η6 -p-cymene)(pyn)Cl]PF6 (Ru-pyn(2)) and characterized well. Single-crystal X-ray diffraction analysis of Ru-bpy(1) revealed that the complex adopts pseudo-octahedral geometry. The MTT assay was performed on human breast carcinoma (MCF-7), cervical carcinoma (HeLa-S3) and lung adenocarcinoma (A549) cells to determine the in vitro cytotoxicity of the complexes. Although the complexes were found to be insensitive to cervical and lung cancer cells at concentrations of up to 100 μM, both the complexes showed efficient cytotoxicity in breast cancer cells. Moreover, these complexes exhibited apoptosis-inducing activity and cell-free antioxidant activity. [ABSTRACT FROM AUTHOR]

An asymmetric bi-nuclear copper(II) complex with both cytotoxic and immunogenic activity towards breast cancer stem cells (CSCs) is reported. The bi-nuclear copper(II) complex comprises of two copper(II) centres bound to flufenamic acid and 3,4,7,8-tetramethyl-1,10-phenanthroline. The bi-nuclear copper(II) complex exhibits sub-micromolar potency towards breast CSCs grown in monolayers and three-dimensional cultures. Remarkably, the bi-nuclear copper(II) complex is up to 25-fold more potent toward breast CSC mammospheres than salinomycin (a gold standard anti-breast CSC agent) and cisplatin (a clinically administered metallodrug). Mechanistic studies showed that the bi-nuclear copper(II) complex readily enters breast CSCs, elevates intracellular reactive oxygen species levels, induces apoptosis, and promotes damage-associated molecular pattern release. The latter triggers phagocytosis of breast CSCs by macrophages. As far as we are aware, this is the first report of a bi-nuclear copper(II) complex to induce engulfment of breast CSCs by immune cells. [ABSTRACT FROM AUTHOR]

Dye-sensitized photoelectrodes may be used as heterogeneous components for fuel-forming reactions in photoelectrochemical cells. There has been increasing interest in developing Earth-abundant cheaper photosensitizers based on first-row transition metals. We describe here the synthesis, characterization, and study of the ground and excited state properties of three Cu(I) complexes bearing ligands with varying electron-accepting capacities and conjugation that may act as photosensitizers for wide bandgap semiconductors. Femtosecond transient absorption studies indicate that the nature of the final excited state is dictated by the extent of conjugation in the electron-accepting ligand, where shorter conjugation leads to the formation of a singly reduced ligand and longer conjugation leads to the formation of a ligandcentered final excited state. These complexes were surface anchored onto nanostructured NiO on conductive fluorine-doped tin oxide glass to fabricate photocathodes. It was found that even though the ligands with increasing conjugation have an effect on the formation of the final excited state in solution, all complexes exhibit similar photocurrents upon white light illumination, suggesting that charge transfer to NiO happens in advance of the formation of the final excited state. [ABSTRACT FROM AUTHOR]

We report the synthesis, structures, and magnetic and luminescence properties of a series of new monoand dinuclear Er3+ complexes derived from sterically demanding aryloxide and fluorinated alkoxide ligands: [4-tBu-2,6-(Ph2CH)2C6H2O]3Er(THF) (1), [(C6F5)3CO]3Er(Me3SiOH) (2), [(C6F5)3CO]3Er[(Me3Si)2NH] (3), [(C6F5)3CO]3Er(C6H5CH3) (4), [(C6F5)3CO]3Er(o-Me2NC6H4CH3) (5) and {[Ph(CF3)2CO]2Er(μ²-OC (CF3)2Ph)}2 (6). In compounds 1, 2, and 4, the Er3+ ion is four-coordinated and adopts a distorted trigonal pyramidal geometry, while in 3, 5, and 6, the coordination geometry of Er3+ is impacted by the presence of several relatively short Er...F distances, making them rather 6-coordinated. All compounds behave as field-induced Single Molecule Magnets (SMMs) and exhibit an Er3+ characteristic near infrared (NIR) emission associated with the 4I13/2 → 4I15/2 transition with a remarkably long lifetime going up to 73 µs, which makes them multifunctional luminescent SMMs. The deconvolution of the NIR emission spectra allowed us to provide a direct probe of the crystal field splitting in these compounds, which was correlated with magnetic data. [ABSTRACT FROM AUTHOR]

We report a novel triangular trinuclear copper(II) complex with a central μ3-OH bridge, [(CuL)3(μ3-OH)(ClO4)2]·CH3OH·H2O (1), stabilised by the oxime-based Schiff base ligand, 3-(((5-bromothiophen-2-yl)methylene)hydrazineylidene)butan-2-one oxime (HL). Comprehensive characterization of 1 has been realised through different analytical and physical methods coupled with spectroscopic techniques. 1 has been structurally characterised by single crystal X-ray diffraction. The antiproliferative capacity of HL and 1 has been evaluated against human lung cancer cell line A549. Compound 1 shows promising efficacy in contrast to HL, which shows a limited cytotoxicity. Contrary to HL, 1 has distinctly impeded the proliferation of lung adenocarcinoma A549 cell lines in a dose-dependent way. Compound 1 has been employed as a potential therapeutic agent for promising cellular transformation of malevolent A549 cell lines. The programmed cell death mechanism of 1 reveals characteristic apoptotic changes in cellular morphology like chromatin condensation, fragmented nuclei, nuclear shrinkage along with blebbing, elevated number of nuclear body fragments and distorted nucleus, while round, clear edged, intact nucleus and uniformly stained round nuclei have been observed in the negative control. Variable-temperature magnetic studies show an antiferromagnetic Cu⋯Cu coupling of −44.6(2) cm−1. The g value as determined by EPR measurement of 1 in frozen N,N-dimethylformamide solution corroborates the experimental magnetic susceptibility values. [ABSTRACT FROM AUTHOR]

Recently, achieving selective cancer therapy with trifling side effects has been a great challenge in the eradication of cancer. Thus, to amplify the cytoselective approach of complexes, herein, we developed a series of Re(I)[2-aryl-1H-imidazo[4,5-f][1,10]phenanthroline] tricarbonyl chloride complexes and screened their potency against HeLa and MCF-7 cell lines together with the evaluation of their toxicity towards a normal kidney cell line (HEK-293). On meticulous investigation, complex [ReI(CO)3Cl(K2-N,N-(2c))] (3c) was found to be the most potent anticancer entity among other complexes. Complex 3c also showed competency to induce apoptosis in MCF-7 cells through G2/M phase cell-cycle arrest in association with the generation of ample reactive oxygen species (ROS), eventually leading to DNA intercalation and internucleosomal cleavage. The order of the cytotoxicity of these complexes depended on their lipophilic character and the electron-withdrawing halogen substitution at the para-position of the phenyl ring in the imidazophenanthroline ligand. [ABSTRACT FROM AUTHOR]

A new magnesium-based metal–organic framework with unprecedented short-chain secondary building units and ultra-micropore channels approaching the kinetic diameters of Xe is fabricated by decorating methyl groups on ligands. Due to the contracted pores, this MOF exhibits very high selectivity values for Xe/Kr, which ranks it among the top porous absorbents. [ABSTRACT FROM AUTHOR]

Separation of Am3+ and Cm3+ is one of the most challenging yet unavoidable steps in the back end of the nuclear cycle. Various ligands evaluated for Am/Cm separation have their own merits and demerits, and not a single ligand has been uniquely proposed for this purpose. In the present work, we evaluated N,N,N′,N′-tetra-n-octyldiglycolamide (TODGA) vis-à-vis N,N,N′,N′-tetra-2-ethylhexyldiglycolamide (T2EHDGA) in combination with a hydrophilic 2,6-bis(1,2,4-triazinyl)pyridine (SO3PhBTP) derivative in the aqueous phase for the separation of Am3+ and Cm3+ from nitric acid medium. The results showed that marginal selectivity for Am3+ over Cm3+ was observed with T2EHDGA in the presence of SO3PhBTP, which was attributed to the difference in the entropy change for their extraction from both the temperature-dependent liquid–liquid extraction and computational studies. [ABSTRACT FROM AUTHOR]

The application of Mg[Ph4Pn] and Li·K[Ph4Pn] in transmetalation reactions to a range of Rh(I) precursors led to the formation of "half-baguette" anti-[Rh I(L) n ]2[μ:η5:η5Ph4Pn] (L = 1,5-cyclooctadiene, norbornadiene, ethylene; n = 1, 2) and syn-[Rh I(CO)2]2[μ:η5:η5Ph4Pn] complexes as well as the related iridium complex anti-[Ir I(COD)]2[μ:η5:η5Ph4Pn]. With CO exclusive syn metalation was obtained even when using mono-nuclear Rh(I) precursors, indicating an electronic preference for syn metalation. DFT analysis showed this to be the result of π overlap between the adjacent M(CO)2 units which overcompensates for dz2 repulsion of the metals, an effect which can be overridden by steric clash of the auxiliary ligands to yield anti-configuration as seen in the larger olefin complexes. syn-[Rh I(CO)2]2[μ:η5:η5Ph4Pn] is a rare example of a twinned organometallic where the two metals are held flexibly in close proximity, but the two d8 Rh(I) centres did not show signs of M–M bonding interactions or exhibit Lewis basic behaviour as in some related mono-nuclear Cp complexes due to the acceptor properties of the ligands. The ligand substitution chemistry of syn-[Rh I(CO)2]2[μ:η5:η5Ph4Pn] was investigated with a series of electronically and sterically diverse donor ligands (P(OPh)3, P(OMe)3, PPh3, PMe3, dppe) yielding new mono- and bis-substituted complexes, with E-syn-[Rh I(CO)(P{OR})3]2[μ:η5:η5Ph4Pn] (R = Me, Ph) characterised by XRD. [ABSTRACT FROM AUTHOR]

A set of mononuclear cobalt(III) octahedral complexes {[Co(LH)(acac)] (Co-1H), [Co(LBr)(acac)] (Co-1Br), and [Co(LNO2)(acac)] (Co-1NO2)} were synthesized using new-generation N/O donors, maleonitrile-tethered, tetradentate heteroscorpionate half-reduced Schiff base ligands, 2-((E)-2-hydroxybenzylideneamino)-3-(pyridin-2-ylmethylamino)maleonitrile (H2LH), 2-((E)-(5-bromo-2-hydroxybenzylidene)amino)-3-((pyridin-2-ylmethyl)amino)maleonitrile (H2LBr), and 2-((E)-2-hydroxy-5-nitrobenzylideneamino)-3-(pyridin-2-ylmethylamino)maleonitrile (H2LNO2). All the compounds were well characterized spectroscopically and structurally. The non-covalent interactions present in the lattice of Co-complexes were studied in detail to explain the molecular architecture using the Hirshfeld surface (HS) analysis. The catalytic activity of CO2 fixation towards epoxides under mild and solvent-free conditions was demonstrated. The synthesized complexes are catalysts that are well-active towards the CO2 activation under ambient conditions, whereas most of the reported catalysts require harsh conditions. [ABSTRACT FROM AUTHOR]

Phosphorus-bridged rigid, bent bis(N-heterocyclic) carbenes have not been reported, so far, despite having structural features that could make them interesting ligands in coordination and main group element chemistry. In previous reports, we had demonstrated that tuning of σ3- and σ4-phosphorus environments in planarised bis(NHCs) affects electronic properties and can provide additional coordination sites. Herein, we report on first examples of synthesis and conversion of 1,4-diphosphabarrelene-related compounds into rigid bent, doubly P-bridged bis(NHCs). The formation of main group element adducts with substrates from group 13, 14 and 15 illustrates opportunities to access novel scaffolds and to create nonplanar branching points. DFT calculations reveal the new bis(NHCs) to be good candidates as novel soft/hard ligands with up to four coordination sites. The synthesis of a dinuclear Fe(CO)4 complex is demonstrated. The thermal retro-[4 + 2] cycloaddition was theoretically and experimentally explored for a variety of ionic and zwitterionic 1,4-diphosphabarrelenes, and the generation and trapping of a dinuclear Fe(0) bis(NHC) complex with a tricyclic 1σ2,4 σ2-diphosphinine scaffold is presented. [ABSTRACT FROM AUTHOR]

A series of Pd(II) complexes of the general formula [PdX(NNS)] (X = Cl, Br, I, NCS and phenyl-tetrazole-thiolato; NNS = 2-quinolinecarboxyaldehyde-N4-phenylthiosemicarbazone) was tested against four malignant cell lines for their antiproliferative properties and the outcomes were compared to those seen in normal mouse splenocytes. Various auxiliary ligands were substituted in order to investigate the impact of the character of the ligand on the cytotoxicity of this class of Pd(II) complexes. The iodo complex was the most cytotoxic compound towards the Caco-2 cell line in this study. The improved apoptosis and necrosis cell modes were in accordance with the fragmentation results of DNA, which revealed increased fragmentation terminals, especially in isothiocyanate and tetrazole-thiolato complexes. After 24 hours, at half the IC50 of each complex, the complex-treated cells exhibited considerable genotoxicity when compared to the corresponding non-treated control especially in the case of isothiocyanate and tetrazole-thiolato complexes. [ABSTRACT FROM AUTHOR]

Cancer is a perilous life-threatening disease, and attempts are constantly being made to create multinuclear transition metal complexes that could lead to the development of potential anticancer medications and administration procedures. Hence, this work aims to design, synthesize, characterize, and assess the anticancer efficacy of ruthenium p-cymene complexes incorporating N,N′-bis(4-substituted benzoyl)hydrazine ligands. The formation of the new complexes (Ru2H1–Ru2H3) has been thoroughly established by elemental analysis, and FT-IR, UV-vis, NMR, and HR-MS spectral techniques. The solid-state molecular structures of the complexes Ru2H1 and Ru2H3 have been determined using the SC-XRD study, which confirms the N, O, and Cl-legged piano stool pseudo-octahedral geometry of each ruthenium(II) ion. The stability of these complexes in the solution state and their lipophilicity profile have been determined. Furthermore, the title complexes were tested for their in vitro anticancer activity against cancerous H460 (lung cancer cells), SkBr3 (breast cancer cells), HepG2 (liver cancer cells), and HeLa (cervical cancer cells) along with non-cancerous (HEK-293) cells. The IC50 results revealed that complex Ru2H3 exhibits potent activity against the proliferation of all four cancer cells and outscored the effect of the standard metallodrug cisplatin. This may be attributed to the presence of a couple of lipophilic electron-donating methoxy groups in the ligand scaffold and also the ruthenium(II) p-cymene motifs. Advantageously, all the complexes (Ru2H1–Ru2H3) displayed cytotoxic specificity only towards cancerous cells by leaving the off-target non-cancerous cells undamaged. Acridine orange/ethidium bromide (AO/EB) staining, Hoechst 33342, mitochondrial membrane potential (MMP), and reactive oxygen species (ROS) staining assays were used to investigate the apoptotic pathway and ROS levels in mitochondria. The results of western blot analysis confirmed that the complexes triggered apoptosis through an intrinsic mitochondrial pathway by upregulating Bax and downregulating Bcl-2 proteins. Finally, the extent of apoptosis triggered by the complex Ru2H3 was quantified with the aid of flow cytometry using the Annexin V-FITC/propidium iodide (PI) double-staining technique. [ABSTRACT FROM AUTHOR]

In this study, we present the synthesis, characterization and in vitro cytotoxicity of six organometallic [Ru(II)(η6-p-cymene)(N,N)Cl]Cl, [Rh(III)(η5-C5Me5)(N,N)Cl]Cl and [Re(I)(CO)3(N,N)Cl] complexes, in which the (N,N) ligands are sterane-based 2,2′-bipyridine derivatives (4-Me-bpy-St-OH, 4-Ph-bpy-St-OH). The solution chemical behavior of the ligands and the complexes was explored by UV-visible spectrophotometry and 1H NMR spectroscopy. The ligands and their Re(I) complexes are neutral at pH = 7.40; this contributes to their highly lipophilic character (log D7.40 > +3). The Ru(II) and Rh(III) half-sandwich complexes are much more hydrophilic, and this property is greatly affected by the actual chloride ion content of the medium. The half-sandwich Ru and Rh complexes are highly stable in 30% (v/v) DMSO/water (<5% dissociation at pH = 7.40); this is further increased in water. The Rh(III)(η5-C5Me5) complexes were characterized by higher water/chloride exchange and pKa constants compared to their Ru(II)(η6-p-cymene) counterparts. The Re(I)(CO)3 complexes are also stable in solution over a wide pH range (2–12) without the release of the bidentate ligand; only the chlorido co-ligand can be replaced with OH− at higher pH values. A comprehensive discussion of the binding affinity of the half-sandwich Ru(II) and Rh(III) complexes toward human serum albumin and calf-thymus DNA is also provided. The Ru(II)(η6-p-cymene) complexes interact with human serum albumin via intermolecular forces, while for the Rh(III)(η5-C5Me5) complexes the coordinative binding mode is suggested as well. They are also able to interact with calf-thymus DNA, most likely via the coordination of the guanine nitrogen. The Ru(II)(η6-p-cymene) complexes were found to be the most promising among the tested compounds as they exhibited moderate-to-strong cytotoxic activity (IC50 = 3–11 μM) in LNCaP as well as in PC3 prostate cells in an androgen receptor-independent manner. They were also significantly cytotoxic in breast and colon adenocarcinoma cancer cell lines and showed good selectivity for cancer cells. [ABSTRACT FROM AUTHOR]

Transition metal complexes exhibiting selective toxicity towards a broad range of cancer types are highly desirable as potential anticancer agents. Herein, we report the synthesis, characterization, and cytotoxicity studies of six new mixed-ligand cobalt(III) complexes of general formula [Co(B)2(L)](ClO4)2 (1–6), where B is a N,N-donor phenanthroline base, namely, 1,10-phenanthroline (phen in 1, 2), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq in 3, 4), and dipyrido[3,2-a:2′,3′-c]phenazine (dppz in 5, 6), and L is the monoanion of 8-hydroxyquinoline (HQ in 1, 3, 5) and 5-chloro-7-iodo-8-hydroxyquinoline (CQ in 2, 4, 6). The X-ray single crystal structures of complexes 1 and 2 as PF6− salts revealed a distorted octahedral CoN5O coordination environment. Complexes demonstrated good stability in an aqueous buffer medium and in the presence of ascorbic acid as a reductant. Cytotoxicity studies using a panel of nine cancer cell lines showed that complex 6, with the dppz and CQ ligands, was significantly toxic against most cancer cell types, yielding IC50 values in the range of 2 to 14 μM. Complexes 1, 3, and 5, containing the HQ ligand, displayed lower toxicity compared to their CQ counterparts. The phenanthroline complexes demonstrated marginal toxicity towards the tested cell lines, while the dpq complexes exhibited moderate toxicity. Interestingly, all complexes demonstrated negligible toxicity towards normal HEK-293 kidney cells (IC50 > 100 μM). The observed cytotoxicity of the complexes correlated well with their lipophilicities (dppz > dpq > phen). The cytotoxicity of complex 6 was comparable to that of the clinical drug cisplatin under similar conditions. Notably, neither the HQ nor the CQ ligands alone demonstrated noticeable toxicity against any of the tested cell lines. The Annexin-V-FITC and DCFDA assays revealed that the cell death mechanism induced by the complexes involved apoptosis, which could be attributed to the metal-assisted generation of reactive oxygen species. Overall, the dppz complex 6, with its remarkable cytotoxicity against a broad range of cancer cells and negligible toxicity toward normal cells, holds significant potential for cancer chemotherapeutic applications. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) have garnered significant interest owing to their tunable structures and versatile properties. In this study, the construction of MOF-74 analogues based on pre-installation of functional ligands has been investigated. Five distinct ligands and their corresponding complexes are synthesized and characterized. The ligands are strategically designed to impart specific functional groups, enabling enhanced reactivity and tailored properties. Building upon the previously synthesized compounds, an efficient method for the directional functionalization of MOF-74 analogues under moderate conditions has been outlined. This method involves pre-installation through directive substitution of the ligands with suitable functional groups viz. –F, –Br, –I, –CH3 and –CN, allowing precise control over the resulting MOF's properties and functionalities. The study presents the characteristics and properties of [Cu(L1)]n (1), [Cu(L3)]n (2), [Cu(L4)]n (3), [Cu(L5)]n (4) and [Cu(L6)]n (5) complexes, highlighting their distinct features and potential applications. The findings from this research contribute to the fundamental understanding of MOF-74 analogues' synthesis and the efficient functionalization of these materials. The outlined methodology opens new avenues for the tailored design of MOFs with desired properties, enabling their potential utilization in diverse applications, such as catalysis, gas storage and luminescence sensing properties. [ABSTRACT FROM AUTHOR]

Tridentate bis(carboxamide) pincers are key ligands used in catalysis, investigational medicinal inorganic compounds, and materials science. This study examined the atropisomerism of a group of bis(carboxamide) pincers with C2 symmetry to elucidate their physical, chemical, and structural behaviour, paving the way for the application of their metal complexes in different fields. One of the five compounds structurally elucidated by X-ray crystallography, 1c, has a pair of intramolecularly constrained isoquinoline ring substituents and crystallized enantiomerically pure in a chiral Sohncke space group. PM6 calculations of the 3-D potential energy surface for the main atropisomerisation reaction coordinate of 1c indicated that the lowest-energy conformer (atropisomer) has the isoquinoline rings canted out-of-plane by almost +30° and −30° relative to the central pyridine ring. The X-ray structure of 1c is located close to this energy minimum. Circular dichroism (CD) spectroscopy on bulk solid samples confirmed the presence of an excess population of one enantiomer (C2-symmetric atropisomer), most notably for compounds 1c, 1e, and 1f. CD spectra could be recorded for all compounds in solution, similarly reflecting an excess population of one atropisomer. The experimental spectra were confirmed by TD-DFT simulations at the CAM-B3LYP/def2-tzvp level of theory. We conclude that the present group of ligands are worthy of further investigation as chelating agents for metal ions with applications in chiral catalysis or biology. [ABSTRACT FROM AUTHOR]

Rare examples of trinuclear [Ni–N2–M–N2–Ni] core (M = Ca, Mg) with linear bridged dinitrogen ligands are reported in this work. The reduction of [iPr2NN]Ni(μ-Br)2Li(thf)2 (1) (iPr2NN = 2,4-bis-(2,6-diisopropylphenylimido)pentyl) with elemental Mg or Ca in THF under an atmosphere of dinitrogen yields the complex {iPr2NNNi(μ-N2)}2M (thf)4 (M = Mg, complex 2 and M = Ca, complex 3). The bridging end-on (μ-N2)2M(thf)4 moiety connects the two [iPr2NNNi]− nickelate fragments. A combination of X-ray crystallography, solution and solid-state spectroscopy have been applied to characterize complexes 2 and 3, and DFT studies have been used to help explain the bonding and electronic structure in these unique Ni–N2–Mg and Ni–N2–Ca complexes. [ABSTRACT FROM AUTHOR]

From paddle–wheel starting material Na3Ru2(CO3)4·6H2O, a family of edge-sharing bi-octahedral (ESBO) diruthenium(IV , IV) compounds formulated as Ru2O2(CO3)2(H2O)2L2·nH2O [L = piperazine (1) or 2-methylpiperazine (2), n = 4, and L = 2,2-dimethylpiperazine (3), n = 12] and Ru2O2(CO3)2(OH)4{M(H2O)4}2·nH2O [M = Mg (4), n = 4, and Ni (5), n = 2] were prepared and structurally characterized. The Ru28+ dimer is chelated and bridged by two CO32− and two μ-O in a trans manner, and the Ru–Ru distances fall in the range 2.3808(6)–2.4001(4) Å. Compound 2 shows the shortest Ru–Ru distance for all known ESBO Ru2 compounds reported thus far. Increasing –CH3 groups of terminal piperazine ligands coordinated to the Ru(μ-O)2(μ-O3C)2Ru core, and according to Raman spectra experiments combined with theoretical calculations, the intense bands of compounds 1–3 appearing at ∼360 cm−1 can be assigned to the stretching of Ru–Ru bonds. [ABSTRACT FROM AUTHOR]

Sterically-hindered N-heterocyclic carbenes (NHCs) with functionalized N-wingtips are a pivotal class of ligands in organic synthesis. Herein, we report the first class of sterically-hindered N-heterocyclic carbenes based on the indazole framework. These ligands combine the strong σ-donation of the carbene center due to the carbene placement at the C3-indazole position with the sterically-hindered and flexible N-substitution with the versatile 2,6-bis(diphenylmethyl)aryl moiety that extends beyond the metal centre for the first time in non-classical N-heterocyclic carbenes. The ligands are readily accessible by the rare Cadogan indazole synthesis of sterically-hindered N-aryl-1-(2-nitrophenyl)methanimines. Steric and electronic characterization as well as catalytic studies in the synthesis of oxazolines are described. Considering the unique properties of indazole-derived carbenes, we anticipate that this class of compounds will find broad application in organic synthesis and catalysis. [ABSTRACT FROM AUTHOR]

trans-9,10-Dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid (deadcH2), in its racemic or R,R enantiomeric forms, has been used to synthesize eight uranyl ion complexes under solvo-hydrothermal conditions. [UO2(deadc)]·1.5CH3CN (1) and [H2NMe2]2[(UO2)2(deadc)3]·2H2O (2) crystallize as monoperiodic coordination polymers in which deadc2− forms both 4- and 7-membered chelate rings. Although synthesized in the same conditions as 2, the enantiomerically pure complex [H2NMe2]4[(UO2)2(O)(R,R-deadc)2]2 (3) is a discrete tetranuclear complex containing two μ3-oxo anions. Association with the zwitterion Ni(tpyc)2, where tpyc− is 2,2′:6′,2′′-terpyridine-4′-carboxylate, gives [(UO2)2(deadc)(deadcH)(NO3)Ni(tpyc)2]·CH3CN·2H2O (4), a rake-shaped monoperiodic assembly. [UO2(deadc)(DMA)] (5), [UO2(deadc)] (6) and [PPh4]2[(UO2)2(R,R-deadc)3] (7) crystallize as diperiodic networks with the fes, sql and hcb topologies, respectively, the thick layers formed being coated on both sides by protruding, hydrophobic dibenzobarrelene groups. Finally, [(UO2)2Ag2(deadc)3(CH3CN)2]·0.5H2O (8) contains monoperiodic uranyl–deadc2− subunits which are assembled into a triperiodic framework by bridging silver(I) cations, the latter interacting with both carboxylate groups and aromatic rings. Except for 6, all these complexes are emissive with photoluminescence quantum yields of 2–26%, and most spectra display the usual vibronic fine structure of uranyl emission. [ABSTRACT FROM AUTHOR]

In this paper, we present four Co-MOFs using R-substituted isophthalic acid (R-H2BDC, R = H, OH and COOH) along with trigonal n-TBT (n = 3 or 4) as organic ligands. These Co-MOFs are formulated as {[Co(1,3-BDC)(4-TBT)2/3]·(H2O)(DMF)1.5}n (Co-MOF-1), {[Co(HO-BDC)(4-TBT)]·(EtOH)2(DMF)2}n (Co-MOF-2), {[Co(HO-BDC)(4-TBT)2/3]·(H2O)3(MeOH)3(DMA)}n (Co-MOF-3) and {[Co3(BTC)2(3-TBT)2(H2O)2]·(H2O)2(EtOH)5(DMA)1.5}n (Co-MOF-4), where H2BDC = isophthalic acid, OH–H2BDC = 5-hydroxyisophthalic acid and H3BTC = 1,3,5-tricarboxybenzene, 4-TBT = 1,3,5- tris(4-pyridyl)benzene and 3-TBT = 1,3,5-tris(3-pyridyl)benzene. Co-MOF-1, 2 and 3 are constructed from the dimeric Co2(COO)2 unit and exhibit 3D frameworks. In Co-MOF-4, the dimeric Co2(COO)2 unit and single nuclear CoII center are connected by BTC3− and 3-TBT ligands into a 3D network. The catalytic experiments revealed that four Co-MOFs can catalyze the oxidative coupling reaction of benzyl alcohols and aniline to imines with good to excellent conversions under solvent-free conditions and an air atmosphere. Co-MOF-4 exhibited the best catalytic performance and the catalyst could be reused for at least five cycles without losing its structural integrity and catalytic activity. [ABSTRACT FROM AUTHOR]

This paper describes the synthesis, and structural and spectroscopic characterizations of two doubly bridged dicopper(II) complexes, [Cu2(μ-H2L)(μ-OMe)](ClO4)4·2H2O (1) and [Cu2(μ-L)(μ-OH)](ClO4)2 (2), with a binucleating ligand (HL) derived from the Schiff base condensation of DFMP and N,N-dimethyldipropylenetriamine, and their biomimetic catalytic activities were related to CAO and phenoxazinone synthase using 3,5-di-tert-butylcatechol and o-aminophenol (OAPH), respectively, as model substrates. Structural studies reveal that the major differences in these structures appear to be from the distinct roles of the tertiary amine groups of the ligands, which are protonated in 1, whereas it coordinates the metal centers in 2. Magnetic studies disclose that two copper(II) centers are strongly antiferromagnetically coupled with slightly different J values, which is further interpreted and discussed. They exhibited very different biomimetic catalytic activities; whereas 2 is an efficient catalyst, complex 1 showed somewhat lower substrate oxidation. The higher reactivity in 2 is rationalized by the strong involvement of the tertiary amine group of the Schiff base ligand, where the substrate oxidation is favored because of the transfer of protons from the substrate to the tertiary amine group, showing the importance of the functional groups in proximity to the bimetallic active site. Emphasis was also given to probing the binding mode of the substrate using an electronically deficient tetrabromomocatechol (Br4CatH2) and the isolated compound [Cu6(μ-HL)2(μ-OH)2(Br4Cat)4](NO3)2·4H2O (3) which suggests that monodentate asymmetric binding of 3,5-di-tert-butylcatechol and OAPH occurs during the course of the catalytic reaction. [ABSTRACT FROM AUTHOR]

The synthesis, photophysics and reverse saturable absorption of two cationic dinuclear Ir(III) complexes bearing fluorenyl-tethered 2-(quinolin-2-yl)quinoxaline (quqo) ligands are reported in this paper. The two complexes possess intense and featureless diimine ligand localized 1ILCT (intraligand charge transfer)/1π,π* absorption bands at ca. 330 and 430 nm, and a weak 1,3MLCT (metal-to-ligand charge transfer)/1,3LLCT (ligand-to-ligand charge transfer) absorption band at >500 nm. Both complexes exhibit weak dual phosphorescence at ca. 590 nm and 710 nm, which are attributed to the 3ILCT/3π,π* and 3MLCT/3LLCT states, respectively. The low-energy 3MLCT/3LLCT state also gives rise to a moderately strong triplet excited-state absorption at 490–800 nm. Because of the stronger triplet excited-state absorption than the ground-state absorption of these complexes at 532 nm, both complexes manifest a moderate reverse saturable absorption (RSA) at 532 nm for ns laser pulses. Expansion of the π-conjugation of the fluorenyl-tethered diimine ligand in Ir-1 causes a slight red-shift of the 1ILCT/1π,π* absorption bands in its UV-vis absorption spectrum and the 3MLCT/3LLCT absorption band in the transient absorption spectrum and slightly enhances the RSA at 532 nm compared to that in Ir-2. This work represents the first report on dinuclear Ir(III) complexes that exhibit RSA at 532 nm. [ABSTRACT FROM AUTHOR]

In this paper it is demonstrated that the nature of the ligands of two Ru2(II , III) paddlewheel complexes dramatically affects the overall anticancer properties in cells. Herein, the complex [Ru2(EB776)4Cl] was found to be more active against a glioblastoma model with respect to its isomer [Ru2(EB106)4Cl]. These different effects depend on the steric hindrance, on the allowed conformations of the complexes and on the presence of hydrophilic regions in [Ru2(EB776)4Cl], which overall lead to a lower "steric protection". [ABSTRACT FROM AUTHOR]

Treatment of the rhodium pincer complexes [RhCl(RPm)] (RPm = N,N′-bis(di-R-phosphinomethyl)perimidinylidene, R = Ph, Cy) with triphenylcyclopropenium hexafluorophosphate affords rhodacyclobutadiene complexes. These in turn react with activated alkynes (RC≡CCO2Me, R = H, CO2Me) to afford unusually stable cyclopropenylvinyls, implicating the intermediacy of σ-cyclopropenyl isomers. In contrast, treatment of [RhCl{py(NHPtBu2)2-2,6}] with the same reagent instead results in double functionalisation (SEAr) at the pincer backbone. [ABSTRACT FROM AUTHOR]

It has been reported that various unusual main group compounds can be stabilized by coordinating with ligands. Here, we report the use of carbone ligands in stabilizing diboron in its neutral and dicationic states by computational quantum mechanical calculations. The neutral [(L2C)·B2·(CL2)] (L = CO, NHC, PMe3, and cAAC) has singlet non-planar cumulenic-type equilibrium geometry where CL2 groups are almost orthogonal to each other. MO analysis indicates that the [(L2C)·B2·(CL2)] can be considered as formed by the interaction of the B2 fragment in the 1Σg+ excited state with two CL2 ligands having σ- and π-type lone pairs. Accordingly, the π delocalization in the C–B–B–C skeleton consists of two mutually orthogonal allylic anionic-type delocalizations along the C–B–B chain. Since one of the π-delocalized MOs of allylic anionic C–B–B is majorly localized on the carbone carbon atom, the carbone ligands formally act as two-electron ligands. On the other hand, the ground state of [(L2C)·B2·(CL2)]2+ shows a singlet planar/pseudo-planar cumulenic geometry when L = NHC and PMe3. The MO analysis indicates that the C–B–B–C skeleton is similar to that of butatriene, viz. one localized B–B π MO, and two delocalized C–B–B–C π MOs, indicating that each carbone acts as a four-electron ligand. Since CO and cAAC are good π-acceptor ligands, [(L2C)·B2·(CL2)]2+ ions (L = CO and cAAC) have triplet non-planar cumulenic ground states. [ABSTRACT FROM AUTHOR]

Iron(II) can show a very rich coordination chemistry with concomitant modulation of its properties as promising functional materials. Metalation of the neutral tridentate nitrogen-donor mer-coordinating ligand 2,6-bis(2-(methyl)-2H-tetrazol-5-yl)pyridine (Me2btp) with Fe(ClO4)2·6H2O through accurate solvent polarity control enables the selective crystallization of [FeHS/LS(Me2btp)2](ClO4)2·MeCN·2.75H2O (2HS/LS·MeCN·2.75H2O) as red rods, where half of the iron(II) centres resides in the low spin (LS, S = 0) state and the other half is in the high spin (HS, S = 2) state. The red rods spontaneously convert into yellow crystals once removed from the mother liquor and exposed to air due to solvent rearrangement within the crystal packing; these new crystals can be assigned to [FeHS(Me2btp)2](ClO4)2·solvent (2HS·solvent) where all the iron(II) centres are now blocked in the HS state, as confirmed by magnetic measurements. The polarity of the crystallization solvent, together with the maintenance of the crystals within the mother liquor, are pivotal for the reactivity and interconversion of different species. Indeed, upon long standing in solution, 2HS/LS·MeCN·2.75H2O converts to another form of red crystals belonging to [FeLS(Me2btp)2][FeHS(Me2btp)(MeCN)2(H2O)](ClO4)4·MeCN (2LS·3HS·MeCN), as confirmed by single crystal X-ray diffraction data. In this co-crystal, the iron(II) in 2 resides in the LS state at all temperatures while the iron(II) in 3 is blocked in the HS state. Well-formed yellow crystals could be also isolated among the red crystals of 2HS/LS·MeCN·2.75H2O, and they could be identified as the unprecedented octacoordinated species [Fe(Me2btp)2(MeCN)(H2O)](ClO4)2·H2O (1·H2O) by single-crystal X-ray diffraction. These yellow crystals are stable in the air, but slowly convert into 2LS·3HS·MeCN if kept in the mother liquor for about one week. 1·H2O can be considered the trapped intermediate in the solid state during the conversion of [FeHS(Me2btp)2]2+ into [FeHS(Me2btp)(MeCN)2(H2O)]2+ in solution, where the two tridentate ligands in the starting species can unfold to accommodate coordinated MeCN and H2O molecules, as confirmed by theoretical calculations, and eventually one of the two Me2btp is completely replaced by the solvent. [ABSTRACT FROM AUTHOR]

Four copper(II)-plumbagin and -bipyridine complexes (Cu1–Cu4) were synthesized as chemodynamic therapy agents with enhanced antitumor activity. As lipophilic and positively charged compounds, Cu1–Cu4 were preferentially accumulated in mitochondria and activated the mitochondrial apoptosis pathway. Mechanistic studies showed that Cu1–Cu4 reacted with GSH to reduce Cu2+ ions to Cu+ ions, catalyzed the formation of toxic hydroxyl radicals (˙OH) from hydrogen peroxide (H2O2) through a Fenton-like reaction, induced mitochondrial dysfunction, and activated caspase-9/3, which eventually led to apoptosis. Cu1–Cu4 arrested HeLa cells in the S phase and eventually killed cancer cells. Cu2 showed a favorable pharmacokinetic profile in mice. Moreover, Cu2 effectively inhibited the growth of HeLa xenografts in nude mice and showed low toxicity in vivo. [ABSTRACT FROM AUTHOR]

Understanding factors that influence the volatility of lanthanide complexes remains an important goal for applications such as gas-phase f-metal separations and the synthesis of lanthanide-containing thin films. Lanthanide complexes often exhibit volatility differences that depend on the ability of ligands to saturate the lanthanide coordination sphere and attenuate intermolecular bonding in the solid state. This can make it difficult to assess how electronic factors associated with differing ligand substituents influence volatility. Here we describe the synthesis, structures, and thermal properties of a series of volatile lanthanide complexes (Ln = Nd, Er, and Yb) containing N4O3 ligands decorated with different alkyl and fluoroalkyl substituents (CF3, CF2CF2CF3, Me, and tBu). These ligands completely enveloped the tested lanthanides to form monomeric complexes with 7-coordinate distorted capped octahedral coordination geometries, as determined using single-crystal X-ray diffraction. Thermogravimetric analysis and bulk sublimation studies show how metal encapsulation affords complexes with the same volatility regardless of metal size, even with lanthanide ions with significantly different radii such as Nd3+ and Yb3+. Most notably, the results show that increasing ligand fluorination, a strategy often used to increase the volatility of metal complexes, is not always beneficial and can significantly attenuate the volatility of lanthanide complexes depending on location with respect to other substituents in the ligand framework. A pair-wise model based on density functional theory shows that the net intermolecular interactions in the unit cell can still be stronger when fluorination is present. In other words, even if individual interactions between neighboring molecules are weaker, the total number of interactions in the solid arising from the nature of crystal packing is equally important to consider. [ABSTRACT FROM AUTHOR]

Valence tautomerism (VT) involves the stimulated reversible intramolecular electron transfer between a redox-active metal and ligand. Dinuclear cobalt complexes bridged by bis(dioxolene) ligands can undergo thermally-induced VT with access to {CoIII-cat-cat-CoIII}, {CoIII-cat-SQ-CoII} and {CoII-SQ-SQ-CoII} states (cat2− = catecholate, SQ˙− = semiquinonate, CoIII refers to low spin CoIII, CoII refers to high spin CoII). The resulting potential for two-step VT interconversions offers increased functionality over mononuclear examples. In this study, the bis(dioxolene) ligand 3,3′,4,4′-tetrahydroxy-5,5′-dimethoxy-benzaldazine (thMH4) was paired with Mentpa (tpa = tris(2-pyridylmethyl)amine, n = 0–3 corresponds to methylation at 6-position of the pyridine rings) to afford [{Co(Mentpa)}2(thM)](PF6)2 (1a, n = 0; 2a, n = 2; 3a, n = 3). Structural, magnetic susceptibility and spectroscopic data show that 1a and 3a remain in the temperature invariant {CoIII-cat-cat-CoIII} and {CoII-SQ-SQ-CoII} forms in the solid state, respectively. In contrast, 2a exhibits incomplete thermally-induced VT between these two tautomeric forms via the mixed {CoIII-cat-SQ-CoII} tautomer. In solution, room temperature electronic absorption spectra are consistent with the assignments from the solid-state, with VT observed only for 2a. From electrochemistry, the proximity of the two 1e−-processes for the thMn− ligand indicates weak electronic communication between the two dioxolene units, supporting the potential for a two-step VT interconversion in thMn− containing complexes. Comparison of the redox potentials of the Co and thMn− processes suggests that only 2a has these processes in sufficient proximity to afford the thermally-induced VT observed experimentally. Density functional theory calculations are consistent with the prerequisite energy ordering for a two-step transition for 2a, and temperature invariant {CoIII-cat-cat-CoIII} and {CoII-SQ-SQ-CoII} states for 1a and 3a, respectively. This work presents the third example, and the first formally conjugated example, of a bridging bis(dioxolene) ligand that can afford two-step VT in a Co complex, suggesting new possibilities towards applications based on multistep switching. [ABSTRACT FROM AUTHOR]

In an effort to explore the coordination chemistry of the coordinative sulfur centers in arachno-ruthenaborane [(Cp*Ru)2(B3H8)(CS2H)] (arachno-1), we have thermolyzed arachno-1 with group-6 metal carbonyls [M(CO)5·THF] (M = Cr, Mo and W). The reaction of arachno-1 with [Cr(CO)5·THF] resulted in the formation of hetero-trimetallic triply bridging borylene [(Cp*Ru)2(μ-CO)(μ3-CH2S2-κ2S′:κ2S′′){Cr(CO)3}(μ3-BH)] (2), bridging boryl–borylene [(Cp*Ru)2(μ-CO){(μ3-BH(CH2S2)-κ2B:κ2S′:κ1S′′)}{Cr(CO)3}(μ3-BH)] (3), and sulfido bridged hetero-trimetallic complex [(Cp*Ru)2(μ-CO)3{Cr(CO)3}(μ3-S)] (4). In 2, one side of Ru2Cr-triangle features a μ3-BH ligand while the other side is quadruply bridged by a methanedithiolato ligand in an unsymmetrical fashion. Unlike 2, in complex 3, one side of the Ru2Cr-triangle has a μ3-BH ligand while the opposite side is bridged by a boryl ligand BH(CH2S2) in an unsymmetrical way (μ3–κ2:κ2:κ1) to the metal centers. Interestingly, when the similar reactions of arachno-1 were performed with heavier group-6 metal carbonyls [M(CO)5·THF] (M = Mo and W), it led to the formation of methanedithiolato bridged hetero-trimetallic chain complexes, [{Cp*Ru(CO)}2(μ-CO)2(μ3-CH2S2-κ2S′:κ2S′′){M(CO)2}] (5, M = Mo; 6, M = W) and sulfido-bridged hetero-trimetallic complexes [(Cp*Ru)2(μ-CO)3{M(CO)3}(μ3-S)] (7, M = Mo; 8, M = W), analogous to 4. In complexes 5 and 6, a Ru2M-chain is symmetrically bridged by a methanedithiolato ligand. On the other hand, in complexes 4, 7, and 8, a sulfido ligand coordinates to two ruthenium and one group-6 metal atoms in μ3-fashion. All the complexes have been characterized by 1H NMR, 13C NMR, UV-vis, IR spectroscopy, and mass spectrometry and their structural architectures have been unambiguously established by single crystal X-ray diffraction studies. In addition, theoretical investigations provided valuable insights into their electronic structures and bonding properties. [ABSTRACT FROM AUTHOR]

Tripodal tetradentate N donor ligands stabilise the most active ATRP catalyst systems. Here, we set out to synthesise the new guanidine ligand TMG-4NMe2uns-penp, inspired by p-substituted tris(2-pyridylmethyl)amine (TPMA) ligands. The impact of changing pyridine against guanidine donors was examined through solid state and solution experiments and density functional theory (DFT) calculations. In the solid state, the molecular structures of copper complexes based on the ligands TMG-4NMe2uns-penp, TMG-uns-penp and TMG3tren were discussed concerning the influence of a NMe2 substituent at the pyridines and the guanidine donors. In solution, the TMG-4NMe2uns-penp system was investigated by several methods, including UV/Vis, EPR and NMR spectroscopy indicating similar properties to that of the highly active TPMANMe2 system. The redox potentials were determined and related to the catalytic activity. Besides the expected trends between these and the ligand structures, there is evidence that guanidine donors in tripodal ligand systems lead to a better deactivation and possibly a faster exchange within the ATRP equilibrium than TPMA systems. Supported by DFT calculations, it derives from an easier cleavable Cu–Br bond of the copper(II) deactivator species. The high activity was stated by a controlled initiator for continuous activator regeneration (ICAR) ATRP of styrene. [ABSTRACT FROM AUTHOR]

We report the synthesis, characterization and anticancer activity of a new Schiff base (H2L) derived from the condensation of pyridoxamine with pyridoxal and its novel copper(II) and oxidovanadium(IV) complexes: [Cu(HL)Cl] (1), [Cu(LH2)(phen)]Cl2 (2), [Cu(LH2)(amphen)]Cl2 (3), [VIVO(HL)Cl] (4), and [VIVO(LH2)(phen)]Cl2 (5), where phen is 1,10-phenanthroline and amphen is its 5-amino derivative. All compounds were characterized by analytical and spectroscopic techniques, namely FTIR, UV-vis and EPR spectroscopy. Their stability in aqueous media was evaluated, revealing that the presence of the phen co-ligand significantly increases the stability. The ternary Cu(II) complexes (2 and 3) impaired cell viability of osteosarcoma cells (MG-63) (IC50 values of 3.6 ± 0.6 and 7 ± 1.9 μM for 2 and 3), while 1 and the VIVO complexes did not show relevant anticancer activity. Complexes 2 and 3 are also more active than cisplatin (CDDP). Synergistic studies between 2 and sorafenib showed significant synergism on MG-63 cells for the following combinations: 2 (2.0 μM) + sorafenib (10.0 μM) and 2 (2.5 μM) + sorafenib (12.5 μM), whilst the combination of 2 and CDDP did not show synergy. Complex 2 interacts with DNA, inducing significant genotoxic effects on MG-63 cells from 1.0 to 2.5 μM and it increases the ROS levels 880% over basal. Moreover, 2 induces apoptosis at 1.0 and 2.0 μM, while its combination with sorafenib induces apoptosis and necrosis. Finally, compound 2 reduces the cell viability of MG-63 spheroids showing an IC50 value 7-fold lower than that of CDDP (8.5 ± 0.4 μM vs. 65 ± 6 μM). The combination of 2 and sorafenib also showed synergism on spheroids, suggesting that the combination of these drugs improves the anticancer effect against bone cancer cells. [ABSTRACT FROM AUTHOR]

Four Ni, Co, Cu, Zn-containing coordination polymers incorporating 4,4′,4′′,4′′′-tetrakiscarboxyphenylsilane (H4tcps) and 1,3,5-tris(2-methyl-1H-imidazol-1-yl)benzene (tmib) ligands, namely [Ni6(tcps)3(tmib)4(H2O)2] (1), [Co6(tcps)3(tmib)4] (2), [Cu2(tcps)(tmib)(H2O)] (3) and [Zn2(tcps)(tmib)] (4), were synthesized by the solvothermal method. Compounds 1 and 2 were isostructural with three-dimensional (3D) (3,4)-connected frameworks. Compounds 3 and 4 possessed (3,4)-connected 3D networks with (6·82)(6·85)(62·82·102)(62·8) and (4·6·8)(4·63·82)(66)(67·83) topology, respectively. The thermal derivatives of compounds 1 and 2, Co-800 and Ni-700, exhibited low OER overpotentials of 338 and 388 mV to achieve a current density of 10 mA cm−2 and hold their electrocatalytic activity for at least 9 hours in 1 M KOH. [ABSTRACT FROM AUTHOR]

The crystal structures and crystallisation behaviours of MII–TbIII–MII heterotrinuclear complexes, [(L)MTbM(L)]NO3 (M = Mn and Zn; L3− stands for a conjugated base of H3L = 1,1,1-tris[(3-methoxysalicylideneamino)methyl]ethane), obtained from various organic solvents (MeOH, EtOH, CH2Cl2 and CHCl3) were investigated. The trinuclear complex cation has two asymmetric centres (Δ or Λ) at two MII sites as a result of the twisted tripodal arms of L3−. Single-crystal X-ray diffraction analysis revealed that all the analysed Zn–Tb–Zn complexes had homochiral structures (Δ,Δ- or Λ,Λ-enantiomers) in each single crystal; however, the type of crystallisation behaviour showed clear differences depending on the type of solvent molecule. Specifically, crystallisation from MeOH or CH2Cl2 resulted in the exclusive formation of the Λ-conglomerates with the Λ,Λ-enantiomers—a phenomenon we recently termed 'absolute spontaneous resolution'. The analogous Mn–Tb–Mn complex crystallised from MeOH also resulted in the same phenomenon as that of Zn–Tb–Zn. In contrast, the meso-type (Δ,Λ) achiral isomer of the Mn–Tb–Mn complex was deposited for the first time in a series of MII–LnIII–MII trinuclear complexes from a CH2Cl2 or EtOH solution. Density functional theory calculations were performed to compare the thermodynamic stability of homochiral (Λ,Λ) and meso-type (Δ,Λ) complex cations of [(L)MnTbMn(L)]+ in MeOH and EtOH. Results were consistent with the molecular structures observed in the crystallographic analysis of the compounds deposited from these solvents. [ABSTRACT FROM AUTHOR]