Electronic and Molecular Structures of a Series of Nickel Bis-1,1-Dithiolates.

A series of homoleptic Ni bis-1,1-dithiolates, [Ni(S2C2RR')2]2- (R = CN, R' = CN, CO2Et, CONH2, Ph, Ph-4-Cl, Ph-4-OMe, Ph-4-NO2, Ph-3-CF3, Ph-4-CF3, Ph-4-CN; R = NO2, R' = H; R = R' = CO2Et) have been synthesized from the reaction of the alkali metal salt of the ligand and nickel chloride, and isolated as tetraphenylphosphonium or tetrabutylammonium salts. The complexes were characterized by X-ray crystallography, high-resolution mass spectrometry, and infrared (IR), nuclear magnetic resonance (NMR) and electronic absorption spectroscopies. The molecular structures show a rigidly square planar Ni(II) center linking two four-membered chelate rings whose dimensions are constant across the series. The electronic effect of the ligand substituents are revealed in the 13C NMR and electronic spectra, and corroborated by density functional calculations. Electron withdrawing groups deshield the low-field CS2 resonance, and the signature charge transfer band in the visible region is red-shifted. These observables have been accurately reproduced computationally, and revealed the Ni contribution to the ground state diminishes with decreasing electron withdrawing capacity of the ligand substituents. In contrast to 1,2-dithiolates, the redox inactivity afforded by 1,1-dithiolates stems from the smaller chelate ring and substantially reduced sulfur content that is key to stabilizing the radical form.

Experimental and Theoretical Investigation of the Mechanism of the Reduction of O2 from Air to O22- by VIVO2+-N,N,N-Amidate Compounds and Their Potential Use in Fuel Cells.

The two-electron reductive activation of O2 to O22- is of particular interest to the scientific community mainly due to the use of peroxides as green oxidants and in powerful fuel cells. Despite of the great importance of vanadium(IV) species to activate the two-electron reductive activation of O2, the mechanism is still unclear. Reaction of VIVO2+ species with the tridentate-planar N,N,N-carboxamide (ΗL) ligands in solution (CH3OH:H2O) under atmospheric O2, at room temperature, resulted in the quick formation of [VV(═O)(η2-O2)(κ3-L)(H2O)] and cis-[VV(═O)2(κ3-L)] compounds. Oxidation of the VIVO2+ complexes with the sterically hindered tridentate-planar N,N,N-carboxamide ligands by atmospheric O2 gave only cis-[VV(═O)2(κ3-L)] compounds. The mechanism of formation of [VV(═O)(η2-O2)(κ3-L)(H2O)] (I) and cis-[VV(═O)2(κ3-L)] (II) complexes vs time, from the interaction of [VIV(═O)(κ3-L)(Η2Ο)2]+ with atmospheric O2, was investigated with 51V, 1H NMR, UV-vis, cw-X-band EPR, and 18O2 labeling IR and resonance Raman spectroscopies revealing the formation of a stable intermediate (Id). EPR, MS, and theoretical calculations of the mechanism of the formation of I and II revealed a pathway, through a binuclear [VIV(═O)(κ3-L)(H2O)(η1,η1-O2)VIV(═O)(κ3-L)(H2O)]2+ intermediate. The results from cw-EPR, 1H NMR spectroscopies, cyclic voltammetry, and the reactivity of the complexes [VIV(═O)(κ3-L)(Η2Ο)2]+ toward O2 reduction fit better to an intermediate with a binuclear nature. Dynamic experiments in combination with computational calculations were undertaken to fully elucidate the mechanism of the O2 reduction to O22- by [VIV(═O)(κ3-L)(Η2Ο)2]+. The galvanic cell {Zn|VIII,VII||Id, [VIVO(κ3-L)(H2O)2]+|O2|C(s)} was manufactured, demonstrating the important applicability of this new chemistry to Zn|H2O2 fuel cells technology generating H2O2 in situ from the atmospheric O2.

New triazole-based coordination complexes as antitumor agents against triple negative breast cancer MDA-MB-468 cell line.

The present work describes the synthesis of a new triazole based ligand 3-(3,5-dimethyl-1H-pyrazol-1-yl)-1-methyl-1H-1,2,4-triazole (LM) and demonstration of its coordination diversity giving rise to a family of seven new coordination complexes, namely: [Ni(LM)3](ClO4)2·C2H6OS (5), [Co2(LM)6](ClO4)4·(C2H5)O (6), [Cd(LM)2Cl2] (7), [Cu(LM)2NO3]NO3 (8), [Fe(LM)3](BF4)2 (9), [Zn(LM)3](BF4)2 (10) and [Zn(LM)2NO3]NO3 (11), whose crystal structure was determined by single-crystal X-ray diffraction. Cytotoxic activity was evaluated against the MDA-MB-468 cancer cell line, which serves as a model for triple-negative breast cancer, and compared to the precursor molecule (L), as well as their coordination complexes (H3O){[NiL3](ClO4)3} (1), [CoL3](ClO4)2·2H2O (2), [CdL2Cl2] (3) and [CuL3](NO3)2 (4), for which the crystal structure was earlier determined. Notably, cadmium complexes 3 and 7 exhibit remarkable cytotoxicity and demonstrated a high selectivity index towards cancer cells when compared to peripheral blood mononuclear cells. Such activity highlights their potential function as anticancer agents.

Design and Modulation of Selectivity toward Vanadium(V) and Uranium(VI) Ions: Coordination Properties and Affinity of Hydroxylamino-Triazine Siderophores.

Based on the strong binding and high selectivity properties of 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (H2bihyat) for [UVIO2]2+, novel binucleating ligands (BLs) N,N',N″,N‴-((1,4-phenylenebis(oxy))bis(1,3,5-triazine-6,2,4-triyl))tetrakis(N-methylhydroxylamine) (H4qtn), N1,N4-bis(4,6-bis(hydroxy(methyl)amino)-1,3,5-triazin-2-yl)benzene-1,4-diamine (H4pdl), and N1,N2-bis(4,6-bis(hydroxy(methyl)amino)-1,3,5-triazin-2-yl)ethane-1,2-diamine (H4enl) were synthesized. Binuclear complexes formed by coordination of hard metal ions with H4qtn are thermodynamically more stable than their mononuclear analogues with H2bihyat due to the increase in entropy accompanying the formation of more chelate rings. Reaction of either H4qtn or H4pdl or H4enl with [UVIO2]2+ and [VVO2]+ resulted in the isolation of the binuclear complexes [(UVIO2)2(µ-qtn)(H2O)4] (1), [(VVO2)2(µ-qtn)][PPh4]2[PPh4] (2), [(UVIO2)2(µ-pdl)(H2O)2(MeOH)2] (3), [(VVO2)2(µ-pdl)][PPh4]2 (4), [(UVIO2)2(µ-enl)(H2O)4] (5), and [(VVO2)2(µ-enl)][PPh4]2 (6). The binuclear complexes 1-6 were characterized by single-crystal X-ray diffraction analysis in solid state and by NMR and ESI-MS in solution. The comparison of the coordination ability of the BLs with either pyridine-2,6-dicarboxylic acid (H2dipic) or H2bihyat or CO32- toward [UVIO2]2+ and [VVO2]+ was investigated by NMR and UV-vis spectroscopies and DFT theoretical calculations, revealing a superior performance of BLs. The selectivity of the BLs for [UVIO2]2+ over [VVO2]+ is decreased compared to that of H2bihyat but increases considerably at pH > 9 values. Formation of the mixed-metal binuclear species [UVIO2(µ-O)VVO2] influences the selectivity and dynamics of the reaction of H4qtn for [UVIO2]2+ and [VVO2]+ in aqueous solution. The results of this study provide crucial information for the ligand design and the development of stronger and more selective systems.

Expeditious access to cis-ß-aryl, γ-alkyl disubstituted (±)-γ-butyrolactones via nickel-hydride catalysis.

The 1,4-reduction of ß- and γ-substituted butenolides using 5 mol% of NiCl2·6H2O and NaBH4 in MeOH for rapid access to cis-ß,γ-disubstituted γ-butyrolactones is described. The reaction was selective for cis-products, which were obtained in good to excellent yields. This study showcased the influence of steric hindrance and angle strain on the diastereoselectivity outcome of conjugate reductions facilitated by in situ generated nickel-hydride.

Pore "Softening" and Emergence of Breathability Effects of New Keplerate Nano-Containers.

The self-assembly of porous molecular nanocapsules offer unique opportunities to investigate a range of interesting phenomena and applications. However, to design nanocapsules with pre-defined properties, thorough understanding of their structure-property relation is required. Here, we report the self-assembly of two elusive members of the Keplerate family, [Mo132 Se60 O312 (H2 O)72 (AcO)30 ]42- {Mo132 Se60 } 1 and [W72 Mo60 Se60 O312 (H2 O)72 (AcO)30 ]42- {W72 Mo60 Se60 } 2, that have been synthesised using pentagonal and dimeric ([Mo2 O2 Se2 ]2+ ) building blocks and their structures have been confirmed via single crystal X-ray diffractions. Our comparative study involving the uptake of organic ions and the related ligand exchange of various ligand sizes by the {Mo132 Se60 } and previously reported Keplerates {Mo132 O60 }, {Mo132 S60 } based on the ligand exchange rates, revealed the emergence of increased "breathability" that dominates over the pore size as we transition from the {Mo132 S60 } to the "softer" {Mo132 Se60 } molecular nano-container.

Fabrication of Epitaxially Grown Mg2Al-LDH-Modified Nanofiber Membranes for Efficient and Sustainable Separation of Water-in-Oil Emulsion.

Efficient separation of water-in-oil emulsion is of great importance but remains highly challenging since such emulsion contains stable tiny droplets with a diameter less than 20 µm. Herein, we reported the fabrication of a modular fibrous functional membrane using an "in situ growth and covalent functionalization" strategy. The as-prepared PAN@LDH@OTS (PAN = polyacrylonitrile; LDH = layered double hydroxides; and OTS = octadecyltrichlorosilane) membrane possessed an interlaced rough nanostructured surface with intriguing superhydrophobic/superlipophilic properties. When applied for the separation of surfactant-stabilized water-in-oil emulsion (SSE), the PAN@LDH@OTS membrane exhibited an ultrahigh permeation flux of up to 4.63 × 104 L m-2 h-1 with an outstanding separation efficiency of >99.92%, outperforming most of the state-of-the-art membranes. In addition, the membrane can maintain a stable permeation flux and superhydrophobic/superlipophilic properties after 20 times of use. Detailed characterization demonstrated that the demulsification of the SSE process was as follows: first, the droplets can be easily adsorbed to the PAN@LDH@OTS membrane due to the improved intermolecular interactions between OTS and the surfactants (Span 80); second, the droplets can be deformed by the electropositive LDH laminate; and third, the deformed tiny emulsion droplets coalesced into large droplets and floated up, and as a result, efficient separation of SSE can be achieved.

Hafnium(IV) Chemistry with Imide-Dioxime and Catecholate-Oxime Ligands: Unique {Hf5} and Metalloaromatic {Hf6}-Oxo Clusters Exhibiting Fluorescence.

Hafnium(IV) molecular species have gained increasing attention due to their numerous applications ranging from high-resolution nanolithography, heterogeneous catalysis, and electronics to the design of molecule-based building blocks in metal-organic frameworks (MOFs), with applications in gas separation, sorption, luminescence sensing, and interim storage of radioactive waste. Despite great potential, their chemistry is relatively underdeveloped. Here, we use strong chelators (2Z-6Z)-piperidine-2,6-dione (H3pidiox) and 2,3-dihydroxybenzaldehyde oxime (H3dihybo) to synthesize the first ever reported pentanuclear {Hf5/H3pidiox} and hexanuclear {Hf6/H3dihybo} clusters (HfOCs). The {Hf6} clusters adopt unique core structures [Hf6IV(µ3-O)2(µ-O)3] with a trigonal-prismatic arrangement of the six hafnium atoms and have been characterized via single-crystal X-ray diffraction analysis, UV-vis spectroscopy in the solid state, NMR, fluorescence spectroscopy, and high-resolution mass spectrometry in solution. One-dimensional (1D) and two-dimensional (2D) 1H NMR and mass spectroscopies reveal the exceptional thermodynamic stability of the HfOCs in solution. Interestingly, the conjunction of the oxime group with the catechol resulted in the remarkable reduction of the clusters' band gap, below 2.51 eV. Another prominent feature is the occurrence of pronounced metalloaromaticity of the triangular {Hf3} metallic component revealed by its NICSzz scan curve calculated by means of density functional theory (DFT). The NICSzz(1) value of -44.6 ppm is considerably higher than the -29.7 ppm found at the same level of theory for the benzene ring. Finally, we investigated the luminescence properties of the clusters where 1 emits light in the violet region despite the lack of fluorescence of the free H3pidiox ligand, whereas the {Hf6} 3 shifts the violet-emitting light of the H3dihybo to lower energy. DFT calculations show that this fluorescence behavior stems from ligand-centered molecular orbital transitions and that HfIV coordination has a modulating effect on the photophysics of these HfOCs. This work not only represents a significant milestone in the construction of stable low-band-gap multinuclear HfIV clusters with unique structural features and metal-centered aromaticity but also reveals the potential of Hf(IV) molecule-based materials with applications in sensing, catalysis, and electronic devices.

A Combined Experimental and Theoretical Investigation of Oxidation Catalysis by cis-[VIV(O)(Cl/F)(N4)]+ Species Mimicking the Active Center of Metal-Enzymes.

Reaction of VIVOCl2 with the nonplanar tetradentate N4 bis-quinoline ligands yielded four oxidovanadium(IV) compounds of the general formula cis-[VIV(O)(Cl)(N4)]Cl. Sequential treatment of the two nonmethylated N4 oxidovanadium(IV) compounds with KF and NaClO4 resulted in the isolation of the species with the general formula cis-[VIV(O)(F)(N4)]ClO4. In marked contrast, the methylated N4 oxidovanadium(IV) derivatives are inert toward KF reaction due to steric hindrance, as evidenced by EPR and theoretical calculations. The oxidovanadium(IV) compounds were characterized by single-crystal X-ray structure analysis, cw EPR spectroscopy, and magnetic susceptibility. The crystallographic characterization showed that the vanadium compounds have a highly distorted octahedral coordination environment and the d(VIV-F) = 1.834(1) Å is the shortest to be reported for (oxido)(fluorido)vanadium(IV) compounds. The experimental EPR parameters of the VIVO2+ species deviate from the ones calculated by the empirical additivity relationship and can be attributed to the axial donor atom trans to the oxido group and the distorted VIV coordination environment. The vanadium compounds act as catalysts toward alkane oxidation by aqueous H2O2 with moderate ΤΟΝ up to 293 and product yields of up to 29% (based on alkane); the vanadium(IV) is oxidized to vanadium(V), and the ligands remain bound to the vanadium atom during the catalysis, as determined by 51V and 1H NMR spectroscopies. The cw X-band EPR studies proved that the mechanism of the catalytic reaction is through hydroxyl radicals. The chloride substitution reaction in the cis-[VIV(O)(Cl)(N4)]+ species by fluoride and the mechanism of the alkane oxidation were studied by DFT calculations.

Mechanistic insights of molecular metal polyselenides for catalytic hydrogen generation.

Molecular metal chalcogenides have attracted great attention as electrocatalysts for the hydrogen evolution reaction (HER). However, efficient utilisation of the active sites and catalytic performance modulation has been challenging. Here we explore the design of immobilized molecular molybdenum polyselenides [Mo2O2S2(Se2)(Sex)]2- that exhibit efficient hydrogen evolution at low overpotential and stability over 1000 cycles. Density functional calculations provide evidence of a unimolecular mechanism in the HER process via the exploration of viable reaction pathways. The discussed findings are of a broad interest in the development of efficient molecular electrocatalytic materials.

Fiber Templated Epitaxially Grown Composite Membranes: From Thermal Insulation to Infrared Stealth.

Thermal insulation materials show a substantial impact on civil and military fields for applications. Fabrication of efficient, flexible, and comfortable composite materials for thermal insulation is thereby of significance. Herein, a "fiber templated epitaxial growth" strategy was adopted to construct PAN@LDH (PAN = polyacrylonitrile; LDH = layered double hydroxides) composite membranes with a three-dimensional (3D) network structure. The PAN@LDH showed an impressive temperature difference of 28.1 °C as a thermal insulation material in the hot stage of 80 °C with a thin layer of 0.6 mm. Moreover, when a human hand was covered with 3 layers of the PAN@LDH-70% composite membrane, it was rendered invisible under infrared radiation. Such excellent performance can be attributed to the following reasons: (1) the hierarchical interfaces of the PAN@LDH composite membrane reduced thermal conduction, (2) the 3D network structure of the PAN@LDH composite membranes restricted thermal convection, and (3) the selective infrared absorption of LDHs decreased thermal radiation. When modified with Dodecyltrimethoxysilane (DTMS), the resulting PAN@LDH@DTMS membrane can be used under high humidity conditions with excellent thermal insulation properties. As such, this work provides a facile strategy for the development of high-performance thermal insulation functional membranes.

Novel family of bis-pyrazole coordination complexes as potent antibacterial and antifungal agents.

A new pyrazole ligand, N,N-bis(2(1',5,5'-trimethyl-1H,1'H-[3,3'-bipyrazol]-1-yl)ethyl)propan-1-amine (L) was synthesized and characterized by 1H-NMR, 13C-NMR, FT-IR and HRMS. The coordination ability of the ligand has been employed for the construction of a new family of coordination complexes, namely: [Cu2LCl4] (1), [ML(CH3OH)(H2O)](ClO4)2 (MII = Ni (2), Co (3)) and [FeL(NCS)2] (4). The series of complexes were characterized using single-crystal X-ray diffraction, HRMS, FT-IR and UV-visible spectroscopy. Moreover, the iron(ii) analogue was investigated by 57Fe Mössbauer spectroscopy and SQUID magnetometry. Single-crystal X-ray structures of the prepared complexes are debated within the framework of the cooperative effect of the hydrogen bonding network and counter anions on the supramolecular formations observed. Furthermore, within the context of biological activity surveys, these compounds were reviewed against different types of bacteria to validate their efficiency, including both Gram-positive as well as Gram-negative bacteria. Enhanced behaviour towards Fusarium oxysporum f. sp. albedinis fungi, were detected for 1 and 4.

Acid/base responsive assembly/dis-assembly of a family of zirconium(IV) clusters with a cyclic imide-dioxime ligand.

The hydrolytically stable dioxime ligand (2Z-6Z)-piperidine-2,6-dione (H3pidiox) acts as a strong chelator mainly with hard metals in high oxidation states, a pre-requisite for potential applications in metal sequestering processes from aqueous solutions. Reaction of ZrCl4 with H3pidiox in methanol gives the mononuclear compound [ZrIV(η1,η1,η2-H2pidiox-O,N,O')2(OH2)2]Cl2·H2O·CH3OH (1), while the same reaction mixture in the presence of KOH gave the pentanuclear ZrOC [ZrIV5(µ2-OH)4(OH2)4(µ2-η1,η1,η2-Hpidiox-O,N,O')4(η1,η1,η1-HpidioxO,N,O')4]·5KCl·3CH3OH·8H2O (2). Compound 1 is formed at very acidic pH = 0, and the pentanuclear ZrOC 2 at higher pH values (pH = 2). Compounds 1 and 2 were characterized by single crystal X-ray structure analysis, multi-nuclear NMR spectroscopy and ESI-MS spectrometry. The single crystal X-ray structure analysis of 1 revealed a mononuclear zirconium(IV) compound containing an eight-coordinate zirconium atom bound to two singly deprotonated H2pidiox- ligands and two water molecules in a severely distorted bicapped octahedral geometry. The pentanuclear ZrOC 2 constitutes the second example of a Zr5 cluster to be reported and the first one in which the four zirconium atoms are arranged in a tetrahedral arrangement with the fifth occupying the center of the tetrahedron. 1D and 2D NMR spectroscopies of the acidic CD3OD solutions of complex 1 reveal a fast equilibrium between 1 and 2. Addition of KOH into a CH3OH solution of 2 results in the controlled fast transformation of 2 to an asymmetric hexanuclear ZrOC 3 as evidenced by the NMR and real-time ESI-MS solution studies. Further addition of KOH to the solution of 3 leads to the ZrOC 4, and on the basis of NMR and ESI-MS data and in comparison with the known hexanuclear titanium(IV)/H3pidiox cluster, it is concluded that the cluster 4 should have a hexanuclear structure. Electrospray ionization mass spectrometry (ESI-MS) demonstrated not only the structural stability 1 and 2 in solution, but also revealed the reversible pH driven dis-assembly/re-assembly process between the monomeric 1 and the pentanuclear ZrOC 2.

Synthesis, Structural and Physicochemical Characterization of a Titanium(IV) Compound with the Hydroxamate Ligand N,2-Dihydroxybenzamide.

The siderophore organic ligand N,2-dihydroxybenzamide (H2dihybe) incorporates the hydroxamate group, in addition to the phenoxy group in the ortho-position and reveals a very rich coordination chemistry with potential applications in medicine, materials, and physical sciences. The reaction of H2dihybe with TiCl4 in methyl alcohol and KOH yielded the tetranuclear titanium oxo-cluster (TOC) [TiIV4(µ-O)2(HOCH3)4(µ-Hdihybe)4(Hdihybe)4]Cl4∙10H2O∙12CH3OH (1). The titanium compound was characterized by single-crystal X-ray structure analysis, ESI-MS, 13C, and 1H NMR spectroscopy, solid-state and solution UV-Vis, IR vibrational, and luminescence spectroscopies and molecular orbital calculations. The inorganic core Ti4(µ-O)2 of 1 constitutes a rare structural motif for discrete TiIV4 oxo-clusters. High-resolution ESI-MS studies of 1 in methyl alcohol revealed the presence of isotopic distribution patterns which can be attributed to the tetranuclear clusters containing the inorganic core {Ti4(µ-O)2}. Solid-state IR spectroscopy of 1 showed the presence of an intense band at ~800 cm-1 which is absent in the spectrum of the H2dihybe and was attributed to the high-energy ν(Ti2-µ-O) stretching mode. The ν(C=O) in 1 is red-shifted by ~10 cm-1, while the ν(N-O) is blue-shifted by ~20 cm-1 in comparison to H2dihybe. Density Functional Theory (DFT) calculations reveal that in the experimental and theoretically predicted IR absorbance spectra of the ligand and Ti-complex, the main bands observed in the experimental spectra are also present in the calculated spectra supporting the proposed structural model. 1H and 13C NMR solution (CD3OD) studies of 1 reveal that it retains its integrity in CD3OD. The observed NMR changes upon addition of base to a CD3OD solution of 1, are due to an acid-base equilibrium and not a change in the TiIV coordination environment while the decrease in the complex's lability is due to the improved electron-donating properties which arise from the ligand deprotonation. Luminescence spectroscopic studies of 1 in solution reveal a dual narrow luminescence at different excitation wavelengths. The TOC 1 exhibits a band-gap of 1.98 eV which renders it a promising candidate for photocatalytic investigations.

Probing the Catalytically Active Species in POM-Catalysed DNA-Model Hydrolysis*.

Phosphoester hydrolysis is an important chemical step in DNA repair. One archetypal molecular model of phosphoesters is para-nitrophenylphosphate (pNPP). It has been shown previously that the presence of molecular metal oxide [Mo7 O24 ]6- may catalyse the hydrolysis of pNPP through the partial decomposition of polyoxomolybdate framework resulting in a [(PO4 )2 Mo5 O15 ]6- product. Real-time monitoring of the catalytic system using electrospray ionisation mass spectrometry (ESI-MS) provided a glance into the species present in the reaction mixture and identification of potential catalytic candidates. Following up on the obtained spectrometric data, Density Functional Theory (DFT) calculations were carried out to characterise the hypothetical intermediate [Mo5 O15 (pNPP)2 (H2 O)6 ]6- that would be required to form under the hypothesised transformation. Surprisingly, our results point to the dimeric [Mo2 O8 ]4- anion resulting from the decomposition of [Mo7 O24 ]6- as the active catalytic species involved in the hydrolysis of pNPP rather than the originally assumed {Mo5 O15 } species. A similar study was carried out involving the same species but substituting Mo by W. The mechanism involving W species showed a higher barrier and less stable products in agreement with the non-catalytic effect found in experimental results.

Synthesis, characterization and pharmacological evaluation of quinoline derivatives and their complexes with copper(ΙΙ) in in vitro cell models of Alzheimer's disease.

Alzheimer's disease (AD) is a neurodegenerative disorder of the central nervous system. The main pathophysiological mechanisms involve cholinergic neurotransmission, beta-amyloid (Αß) and Tau proteins, several metal ions and oxidative stress, among others. Current drugs offer only relief of symptoms and not a cure of AD. Accumulating evidence suggests that multifunctional compounds, targeting multiple pathophysiological mechanisms, may have a great potential for the treatment of AD. In this study, we report on the synthesis and physicochemical characterization of four quinoline-based metal chelators and their respective copper(II) complexes. Most compounds were non-toxic at concentrations ≤5 µM. In neuroprotection studies employing undifferentiated and differentiated SH-SY5Y cells, the metal chelator N2,N6-di(quinolin-8-yl)pyridine-2,6-dicarboxamide (H2dqpyca) appeared to exert significant neuroprotection against both, Aß peptide- and H2O2-induced toxicities. The copper(II) complex [CuII(H2bqch)Cl2].3H2O (H2bqch = N,N'-Bis(8-quinolyl)cyclohexane-1,2-diamine) also protected against H2O2-induced toxicity, with a half-maximal effective concentration of 80 nM. Molecular docking simulations, using the crystal structure of the acetylcholinesterase (AChE)-rivastigmine complex as a template, indicated a strong interaction of the metal chelator H2dqpyca, followed by H2bqch, with both the peripheral anionic site and the catalytic active site of AChE. In conclusion, the sufficient neuroprotection provided by the metal chelator H2dqpyca and the copper(II) complex [CuII(H2bqch)Cl2].3H2O along with the evidence for interaction between H2dqpyca and AChE, indicate that these compounds have the potential and should be further investigated in the framework of preclinical studies employing animal models of AD as candidate multifunctional lead compounds for the treatment of the disease.

Synthesis, Structural, and Physicochemical Characterization of a Ti6 and a Unique Type of Zr6 Oxo Clusters Bearing an Electron-Rich Unsymmetrical {OON} Catecholate/Oxime Ligand and Exhibiting Metalloaromaticity.

The chelating catechol/oxime ligand 2,3-dihydroxybenzaldehyde oxime (H3dihybo) has been used to synthesize one titanium(IV) and two zirconium(IV) compounds that have been characterized by single-crystal X-ray diffraction and 1H and 13C NMR, solid-state UV-vis, and ESI-MS spectroscopy. The reaction of TiCl4 with H3dihybo and KOH in methanol, at ambient temperature, yielded the hexanuclear titanium(IV) compound K2[TiIV6(µ3-O)2(µ-O)3(OCH3)4(CH3OH)2(µ-Hdihybo)6]·CH3OH (1), while the reaction of ZrCl4 with H3dihybo and either nBu4NOH or KOH also gave the hexanuclear zirconium(IV) compounds 2 and 3, respectively. Compounds 1-3 have the same structural motif [MIV6(µ3-Ο)2(µ-Ο)3] (M = Ti, Zr), which constitutes a unique example with a trigonal-prismatic arrangement of the six zirconium atoms, in marked contrast to the octahedral arrangement of the six zirconium atoms in all the Zr6 clusters reported thus far, and a unique Zr6 core structure. Multinuclear NMR solution measurements in methanol and water proved that the hexanuclear clusters 1 and 3 retain their integrity. The marriage of the catechol moiety with the oxime group in the ligand H3dihybo proved to be quite efficient in substantially reducing the band gaps of TiO2 and ZrO2 to 1.48 and 2.34 eV for the titanium and zirconium compounds 1 and 3, respectively. The application of 1 and 3 in photocurrent responses was investigated. ESI-MS measurements of the clusters 1 and 3 revealed the existence of the hexanuclear metal core and also the initial formation of trinuclear M3 (M = Ti, Zr) building blocks prior to their self-assembly into the hexanuclear M6 (M = Ti, Zr) species. Density functional theory (DFT) calculations of the NICSzz scan curves of these systems revealed that the triangular M3 (M = Ti, Zr) metallic ring cores exhibit pronounced metalloaromaticity. The latter depends upon the nature of the metallic center with NICSzz(1) values equal to -30 and -42 ppm for the Ti (compound 1) and Zr (compound 2) systems, respectively, comparable to the NICSzz(1) value of the benzene ring of -29.7 ppm calculated at the same level of theory.

Electrocatalytic hydrogen production by dinuclear cobalt(II) compounds containing redox-active diamidate ligands: a combined experimental and theoretical study.

The chiral dicobalt(ii) complex [CoII2(µ2-L)2] (1) (H2L = N2,N6-di(quinolin-8-yl)pyridine-2,6-dicarboxamide) and its tert-butyl analogue [CoII2(µ2-LBu)2] (2) were synthesized and structurally characterized. Addition of one equivalent of AgSbF6 to the dichloromethane solution of 1 and 2 resulted in the isolation of the mixed-valent dicobalt(iii,ii) species [CoIIICoII(µ2-L)2]SbF6 (3) and [CoIIICoII(µ2-LBu)2]SbF6 (4). Homovalent 1 and 2 exhibited catalytic activity towards proton reduction in the presence of acetic acid (AcOH) as the substrate. The complexes are stable in solution while their catalytic turnover frequency is estimated at 10 and 34.6 h-1 molcat-1 for 1 and 2, respectively. Calculations reveal one-electron reduction of 1 is ligand-based, preserving the dicobalt(ii) core and activating the ligand toward protonation at the quinoline group. This creates a vacant coordination site that is subsequently protonated to generate the catalytically ubiquitous Co(iii) hydride. The dinuclear structure persists throughout where the distal Co(ii) ion modulates the reactivity of the adjacent metal site by promoting ligand redox activity through spin state switching.

Investigating Complex Magnetic Anisotropy in a Co(II) Molecular Compound: A Charge Density and Correlated Ab Initio Electronic Structure Study.

Understanding magnetic anisotropy and specifically how to tailor it is crucial in the search for high-temperature single-ion magnets. Herein, we investigate the magnetic anisotropy in a six-coordinated cobalt(II) compound that has a complex geometry and distinct triaxial magnetic anisotropy from the perspective of the electronic structure, using electronic spectra, ab initio calculations, and an experimental charge density, of which the latter two provides insight into the d-orbital splitting. The analysis showed that the d-orbital splitting satisfactorily predicted the complex triaxial magnetic anisotropy exhibited by the compound. Furthermore, a novel method to directly compare the ab initio results and the d-orbital populations obtained from the experimental charge density was developed, while a topological analysis of the density provided insights into the metal-ligand bonding. This work thus further establishes the validity of using d-orbitals for predicting magnetic anisotropy in transition metal compounds while also pointing out the need for a more frequent usage of the term triaxial anisotropy in the field of single-molecule magnetism.

Spontaneous formation of autocatalytic sets with self-replicating inorganic metal oxide clusters.

Here we show how a simple inorganic salt can spontaneously form autocatalytic sets of replicating inorganic molecules that work via molecular recognition based on the {PMo12} ≡ [PMo12O40]3- Keggin ion, and {Mo36} ≡ [H3Mo57M6(NO)6O183(H2O)18]22- cluster. These small clusters are able to catalyze their own formation via an autocatalytic network, which subsequently template the assembly of gigantic molybdenum-blue wheel {Mo154} ≡ [Mo154O462H14(H2O)70]14-, {Mo132} ≡ [MoVI72MoV60O372(CH3COO)30(H2O)72]42- ball-shaped species containing 154 and 132 molybdenum atoms, and a {PMo12}⊂{Mo124Ce4} ≡ [H16MoVI100MoV24Ce4O376(H2O)56 (PMoVI10MoV2O40)(C6H12N2O4S2)4]5- nanostructure. Kinetic investigations revealed key traits of autocatalytic systems including molecular recognition and kinetic saturation. A stochastic model confirms the presence of an autocatalytic network involving molecular recognition and assembly processes, where the larger clusters are the only products stabilized by the cycle, isolated due to a critical transition in the network.