Symmetric Ligand Research Articles

Synthesis, characterization and magnetic properties of a hexanuclear copper (II) complex with hydroxido, alkoxido and phenoxido bridges

A new CuII6 complex, formulated as [Cu6(L)3(µ3-OH)(H2O)(OH)(NO3)]·2H2O(1) has been prepared using the symmetrical N2O3-donor Schiff-base ligand H3L = N,N′-(2-hydroxypropane-1,3-diyl)bis(2-hydroxyacetophenimine). Compound 1 has been structurally and spectroscopically characterized. Single crystal X-ray diffraction analysis reveals that 1 crystallizes in the triclinic space group P-1 and consists of a CuII6 complex where each deprotonated ligand chelates two CuII centres. Three of the six independent CuII centres are arranged in an almost equilateral triangle with double Cu-O-Cu bridges, formed by a μ3-hydroxido and phenoxido bridges. Each of the three CuII centres in the triangle is further connected to one CuII centre through a single alkoxido bridge. The magnetic properties indicate the presence of moderate and weak antiferromagnetic interactions through the double and single oxido bridges, respectively.

Evolution of Frustrated Coordination in Eutectic Electrolyte Driven by Ligand Asymmetry toward High-Performance Zinc Batteries.

Eutectic electrolytes hold promise for aqueous zinc metal batteries in sustainable energy storage chemistries, yet improvement from perspective of molecule configurational engineering are ambiguous. Herein, we propose design strategy of increasing asymmetric molecular geometry in organic ligands to regulate frustrated coordination and disordered structure for eutectic electrolytes toward enhanced zinc metal batteries. The introduced asymmetry in eutectic component gives rise to relatively weak coordination strength and configurational disorder interaction among cation-anion-ligand, leading to suppressed local aggregation, steady eutectic phase and improved Zn2+diffusion kinetics. Such highly frustrated coordination state also enables disruption of hydrogen bonding network and reinforcement of anion participation, which results in confined side reactions, decreased water activity and the formation of inorganic-enriched solid electrolyte interphase. In comparison to highly symmetric ligands, asymmetric ligand-involved eutectic electrolytes with configurational disorderdeliver high Coulombic efficiency of 99.4 %, stabilized Zn plating/stripping of 5000 h and impressive rate capability even under harsh conditions such as small N/P, low temperature. The rationale in this work advances the deep understanding of asymmetric molecular engineering in eutectic electrolytes and showcases suitability of frustrated coordination to achieve high-performance zinc metal batteries.

Synthesis, Urease Inhibition, Molecular Docking, and Optical Analysis of a Symmetrical Schiff Base and Its Selected Metal Complexes.

Designing and developing small organic molecules for use as urease inhibitors is challenging due to the need for ecosystem sustainability and the requirement to prevent health risks related to the human stomach and urinary tract. Moreover, imaging analysis is widely utilized for tracking infections in intracellular and in vivo systems, which requires drug molecules with emissive potential, specifically in the low-energy region. This study comprises the synthesis of a Schiff base ligand and its selected transition metals to evaluate their UV/fluorescence properties, inhibitory activity against urease, and molecular docking. Screening of the symmetrical cage-like ligand and its metal complexes with various eco-friendly transition metals revealed significant urease inhibition potential. The IC50 value of the ligand for urease inhibition was 21.80 ± 1.88 µM, comparable to that of thiourea. Notably, upon coordination with transition metals, the ligand-nickel and ligand-copper complexes exhibited even greater potency than the reference compound, with IC50 values of 11.8 ± 1.14 and 9.31 ± 1.31 µM, respectively. The ligand-cobalt complex exhibited an enzyme inhibitory potential comparable with thiourea, while the zinc and iron complexes demonstrated the least activity, which might be due to weaker interactions with the investigated protein. Meanwhile, all the metal complexes demonstrated a pronounced optical response, which could be utilized for fluorescence-guided targeted drug delivery applications in the future. Molecular docking analysis and IC50 values from in vitro urease inhibition screening showed a trend of increasing activity from compounds 7d to 7c to 7b. Enzyme kinetics studies using the Lineweaver-Burk plot indicated mixed-type inhibition against 7c and non-competitive inhibition against 7d.

Oxidation State and Halogen Influence on the NHC‐Gold‐Halide‐Catalyzed Cyclization of Propargylic Amides

The homogeneously catalyzed cycloisomerization reaction of propargylic amides was tested as benchmark reaction for two homologous series of Au(I) and Au(III) complexes with NHC ligands. This reaction is known to afford either aromatic oxazoles or dihydrooxazoles, depending on the oxidation state of the applied gold catalysts. For this purpose, symmetric and unsymmetric NHC ligands with mixed alkyl or benzyl substituents (1,3‐dimethyl‐imidazolyl‐2yl or 1‐benzyl‐3‐methyl‐imidazolyl‐2‐yl) and the corresponding Au(I) and Au(III) derivatives were prepared and characterized by analytical methods, IR and 1H and 13C NMR spectroscopies, and by X‐ray diffraction methods. Ten NHC‐gold(I) and NHC‐gold(III) complexes were tested on the cyclization reactions by adding gold catalysts in the presence and absence of AgPF6.Noteworthy, only the 1‐benzyl‐3‐methyl‐gold(III) trichloride was able to give selectively the aromatic oxazole without the addition of the silver salt. Interestingly, on contrary to what is reported in the literature, the use of gold(I) or gold(III) complexes does not influence the chemoselectivity of the cyclization reaction, while the halide bound to the metal does. In this regard, a mechanism purposing the dihydrooxazole as an intermediate for the formation of aromatic oxazole is proposed.

Highly Anisotropic Pd2Lab 2Lcc 2 and Pd2Lab 2Lcd 2 Type Cages by Heteromeric Completive Self-Sorting.

Pd(II)-based low-symmetry coordination cages possessing anisotropic cavities are of great interest. The common strategies employed to achieve such cages utilize either more than one type of symmetrical ligands (e.g., Laa, Lbb etc.) or only one type of unsymmetrical ligand (e.g., Lab). To significantly enhance the anisotropy, we have designed two unsymmetrical bidentate ligands i.e., Lab and Lcd, aiming at a low-symmetry Pd2Lab 2Lcd 2-type cage. It was accomplished by high-fidelity integrative self-sorting of two different low-symmetry cages having Pd2Lab 4 and Pd4Lcd 8-type architectures (homoleptic complexes of the designed ligands). Structural constraints and geometry complementarity in the ligand design drive the non-statistical exclusive self-assembly of the Pd2Lab 2Lcd 2-type cage. By taking advantage of the complemental geometries between ligands, a low-symmetry Pd2Lab 2Lcc 2-type cage was also obtained. Heteromeric completive self-sorting of three homoleptic assemblies (Pd2Lab 4, Pd4Lcc 8 and Pd4Lcd 8-type cages) into an exclusive mixture of Pd2Lab 2Lcd 2 and Pd2Lab 2Lcc 2-type mixed ligated assemblies was demonstrated through cage-to-cage transformations.

Highly Anisotropic Pd2Lab2Lcc2 and Pd2Lab2Lcd2 Type Cages by Heteromeric Completive Self‐Sorting

AbstractPd(II)‐based low‐symmetry coordination cages possessing anisotropic cavities are of great interest. The common strategies employed to achieve such cages utilize either more than one type of symmetrical ligands (e.g., Laa, Lbb etc.) or only one type of unsymmetrical ligand (e.g., Lab). To significantly enhance the anisotropy, we have designed two unsymmetrical bidentate ligands i.e., Lab and Lcd, aiming at a low‐symmetry Pd2Lab2Lcd2‐type cage. It was accomplished by high‐fidelity integrative self‐sorting of two different low‐symmetry cages having Pd2Lab4 and Pd4Lcd8‐type architectures (homoleptic complexes of the designed ligands). Structural constraints and geometry complementarity in the ligand design drive the non‐statistical exclusive self‐assembly of the Pd2Lab2Lcd2‐type cage. By taking advantage of the complemental geometries between ligands, a low‐symmetry Pd2Lab2Lcc2‐type cage was also obtained. Heteromeric completive self‐sorting of three homoleptic assemblies (Pd2Lab4, Pd4Lcc8 and Pd4Lcd8‐type cages) into an exclusive mixture of Pd2Lab2Lcd2 and Pd2Lab2Lcc2‐type mixed ligated assemblies was demonstrated through cage‐to‐cage transformations.

Two symmetric Schiff base complexes: Inhibition of cell proliferation, inducing apoptosis and suppressing migration

Two complexes [Cu4L4] (1) and [Zn2Cl4L]·2[N(CH2CH3)4] (2) are synthesized and characterized with UV–Vis, IR, PXRD and TGA using a symmetrical flexible Schiff base ligand 2,2′-(1,4-phenlenebis(nitrilomethylylidene)-bis(6- methoxyphenol) (H2L). Crystallographic analysis reveals that complex 1 is a mirror symmetric single molecule with a rhombic crossing structure linked by four Cu(II) ions and four ligands encircling each other. Complex 2 is a centrosymmetric single molecule with one ligand connecting two zinc chloride salts to form an anion framework with two tetraethylammonium cations to balance charge. Antiproliferative activity of both complexes against four cancer cells and two normal cells was investigated, and the results show that complex 2 had the strongest inhibitory effect on A549 cells with IC50 value much lower than cisplatin and lower toxicity to two normal cells. Mechanistic studies showed that complex 2 could induce apoptosis of A549 cells, and inhibit cell invasion and migration of SMMC-7721 cells and A549 cells at a low concentration effectively. This work could provide a basis for developing novel metal-based anticancer agents.

Self-assembled Co(II) and Co(III) [M2L3] helicates and [M4L6] tetrahedra from an unsymmetrical quaterpyridine ligand.

In order to bind guest molecules with exquisite selectivity, biological host molecules often employ low symmetry binding pockets. The majority of metallosupramolecular assemblies, however, rely on symmetrical ligands to form high-symmetry assemblies that enclosing similarly symmetrical cavities. Here we employ an unsymmetrical quaterpyridine ligand in combination with cobalt(II) to form a mixture of low-symmetry [M2L3] helicates and [M4L6] tetrahedra and their subsequent oxidation to Co(III)-containing assemblies.

Theoretical study of the ability of symmetric and asymmetric N-donor ligands to separate Am(III) and Eu(III) and the bonding nature

In the reprocessing of spent nuclear fuel, nitrogen-donor extractants are more effective in separating actinides and lanthanides. In this article, a series of heterocyclic N-donor ligands with different backbones and different side chain substituents are systematically investigated to analyze their extraction selectivity and complexation abilities for Am(Ⅲ) and Eu(Ⅲ) by using scalar relativistic density functional theory (DFT). Through the analysis of geometric structures and bond properties of the complexes by means of the NBO and QTAIM methods, it was observed that the coordination ability of the N-donor ligand with Am(Ⅲ) was stronger than with Eu(Ⅲ). Thermodynamic analysis showed that these ligands have good extraction ability and separation performance for Am(III) and Eu(III), the backbone and side chain substituents of the ligands and also the organic solvents have significant influences on the extraction selectivity of the ligands for Am(III) and Eu(III) ions. This work provides some theoretical insights for the design of N-donor extractants with good separation performance for lanthanides and actinides.

Symmetrical Ligand's Fabricated Porous Silicon Surface Based Photoluminescence Sensor for Metal Detection and Entrapment.

This study was based on the development of surface-based photoluminescence sensor for metal detection, quantification, and sample purification employing the solid sensory chip having the capability of metal entrapment. The Co(II), Cu(II) and Hg(II) sensitive fluorescence sensor (TP) was first synthesized and characterized its sensing abilities towards tested metal ions by using fluorescence spectral investigation while the synthesis and complexation of the receptor was confirmed by the chromogenic, optical, spectroscopic and spectrometric analysis. Under optical investigation, the ligand solution exhibited substantial chromogenic changes as well as spectral variations upon reacting with copper, cobalt, and mercuric ions, while these behaviors were not seen for the rest of tested metallic ions i.e., Na+, Ag+, Ni2+, Mn2+, Pd2+, Pb2+, Cd2+, Zn2+, Sn2+, Fe2+, Fe3+, Cr3+, and Al3+. These colorimetric alterations and spectral shifting could potentially be employed to detect and quantify these specific metal ions. After the establishment of the ligand's selective complexation ability towards selected metals, it was fabricated over the substituted porous silicon surface (FPS) keeping in view of the development of surface-based photoluminescence sensor (TP-FPS) for the selected metal sensation and entrapment to purify the sample just be putting off the metal entrapped sensory solid chip. Surface characterization and ligand fabrication was inspected by plan and cross sectional electron microscopic investigations, vibrational and electronic spectral analysis. The sensitivity of the ligand (TP) in the solution phase metal discrimination was determined by employing the fluorescence titration analysis of the ligand solution after progressive induction of Co2+, Cu2+, and Hg2+, which afford the detection limit values of 2.14 × 10- 8, 3.47 × 10- 8 and 3.13 × 10- 3, respectively. Concurrently, photoluminescence titration of the surface fabricated sensor (TP-FPS) revealed detection limit values of 3.14 × 10- 9, 7.43 × 10- 9, and 8.21 × 10- 4, respectively, for the selected metal ions.

Modeling Complex Ligands for High Oxidation State Catalysis: Titanium Hydroamination with Unsymmetrical Ligands.

A method for modeling high oxidation state catalysts is used on precatalysts with unsymmetrical and symmetrical bidentate ligands to get a more detailed understanding of how changes to ancillary ligands affect the hydroamination of alkynes catalyzed by titanium. To model the electronic donor ability, the ligand donor parameter (LDP) was used, and to model the steric effects, percent buried volume (% Vbur) was employed. For the modeling study, 7 previously unpublished unsymmetrical Ti(XX')(NMe2)2 precatalysts were prepared, where XX' is a chelating ligand with pyrrolyl/indolyl linkages. The rates of these unsymmetrical and 10 previously reported symmetrical precatalysts were used with the model kobs = a + b(LDP)1 + c(LDP)2 + d(% Vbur)1 + e(% Vbur)2, where a-e were found through least-squares refinement. The model suggests that (1) the two attachment points of the bidentate ligand XX' are in different environments on the metal (e.g., axial and equatorial in a trigonal bipyramidal or square pyramidal structure), (2) the position of the unsymmetrical ligand on the metal is determined by the electronics of the ligand rather than the sterics, and (3) that one side of the chelating ligand's electronics strongly influences the rate, while the other side's sterics more strongly influences the rate. From these studies, we were able to generate catalysts fitting to this model with rate constants larger than the fastest symmetrical catalyst tested.

Co−Fe‐based Heterometallo‐Supramolecular Polymer for Non‐Enzymatic Electrochemical Nitrite Detection and the Study of Electron Transfer Kinetics

AbstractHere, we report the fabrication of Heterometallo‐supramolecular polymer (H‐SMP) for the selective oxidation of nitrite with the investigation of some kinetic parameters by the complex formation of Co(II) and Fe(II) salts with the symmetrical ligand which is composed of terpyridine moieties specially referred to as [4′,4′′′′‐(1,4‐Phenylene)bis(2,2′:6′,2′′‐terpyridine)] to form polyCoFe. The characterization of polyCoFe was carried out using UV‐Vis titration, FT‐IR and SEM. The viscosity measurement of H‐SMP was utilized to calculate its molecular weight using Mark‐Houwink‐Sakurada equation. The electrochemical performance of polyCoFe_GCE was evaluated using the CV and EIS techniques. The kinetics of the irreversible electro‐oxidation mechanism were investigated by introducing variations in scan‐rate and pH. The concurrence observed between the experimental and simulated CV results provided additional evidence supporting the accuracy and reliability of the determined kinetic parameters. We investigated the efficiency of polyCoFe_GCE for nitrite detection at various concentrations using CV as well as amperometry methods. The amperometric technique showed a wide linear range of 0.66 to 194.15 μM and a low detection limit of 0.11 μM. In addition, modified electrode underwent interference, stability, and reproducibility tests. Real samples were analyzed using both CV and amperometry methods, and the obtained results were compared with those obtained from standard solutions.

Treatment activity of hydrogels loaded with metal–organic frameworks of bleomycin on hemangioma

In the current paper, through utilizing two symmetrical pentacarboxylate ligands, namely, 3,5-di(2′,5′-dicarboxylphenyl)benzoic (H5L1) and 3,5-di(2′,4′ dicarboxylphenyl)benzoic acid (H5L2), two fresh Co(II)-basd coordination polymers (CPs), [Co5(μ3-H2O)2(L1)2]·3DMA·4H2O (1, DMA is N,N-dimethylacetamide) along with [Co3(μ3-OH)L2(H2O)3]·H2O (2) have been synthesized under the conditions of solvothermal. With hyaluronic acid (HA) and carboxymethyl chitosan (CMCS) as raw materials, HA/CMCS hydrogel was prepared by chemical synthesis and its internal microstructure was observed by scanning electron microscope. Using bleomycin as a drug model, we designed and synthesized two metallogel particle frameworks encapsulating bleomycin drugs and compared the effects of the two metallogel particle frameworks as drug carriers for delivering bleomycin drugs for the treatment of hemangiomas.

2D Conjugated Metal-Organic Frameworks: Defined Synthesis and Tailor-Made Functions.

Conspectus2D conjugated metal-organic frameworks (2D -MOFs) have emerged as a class of graphene-like materials with fully π-conjugated aromatic structures. Their unique structural characteristics provide abundant physiochemical features, including regular nanochannels, high electrical conductivity, and customizable band gaps. Recent intensive research has significantly advanced this field, yet the exploration of 2D c-MOFs with enhanced features is limited by the availability of organic linkages and topologies. Designing novel ligands is essential for the construction of new 2D c-MOFs with high crystallinity, excellent conductivity, and tailor-made functions.In this Account, we summarize our recent contributions in fine-tuning the topology of 2D c-MOFs through precise ligand design, thereby giving them fantastic structures and tailor-made functions. First, we propose the concept of replacing planar ligands by nonplanar ligands on conductive MOF skeletons. The incorporation of nonplanar ligands improves the solubility of large π-conjugated organic molecules without interfering with the interlayer π-stacking. Our investigation discovered that conjugate polycyclic aromatics-based ligands can be synthesized through in situ Scholl reactions by means of oxidative cyclodehydrogenation of a nonplanar precursor ligand during the solvothermal synthesis process. Hence, fully conjugated 2D c-MOFs can be directly synthesized from nonplanar organic ligands, simplifying and diversifying the preparation of 2D c-MOFs. Accordingly, the design flexibility of the ligands expands the topological structures and pore types. By controlling the synthesis conditions, we can successfully induce either a rhombus or a kagome topology from a nonplanar D2 symmetric ligand. Moreover, by employing a ligand engineering strategy, we incrementally increase the number of coordination functional groups on a twisted hexabenzocoronene core, resulting in the formation of three distinct symmetric hydroxyl ligands. These ligands elicit diverse target topologies and pore sizes, resulting in variances in the coordination node density on the skeletons. This, in turn, leads to differences in electron transfer abilities, ultimately causing variations in the electrical conductivity and mobility. In addition, we employ a straightforward coupling method to incorporate redox components, such as salphen and pyrazine, into nonplanar ligands, facilitating the synthesis of 2D c-MOFs with highly active centers. This strategy confers upon the resulting frameworks substantial capacity for catalysis and energy storage, offering a good platform for elucidating the structure-property relationships at the molecular level. Moreover, the well-defined synthesis of 2D c-MOFs imparts them with specific properties, particularly in the fields of electrical, electrochemical, and spintronic applications. At the end, the primary challenges facing 2D c-MOFs in achieving tailor functions and their practical applications are proposed. This account is expected to evoke new inspirations and innovative research in the field of 2D c-MOFs, especially in emerging interdisciplinary research areas.

Synthesis, structure, and magnetic properties of cubane-type tetranuclear Ni(II) and Cu(II) complexes with amide-containing polydentate ligand

Abstract Synthesis, structure, and magnetic properties of a tetranuclear metal complex with a symmetrical polydentate ligand, trans-(±)-1,2-(2-hydroxy-3-methoxybenzamido)cyclohexane (H2L), were characterized. The complexes have tetranuclear cubane cores with the formulae [Ni4(L)2(μ3-OMe)4(CH3OH)4] (1) and [Cu4(L)2(μ3-OMe)4(CH3OH)2] (2), whose cluster units are each composed of chiral ligands [(R, R)- or (S, S)-L]. The magnetic properties of the two compounds were characterized by 1 being ferromagnetic and 2 being antiferromagnetic.

Tuning the Softness of the Pendant Arms and the Polyazamacrocyclic Backbone to Chelate the 203Pb/212Pb Theranostic Pair.

A series of macrocyclic ligands were considered for the chelation of Pb2+: 1,4,7,10-tetrakis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO4S), 1,4,7-tris[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO3S), 1,4,7-tris[2-(methylsulfanyl)ethyl]-10-acetamido-1,4,7,10-tetraazacyclododecane (DO3SAm), 1,7-bis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane-4,10-diacetic acid (DO2A2S), 1,5,9-tris[2-(methylsulfanyl)ethyl]-1,5,9-triazacyclododecane (TACD3S), 1,4,7,10-tetrakis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetrazacyclotridecane (TRI4S), and 1,4,8,11-tetrakis[2-(methylsulfanyl)ethyl]-1,4,8,11-tetrazacyclotetradecane (TE4S). The equilibrium, the acid-mediated dissociation kinetics, and the structural properties of the Pb2+ complexes formed by these chelators were examined by UV-Visible and nuclear magnetic resonance (NMR) spectroscopies, combined with potentiometry and density functional theory (DFT) calculations. The obtained results indicated that DO4S, DO3S, DO3SAm, and DO2A2S were able to efficiently chelate Pb2+ and that the most suitable macrocyclic scaffold for Pb2+ is 1,4,7,10-tetrazacyclododecane. NMR spectroscopy gave insights into the solution structures of the Pb2+ complexes, and 1H-207Pb interactions confirmed the involvement of S and/or O donors in the metal coordination sphere. Highly fluxional solution behavior was discovered when Pb2+ was coordinated to symmetric ligands (i.e., DO4S and DO2A2S) while the introduction of structural asymmetry in DO3S and DO3SAm slowed down the intramolecular dynamics. The ligand ability to chelate [203Pb]Pb2+ under highly dilute reaction conditions was explored through radiolabeling experiments. While DO4S and DO3S possessed modest performance, DO3SAm and DO2A2S demonstrated high complexation efficiency under mild reaction conditions (pH = 7, 5 min reaction time). The [203Pb]Pb2+ complexes' integrity in human serum over 24 h was appreciably good for [203Pb][Pb(DO4S)]2+ (80 ± 5%) and excellent for [203Pb][Pb(DO3SAm)]2+ (93 ± 1%) and [203Pb][Pb(DO2A2S)] (94 ± 1%). These results reveal the promise of DO2A2S and DO3SAm as chelators in cutting-edge theranostic [203/212Pb]Pb2+ radiopharmaceuticals.

Theoretical studies and evaluation of anticancer properties of two cobalt(III) Schiff base complexes derived from 3,5-dichloro-2-hydroxybenzaldehyde and 1,2-phenylene diamine

This research aimed to synthesize a tetradentate symmetrical ligand, H2L, through the condensation reaction between 3,5-dichloro salicylaldehyde and 1,2-phenylenediamine. The produced ligand contains [N2O2] donor atoms and forms two new Co(III) Schiff base complexes, namely [CoIII(L)(1-MeIm)2]ClO4 (1) and [CoIII(L)(mrpln)2]ClO4 (2). Then, the structural characterization of these compounds was further examined by experimental techniques such as single x-ray diffraction, CHNS analysis, FT-IR spectroscopy, UV–Vis spectroscopy, and theoretical quantum chemical calculations. Furthermore, the structure's HOMO-LUMO energy gap and molecular electrostatic potential (MEP) were measured using the B3LYP/6–311 G method and compared to experimental data. Hirshfeld surface analysis was employed to investigate intermolecular interactions inside the crystal structures. Subsequently, an investigation was conducted to examine the biological characteristics of the ligand (H2L) and its complexes about SW-480 cancer cells, revealing significant anti-cancer effects. Molecular docking assessments were performed on both complexes to determine their propensity for binding the protein B-cell lymphorna (BCL-2, PDB ID: 4LXD).

Phen-2NO, a new C2-symmetric rigid-featured tetradentate ligand, and its application in the asymmetric alkylation reaction of indoles

A 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 were rationally designed and developed.

Naphthyridine–2NO, a new C2-symmetric rigid tetradentate bimetallic ligand and its application in asymmetric Friedel–Crafts alkylation

The development of a series of novel and easily accessed chiral naphthyridine-type binucleating ligands for asymmetric catalysis.

Binucleating Jäger-type {(N2O2)2}4- ligands: magnetic and electronic interactions of Fe(II), Ni(II) and Cu(II) across an in-plane TTF-bridge.

The simultaneous presence of different electrophores provides an interesting playground for responsive materials. Herein, we present the incorporation of a twice-reversibly oxidizable tetrathiafulvalene (TTF) unit into a binucleating ligand, bridging two metal centers in a fully conjugated plane. A two-step synthesis scheme gave the D2h symmetric Schiff base-like ligand H4L in moderate yields from which the corresponding copper(II) [Cu2L], nickel(II) [Ni2L], [Ni2L(py)4] and iron(II) complexes [Fe2L(py)4], [Fe2L(dmap)4] and [Fe2L(bpee)2]·1 Tol could be obtained. Characterization was performed through 1H-NMR, IR, UV-vis and 57Fe-Mössbauer spectroscopy, SQUID magnetometry and cyclic voltammetry, supported by density functional theory (DFT) calculations. Single crystal X-ray analysis of [Ni2L(py)4] revealed six-coordinate paramagnetic centers, whereas [Ni2L] underwent gradual coordination induced spin state switching (CISSS) in solution. The magnetic independence of both metal centers is echoed by close-to-ideal Curie-plots of the [Cu2L] system and the gradual spin crossover of all iron(II) compounds. By contrast, cyclic voltammetry measurements in solution indicated oxidation-dependent TTF-metal interactions, as well as metal-metal interactions. The reversible TTF-borne events in H4L and [Ni2L] are overlaid with metal-borne events in the case of [Fe2L(py)4], as is corroborated by an analysis of the frontier orbital landscapes and through diagnostic spectral features upon chemical oxidation.