Terpyridine Ligands Research Articles

Jahn-Teller distortion in bis(terpyridine)nickel(III) – Elongation or compression?

DFT methods were used to evaluate the type of Jahn-Teller distortion in the low spin d7 bis(terpyridine)nickel(III) doublet. The strain of the tridentate terpyridine ligand in bis(terpyridine)nickel(III) leads to longer Ni(III)-N terminal bond lengths than the Ni(III)-N central bonds. In addition, in all DFT optimized bis(terpyridine)nickel(III) molecules, the one set of Ni(III)-N terminal bonds are longer than the other set of Ni(III)-N terminal bonds. Three pairs of Ni(III)-N bonds are present in bis(terpyridine)nickel(III), namely 2 longer Ni(III)-Nterminal1 terminal bonds, 2 medium length Ni(III)-Nterminal2 terminal bonds and 2 shorter Ni(III)-Ncentral central bonds, similar to orthorhombic Jahn-Teller distortion in octahedral complexes. Evaluation of bond length differences, contraction of bonds, spin density plots and the character of the singly occupied molecular orbital (SOMO) and singly unoccupied molecular orbital (SUMO), led to a set of criteria to consider in evaluating the type of Jahn-Teller distortion in the low spin d7 bis(terpyridine)nickel(III) doublet. Jahn-Teller distortion can lead to elongation (z-out) or compression (z-in) of a pair of opposite Ni-N bonds. One key criteria found, is, if the difference in bond length between Ni(III)-Nterminal1 and Ni(III)-Nterminal2 is smaller than the difference in bond length of Ni(III)-Nterminal2 and Ni(III)-Ncentral, then it is a Jahn-Teller compression geometry (and vice versa for a Jahn-Teller elongation geometry).

Studies on Structure, optical and magnetic properties of Cd, Zn, Mn and Co complexes of terpyridine ligand

In order to further enrich the research on the synthesis of complexes with terpyridine ligand and transition metals, in this work, 4′-(4-(1H-imidazol-1-yl)phenyl)-2,2′:6′,2′'-terpyridine (Iptpd), 1,2-benzenedicarboxylic acid (1,2-BA) were used to construct metal complexes with Cd2+, Zn2+, Mn2+ and Co2+ by solvothermal reaction, and five complexes were constructed, namely, [Cd(Iptpd)(NO3)2]n (1), [Mn(Iptpd)(NO3)2]n (2), [Zn(Iptpd) (NO3)2·2H2O]n (3), [Mn(Iptpd)(1,2-BA)]2 (4) and [Co3(Iptpd)2(1,2-BA)2(NO3)2·10H2O]n (5); Single crystal x-ray diffraction analyses reveal that complexes 1, 2, 3 and 5 have one-dimensional chain structure, 4 is a binuclear structure. In addition, Luminescence behavior of complexes 1 and 3, magnetic properties of complexes 2 and 4 were investigated. The fluorescent test result shows that complex 1 and 3 have weak fluorescence performance and the fluorescence intensity is lower than that of ligand; The magnetic results indicate that complex 2 has ferromagentic property and 4 has antiferromagentic property.

Synthesis, characterization, antiproliferative activity and DNA binding calculation of substituted-phenyl-terpyridine copper(II) nitrate complexes

Ten 4′- (R-phenyl) -2,2′: 6′, 2′ – terpyridine ligands (R = hydrogen (L1), hydroxyl (L2), methoxyl (L3), methylsulfonyl (L4), methyl (L5), phenyl (L6), fluoro (L7), chloro (L8), bromo (L9), and iodo (L10)) were synthesized. The reaction of these ligands with copper(II) nitrate led to complexes 1–10. The characterization of 1–10 was carried out by means of mass spectrometry, elemental analysis, infrared spectroscopy and X-ray single crystal diffraction. Four cell lines including esophageal cancer cell line (Eca-109), human liver cancer cell line (Bel-7402), human breast cancer cell line (SIHa) and human normal liver cell line (HL-7702) were selected to carry out antiproliferation and cytotoxicity experiments in vitro. The results showed that the complexes have strong inhibitory ability on the growth of tumor cells. In order to study the anticancer mechanism of the complexes, the binding mode and binding ability of the complexes with DNA were further determined and discussed with UV–Vis spectroscopy and circular dichroism. The effects of the lowest binding energy and hydrogen bond on the binding were studied using molecular docking calculation.

Synthesis and characterization of a new ruthenium (II) terpyridyl diphosphine complex

Ruthenium complexes have been prepared for several applications, mostly for electrocatalysis, catalytic hydrogenation, energy conversion, photolysis, medicinal chemistry, among other fields. Bipyridine and terpyridine ligands are commonly found in the metal coordination sphere, including ruthenium, largely due to the high stability exhibited by the resulting complex and the possibility of greater stereochemical control during synthesis. The combination of substituted terpyridine ligands with diphosphine ligands to the metal ruthenium occurs to a lesser extent and its catalytic potential has been examined in several studies. This paper describes the synthesis of a new ruthenium (II) aqua complex containing aryl diphosphine and substituted terpyridine ligands: [Ru(L)(totpy)(OH2)](ClO4)2 (L=Ph2PCH2CH2PPh2); (totpy=4´-(4-tolyl)-2,2´:6´,2´´-terpyridine). The synthesis route was conducted in three steps; the final and the intermediate products have shown good reaction yields; the results of the characterization of the aqua complex by cyclic voltammetry, UV-visible spectroscopy and elemental analysis are consistent with the proposed chemical structure.

Crystal structures and solid-state luminescent properties of Eu(III), Gd(III) and Tb(III) complexes with hexafluoroacetylacetone and 4′-substituted terpyridine ligands

Six mononuclear lanthanide complexes [Ln(hfac)3(ptpy)] (Ln(III) = Eu (1), Gd (2), Tb (3)) and [Ln(hfac)3(ftpy)] (Ln(III) = Eu (4), Gd (5), Tb (6)), synthesized with 1,1,1,5,5,5-hexafluoroacetylacetone (hfac) as a first ligand and 4′-phenyl-2,2′:6′,2″-terpyridine (ptpy) or 4′-furan-2,2′:6′,2″-terpyridine (ftpy) as a second ligand, were characterized by elemental analyses, infrared spectroscopy, single-crystal X-ray diffraction, and powder X-ray diffraction. Thermogravimetric analyses indicate that these ternary lanthanide complexes possess very good thermal stability. Solid-state samples of 1-Eu and 4-Eu exhibit characteristic red luminescence at CIE: 0.6721, 0.3276 and CIE: 0.6859, 0.3139, with absolute quantum yields of 59.95% and 83.14% and luminescence lifetimes of 0.819 and 0.727 ms, respectively. Solid-state samples of 3-Tb and 6-Tb display characteristic green luminescence at CIE: 0.2736, 0.7167 and CIE: 0.2674, 0.7219, with absolute quantum yields of 2.58% and 0.52% and luminescence lifetimes of 0.040 and 0.033 ms, respectively. The results suggest that terpyridine is a good sensitizer for Eu(III), while hfac is a good sensitizer for Tb(III). In solid-state, the synergistic sensitization effect of hfac and terpyridine is significant for Eu(III), but less for Tb(III). And the electron-donating substituent at the 4′-position make terpyridine more suitable for the sensitization of Eu(III), but unfavorable for Tb(III).

Probing Electronic Effects in Tridentate Copper(I) Complexes by CIVP Spectroscopy.

Ligand electronic effects play an important role in catalysis, where small changes to ligand structure can bring about large changes in catalytic activity. Therefore, accurate experimental quantification of ligand electronic properties plays a crucial role in understanding and tuning chemical reactivity. In this work, we used cryogenic ion vibrational predissociation (CIVP) spectroscopy to experimentally quantify electronic effects in terpyridine ligands, as simple model systems, by measuring CIVP spectra of their copper complexes tagged by N2 molecules. We used the N2 stretching vibration as a reporter chromophore to probe electronic effects of the investigated ligands and employed quantum chemical calculations to better understand how different substituents influence the vibrational frequencies of the stretching vibration of the chromophore. Our data show that the electronic character, as well as position and number of substituents, can affect the N≡N vibrational frequency, and that the N≡N bond serves as a sensitive probe for electronic and steric effects.

Ligand-Metal Cooperation Enables Net Ring-Opening C-C Activation / Difunctionalization of Cyclopropyl Ketones.

Reactions that cleave C-C bonds and enable functionalization at both carbon sites are powerful strategic tools in synthetic chemistry. Stereodefined cyclopropyl ketones have become readily available and would be an ideal source of 3-carbon fragments, but general approaches to net C-C activation / difunctionalization are unknown. Herein we demonstrate the cross-coupling of cyclopropyl ketones with organozinc reagents and chlorotrimethylsilane to form 1,3-difunctionalized, ring-opened products. A combination of experimental and theoretical studies rule out more established mechanisms and shed light on how cooperation between the redox-active terpyridine (tpy) ligand and the nickel atom enables the C-C bond activation step. The reduced (tpy•-)NiI species activates the C-C bond via a concerted asynchronous ring-opening transition state. The resulting alkylnickel(II) intermediate can then be engaged by aryl-, alkenyl-, and alkylzinc reagents to furnish cross-coupled products. This allows quick access to products that are difficult to make by conjugate addition methods, such as β-allylated and β -benzylated enol ethers. The utility of this approach is demonstrated in the synthesis of a key (±)-taiwaniaquinol B intermediate and the total synthesis of prostaglandin D1.

Nickel chloride complexes with substituted 4'-phenyl-2',2':6',2″-terpyridine ligands: synthesis, characterization, anti-proliferation activity and biomolecule interactions.

A series of Ni(II) sandwich-like coordinated compounds were synthesized by the reaction of nickel dichloride and ten 4'-(4-substituent phenyl)-2',2':6',2″-terpyridine ligands, and their structures were confirmed by elemental analysis, FT-IR, ESI-MS, solid state ultraviolet spectroscopy and X-ray single crystal diffraction analysis. Three human cancer cell lines and a normal human cell line were used for anti-proliferation potential study: human lung cancer cell line (A549), human esophageal cancer cell line (Eca-109), human liver cancer cells (Bel-7402) and normal human liver cells (HL-7702). The results show that these nickel complexes possess good inhibitory effects on the cancer cells, outperforming the commonly used clinical chemotherapy drug cisplatin. Especially, complexes 3 (-methoxyl) and 7 (-fluoro) have strong inhibitory ability against Eca-109 cell line with IC50 values of 0.223μM and 0.335μM, complexes 4 and 6 showed certain cell selectivity, and complex 6 can inhibit cancer cells and slightly poison normal cells when the concentration was controlled. The ability of these complexes binding to CT-DNA was studied by UV titration and CD spectroscopy, and CD spectroscopy was also used to study the secondary structural change of BSA under the action of the complexes. The binding of these complexes with DNA, DNA-Topo I and bovine serum protein has been simulated by molecular docking software, and the docking results and optimal binding conformation data showed that they interacted with DNA in the mode of embedded binding, which is consistent with the experimental results. These complexes are more inclined to move to the cleavage site when docking with DNA-Topo I, so as to play a role of enzyme cleavage, while BSA promotes the action of the complexes by binding to effective binding sites.

Characterizing guanine’s binding modes with potential Ru(II) monofunctional adducts: A local vibrational mode study

We have investigated the bonding features of 18 Ruthenium(II) polypyridyl complexes of the type [Ru(tpy)(L)-(Guo)]n+, containing a tridentate 2,2′:6′,2′′-terpyridine ligand (tpy) and various bidentate ancillary ligands L, which form monofunctional adducts with guanine derivatives, such as guanosine (Guo). The main scaffold is motivated by the work of Simović et al. (2019). These complexes have been proposed to form a covalent bond with the nucleobase Guanine at its N7 position. This work illustrates the power of our local mode analysis in characterizing the strength of chemical interactions for experimentalists and theoreticians alike.

Terpyridine Based Heteroleptic Ruthenium Complexes: Influence of Donor and Acceptor Ligands in Photosensitization

AbstractWe report heteroleptic ruthenium complexes of terpyridine (tpy) ligands with directly linked carboxylic acid anchors. These complexes feature methyl or methoxy‐substituted 4′−Phtpy as donor ligands. We prepared these heteroleptic complexes from the ruthenium (II) precursor via a milder route to preclude the homoleptic complex formation. The donor−acceptor arrangement of tpy ligands in these ruthenium complexes renders visible light absorption giving metal and ligand‐to‐ligand charge transfer excitations at c.a. 490 nm. We evaluate the effect of the tpy donor substituents on the light‐harvesting ability in Dye‐Sensitized Solar Cells (DSSCs) and compare their photosensitizing ability with heteroleptic complexes bearing phenyl spacer at the acceptor end. Further, scrutinizing their photovoltaic performance, we studied their electron transfer kinetics in DSSCs using electrochemical impedance spectroscopy. This paper presents the structure‐photosensitization relationship of these heteroleptic ruthenium complexes through a combined experimental and computational approach.

Spin Crossover and Fluorine-Specific Interactions in Metal Complexes of Terpyridines with Polyfluorocarbon Tails.

In coordination chemistry and materials science, terpyridine ligands are of great interest, due to their ability to form stable complexes with a broad range of transition metal ions. We report three terpyridine ligands containing different perfluorocarbon (PFC) tails on the backbone and the corresponding FeII and CoII complexes. The CoII complexes display spin crossover close to ambient temperature, and the nature of this spin transition is influenced by the length of the PFC tail on the ligand backbone. The electrochemical properties of the metal complexes were investigated with cyclic voltammetry revealing one oxidation and several reduction processes. The fluorine-specific interactions were investigated by EPR measurements. Analysis of the EPR spectra of the complexes as microcrystalline powders and in solution reveals exchange-narrowed spectra without resolved hyperfine splittings arising from the 59 Co nucleus; this suggests complex aggregation in solution mediated by interactions of the PFC tails. Interestingly, addition of perfluoro-octanol in different ratios to the acetonitrile solution of the sample resulted in the disruption of the F F interactions of the tails. To the best of our knowledge, this is the first investigation of fluorine-specific interactions in metal complexes through EPR spectroscopy, as exemplified by exchange narrowing.

Spin‐Crossover Grafted Monolayer of a Co(II) Terpyridine Derivative Functionalized with Carboxylic Acid Groups

AbstractThe synthesis and characterization of a new Co(II) spin‐crossover (SCO) complex based on 4′‐(4‐carboxyphenyl)−2,2′:6′,2″‐terpyridine ligand are reported. This complex can be successfully grafted on silver surface maintaining the SCO behavior. Thus, atomic force microscopy (AFM), matrix assisted laser desorption ionization – time‐of‐flight mass spectrometry (MALDI‐TOF MS), Raman spectroscopy, and XPS measurements, upon surface deposition, evidence the formation of a monolayer of intact molecules grafted through carboxylate groups to the Ag surface. Three different techniques: Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS), and X‐ray absorption spectroscopy (XAS), supported by first‐principles calculations, confirm that the deposited molecules undergo a gradual spin transition with temperature. This phenomenon is unprecedented for a monolayer of molecules directly grafted onto a metallic surface from solution.

Landscape of Network Connectivity in Transient Polymer Networks with Competing Homo- and Hetero-complementary Bonds

Polymer networks expose a wide range of mechanical properties depending on their microstructure and connectivity. Specifically, transient networks based on end-linking of mixed telechelic polymer precursors capable of forming competing homo- and hetero-complementary bonds demonstrate a wide range of network structures and consequently mechanical properties depending on the composition and reactivity of employed precursors. To address this gap, the Miller–Macosko’s recursive model is extended to tetra-arm polymer precursors capable of forming homo- and hetero-complementary bonds. As such, the composition and time evolution of n-fold network connectivities are visualized as a function of precursor composition and bond selectivity. The model potential is highlighted by confronting its predictions with the rheological behavior of transient metallo-supramolecular polymer networks (MSPNs) obtained by mixing tetra-arm poly(ethylene glycol) functionalized with either sterically demanding mesitylene-substituted phenanthroline or unsubstituted slim phenanthroline or terpyridine ligands. The former precursor is incapable of homoleptic complexation; however, in combination with the latter two, they can form a mixture of homo- and heteroleptic complexes, depending on the coordination geometry preference of the utilized metal ion. These results not only visualize the connectivity landscape that can be explored in transient polymer networks, even beyond MSPNs, but can also provide a selectivity index for competing transient bonds based on rheological properties.

Six novel Zn(II)/Cd(II) coordination polymers based on a rigid tridentate imidazolyl terpyridine ligand fine-tuned by different carboxylates: Syntheses, structural diversities and luminescence properties

Six novel coordination polymers (CPs) based on a rigid tridentate ligand, 4′-(4-(imidazol-1-yl)phenyl)-4,2′:6′,4′'-terpyridine (imphtpy), namely {[Zn2(imphtpy)2(p-bdc)2]·(H2O)}n (1), [Zn(imphtpy)(m-bdc)]n (2), {[Zn(imphtpy)(qda)1.5]·(H2O)}n (3), [Cd2(imphtpy)2(m-bdc)2]n (4), [Cd(imphtpy)(abtc)0.5]n (5) and [Cd(imphtpy)(qda)]n (6), (p-H2bdc = 1,4-benzenedicarboxylic acid, m-H2bdc = 1,3-benzenedicarboxylic acid, H2qda = hydroquinone-o,o'-diacetic acid and H4abtc = 3,3′,5,5′-azobenzenetetracarboxylic acid), have been solvothermally synthesized and characterized by elemental analysis, IR spectroscopy, powder X-ray diffraction (PXRD), thermogravimetric (TG) analysis and single-crystal X-ray diffraction. Complex 1 displays a pseudo four-fold interpenetration of dia network in a [2 + 2] mode. Complex 2 exhibits a 2D → 2D polycatenane of two-fold interpenetrated network with the sql topology. Complex 3 shows a interdigitated 2D layer with the sql topology, which is further extended into a 3D supramolecular framework through π-π interactions and hydrogen bonds. Complex 4 features a two-fold interpenetrated (4,4)-connected 3D + 3D → 3D framework with the bbf topology. Complex 5 reveals a 2D network constructed by binuclear Cd2(CO2)4 secondary building unit (SBU) with the sql topology which is further packed into a 3D supramolecular framework through π-π interactions. Complex 6 is a 3D network constructed by binuclear Cd2(CO2)2O2 SBU with the uninodal 6-c pcu topology. These results indicate that the versatile coordination networks of imphtpy and various polycarboxylate ligands play crucial roles in modulating the structural topologies of coordination networks. In addtion, photoluminescence properties have been explored for complexes 1–6 in the solid state at room temperature, which are derived from metal perturbed intraligand charge transfer (ICT) or ligand-to-ligand charge transfer.

In vitro and in vivo antitumor activities of Ru and Cu complexes with terpyridine derivatives as ligands

Six terpyridine ligands(L1-L6) with chlorophenol or bromophenol moiety were obtained to prepare metal terpyridine derivatives complexes: [Ru(L1)(DMSO)Cl2] (1), [Ru(L2)(DMSO)Cl2] (2), [Ru(L3)(DMSO)Cl2] (3), [Cu(L4)Br2]·DMSO (4), Cu(L5)Br2 (5), and [Cu(L6)Br2]⋅CH3OH (6). The complexes were fully characterized. Ru complexes 1–3 showed low cytotoxicity against the tested cell lines. Cu complexes 4–6 exhibited higher cytotoxicity against several tested cancer cell lines compared to their ligands and cisplatin, and lower toxicity towards normal human cells. Copper(II) complexes 4–6 arrested T-24 cell cycle in G1 phase. The mechanism studies indicated that complexes 4–6 accumulated in mitochondria of T-24 cells and caused significant reduction of the mitochondrial membrane potential, increase of the intracellular ROS levels and the release of Ca2+, and the activation of the Caspase cascade, finally inducing apoptosis. Animal studies showed that complex 6 obviously inhibited the tumor growth in a mouse xenograft model bearing T-24 tumor cells without significant toxicity.

Substituent effect on the oxidation and reduction of electronically altered iron(II)-terpyridine derivatives – DFT study

Structure, reactivity, and redox properties play an important role in many biological processes. The structures of two types of series of related iron(II) compounds, namely iron(II)-terpyridine and iron(II)-tris-azinyl derivatives, were optimized in the gaseous as well as solvated states by means of density functional theory (DFT). From the optimized geometries of the molecules, their frontier orbital energies (ELUMO/EHOMO), electronic chemical potential (μ), electrophilicity index, (ω), Merz-Kollman electric potential, Gibbs Free energy, Mulliken and Natural Bond Orbital charges were determined. The DFT calculated reactivity parameters were related to the experimentally reported iron-based oxidation and ligand-based reduction potential of the series of iron(II)-terpyridine and tris-azinyl derivatives. Results obtained show that the relationship between the experimental and DFT calculated Fe(II/III) redox potential gave the most accurate relationship (R2 = 0.97), though a systematic error, depending on the choice of the reference system, was obtained. Relationships between the experimental iron-based oxidation (EFe(II/III)) or ligand-based reduction (ELigand) of the iron(II) complexes, and solvent phase calculated HOMO and LUMO energies respectively (R2 = 0.96 and 0.95 respectively), lead to more accurate relationships with higher R2 values than the relationships involving the gas phase calculations (R2 = 0.87 and 0.88 respectively). More relationships, that can be used to predict the oxidation and reduction of related iron(II) derivatives containing two substituted terpyridine or tris-azinyl analogues of the terpyridine ligand, were obtained to a high accuracy.

Connectivity Defects in Metallo-Supramolecular Polymer Networks at Different Self-Sorting Regimes

The properties of polymer networks depend on their connectivity, specifically on the presence of connectivity defects like loops and dangling ends. While chemically crosslinked networks have a frozen distribution of defects on multiple length scales, equivalent transient ones are capable of self-repairing. To study this potential, we employ spatial hindrance as an effective self-sorting mechanism to develop metallo-supramolecular polymer networks based on heteroleptic complexes. We functionalize tetra-arm poly(ethylene glycol) (tetraPEG) chains with the mesitylene-substituted phenanthroline ligand, which is incapable of homoleptic complexation, yet it can form heteroleptic complexes with tetraPEG precursors functionalized with unsubstituted phenanthroline or terpyridine ligands. This way, the formation of primary loops can be avoided upon selective formation of heteroleptic complexes. Nevertheless, the coordination geometry preference of the utilized metal ion can tune the extent of self-sorting and consequently the network structure and defect composition. The latter is pursued via MQ-NMR, and periodic density functional theory simulations are used to visualize the structure and explain its relationship with the dynamics as measured by rheology. Our results demonstrate that Cu(I) can inherently adopt the geometry requirements of both desired heteroleptic complexes by benefiting from the π-stabilization effect, thereby creating a network with the least primary loops and dangling ends.

Construction of 1,3,5-Triazine-Based Prisms and Their Enhanced Solid-State Emissions.

In this study, two trigonal prisms based on the 1,3,5-triazine motif (SA and SB), distinguished by hydrophobic groups, were prepared by the self-assembly of tritopic terpyridine ligands and Zn(II) ions. SA and SB exhibited high luminescence efficiencies in the solid state, overcoming the fluorescence quenching of the 1,3,5-triazine group caused by π-π interactions. Notably, SA and SB exhibited different luminescence behaviors in the solution state and aggregation state. SB with 12 alkyl chains exhibited extremely weak fluorescence in a dilute solution, but its fluorescence intensity and photoluminescence quantum yield (PLQY) were significantly enhanced in the aggregated state (with the increase in the water fraction), especially in the solid state. Different from the gradually enhanced efficiency of SB, the PLQY of SA gradually decreased with the increase in aggregation but still maintained a high luminescence efficiency. These two complexes exhibited different modes to solve the fluorescence quenching of 1,3,5-triazine in the solid state. The hierarchical self-assembly of SB exhibited nanorods owing to the hydrophobic interactions of alky chains, while SA aggregated into spheres under the influence of π-π interactions.

Developing terpyridine-based metal complexes for non-aqueous redox flow batteries

This paper describes the design and synthesis of a series of terpyridine-based complexes of the first-row transition metals Cr, Mn, Fe, and Co for non-aqueous redox flow batteries (NARFBs). Electrochemical studies reveal that these complexes can undergo multi-electron transfer redox reactions. In particular, the Mn and Fe-based complexes exhibit both low negative redox potentials and high positive redox potential, permitting them to serve as a bipolar electrolyte for symmetric RFBs with a cell voltage of more than 2 V. The solubility of these complexes can be effectively improved by incorporating a polyether substituent on the terpyridine ligand and counter anion optimization. The iron complex [Fe(tpy-O(CH2CH2O)3CH3)2][TFSI]2 shows a high solubility of 0.76 M in MeCN. The fabricated iron-based symmetric NARFB demonstrates a superior battery performance with a high cell voltage of 2.3 V, columbic efficiency of 97%, energy efficiency as high as 88%, and stable charge-discharge capacity retention of 60% after 160 cycles, corresponding to 99.75 % capacity retention per cycle. The post-cycling cyclic voltammetry (CV), UV-Vis, and 1H-NMR characterizations indicate only minor chemical decomposition of the cycled complex, confirming its good charging-discharging stability.

Electrochemistry and Spin‐Crossover Behavior of Fluorinated Terpyridine‐Based Co(II) and Fe(II) Complexes

AbstractDue to their ability to form stable molecular complexes that have tailor‐made properties, terpyridine ligands are of great interest in chemistry and material science. In this regard, we prepared two terpyridine ligands with two different fluorinated phenyl rings on the backbone. The corresponding CoII and FeII complexes were synthesized and characterized by single‐crystal X‐ray structural analysis, electrochemistry and temperature‐dependent SQUID magnetometry. Single crystal X‐ray diffraction analyses at 100 K of these complexes revealed Co−N and Fe−N bond lengths that are typical of low spin CoII and FeII centers. The metal centers are coordinated in an octahedral fashion and the fluorinated phenyl rings on the backbone are twisted out of the plane of the terpyridine unit. The complexes were investigated with cyclic voltammetry and UV/Vis‐NIR spectroelectrochemistry. All complexes show a reversible oxidation and several reduction processes. Temperature dependent SQUID magnetometry revealed a gradual thermal SCO behavior in two of the complexes, while EPR spectroscopy provided further insights on the electronic structure of the metal complexes, as well as site of reduction.