Terpyridyl Complexes Research Articles

A Bichromophoric Approach to Induce Luminescence - A Blend of Experimental and Theoretical Studies.

Two homoleptic terpyridyl complexes of Ru(II), 1 and Fe(II), 2 were synthesized using a ligand L1 that contained a phenyl spacer between an anthracenyl (An) and a terpyridyl (tpy) moiety. An equilibrated-bichromophoric strategy was adopted to induce photoluminescence in 1 and 2. A glimpse into the excited state photophysical properties of 1 and 2 revealed that 1 exhibited NIR emission at ~700 nm with an excited state lifetime components of 1.33 and 6.52 ns. On the other hand, 2 was found to be non-luminescent. The origin of emission in case of 1 was attributed to the effect of phenyl spacer which rendered the 3An state to be nearly isoenergetic to the emissive 3MLCT state of 1 facilitating 3MLCT-3An equilibrium. This fact was supported by experimental (photocurrent generation) and theoretical (potential energy diagram) evidences.

Pd(II) and Pt(II) terpyridyl complexes: topoisomerase I inhibition and cytotoxicity

Abstract Pd(II) and Pt(II) terpyridyl complexes [MCl(terpy-COOH)]Cl where M = Pd(1) or Pt(2); terpy-COOH = 2,2′:6′,2″-terpyridine-4′-carboxylic acid] were synthesized. The Pd(II) complex was rapidly hydrolyzed because a Pd(II) ion was active in ligand substitution, while hydrolysis of the Pt(II) complex was slow because of its inactivity. Their topoisomerase inhibitory activity was examined: the Pd complex showed higher activity than the Pt complex. The complexes also bound with calf thymus DNA (ct-DNA): the binding constant of 1 was about twice as large as that of 2. The model studies suggested that the Pd complex coordinated faster with the His residue, to which topoisomerase bound phosphate ester, than the Pt complex. The cytotoxicity against HeLa cells was evaluated by adding bovine serum albumin (BSA): the Pd complex 1 was more cytotoxic than cisplatin, while no cytotoxicity was observed for the Pt complex 2. The binding constants of 2 with BSA were confirmed to be similar to those of 1. It is fascinating that the Pd complex, which has been conventionally considered to have low anticancer activity, shows higher cytotoxicity than the Pt complex with the same structure.

Bridging molecular photosensitizer and catalyst on carbon nanotubes toward enhanced selectivity and durability for CO2 photoreduction

Homogenous molecular photocatalysts for CO2 reduction, especially metal complex-based photosensitizer‒catalyst assemblages, have been attracting extensive research interests due to their efficiency and customizability. However, their low durability and recyclability limit practical applications. In this work, we immobilized the catalysts of metal terpyridyl complexes and the photosensitizer of [Ru(bpy)3]Cl2 onto the surface of carbon nanotubes through covalent bonds and electrostatic interactions, respectively, transforming the homogeneous system into a heterogeneous one. Our characterizations prove that these metal complexes are well dispersed on CNTs with a high loading (ca. 12 wt.%). Photocatalytic measurements reveal that catalytic activity is remarkably enhanced when the molecular catalysts are anchored, which is three times higher than that of homogeneous molecular catalysts. Moreover, when the photosensitizer of [Ru(bpy)3]Cl2 is immobilized, the side reaction of hydrogen evolution is completely suppressed and the selectivity for CO production reaches 100%, with its durability also significantly improved. This work provides an effective pathway for constructing heterogeneous photocatalysts based on rational assembly of efficient molecular photosensitizers and catalysts.

Solution Structures of Europium Terpyridyl Complexes with Nitrate and Triflate Counterions in Acetonitrile.

Lanthanide-ligand complexes are key components of technological applications, and their properties depend on their structures in the solution phase, which are challenging to resolve experimentally or computationally. The coordination structure of the Eu3+ ion in different coordination environments in acetonitrile is examined using ab initio molecular dynamics (AIMD) simulations and extended X-ray absorption fine structure (EXAFS) spectroscopy. AIMD simulations are conducted for the solvated Eu3+ ion in acetonitrile, both with or without a terpyridyl ligand, and in the presence of either triflate or nitrate counterions. EXAFS spectra are calculated directly from AIMD simulations and then compared to experimentally measured EXAFS spectra. In acetonitrile solution, both nitrate and triflate anions are shown to coordinate directly to the Eu3+ ion forming either ten- or eight-coordinate solvent complexes where the counterions are binding as bidentate or monodentate structures, respectively. Coordination of a terpyridyl ligand to the Eu3+ ion limits the available binding sites for the solvent and anions. In certain cases, the terpyridyl ligand excludes any solvent binding and limits the number of coordinated anions. The solution structure of the Eu-terpyridyl complex with nitrate counterions is shown to have a similar arrangement of Eu3+ coordinating molecules as the crystal structure. This study illustrates how a combination of AIMD and EXAFS can be used to determine how ligands, solvent, and counterions coordinate with the lanthanide ions in solution.

Tuning the reactivity of ruthenium(II) terpyridyl complexes using auxiliary ligands: kinetic and mechanistic studies

Tuning the reactivity of ruthenium(II) terpyridyl complexes using auxiliary ligands: kinetic and mechanistic studies

Creation of an unexpected plane of enhanced covalency in cerium(III) and berkelium(III) terpyridyl complexes

Controlling the properties of heavy element complexes, such as those containing berkelium, is challenging because relativistic effects, spin-orbit and ligand-field splitting, and complex metal-ligand bonding, all dictate the final electronic states of the molecules. While the first two of these are currently beyond experimental control, covalent M‒L interactions could theoretically be boosted through the employment of chelators with large polarizabilities that substantially shift the electron density in the molecules. This theory is tested by ligating BkIII with 4’-(4-nitrophenyl)-2,2’:6’,2”-terpyridine (terpy*), a ligand with a large dipole. The resultant complex, Bk(terpy*)(NO3)3(H2O)·THF, is benchmarked with its closest electrochemical analog, Ce(terpy*)(NO3)3(H2O)·THF. Here, we show that enhanced Bk‒N interactions with terpy* are observed as predicted. Unexpectedly, induced polarization by terpy* also creates a plane in the molecules wherein the M‒L bonds trans to terpy* are shorter than anticipated. Moreover, these molecules are highly anisotropic and rhombic EPR spectra for the CeIII complex are reported.

A “nucleophilic” iodine in a halogen-bonded iodonium complex manifests an unprecedented I+···Ag+ interaction

Summary When an electron is removed from a halogen atom, it forms a halenium ion X+ (X = I, Br, Cl). In halogen bonding (XB), X+ is considered as a strong XB donor, and when interacting with two XB acceptors (e.g., pyridine), it forms a halonium XB complex with a [N–I–N] three-center-four-electron bond with the two XB acceptors. An unprecedented I+···Ag+ interaction occurs between a [L1–I–L1]+ halogen-bonded complex and a [L2–Ag–L2]+ complex in which the iodonium ion acts like a nucleophile and donates electrons to the silver(I) cation. The X-ray diffraction analysis reveals a short contact [3.4608(3) A] between the I+ and Ag+ cations, and ITC measurements give a ΔG of −6.321 kcal/mol and Ka∼37,000 M−1 for the 1:1 complex. The DFT computational study on the nature of the I+···Ag+ interaction indicates that the I+ is nucleophilic in character, manifesting an unusual and strongly attractive interaction between the I+ and Ag+ cations.

Anti-adhesive action of novel ruthenium(II) chlorophenyl terpyridine complexes with a high affinity for double-stranded DNA: in vitro and in silico

Interactions of three Ru(II) chlorophenyl terpyridine complexes: [Ru(Cl-Ph-tpy)(en)Cl]Cl (1), [Ru(Cl-Ph-tpy)(dach)Cl]Cl (2) and [Ru(Cl-Ph-tpy)(bpy)Cl]Cl (3) (Cl-Ph-tpy = 4′-(4-chlorophenyl)-2,2′:6′,2′′-terpyridine, en = 1,2-diaminoethane, dach = 1,2-diaminocyclohexane, bpy = 2,2′-bipyridine) with human serum albumin (HSA), calf thymus DNA and a double-helical oligonucleotide d(CGCGAATTCGCG)2 (1BNA) were examined. Fluorescence emission studies were used to assess the interactions of complexes with HSA, which were of moderate strength for 1 and 2. Molecular docking allowed us to predict mostly π-π stacking and van der Waals interactions between the complexes and the protein. We suggest that the complexes bind to a novel site on HSA, which is different from its druggable sites I, II or III. We suggest a partial intercalation of complexes through the minor groove as a possible mode of interaction with double-helical DNA. Finally, when applied to normal extravillous cell line HTR8/SVneo and JAr choriocarcinoma cell line, complexes 1 and 2 exerted anti-adhesive properties at very low doses, whereas complex 3 had a negligible effect. The obtained results are completion of our studies of Ru(II) terpyridyl complexes that carry N-N ancillary ligands. We suggest a new research direction towards studying the cellular effects of Ru(II) polypyridyl compounds.

Opto-Electroactive Amino- and Pyridyl-Terminated Monolayers of RuII–Terpyridyl Complexes and Their Usage as Hg2+ Sensors

Robust opto-electroactive monolayers of three different RuII–terpyridyl complexes with amino and pyridyl termination are fabricated on SiOx-based substrates using siloxane-based attachment chemistry and either pyridyl or amine linkage to the preliminary prepared template. The UV–vis spectra of these monolayers display the characteristic metal-to-ligand charge-transfer bands, with a bathochromic shift compared to the spectra of the respective metalloligands dissolved in acetonitrile solution. This shift is notably larger for the pyridyl-linked monolayers compared to the amino-linked film, correlating qualitatively with the molecular grafting density. Cyclic voltammograms of the monolayers covalently attached onto indium tin oxide electrodes show reversible switching between the two redox states (Ru2+ to Ru3+ and vice versa), with a typical one-electron redox behavior. The sensing response of the monolayers to a series of different metal ions was tested, with the amino-decorated films showing a particularly...

Examination of Structure and Bonding in 10-Coordinate Europium and Americium Terpyridyl Complexes.

M(TpyNO2)(NO3)3(H2O)·THF (M = La, Nd, Sm, Eu, Tb, Am; TpyNO2 = 4'-nitrophenyl terpyridyl) have been prepared from the reaction of M(NO3)3· nH2O with TpyNO2 in THF. Structural analysis shows that the metal centers are 10-coordinate, providing the first example of AmIII with this coordination number. Further spectroscopic and theoretical evaluation of these complexes reveals utilization of the 5f orbitals in bonding in the AmIII complex. Comparison of Nd-L, Eu-L, and Am-L bond distances demonstrates that some caution should be taken in comparing EuIII versus AmIII in extraction experiments.

Enhancement of metal-metal interactions inside a large-cavity synthetic host in water.

The encapsulation of a series of metal-terpyridyl complexes in cucurbit[10]uril (CB[10]) in water is described. A strong enhancement of metal-metal and π-π interactions is observed due to double confinement in the large cavity. Furthermore, a linear supramolecular polymer featuring host-enhanced metallophilic interactions in water can be prepared.

On the contribution of f electrons to the quadratic hyperpolarizability: the case of lanthanide terpyridyl complexes.

Over the last decades, trivalent lanthanide ions (Ln3+) have gained much attention due to their peculiar luminescence, which opened the way to a broad range of applications, from medical diagnostic to lasers. Their impact on nonlinear optical (NLO) properties also attracted interest, especially in the framework of lanthanide complexes. Several experimental studies demonstrated that the quadratic hyperpolarizability varies with the number of 4f-electrons, with a stronger effect on dipolar than octupolar components. The main interpretation put forward to explain the observed trends relied on the polarizable character of the 4f-electrons. We report here a first step towards understanding the role of 4f-electrons in NLO responses, considering a series of dipolar terpyridyl-trinitro lanthanide complexes LLn(NO3)3 (Ln = Gd, Dy, Yb, Lu as well as La and Y; L = terpyridil-like ligand). Using DFT and TD-DFT we investigate their linear and non-linear optical properties. Consistently with earlier experimental findings, simulated UV-visible spectra show minor changes by varying Ln. The same holds for dipole moments and polarizabilities, whereas the nature of the lanthanide affects hyperpolarizabilities. It is shown that the observed changes are not a direct effect of the 4f-electrons that behave like core electrons.

Covalently Assembled Monolayers of Homo- and Heteroleptic FeII -Terpyridyl Complexes on SiOx and ITO-Coated Glass Substrates: An Experimental and Theoretical Study.

Well-defined FeII -terpyridyl monolayers were fabricated on SiOx and conductive ITO-coated glass substrates through covalent-bond formation between the metallo-organic complexes and a preassembled coupling layer. Three different homo- and heteroleptic complexes with terminal pyridyl, amine, and phenyl groups were tested. All the films were found to be densely packed and homogeneous, and consist of molecules standing upright. They exhibited high thermal (up to ≈220 °C) and temporal (up to 5 h at 100 °C) stability. The UV/Vis spectra of the monolayers showed pronounced metal-to-ligand charge-transfer bands with a significant redshift compared with the solution spectra of the metallo-ligands with a pendant pyridyl group quaternized with the coupling layer, whereas the shift was significantly smaller when the coupling layer was bonded to the primary amine (-NH2 ) group of the complex. Cyclic voltammograms of the monolayers showed reversible, one-electron redox behavior and suggested strong electronic coupling between the confined molecules and the underlying substrate. Analysis of the electrochemistry data allowed us to estimate the charge-transfer rate constant between the metal center and the substrate. Additionally, detailed quantum-chemical calculations were performed to support and rationalize the experimentally observed photophysical properties of the FeII -terpyridyl complexes both in the solution state and when bound to a SiOx -based substrate.

Nanometric Assembly of Functional Terpyridyl Complexes on Transparent and Conductive Oxide Substrates: Structure, Properties, and Applications.

Over the last few decades, molecular assemblies on solid substrates have become increasingly popular, challenging the traditional systems and materials in terms of better control over molecular structure and function at the nanoscale. A variety of such assemblies with high complexity and adjustable properties was generated on the basis of organic, inorganic, organometallic, polymeric, and biomolecular building blocks. Particular versatile elements in this context are terpyridyls due to their wide design flexibility, ease of functionalization, and ability to coordinate to a broad variety of transition-metal ions without forming diastereoisomers, which facilitates tuning of their optical and electronic properties. Specifically, metal-terpyridyl complexes are worthy building blocks for generating optoelectronically active assemblies on technologically relevant transparent and conductive oxide substrates. In this context, the present Account summarizes our recent results on the preparation, characterization, and applications of nanometric (2-10 nm) surface-confined molecular assemblies of Cu2+, Fe2+, Ru2+, and Os2+-terpyridyl complexes on SiOx-based substrates (glass, quartz, silicon, and ITO-coated glass). These assemblies rely on covalent bond formation between the iodo-/chloro-terminated functionalized SiOx substrates and the pendant group (mostly pyridyl) hosted on the terpyridyl complexes. Such an anchoring provides excellent thermal, temporal, radiative, and electrochemical stability to the assemblies as needed for technological applications. The functional, covalently assembled monolayers were extended to fabricate molecular dyads (bilayers), triads (trilayers), and oligomers by an established layer-by-layer procedure using suitable metallolinkers such as Cu2+, Ag+, and Pd2+. The chemical, optical, and electrochemical properties of these assemblies could be precisely adjusted by selection of proper metal-terpyridyl complexes and/or metallolinkers, so that the resulting systems served, relying on the specific design, as sensors, catalysts, molecular logic gates, and photochromic devices. For instance, a Cu-terpyridyl-based assembly on a glass substrate showed "turn on" detection of ascorbic acid. In another example, heterometallic molecular triads were exposed to redox-active NO+ for selective oxidation of the metal ions, and the optical readout was utilized for configuring multiple-input-based molecular logic gates. Furthermore, bias-driven (+0.6 to +1.6 V vs Ag/AgCl) optical properties of the heteroleptic Ru2+/Os2+-terpyridyl monolayers were modulated and "read out" by spectro-electrochemical techniques demonstrating high charge/information density (3-4 × 1014 electrons/cm2). Moreover, the manipulation of the M2+/3+ (M = Fe, Ru, and Os) redox wave in the assembly provided the possibility to create mixed-valence redox-states paving the way toward the fabrication of "multi-bit" memory systems. We truly believe that due to these intriguing characteristics and excellent stability, terpyridyl-based molecular assemblies have the potential to become a versatile platform for the next generation of smart optoelectronic devices.

Tuning Light Absorption in Platinum(II) Terpyridyl π-Conjugated Complexes: A First-Principle Study.

Platinum(II) terpyridyl complexes with a donor-acceptor (D-A) framework have long been considered as a promising component of dye-sensitized solar cells (DSSCs). To revealing the structure-property relationship of these highly modular systems, we have conducted a first-principle study at the time-dependent density functional theory (TDDFT) level on the [Pt(tBu3tpy)(-C≡C-Ph)n]+ (tBu3tpy is 4,4',4″-tri-tert-butyl-2,2':6',2″-terpyridine) complexes. It was found that their visible absorbance could be improved by elongating the donor chain with n (-C≡C-Ph) units, reaching a maximum at n = 16. It is noteworthy that such a simple concatenating protocol enables a remarkable charge transfer distance as long as 5 nm, implying a promising solution for the bottleneck problem of low charge separation rate in DSSCs. Furthermore, using a A-D-A system (two Pt(tBu3tpy) acceptors bridged by one donor) effectively doubles the visible-harvesting ability, and twisting an benzene ring in the chain of donors to break π-conjugations can tune down light absorption in a quantitatively angular dependent manner. Finally, replacing the C≡C bond linker with C═C double bond in donor leads to comparable light absorption ability while bestowing structural flexibility. These structure-property relationships thus provide efficient knobs for molecular rational design toward high performance dye-sensitized solar cells.

Self-assembly of a supramolecular hexagram and a supramolecular pentagram

Five- and six-pointed star structures occur frequently in nature as flowers, snow-flakes, leaves and so on. These star-shaped patterns are also frequently used in both functional and artistic man-made architectures. Here following a stepwise synthesis and self-assembly approach, pentagonal and hexagonal metallosupramolecules possessing star-shaped motifs were prepared based on the careful design of metallo-organic ligands (MOLs). In the MOL design and preparation, robust ruthenium–terpyridyl complexes were employed to construct brominated metallo-organic intermediates, followed by a Suzuki coupling reaction to achieve the required ensemble. Ligand LA (VRu2+X, V=bisterpyridine, X=tetraterpyridine, Ru=Ruthenium) was initially used for the self-assembly of an anticipated hexagram upon reaction with Cd2+ or Fe2+; however, unexpected pentagonal structures were formed, that is, [Cd5LA5]30+ and [Fe5LA5]30+. In our redesign, LB [V(Ru2+X)2] was synthesized and treated with 60° V-shaped bisterpyridine (V) and Cd2+ to create hexagonal hexagram [Cd12V3LB3]36+ along with traces of the triangle [Cd3V3]6+. Finally, a pure supramolecular hexagram [Fe12V3LB3]36+ was successfully isolated in a high yield using Fe2+ with a higher assembly temperature.

Interactions Between Thiocyanate-Free Bis-Tridentate Ru Complexes and Iodide in Dye-Sensitized Solar Cells

Abstract The intermolecular interactions of thiocyanate-free Ru terpyridyl complexes containing a 2,6-disubstituted pyridine as a tridentate donor ligand (BTP, FT19, and TUS-29 dyes) with iodide ions are investigated using density functional theory. Similar to N749 dye with three thiocyanate ligands, the oxidized thiocyanate-free complexes mainly interact with I − and I 2 − ions via the donor ligands. Oxidized BTP with a pyridine-2,6-ditetrazolyl ligand can be regenerated by three different mechanisms: (A) by one I − through a one-step mechanism, (B) by two I − ions via a two-step mechanism, or (C) by I 2 − via a one-step mechanism. Oxidized FT19 with a pyridine-2,6-dicarboxylate ligand can be regenerated via mechanism B or C. Although oxidized TUS-29 with a pyridine-2,6-dicarboxyamidato ligand can be reduced through mechanism C, the regeneration reaction is rather incomplete. The much lower dye-sensitized solar cell performance using TUS-29 dye than N749 is attributed to its inferior regeneration ability.

Insight into Electron-Donating Ancillary Ligands in Ruthenium Terpyridyl Complexes Configuration on Performances of Dye-Sensitized Solar Cells

Three heteroleptic ruthenium terpyridyl complexes, RC-T51, RC-T52, and RC-T53, with efficient electron-donating ancillary ligands were molecularly designed, synthesized and applied as sensitizers for dye-sensitized solar cell. With the replacement of labile isothiocyanates (NCS) ligand by electron-donating ancillary ligands, all the RC dyes exhibited superior optical properties and suitable electrochemical characteristics. The lowest excited-state decay dynamic analysis for RC dyes were carried out by time-resolved photoluminescence measurements. Among the RC dyes, the solar cell sensitized by RC-T53 achieved the best short-circuit current density of 14.20 mA cm–2 and power conversion efficiency of 6.17%. Compared with N749, DFT calculations, and transient absorbance decay kinetics rationalized the relatively inferior performances of RC dyes which were ascribed to the improper delocalization of the HOMO energy level and the inefficient dye generation process. Substituting the labile NCS ligand by electron...

Binuclear alkynylplatinum(ii) terpyridine complexes with flexible bridges behave as organogelators for several organic solvents

New binuclear alkynylplatinum(ii) terpyridyl complexes with flexible bridges have been synthesized and characterized by 1H NMR, mass spectra and elemental analysis.

Metal-ions linked surface-confined molecular dyads of Zn-porphyrin–metallo-terpyridine: an experimental and theoretical study

Solid state molecular engineering is performed on SiOx-substrates by combining transition metal ions and metallo-porphyrins and terpyridyl complexes.