Terpyridine-metal complexes: effects of different substituents on their physico-chemical properties and density functional theory studies

Response of a Tethered Zn-Bis-Terpyridine Complex to an External Mechanical Force: A Computational Study of the Roles of the Tether and Solvent

Polymeric materials containing weak sacrificial bonds can be designed to engineer self-healing and higher toughness, improve melt-processing, or facilitate recycling. However, they usually exhibit a lower mechanical strength and are subject to creep and fatigue. For improving their design, it is of interest to investigate their mechanical response on the molecular scale. We report on a computational study of the response to a mechanical external force of a Zinc(II) bis-methyl phenyl-terpyridine ([Zn-bis-Terpy]2+) complex included in a cyclic poly(ethylene glycol) (PEG) tether designed to maintain the two partners of the metal-ligand bonds in close proximity after the rupture of the complex. The mechanical response is studied as a function of the pulling distortion by using the CoGEF isometric protocol, including interactions with a polar solvent (DMSO). We show that tethering favors recombination but destabilizes the complex before bond rupture because of the interactions of the PEG units with Terpy ligands. Similar effects occur between the DMSO molecules and the complex. Our results on the molecular scale are relevant for single-molecule force spectroscopy experiments. Interactions of the complex with solvent molecules and/or with the tether lead to a dispersion of the rupture force values, which could obscure the interpretation of the results.

Unveiling the multifaceted nature of terpyridine-based metal complexes: a synergistic study of their photophysical and electrochemical behavior with computational insights

This manuscript provides a comprehensive overview of the synthesis, characterization, and photophysical and electrochemical properties of terpyridine-based metal complexes (C1-C20). The synthesis of these terpyridine (TPY) complexes involves the coordination of TPY ligands (L1-L11) with transition metal ions, leading to a variety of novel structural and electronic configurations. The characterization of TPY ligands and their complexes is carried out using various techniques, including UV-Vis spectroscopy, NMR, FTIR and mass spectrometry. To the best of our knowledge, for the first time, we comprehensively investigate the photophysical, solvatochromic, electrochemical, and computational properties of an extensive series of TPY-based metal complexes (C1-C20) within a single framework. The solvatochromic behavior of the synthesized complexes (C1-C20) is explored, revealing their sensitivity to solvent polarity, which is a key factor influencing their photophysical properties. The TPY-based complexes (C1-C20) exhibited solvent-dependent fluorescence behavior, with distinct ILCT and MLCT mechanisms, and enhanced fluorescence in specific solvents, particularly for Zn(ii) and Cu(ii) complexes. The absorption and emission characteristics of the complexes are studied in dilute solutions to explore their structure-property relationships. Additionally, the electrochemical properties of the TPY-based metal complexes (C1-C20) are investigated, highlighting their redox activity and potential for use in energy storage and conversion applications. Density functional theory (DFT) calculations are employed to provide detailed insights into the electronic structure and reactivity of these complexes, supporting the experimental observations. The correlation of electronic band gaps with photophysical and electrochemical behaviors showed compounds as promising candidates with efficient charge transfer and strong fluorescence. The integrated analyses reveal the exceptional potential of this scaffold for advanced materials applications, highlighting its versatility and significance in cutting-edge research.

Alkoxy-modified terpyridine complexes as efficient photocatalysts for diclofenac potassium degradation in pharmaceutical wastewater

This study explores the synthesis and application of terpyridine-based metal complexes (C1-C6) for the degradation of diclofenac potassium (DCF), a widely used pharmaceutical pollutant. Terpyridine (TPY) ligands and their metal complexes were synthesized and characterized using FTIR, UV-Vis, 1H NMR, 13C NMR spectroscopy, and mass spectrometry. The novelty of this study lies in the fact that, for the first time, such structures were investigated/explored as potential photocatalysts for the degradation of DCF. The study demonstrates that the target complex compounds exhibit remarkable catalytic efficiency, facilitating the effective degradation of the target pollutant, DCF. The catalytic efficiency of the complexes (C1-C6) in the degradation process was investigated under optimized conditions, including pH and catalyst concentration. A detailed mechanistic study was conducted to elucidate the pathways involved in diclofenac degradation. Kinetic parameters were determined, demonstrating the reaction followed pseudo first-order kinetics. Furthermore, the recyclability of the TPY complexes was assessed over multiple degradation cycles, confirming their stability and reusability. Moreover, computational chemistry techniques utilizing density functional theory (DFT) efficiently explain the electrical properties of the target molecules. The molecular electrostatic potential (MEP) is a theoretical model widely utilized in catalyst chemistry to examine potential sites for nucleophilic and electrophilic attacks on photocatalysts and pollutants using a reactivity map. The density of states (DOS) indicated that C5 exhibited enhanced photoactivity owing to the more prominent localization and delocalization of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). The adsorption route of DCF on C2, C4, and C5 was accurately predicted using molecular electrostatic potential (MEP) descriptors. This study highlights the potential of TPY-based catalysts as efficient and sustainable materials for the remediation of pharmaceutical contaminants in water systems. The enhanced photocatalytic performance is attributed to the optimized electronic structure and the strategic incorporation of alkoxy-functionalized TPY scaffolds. Compared to previous studies on methylene blue (MB) degradation, the newly synthesized complexes exhibit significantly higher efficiency, particularly in the degradation of DCF, demonstrating superior reaction kinetics and recyclability. These findings underscore their promise as next-generation photocatalysts for environmental applications.

A Terpyridine Based 1,2,3-Triazol-1,4-diyl-Fluoroionophore-A Fluorometric Study Towards 3d Metal Ions in Acetonitrile

In this paper, we report on the sensing role of the 1,2,3-triazol unit in a 1,4-diyl arrangement in a fully π-conjugated fluorescent probe 1 (cf. Scheme 1) towards the fluorometric detection of 3d metal ions. The 1,2,3-triazol-1,4-diyl-fluoroionophore 1 was designed in a donor(D)-acceptor(A) arrangement with a 1,2,3-triazol unit as a π-linker between a terpyridine (A) ionophore and a diethylaminocoumarin (D) fluorophore to study the fluorescence behavior towards the divalent 3d metal ions Mn2+, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+. This fluoroionophore 1 is based on an intramolecular charge transfer (ICT) and shows a moderate quantum yield (φf) of 0.508 in acetonitrile. A modulation of the ICT process in 1 through Fe2+, Co2+, Cu2+, Ni2+ and Zn2+ leads to a small red shift of the lowest energetically lying absorption UV/Vis absorption band and to a very strong 3d metal ion induced fluorescence quenching. It should be considered, that the installation of a 1,2,3-triazole unit as a fully π-linker in ICT probes originates no ratiometric fluorescence response towards Fe2+, Co2+, Cu2+, Ni2+ and Zn2+.

Noncoordinating Anions as Key Modulators of Supramolecular Structures, Optical and Electrical Properties in Nickel(II) Complexes

This study explores the synthesis, structural characterization, and examination of two nickel(II) complexes, [Ni(N 3 L 1 )2](NO3)2 (complex 1) and [Ni(N 3 L 1 )2](ClO4)2 (complex 2), using the newly synthesized organic heterocyclic chelating ligand N 3 L 1 [4-imidazole-2,6-di(pyrazinyl)pyridine]. Through single-crystal X-ray diffraction, we have detailed the crystal structures of these complexes, highlighting their distorted octahedral geometries and diverse supramolecular interactions including π···π stacking, anion···π, and hydrogen bonding. These interactions crucially influence the formation of distinct one- and two-dimensional supramolecular architectures. Density functional theory (DFT) calculations were utilized to probe these noncovalent interactions, revealing insights into their stereoelectronic influence and stability in the solid state. Additionally, the electronic properties of the complexes were explored through their electrical characterizations in Schottky diodes, which suggest the potential of these complexes in Schottky diode based electronic devices applications. Notably, complex 2, incorporating perchlorate anions, exhibited better electrical properties than complex 1. This work aims to elucidate the role of noncoordinating counteranions in the structural integrity and photophysical behavior of these complexes, while also providing a structure-function correlation through detailed theoretical analysis.

Synthesis, Electrochemistry and Density Functional Theory of Osmium(II) Containing Different 2,2':6',2″-Terpyridines

In coordination chemistry, 2,2':6',2″-terpyridine is a versatile and extensively studied tridentate ligand. Terpyridine forms stable complexes with a variety of metal ions through coordination sites provided by the three nitrogen atoms in its pyridine rings. This paper presents an electrochemical study on various bis(terpyridine)osmium(II) complexes, addressing the absence of a systematic investigation into their redox behavior. Additionally, a computational chemistry analysis was conducted on these complexes, as well as on eight previously studied osmium(II)-bipyridine and -phenanthroline complexes, to expand both the experimental and theoretical understanding. The experimental redox potentials, Hammett constants, and DFT-calculated energies show linear correlations due to the electron-donating or electron-withdrawing nature of the substituents, as described by the Hammett constants. These substituent effects cause shifts to lower or higher redox potentials, respectively.

A Mononuclear [PtCl(tpy)]PF6 Complex for a Yellow Emitting Solution-Processable Organic Light Emitting Diode

We report square planar mononuclear Pt(II)-complexes of terpyridines in the form of [PtCl(L1/L2)]PF6 as phosphorescent emitters (where L1 = 4-(3-pyridine)2,2':6',2''-terpyridine and L2 = 4'-(3-pyridinyl)-4,4''-di(tert-butyl)-2,2':6'2''-terpyridine). Complex 2 showed emission at 534 nm in the DCM solution with photoluminescence quantum efficiency (ΦPL) = 14%, while in the mCBP host (5-wt % doped), the emission shifted to 584 nm with ΦPL = 37.8% and a phosphorescence lifetime (τphos) of 37.8 μs. Complex 2 in mCBP was used to fabricate a solution-processed phosphorescent organic light-emitting diode (PhOLED) which showed maximum external quantum efficiency (EQEmax) = 7.4% with yellow emission at λEL = 570 nm and exhibited a low efficiency roll-off with an EQE drop to 7.0% at 1000 cd/m2.

Manipulating the Coordination Structure of Molecular Cobalt Sites in Periodic Mesoporous Organosilica for CO2 Photoreduction

Photocatalytic CO2 reduction, including reaction rate, product selectivity, and longevity, is highly sensitive to the coordination structure of the catalytic active sites, and the precise design of the active site remains a challenge in heterogeneous catalysts. Herein, we report on the modulation of the coordination structure of MN x -type active sites (M = Co or Ni; x = 4 or 5) anchored on a periodic mesoporous organosilica (PMO) support to improve photocatalytic CO2 reduction. The PMO was functionalized with pendant 3,6-di(2'-pyridyl)pyridazine (dppz) groups to allow immobilization of molecular Co and Ni complexes with polypyridine ligands. A comparative analysis of CO2 photoreduction in the presence of an organic photosensitizer (4CzIPN, 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene) and a conventional [Ru(bpy)3]Cl2 sensitizer revealed strong influence of the coordination environment on the catalytic performance. CoN5-PMO demonstrated a superior CO2 photoreduction activity than the other materials and displayed a cobalt-based turnover number (TONCO) of 92 for CO evolution at ∼75% selectivity after 3 h irradiation in the presence of 4CzIPN. The hybrid CoN5-PMO catalyst exhibited better activity than its homogeneous [CoN5] counterpart, indicating that the heterogenization promotes the formation of isolated active sites with improved longevity and faster catalytic rate.

Recent developments in the synthesis and applications of terpyridine-based metal complexes: a systematic review

Terpyridine-based metal complexes have emerged as versatile and indispensable building blocks in the realm of modern chemistry, offering a plethora of applications spanning from materials science to catalysis and beyond. This comprehensive review article delves into the multifaceted world of terpyridine complexes, presenting an overview of their synthesis, structural diversity, and coordination chemistry principles. Focusing on their diverse functionalities, we explore their pivotal roles in catalysis, supramolecular chemistry, luminescent materials, and nanoscience. Furthermore, we highlight the burgeoning applications of terpyridine complexes in sustainable energy technologies, biomimetic systems, and medicinal chemistry, underscoring their remarkable adaptability to address pressing challenges in these fields. By elucidating the pivotal role of terpyridine complexes as versatile building blocks, this review provides valuable insights into their current state-of-the-art applications and future potential, thus inspiring continued innovation and exploration in this exciting area of research.

DFT study of the spectroscopic behaviour of different iron(II)-terpyridine derivatives with application in DSSCs

Through a comprehensive computational analysis utilizing Density Functional Theory (DFT), we clarify the electronic structure and spectroscopic properties of modified iron(II)-terpyridine derivatives, with the aim of enhancing the efficiency of Dye-Sensitized Solar Cells (DSSCs). We optimized a series of nineteen iron(II)-terpyridine derivatives and related compounds in acetonitrile (MeCN) as the solvent using TDDFT, evaluating their potential as dyes for DSSCs. From the conducted computations on the optimized geometries of the nineteen [Fe(Ln)2]2+ complexes, containing substituted terpyridine and related ligands L1-L19, we determined the wavelengths (λ in nm), transition energy (E in eV), oscillator strength (f), type of transitions, excited state lifetime (τ), light harvesting efficiency (LHE), frontier orbital character and their energies (ELUMO/EHOMO), natural transition orbitals (NTOs), injection driving force of a dye (ΔGinject), and regeneration driving force of a dye (ΔGregenerate). Results show that the theoretically calculated values for assessing dye efficiency in a DSSC correlate with available experimental values. The UV-visible spectra of [Fe(Ln)2]2+ exhibited a peak above 500 nm (λmax) in the visible region, attributed to the ligand-to-metal charge transfer band (LMCT) in literature, and a significant absorbance peak at approximately 300 nm (λA,max) in the UV region. The M06-D3/CEP-121G method replicated all reported λmax and λA,max values with a mean absolute deviation (MAD) of 21 and 18 nm, respectively. Our findings underscore the connections between electronic modifications and absorption spectra, emphasizing their impact on the light-harvesting capabilities and overall performance of DSSCs. This research contributes to the advancement of fundamental principles governing the design and optimization of novel photovoltaic materials, facilitating the development of more efficient and sustainable solar energy technologies.

Synthesis, characterization and structural analysis of complexes from 2,2':6',2''-terpyridine derivatives with transition metals

The synthesis and structural characterization of three families of coordination complexes synthesized from 4'-phenyl-2,2':6',2''-terpyridine (8, Ph-TPY), 4'-(4-chlorophenyl)-2,2':6',2''-terpyridine (9, ClPh-TPY) and 4'-(4-methoxyphenyl)-2,2':6',2''-terpyridine (10, MeOPh-TPY) ligands with the divalent metals Co2+, Fe2+, Mn2+ and Ni2+ are reported. The compounds were synthesized from a 1:2 mixture of the metal and ligand, resulting in a series of complexes with the general formula [M(R-TPY)2](ClO4)2 (where M = Co2+, Fe2+, Mn2+ and Ni2+, and R-TPY = Ph-TPY, ClPh-TPY and MeOPh-TPY). The general formula and structural and supramolecular features were determinated by single-crystal X-ray diffraction for bis(4'-phenyl-2,2':6',2''-terpyridine)nickel(II) bis(perchlorate), [Ni(C21H15N3)2](ClO4)2 or [Ni(Ph-TPY)2](ClO4)2, bis[4'-(4-methoxyphenyl)-2,2':6',2''-terpyridine]manganese(II) bis(perchlorate), [Mn(C22H17N3O)2](ClO4)2 or [Mn(MeOPh-TPY)2](ClO4)2, and bis(4'-phenyl-2,2':6',2''-terpyridine)manganese(II) bis(perchlorate), [Mn(C21H15N3)2](ClO4)2 or [Mn(Ph-TPY)2](ClO4)2. In all three cases, the complexes present distorted octahedral coordination polyhedra and the crystal packing is determined mainly by weak C-H...π interactions. All the compounds (except for the Ni derivatives, for which FT-IR, UV-Vis and thermal analysis are reported) were fully characterized by spectroscopic (FT-IR, UV-Vis and NMR spectroscopy) and thermal (TGA-DSC, thermogravimetric analysis-differential scanning calorimetry) methods.

Early bird or night owl? Controlling the ultrafast photodynamics of triphenylamine substituted 2,2':6',2''-terpyridine

Controlling the ultrafast photodynamics of metal-free organic molecules has great potential for technological applications. In this work, we use solvent polarity and viscosity as "external knobs" to govern the photodynamics of an electron-donating derivative of 2,2':6',2''-terpyridine (terpy), namely 4'-(4-(di(4-tert-butylphenyl)amine)phenyl)-2,2':6',2''-terpyridine (tBuTPAterpy). We combine femtosecond fluorescence upconversion (FlUC), transient absorption (TA) and quantum mechanical calculations to provide a comprehensive description of the tBuTPAterpy's photodynamics. Our results demonstrate that, by changing the solvent, the time scale of light-induced conformational changes of the system can be tuned over two orders of magnitude, controlling the tBuTPAterpy fluorescence spectral region and yield. As a result, depending on the local environment, tBuTPAterpy can act either as an "early bird" or a "night owl", with a tunability that makes it a promising candidate for metal-free sensors.

Building Surfaces with Controlled Site-Density of Anchored Human Serum Albumin

Stable and uniform layers of protein molecules at the surface are important to build passive devices as well as active constructs for smart biointerfaces for a large number of biomedical applications. In this context, a strategy to build-up surfaces able to anchor protein molecules on specific and controlled surface sites has been developed. Human serum albumin (HSA) has been chosen as a model protein due to its important antithrombogenic properties and its features in cell response highly valuable for in vivo devices. Uniform self-assembled monolayers of 2,2':6'2″-terpyridines (SAM), whose sites were further employed to chelate copper and iron ions, forming SAM-Cu(II) and SAM-Fe(II) complexes, have been developed. The effect of two metal cations on the physicochemical features of SAM, including thickness, Young's modulus, and tip-monolayer adhesion factors, has been investigated. Protein adsorption at different concentrations showed that the copper ion-templated surfaces exhibit highly specific mass uptake, kinetic behavior, and recognition and anchoring of HSA molecules owing to the coordination sphere of the different cations. The results pave the way to the development of a more general strategy to obtain ordered and density-tuned arrays of specific metal cations, which in turn would drive the anchoring of precise proteins for different biological functions.

Solvent Effect on the Photophysical Properties of Terpyridine Incorporating Pyrene Moiety: Estimation of Dipole Moments by Solvatochromic Shift Methods

The absorption and fluorescence emission spectra of terpyridine incorporating pyrene moiety (Tpy-pyr) have been recorded in extensive variety of solvents having different polarities. The effect of the solvent on the spectral characteristics are examined. It is shown that Tpy-pyr exhibit positive solvatochromism, large Stokes shift values in polar solvents, and fluorescence in the long wavelength region of the visible range. A linear increasing trend with Stokes shift indicates the presence of Tpy-pyr - solvent interaction. The acquired results could be attributed to the formation of excited states with intramolecular charge transfer. The fluorescence quantum yield was drastically reduced in polar protic solvents and the formation of the twisted states with charge transfer was proposed. Both ground and excited state dipole moments (µg and µe) were determined experimentally by Lippert-Mataga, Reichardt, Bilot-Kawski, Bakhshiev and Kawski-Chamma-Viallet solvatochromic methods analyzed on the base of the microscopic solvent polarity functions. The µg and µe dipole moment of Tpy-pyr estimated from density functional theory (DFT) and those determined experimentally from solvatochromic methods are compared and the results are discussed.

Terpyridine Glycoconjugates and Their Metal Complexes: Antiproliferative Activity and Proteasome Inhibition

Metal terpyridine complexes have gained substantial interest in many application fields, such as catalysis and supramolecular chemistry. In recent years, the biological activity of terpyridine and its metal complexes has aroused considerable regard. On this basis, we synthesised new terpyridine derivatives of trehalose and glucose to improve the water solubility of terpyridine ligands and target them in cancer cells through glucose transporters. Glucose derivative and its copper(II) and iron(II) complexes showed antiproliferative activity. Interestingly, trehalose residue reduced the cytotoxicity of terpyridine. Moreover, we tested the ability of parent terpyridine ligands and their copper complexes to inhibit proteasome activity as an antineoplastic mechanism.

A New Unnatural Amino Acid Derived from the Modification of 4′-(p-tolyl)-2,2′:6′,2″-terpyridine and Its Mixed-Ligand Complexes with Ruthenium: Synthesis, Characterization, and Photophysical Properties

The modification of the methyl group of 4′-(p-tolyl)-2,2′:6′,2″-terpyridine produced the novel unnatural amino acid 3-(4-([2,2′:6′,2″-terpyridin]-4′-yl)phenyl)-2-aminopropanoic acid (phet). Mononuclear heteroleptic ruthenium complexes of the general formulae [Ru(L1)(L2)](PF6)2 (L1 = 2-acetylamino-2-(4-[2,2′:6′,2″]terpyridine-4′-yl-benzyl)-malonic acid diethyl ester, (phem), 3-(4-([2,2′:6′,2″-terpyridin]-4′-yl)phenyl)-2-aminopropanoic acid, (phet), and L2 = 2,2′:6′,2″-terpyridine (tpy), 4′-phenyl-2,2′:6′,2″-terpyridine (ptpy), 4′-(p-tolyl)-2,2′:6′,2″-terpyridine (mptpy)), as well as the homoleptic [Ru(phem)2](PF6)2 and [Ru(phet)2](PF6)2, were synthesized and characterized by means of NMR spectroscopic techniques, elemental analysis, and high-resolution mass spectrometry. The photophysical properties of the synthesized complexes were also studied.

Electronic and structural data of 4’-substituted bis(2,2’;6’2’’-terpyridine)manganese in mono-, bis-, tris- and tetra-cationic states from DFT calculations

This data article provides density functional theory calculated structural (bond lengths and angles, coordinates of optimized geometries) and electronic (Mulliken spin population and character of frontier molecular orbitals) data of a series of 4’-substituted bis(2,2’;6’2’’-terpyridine)manganese complexes in four different oxidation states. The bis-cationic (n = 2) [Mn(tpy)₂]²⁺ complexes are experimentally well known (Sjödin et al., 2008), while little or none experimental structural data of the tetra-cationic (n = 4, Romain et al., 2009, 2009), tris-cationic (n = 3, Romain et al., 2009) and mono-cationic (n = 1, Wang et al., 2014) [Mn(tpy)₂]ⁿ⁺ complexes are available. For more insight into the provided data, see related research article “Redox chemistry of bis(terpyridine)manganese(II) complexes – a molecular view” (Conradie, 2022).

Fine-Tuning Metal and Ligand-Centered Redox Potentials of Homoleptic Bis-Terpyridine Complexes with 4'-Aryl Substituents

Homoleptic transition-metal complexes of 2,2':6',2″-terpyridine (terpy) and substituted derivatives of the form [M(R-terpy)₂]²⁺ display a wide range of redox potentials that correlate well to the Hammett parameter of the terpy substituents. Less is known about the impact of incorporating a phenyl spacer between the functional group responsible for controlling the electron density of terpy and how that translates to metal complexes of the form [M(4'-aryl-terpy)₂]²⁺, where M = Mn, Fe, Co, Ni, and Zn. Herein, we report our studies on these complexes revealed a good correlation of redox potentials of both metal- and ligand-centered events with the Hammett parameters of the aryl substituents, regardless of aryl-substitution pattern (i.e., the presence of multiple functional groups, combinations of withdrawing and donating functional groups). The phenyl spacer results in 60-80% attenuation of electron density as compared to the 4'-substituted terpy analogue, depending on the metal and redox couple analyzed. Density functional theory calculations performed on a simple model system revealed a strong correlation between the Hammett parameters and lowest unoccupied molecular orbital energies of the corresponding substituted pyridine models, thus serving as an inexpensive predictive tool when coupled with electrochemical data. Overall, these data suggest that such ligand modifications may be used in combination with previous approaches to further fine-tune the redox potentials of homoleptic transition-metal complexes, which may have applications in photochemical and electrochemical catalytic processes.

Steric crowding of a series of pyridine based ligands influencing the photophysical properties of Zn(II) complexes

The combination of α-acetamidocinnamic acid (HACA) and different N, N,N and N,N,N pyridines (dPy) leads to crowded Zn(ii) metal centers. The increasing bulkiness competes with the chelation enhanced effect (CHEF) in the resulting quantum yields.