Transition Metal Ion Complexes Research Articles

Dynamic doping and degradation in sandwich-type light-emitting electrochemical cells

Photoluminescence spectroscopy has been performed in situ during device operation and after switch-off on ionic transition metal complex (iTMC)-based sandwich-type light-emitting electrochemical cells (LECs). It is demonstrated that the photoluminescence of the LECs decreases with increasing operating time. For operating times up to three hours the decline in photoluminescence is fully recoverable after switching off the bias. These results imply that doping of the iTMC layer is responsible, not only, for the turn-on of LECs but also for their lifetimes.

Optoelectronic properties of OLEC devices based on phenylquinoline and phenylpyridine ionic iridium complexes

Ionic transition metal complexes (iTMCs) have already been demonstrated to be a promising type of material to fabricate low-cost light sources, which are much more competitive in terms of realization costs with respect to standard organic light emitting diodes. The device performance, optical and morphological properties of thin films of two different complexes [Ir(phenylpyridine)(2)(5-Me-1,10-phen)][PF(6)] and [Ir(phenylquinoline)(2)(5-Me-1,10-phen)][PF(6)] have been measured and compared. The use of an ionic liquid as part of the processing procedure shows advantages in terms of low operation voltage, which is as low as 3.5 Volts. However, it leads to drawbacks in terms of device lifetime, limited to t(1/2) = 2 min, and maximum achievable brightness (1425 cd m(-2) vs. 3040 cd m(-2) without ionic liquid, for the complex [Ir(phenylpyridine)(2)(5-Me-1,10-phen)][PF(6)]).

Iridium (III) complexes as promising emitters for solid-state Light-Emitting Electrochemical Cells (LECs)

Light–emitting Electrochemical Cells (LECs) constitute one of the most recent generations of Organic Light–Emitting Diodes (OLEDs). The main difference between LECs and OLEDs is that LECs include mobile ions in the active layer. Ionic transition–metal complexes and especially ionic iridium (III) complexes have recently attracted widespread attention as potential electroluminescent materials for LECs. Herein, we present an overview of LECs incorporating ionic iridium (III) complexes as phosphorescent emitters. Synthetic strategies developed to introduce iridium (III) complexes in the active layer are also reviewed. Despite the numerous intrinsic drawbacks still remaining, recent advances make iridium–based LECs promising devices for future commercial and scientific applications.

Binding motifs of silver in prion octarepeat model peptides: a joint ion mobility, IR and UV spectroscopies, and theoretical approach

Transition metal-ion complexation is essential to the function and structural stability of many proteins. We studied silver complexation with the octarepeat motif ProHisGlyGlyGlyTrpGlyGln of the prion protein, which shows competitive sites for metal chelation including amide, indole and imidazole groups. This octapeptide is known as a favourable transition metal binding site in prion protein. We used ion mobility spectrometry (IMS), infrared multiple photon dissociation (IRMPD) spectroscopy and density functional theory calculations (DFT) to identify the binding motifs of a silver cation on HisGlyGlyGlyTrp peptide as well as on peptide subsequences. Ultra-violet photodissociation (UVPD) and collision induced dissociation mass spectrometry together with the time-dependent density functional method was then exploited to study the influence of binding sites on optical properties and on the ground and excited states reactivity of the peptide. We show that the metal cation is bound to the π-system of the indole group and a nitrogen atom of the imidazole group and that charge transfers from the indole group to the silver cation occur in excited electronic states.

Crystal structures of low-melting ionic transition-metal complexes with N-alkylimidazole ligands

A series of ionic liquids with copper(II), nickel(II) or cobalt(II)-containing cations have been synthesised and characterised, where possible with single crystal X-ray diffraction. A number of N-methylimidazole (MeIm), N-ethylimidazole (EtIm), N-butylimidazole (BuIm) or N-hexylimidazole (HeIm) ligands are coordinated to the metal centres and bis(trifluoromethyl)sulfonyl imide (Tf2N) anions provide the charge balance. Two types of metal complexes have been analysed. One has the general formula [Cu(AlkIm)4][Tf2N]2 (AlkIm = MeIm, EtIm, BuIm and HeIm) and contains square planar copper(II) centres with longer interactions to oxygen atoms of bis(trifluoromethylsulfonyl)imide anions. The other type of metal complex has a metal : ligand ratio of 1 : 6, with composition [M(MeIm)6][Tf2N]2 (M = Cu, Ni, Co) and contains octahedral metal centres. The ionic liquids have low melting points and the change in melting points is discussed as a function of alkyl chain length on the imidazole ligand and as a function of the metal centre. The metal–ligand interactions and intermolecular interactions in the crystal structures are analysed and related to the properties of the metal complexes.

Establishing Dual Electrogenerated Chemiluminescence and Multicolor Electrochromism in Functional Ionic Transition-Metal Complexes

A combination of electrochromism and electroluminescence in functional materials could lead to single-layer dual electrochromic/electroluminescent (EC/EL) display devices, capable of simultaneous operation in emissive and reflective modes. Whereas such next generation displays could provide optimal visibility in any ambient lighting situation, materials available that exhibit such characteristics in the active layer are limited due to the required intrinsic multifunctionality (i.e., redox activity, electroluminescence, electrochromism, and ion conductivity) and to date can only be achieved via the rational design of ionic transition-metal complexes. Reported herein is the synthesis and characterization of a new family of acrylate-containing ruthenium (tris)bipyridine-based coordination complexes with multifunctional characteristics. Potential use of the presented compounds in EC/EL devices is established, as they are applied as cross-linked electrochromic films and electrochemiluminescent layers in light-emitting electrochemical cell devices. Electrochromic switching of the polymeric networks between yellow, orange, green, brown and transmissive states is demonstrated, and electrochemiluminescent devices based on the complexes synthesized show red-orange to deep red emission with λ(max) ranging from 680 to 722 nm and luminance up to 135 cd/m(2). Additionally, a dual EC/EL device prototype is presented where light emission and multicolor electrochromism occur from the same pixel comprised of a single active layer, demonstrating a true combination of these properties in ionic transition-metal complexes.

Light-Emitting Coaxial Nanofibers

Ionic transition-metal complex (iTMCs)-based electro-luminescent nanofibers (TELFs) are developed by using coelectrospinning. A single TELF consists of a Galistan liquid metal core (cathode), an iTMC-based polymer shell, and an ITO thin film coating (anode). Lights emitted from the TELFs can be detected by a CCD camera at 4.2 V and seen by naked eyes at 5.6 V in nitrogen. The TELFs are structurally self-supporting but do not require a physical substrate (generally relatively bulky and heavy) to support them, rendering one-dimensional light sources more flexible, lightweight, and conformable. This technology can be beneficial to many research and development areas such as optoelectronic textile, bioimaging, chemical and biological sensing, high-resolution microscopy, and flexible panel displays, particularly as iTMCs with emission at different wavelengths are available.

Ionic Liquids as Solvents for Ionic Transition-Metal Catalysts

This review deals with the catalytic application of ionic transition-metal complexes using different ionic liquids as solvents. Additionally, so-called organometallic ionic liquids have been described with regard to their activity in several types of reaction. In most cases the catalysis was additionally performed under homogeneous conditions allowing a comparison between the use of ILs and conventional organic solvents. In all described cases the biphasic performance led to a higher recyclability of the catalytic system.

Recent advances in light-emitting electrochemical cells

Light-emitting electrochemical cells (LECs) are solution-processable thin-film electroluminescent devices consisting of a luminescent material in an ionic environment. The simplest type of LEC is based on only one material, ionic transition-metal complexes (iTMCs). These materials are of interest for different scientific fields such as chemistry, physics, and technology as selected chemical modifications of iTMCs resulted in crucial breakthroughs for the performance of LECs. This short review highlights the different strategies used to design these compounds with the aim to enhance the performances of LECs.

Novel emissive podands based on 8-OH-quinoline: Synthesis, fluorescence materials, DFT and complexation studies

Two novel chemosensors with podand structures (L1 and L2) derived from 1,5-bis(2-aminophenoxy)-3-oxopenthane bearing two flexible 8-hydroxyquinoline units have been synthesized and characterized.Several nitrate complexes of transition (Cu2+), post-transition (Zn2+) and lanthanide (Eu3+ and Sm3+) metal ions have been synthesized with tetrafluoroborate salts and characterized. In order to study their potential utility as fluorescent probes, the coordination ability of chemosensors (L1 and L2) towards those metal ions has been explored in solution (by UV–Vis and emission spectroscopy) and in gas phase (by MALDI mass spectrometry).Density functional theory has been employed to explore the emission properties of the three-protonation states of the chemosensor. From this study, the anomalous red shift observed in the fluorescence spectra of the dianionic sensors can be attributed to subtle structural differences between their anionic and dianionic forms. Furthermore, a plausible explanation for the low fluorescence of the neutral form is provided in the form of a non-radiative relaxation involving the imine double-bond isomerization.All new compounds have been characterized by microanalysis, melting points, IR, UV–Vis and fluorescence emission spectroscopy and MALDI-TOF-mass spectrometry.

Some transition metal ions complexes of tricine (Tn) and amino acids: pH-titration, synthesis and antimicrobial activity

Equilibrium studies have been carried out on complex formation of M(II) (M=Co(II), Cu(II) and Zn(II)) with tricine (Tn) and L=amino acids in aqueous solution, at 25°C and ionic strength of I=0.1M (NaNO3). The ternary complexes of amino acids are formed by simultaneous reactions. The concentration distribution of the complexes is evaluated. The solid complexes of [M(II)–Tn–Histidine (Hist)] have been synthesized and characterized by elemental analysis, infrared, magnetic and conductance measurements. The synthesized complexes have been screened for their antibacterial activities and the complexes show a significant antibacterial activity against four bacterial species: Staphylococcus aureus (Gram +ve), Streptococcus pyogenesr (Gram +ve), Serratia marcescens (Gram −ve) and Escherichia coli (Gram −ve). The activity increases by increasing the concentration of the complexes.

Redox Noninnocence of Nitrosoarene Ligands in Transition Metal Complexes

Studies on the coordination of nitrosoarene (ArNO) ligands to late-transition metals are used to provide the first definition of the geometric, spectroscopic, and computational parameters associated with a PhNO electron-transfer series. Experimentally, the Pd complexes PdCl(2)(PhNO)(2), PdL(2)(PhNO)(2), and PdL(2)(TolNO) (L = CNAr(Dipp2); Ar(Dipp2) = 2,6-(2,6-(i)Pr(2)C(6)H(3))(2)-C(6)H(3)) are characterized as containing (PhNO)(0), (PhNO)(•1-), and (TolNO)(2-) ligands, respectively, and the structural and spectroscopic changes associated with this electron transfer series provide the basis for an extensive computational study of these and related ArNO-containing late-transition metal complexes. Most notable from the results is the unambiguous characterization of the ground state electronic structure of PdL(2)(PhNO)(2), found to be the first isolable, transition metal ion complex containing an η(1)-N-bound π-nitrosoarene radical anion. In addition to the electron transfer series, the synthesis and characterization of the Fe complex [Fe(TIM)(NCCH(3))(PhNO)][(PF(6))(2)] (TIM = 2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene) allows for comparison of the geometric and spectroscopic features associated with metal-to-ligand π-backbonding as opposed to (PhNO)(•1-) formation. Throughout these series of complexes, the N-O, M-N, and C-N bond distances as well as the N-O stretching frequencies and the planarity of the ArNO ligands provided distinct parameters for each ligand oxidation state. Together, these data provide a delineation of the factors needed for evaluating the oxidation state of nitrosoarene ligands bound to transition metals in varying coordination modes.

Synthesis and Characterization of some New Four Coordinated IIB Transition Metal Ion Complexes

Complexes of Zn(II) and Hg(II) with new Schiff bases ligands of (N,N-bis(4-chlorobenzylidene)propane-1,2-diamine(L 1 ), N,N-bis(3-nitrobenzylidene)propane-1,2-diamine(L 2 ) and N,N-bis(4-nitrobenzylidene)propane-1,2-diamine(L 3 )) with general formula MLX 2 in which X= Cl - , Br - and I - have been prepared using 1:1 metal-to-ligand ratios and characterized by elemental analysis, FT-Infrared and Ultraviolet-Visible spectra, 1 H NMR (Nuclear Magnetic Resonance), 13 C NMR and molar conductance. All compounds are non-electrolytes in DMF. The complexes exhibit a pseudo tetrahedral geometry around the metal center.

Synthesis and characterization of some new four coordinated IIB transition metal ion complexes

Complexes of Zn(II) and Hg(II) with new Schiff bases ligands of (N,N-bis(4-chlorobenzylidene)propane-1,2-diamine(L1 ), N,N-bis(3-nitrobenzylidene)propane-1,2-diamine(L2 ) and N,N-bis(4-nitrobenzylidene)propane-1,2-diamine(L3 )) with general formula MLX2 in which X= Cl- , Br- and I- have been prepared using 1:1 metal-to-ligand ratios and characterized by elemental analysis, FT-Infrared and Ultraviolet–Visible spectra, 1 H NMR (Nuclear Magnetic Resonance), 13C NMR and molar conductance. All compounds are non-electrolytes in DMF. The complexes exhibit a pseudo tetrahedral geometry around the metal center. Keywords: Schiff base, Zinc complex, Mercury complex, Bidentate, asymmetrical.

Joint analysis of ESR lineshapes and 1H NMRD profiles of DOTA-Gd derivatives by means of the slow motion theory.

The "Swedish slow motion theory" [Nilsson and Kowalewski, J. Magn. Reson. 146, 345 (2000)] applied so far to Nuclear Magnetic Relaxation Dispersion (NMRD) profiles for solutions of transition metal ion complexes has been extended to ESR spectral analysis, including in addition g-tensor anisotropy effects. The extended theory has been applied to interpret in a consistent way (within one set of parameters) NMRD profiles and ESR spectra at 95 and 237 GHz for two Gd(III) complexes denoted as P760 and P792 (hydrophilic derivatives of DOTA-Gd, with molecular masses of 5.6 and 6.5 kDa, respectively). The goal is to verify the applicability of the commonly used pseudorotational model of the transient zero field splitting (ZFS). According to this model the transient ZFS is described by a tensor of a constant amplitude, defined in its own principal axes system, which changes its orientation with respect to the laboratory frame according to the isotropic diffusion equation with a characteristic time constant (correlation time) reflecting the time scale of the distortional motion. This unified interpretation of the ESR and NMRD leads to reasonable agreement with the experimental data, indicating that the pseudorotational model indeed captures the essential features of the electron spin dynamics.

Stability Constants of Mixed Ligand Complexes of Transition Metal(II) Ions with Salicylidene‐4‐methoxyaniline as Primary Ligand and 5‐Bromosalicylidene‐4‐nitroaniline as Secondary Ligand

Binary and ternary complexes of the type M‐Y and M‐X‐Y [M = Mn(II), Ni(II), Cu(II) and Zn(II); X = salicylidene‐4‐methoxyaniline and Y=5‐bromosalicylidene‐4‐nitroaniline] have been examined pH‐metrically at 27±0.5 °C and at constant ionic strength, μ= 0.1 M (KCl) in 75 : 25(v/v) 1,4‐dioxne‐water medium. The stability constants for binary (M‐Y) and ternary (M‐X‐Y) systems were calculated. The relative stability (Δ log KT) values of the ternary complexes with corresponding binary complexes for all the metal(II) ions in the present study found to be negative indicating that ternary 1:1:1 (M‐X‐Y) complexes are less stable than binary 1:1 (M‐Y) complexes. In the ternary system studied, the order of stability constants of mixed ligand complexes with respect to the metal ions was found to be Cu(II) > NI(II) > Mn(II) > Zn(II); which is same as in the corresponding binary (M‐Y) systems.

Evaluation of Stability of Complexes of Inner Transition Metal Ions with 2‐Oxo‐1‐pyrrolidine Acetamide and Role of Systematic Errors

BEST FIT models were used to study the complexation of inner transition metal ions like Y(III), La(III), Ce(III), Pr(III), Nd(III), Sm(III), Gd(III), Dy(III) and Th(IV) with 2‐oxo‐1‐pyrrolidine acetamide at 30 °C in 10%, 20, 30, 40, 50% and 60% v/v dioxane‐water mixture at 0.2 M ionic strength. Irving Rossotti titration method was used to get titration data. Calculations were carried out with PKAS and BEST Fortran IV computer programs. The expected species like L, LH+, ML, ML2 and ML(OH)3, were obtained with SPEPLOT. Stability of complexes has increased with increasing the dioxane content. The observed change in stability can be explained on the basis of electrostatic effects, non electrostatic effects, solvating power of solvent mixture, interaction between ions and interaction of ions with solvents. Effect of systematic errors like effect of dissolved carbon dioxide, concentration of alkali, concentration of acid, concentration of ligand and concentration of metal have also been explained here.

High stability light-emitting electrochemical cells from cationic iridium complexes with bulky 5,5′ substituents

We explore the photophysical, electrochemical, and electroluminescent properties of the ionic transition metal complex [(ppy)2Ir(bpy*)](PF6) where ppyH is 2-phenylpyridine and bpy* is 5,5′-diaryl-2,2′-bipyridine. Single layer devices of the structure ITO/[(ppy)2Ir(bpy*)](PF6)/Au exhibited high stability, with half-lives on the order of 100 h at a bias of −4 V. Long lifetimes are achieved through the bulky nature of the aryl substituents, which serves to limit chromophore–chromophore self-quenching, and 5,5′ positioning of these bulky groups is clearly advantageous for device performance.

P–n Metallophosphor based on cationic iridium(iii) complex for solid-state light-emitting electrochemical cells

An ionic transition-metal complex for improved charge transporting properties was designed, containing both n-type dimesitylboryl (BMes2) and p-type carbazole groups. The complex, [Ir(Bpq)2(CzbpyCz)]PF6 (1) (Bpq = 2-[4-(dimesitylboryl)phenyl] quinoline, CzbpyCz = 5,5′-bis(9-hexyl-9H-carbazol-3-yl)-2,2′-bipyridine) and its equivalent in which the BMes2 groups were substituted with carbazole moieties were evaluated on the photoluminescence and excited state properties in detail. According to the photophysical and electrochemical properties, we concluded that the BMes2 groups can increase the conjugation length of the cyclometalated C^N ligands and greatly enhance the phosphorescence efficiency over the carbazole groups. In addition, the bulky BMes2 groups are effective in preventing the molecular aggregation in film. Both complexes were used to prepare single component light-emitting electrochemical cells (LECs). The electroluminescent devices show the typical behavior of LECs. The LEC based on the complex containing both electron- and hole-transporting groups shows the best performance. This work demonstrated that the design and synthesis of p–n metallophosphors will be beneficial for the improvement of device performances.

Stability Constants of Mixed Ligand Complexes of Transition Metal(II) ions with N‐(2‐hydroxybenzylidene)‐2,3‐dimethylaniline as Primary Ligand and N‐(2‐hydroxy‐1‐naphthylidene)‐4‐nitroaniline as Secondary Ligand

Binary and ternary complexes of the type M‐Y and M‐X‐Y [M=Co(II), Ni(II), Cu(II) and Zn(II); X=N‐(2‐hydroxybenzylidene)‐2,3‐dimethylaniline and Y = N‐(2‐hydroxy‐1‐naphthylidene)‐4‐nitroaniline] have been examined pH‐metrically at 27±0.5 °C and at constant ionic strength, μ=0.1 M (KCl) in 75:25(v/v) 1,4‐dioxne‐water medium. The stability constants for binary (M‐Y) and ternary (M‐X‐Y) systems were calculated.