Transition Metal Ion Complexes Research Articles

Degradation of Ir(ppy)2(dtb-bpy)PF6 iTMC OLEDs

AbstractSimplicity of construction and operation are advantages of iTMC (ionic transition metal complex) OLEDs compared with multi-layer OLED devices. Unfortunately, lifetimes do not compare favorably with the best multi-layer devices. We have previously shown for Ru(bpy)3(PF6)2 based iTMC OLEDs that electrical drive produces emission-quenching dimers of the active species. We report evidence here that a chemical process may also be implicated in degradation of devices based on Ir(ppy)2(dtb-bpy)PF6 albeit by a very different mechanism. It appears that degradation of operating devices made with this Ir-based complex is related to current-induced heating of the organic layer, resulting in loss of the dtb-bpy ligand. (The dtb-bpy ligand is labile compared with the cyclometallated ppy ligands.) Morphological changes observed in electrically driven Ir(ppy)2(dtb-bpy)PF6 OLEDs provide evidence of substantial heating during device operation. Evidence from UV-vis spectra in the presence of an electric field as well as MALDI-TOF mass spectra of the OLED materials before and after electrical drive add support for this model of the degradation process.

Frequency domain Fourier transform THz-EPR on single molecule magnets using coherent synchrotron radiation

Frequency domain Fourier transform THz electron paramagnetic resonance (FD-FT THz-EPR) based on coherent synchrotron radiation (CSR) is presented as a novel tool to ascertain very large zero field splittings in transition metal ion complexes. A description of the FD-FT THz-EPR at the BESSY II storage ring providing CSR in a frequency range from 5 cm(-1) up to 40 cm(-1) at external magnetic fields from -10 T to +10 T is given together with first measurements on the single molecule magnet Mn(12)Ac where we studied DeltaM(S) = +/-1 spin transition energies as a function of the external magnetic field and temperature.

Annealing assisted mechanochemical syntheses of transition-metal coordination compounds and co-crystal formation

This article focuses on heating or annealing process in the mechanochemical preparation of coordination compounds in the solid state. Heating of metal complexes often promotes the liberation of weakly coordinated ligands and results in the complex with its coordination geometry unsaturated. Such “activated” complexes can be used as the building blocks of coordination polymers in the solid state. As one example, our recent work on [M(CNacac)2]∞ (CNacac = 3-cyano-pentane-2,4-dionato, M = MnII, FeII, CoII, NiII, CuII and ZnII) is presented. Further, co-grinding and annealing treatments of an enantiomeric pair of chiral crystals of [M(phen)3](PF6)2 (M = RuII and OsII, phen = 1,10-phenanthoroline) afford diffusion and rearrangement of transition metal complex ions to form co-crystal phases of racemic or quasi-racemic compounds by way of recognizing chirality. Our latest result of co-crystal formation via chirality transfer between optically stable and labile metal complexes is also briefly introduced.

Decreased Turn‐On Times of Single‐Component Light‐Emitting Electrochemical Cells by Tethering an Ionic Iridium Complex with Imidazolium Moieties

We report a significant decrease in turn-on times of light-emitting electrochemical cells (LECs) by tethering imidazolium moieties onto a cationic Ir complex. The introduction of two imidazolium groups at the ends of the two alkyl side chains of [Ir(ppy)(2)(dC6-daf)](+)(PF(6))(-) (ppy = 2-phenylpyridine, dC6-daf = 9,9'-dihexyl-4,5-diazafluorene) gave the complex [Ir(ppy)(2)(dC6MIM-daf)](3+)[(PF(6))(-)](3) (dC6MIM-daf = 9,9-bis[6-(3-methylimidazolium)hexyl]-1-yl-4,5-diazafluorene). Both complexes exhibited similar photoluminescent/electrochemical properties and comparable electroluminescent efficiencies. The turn-on times of the LECs based on the latter complex, however, were much lower than those of devices based on the former. The improvement is ascribed to increased concentrations of mobile counterions ((PF(6))(-)) in the neat films and a consequent increase in neat-film ionic conductivity. These results demonstrate that the technique is useful for molecular modifications of ionic transition-metal complexes (ITMCs) to improve the turn-on times of LECs and to realize single-component ITMC LECs compatible with simple driving schemes.

Endohedral and Exohedral Complexes of T8-Polyhedral Oligomeric Silsesquioxane (POSS) with Transition Metal Atoms and Ions

The equilibrium geometries of the exohedral and endohedral complexes of the polyhedral oligomeric silsesquioxane (POSS) cage (HSiO3/2)8 containing the transition metal atoms or ions Sc0,+, Cr0,+, Fe0,+, Co0,+, Ni0,+, Cu0,+, Zn0,+, Mo0,+, W0,+, Ru0,+, Os0,+ have been investigated at the B3LYP/LanL2DZ levels. All these species form endohedral complexes with the T8-POSS cage except Sc0,+, Mo0, and W0,+. The Mo0 and W0,+ species as well as Cr0,+, Fe0,+, Co0,+, Ni0,+, Cu+, Zn+, Ru0,+, Os0 form stable exohedral complexes. Geometries, electronic properties and ionization potentials were computed. The Si−O and Si−H bond lengths in the cationic endohedral complexes are shorter than in the corresponding complexes of neutral transition metal atoms. The zero-point corrected inclusion energies of the endohedral species X@(SiHO3/2)8 (X = Fe+, Co+, Ni+, Cu+, Os+) are all negative, suggesting that these complexes are more stable than their isolated components. All exohedral complexes have energies that are lower than their corresponding endohedral analogs. Transition metal atom encapsulation raised the HOMO and lowered the LUMO energies, reducing the HOMO−LUMO gaps of every complex compared to that of the pure cage. The HOMO−LUMO gap of the empty cage is 8.1 eV while the endohedral complexes exhibit gaps between 1.2 and 4.96 eV. Insertion of Cr, Fe, Co, Ni, Cu, or Zn into the POSS cage is more favorable in water than in the gas phase. However, insertion of Co+, Ni+, Cu+, or Zn+ into the POSS cage is less favorable in water than in the gas phase. Overall, both the neutral and ionic endohedral transition metal complexes, X@(SiHO3/2)10, (X = Cr0,+, Fe0,+, Co0,+, Ni0,+, Cu0,+, Zn0,+, Ru0,+, Os0,+) appear to be viable synthetic targets.

New transition metal ion complexes with benzimidazole-5-carboxylic acid hydrazides with antitumor activity

Metal complexes of 2-methyl-1 H-benzimidazole-5-carboxylic acid hydrazide ( 4a; L 1) and its Schiff base 2-methyl- N-(propan-2-ylidene)-1 H-benzimidazole-5-carbohydrazide ( 5a; L 2) with transition metal ions e.g., copper, silver, nickel, iron and manganese were prepared. The complexes formed were 1:1 or 1:2 M:L complexes and have the structural formulae [Cu(L 1)Cl(H 2O)]Cl·3H 2O ( 6), [Ag(L 1)NO 3(H 2O)] ( 7), [Ni(L 1)Cl 2(H 2O) 2]·H 2O ( 8), [Fe(L 1)Cl 3(H 2O)]·3H 2O ( 9) and [Mn(L 1) 2Cl(H 2O)]Cl·3H 2O ( 10) for ligand L 1, and [Cu(L 2)Cl 2(H 2O) 2]·H 2O ( 11), [Ag(L 2) 2]NO 3·H 2O ( 12), [Ni(L 2) 2Cl 2]·5H 2O ( 13), [Fe(L 2) 2Cl 2]Cl·2H 2O ( 14) and [Mn(L 2)Cl 2(H 2O) 2]·H 2O ( 15) for ligand L 2. The antitumor activity of the synthesized compounds has been studied. The silver complex 7 was found to display cytotoxicity (IC 50 = 2 μM) against both human lung cancer cell line A549 and human breast cancer cell line MCF-7.

Synthesis, spectroscopic characterization and magnetic properties of homo- and heterodinuclear complexes of transition and non-transition metal ions with a new Schiff base ligand

Four homodinuclear complexes of Ni(II)–Ni(II), Cu(II)–Cu(II), Co(II)–Co(II) and Co(III)–Co(II) and five heterodinuclear complexes of Co(III)–Zn(II), Co(III)–Cu(II), Co(III)–Ni(II), Cu(II)–Zn(II) and Zn(II)–Cu(II) with the octadentate Schiff base compartmental ligand 1,8- N-bis(3-carboxy)disalicylidene-3,6-diazaoctane-1,8-diamine (H 4fsatrien) have been synthesized. The complexes have been characterized with the help of elemental analyses, molecular weights, molar conductances, magnetic susceptibilities and spectroscopic (UV–vis, IR, ESR) data. Cryomagnetic data also helped to elucidate the structural features of the Cu(II) complexes.

Effect of Coordination Modes of HL Ligand on the Molecular Architecture of Its Transition Metal Complexes (HL = 5-Methyl-2-Phenyl-4-[(2-o-Tolylamino)-Phenylmethylene]pyrazol-3(2H)-one)

Two Ag+ complexes [Ag(HL)2(PF6)] (1) and [(AgL) n · n(CH2Cl2) · n(0.5H2O)] (2) (HL = 5-methyl-2-phenyl-4-[(2-o-tolylamino)-phenylmethylene]pyrazol-3(2H)-one) were synthesized and structurally characterized by EA analysis, IR spectra and X-ray crystallography. The result shows that two expected coordination modes (Modes I and III in Scheme 1) of the HL ligand, can be observed in its Ag+ complexes, while not in other transition metal ions (Ni2+, Co2+ or Cu2+) complexes whether deprotonation or not for the HL ligand. Three possible coordination modes (Modes I, II or III in Scheme 1) of the selected HL (HL = 5-methyl-2-phenyl-4-[(2-o-tolylamino)-phenylmethylene]pyrazol-3(2H)-one) ligand, can be adopted, in which Modes I and III can be observed in its two Ag+ complexes [Ag(HL)2(PF6)](1) and [(AgL) n · n(CH2Cl2) · n(0.5H2O)] (2), while Mode II just observed in its transition metal ions (Cu2+, Ni2+, or Co2+) complexes, resulting from the deprotonatd form of the HL ligand and the coordination characters of transition metal ions.

Molecular Self‐Assembly, Chemical Lithography, and Biochemical Tweezers: A Path for the Fabrication of Functional Nanometer‐Scale Protein Arrays

Exploration of the immensurable gene products of the ∼25000 human genes and mapping of dynamic protein interaction networks are key challenges in current biological research. [1] Highly parallel protein chip technologies deliver promising tools for these challenges even down to the singlemolecule level. [2] Whereas DNA molecules are robust and easy to immobilize in a functional manner—as seen in the triumph of DNA chip technology [3] —proteins are highly sensitive and chemically heterogeneous entities denaturing rapidly in vitro. Using multivalency as a design principle, a chemical recognition unit with exceptionally high affinity for proteins was designed, while maintaining their functionality. [4] These multivalent chelator heads consist of cumulated N-nitrilotriacetic acid (NTA) moieties, which provide chemical recognition for histidine-tagged proteins by complexation of transition metal ions, for example, Ni(II). These strong as well as specific binding capabilities can easily be switched on and off by addition or removal of Ni(II) ions. Such properties make tris-NTA chelators ideal “biochemical tweezers” for attaching proteins to surfaces and releasing them again. A tris-NTAunit coordinates six imidazole moieties and, thus, perfectly matches the coordination demands of a hexahistidine tag with binding affinities in the nanomolar range. [5] For the generation of structured protein arrays, a lithography step is necessary. Both electron-beam lithography (EBL) or extreme UV interference lithography (EUV-IL) are promising for this task. EBL gives the largest variation of pattern shapes and lateral dimensions in a very controlled manner. [6] The application of focused e-beams provides a chance to even generate structures capable of immobilizing single biological molecules. EUV-IL can create highly parallel patterns over large areas in a single processing step with the resolution approaching the EBL limit, [7] which is of great potential for applications in nanotechnology. In this Communication we present a new path for the fabrication of solid templates for the laterally defined and functional immobilization of proteins. The technology is based on the combination of electron-induced chem

Phytate treatment of metallo-gallate inks: Investigation of its effectiveness on model and historic paper samples

The aim of this study was to confirm the stabilizing effect of phytate treatment on iron gall ink degraded cellulose and papers on a molecular level. The impact of iron gall ink degradation on the cellulose molecule and its stabilization can be studied with very low sample amounts by fluorescence labelling of carbonyl groups in combination with GPC-MALLS to determine the weight averaged molecular weight. The aqueous phytate treatment, a complexation of transition metal ions using calcium phytate, and a deacidification treatment using calcium hydrogen carbonate, was applied on Whatman filter paper, and on modern and historic rag paper. Model iron gall inks were plotted on the test papers, while all historic rag papers contained iron gall ink. To gain insight into the long term stability, an ageing step was performed after the phytate treatment, and treated samples were compared to untreated ones. The positive impact of this treatment was verified for the first time on a molecular level, showing that molecular weight and carbonyl group content were significantly stabilized. The stabilization was proven on the inked areas and on pure cellulose. It was also confirmed the even copper containing inks will benefit from the treatment.

Improved Turn-On Times of Light-Emitting Electrochemical Cells

Electroluminescent devices from ionic transition metal complexes (iTMCs) are attractive candidates for display and lighting applications. A major limitation of application of iTMC devices is their turn-on times, which range from minutes to hours at 3 V. We report novel ruthenium and iridium complexes with pendant triethylammonium groups bonded to the ligands with methylene units of various lengths. These materials lead to devices with turn-on times at 3 V as short as 2.5 min for the iridium complexes and as low as 5 s for the ruthenium complexes.

Double layer effects in the electroreduction of transition metal ions

Experimental data for the reduction of transition metal complex ions obtained recently at mercury and single-crystal gold electrodes are reviewed. It is shown that the effective charge on the reactant is generally not the same as the nominal charge, but that it may be found on a basis of an analysis of the kinetic data together with the appropriate double layer data. In addition, the effective charge on the product is usually smaller than the nominal value. As a result, the analysis of the double layer effect involves the construction of corrected Tafel plots, which differ significantly from those described in the early work of Frumkin.

Polymer anchored Schiff base complexes of transition metal ions and their catalytic activities in oxidation of phenol

The polymer anchored transition metal complexes of N, N′-bis( o-hydroxy acetophenone)ethylene diamine (HPED) Schiff base were prepared by reacting N, N′-bis(4-amino- o-hydroxy acetophenone)ethylene diamine (AHPED) Schiff base with cross-linked chloromethylated polystyrene beads and then loading of iron(III), cobalt(II) and nickel(II) ions in methanol. The N, N′-bis (4-amino- o-hydroxy acetophenone)ethylene diamine (AHPED) Schiff base was prepared by nitrosation and reduction of nitrosated HPED Schiff base in presence of Fe/HCl catalyst. The loading of AHPED Schiff base on chloromethylated polystyrene beads was 86% (2.58 mmol g −1 of beads). The AHPED Schiff base anchored polymer beads have shown 85%, 86% and 89% comlexation for iron(III), cobalt(II) and nickel(II) ions from solution of metal salts (2.6 mmol), whereas unsupported HPED Schiff base shown 80%, 88% and 77% comlexation for iron(III), cobalt(II) and nickel(II) ions. The free and polymer supported metal complexes were analyzed for molecular weight (Mw) and composition by elemental analysis. The UV, IR and magnetic measurements of free and polymer supported metal complexes have confirmed the octahedral geometry for iron(III) and square planar geometry for cobalt(II) and nickel(II) ions complexes. The thermogravimetric analysis (TGA) of Schiff base has shown 55% weight loss at 500 °C but iron(III), cobalt(II) and nickel(II) ions complexes have shown 30%, 40% and 48% weight loss at same temperature. The iron(III), cobalt(II) and nickel(II) ions complexes have shown temperature of maximum decomposition rate ( T max) as 325, 319 and 281 °C, respectively. The unsupported HPED Schiff base complexes of metal ions were found to be less stable although the trend in their thermal stability was almost same. The catalytic activity of free and polymer anchored HPED Schiff base complexes was evaluated by studying the oxidation of phenol at 70 °C. The percent conversion of phenol and turn over number (TON) was found to be optimum at 1:1:1 molar ratio of phenol, H 2O 2 and metal ions in both free and polymer supported metal complexes. The activation energy for oxidation of phenol by polymer supported HPED Schiff base complex of iron(III) was found to be low (25 kJ mol −1) in comparison to HPED Schiff base complexes of cobalt(II) (57 kJ mol −1) and nickel(II) ions (31 kJ mol −1). On the basis of literature report, a mechanism for oxidation of phenol has been proposed.

Electroluminescent devices from ionic transition metal complexes

Ionic transition metal complexes (iTMCs) are receiving increased attention as materials capable of yielding efficient electroluminescent devices with air-stable electrodes. The operational characteristics of these devices are dominated by the presence of mobile ions that redistribute under an applied bias and assist in electronic charge injection. This article reviews recent efforts in the field of iTMC devices: i) to understand their physics, ii) to improve their efficiency, colour, turn-on time and lifetime, and iii) to expose their potential applications.

Origin of the large spectral shift in electroluminescence in a blue light emitting cationic iridium(iii) complex

A new, but archetypal compound [Ir(ppy-F2)2Me4phen]PF6, where ppy-F2 is 2-(2′,4′-fluorophenyl)pyridine and Me4phen is 3,4,7,8-tetramethyl-1,10-phenanthroline, was synthesized and used to prepare a solid-state light-emitting electrochemical cell (LEEC). This complex emits blue light with a maximum at 476 nm when photoexcited in a thin film, with a photoluminescence quantum yield of 52%. It yields an efficient single-component solid-state electroluminescence device with a current efficiency reaching 5.5 cd A−1 and a maximum power efficiency of 5.8 Lm Watt−1. However, the electroluminescence spectrum is shifted with respect to the photoluminescence spectrum by 80 nm resulting in the emission of green light. We demonstrate that this unexpected shift in emission spectrum does not originate from the mode of excitation, nor from the presence of large concentrations of ions, but is related to the concentration of the ionic transition metal complex in the thin film. The origin of the concentration-dependent emission is extensively commented on and argued to be related to the population of either 3LC π–π* or 3MLCT triplet states, in diluted and concentrated films, respectively. Using quantum chemical calculations we demonstrate that three low-energy triplet states are present with only 0.1 eV difference in energy and that their associated emission wavelengths differ by as much as 60 nm from each other.

Degradation in iTMC OLEDs

AbstractThe processes underlying degradation of organic light emitting diodes (OLEDs) are gradually becoming understood. In ruthenium-based ionic transition metal complex (iTMC) OLEDs, a dimeric species forms during device operation that quenches light emission [1]. Water has been implicated in this degradation process [2]. We report recent studies on degradation of OLEDs fabricated with Ir(ppy)2(dtb-bpy)PF6 [ppy = 2-phenylpyridine, dtb-bpy = 4,4'-di-tert-butyl 2,2'-bipyridine [3]. We have found that applying a thicker-than-usual metal electrode results in shorter turn-on times and higher light emission, though little improvement in lifetime. It appears that the degradation of these devices occurs by a different mechanism from that of the ruthenium-based devices and may involve local heating leading to chemical decomposition of the organic material.Observation of recurring but often transient dark-colored substances in both the Ru(bpy)3(PF6)2 and Ir(ppy)2(dtb-bpy)PF6 systems, seen both in the solid state and in solution samples, may also be indicative of decomposition.

Octahedral and trigonal prismatic structure preferences in a bicyclic hexaamine cage for zinc(ii), cadmium(ii) and mercury(ii) ions

The synthesis and characterisation of complexes of the hexaamine cage ligand facial-1,5,9,13,20-pentamethyl-3,7,11,15,18,22-hexaazabicyclo[7.7.7]tricosane (fac-(Me)(5)-D(3 h)tricosaneN(6)) with Zn(II), Cd(II) and Hg(II) is reported. Single crystal X-ray structural analyses of the Cd(II) and Hg(II) complexes reveal that the coordination spheres of both cations have an unusual trigonal prismatic stereochemistry organised by the ligand substituents and cavity size. This is unprecedented for hexaamine complexes of these metal ions, and in stark contrast to the distorted octahedral stereochemistry found previously for the analogous Zn(II) complex. An X-ray structural analysis of single crystals of the diprotonated ligand [fac-(Me)(5)-D(3h)tricosaneN(6) - 2H](CF(3)SO(3))(2) shows that it also prefers to adopt a trigonal prismatic structure. The (13)C NMR spectra of the metal complexes indicate that their structures are preserved at 20 degrees C in solution. However, heating the Zn(II) complex to approximately 130 degrees C appears to convert it to the trigonal prismatic form. In contrast cooling the trigonal prismatic Hg(II) complex to -80 degrees C does not convert it to the octahedral structure. The results are also compared to the structures of various other transition metal ion complexes of the same or similar ligands. This comparison yields overall an appreciation of the factors that determine the final structures of complexes formed with such tricosaneN(6) ligands.

A perspective on applications of ligand-field analysis: inspiration from electron paramagnetic resonance spectroscopy of coordination complexes of transition metal ions

This paper describes in a somewhat personal way an overview of the use of electron paramagnetic resonance (EPR) spectroscopy, including high-frequency and -field EPR (HFEPR) to unravel the electronic structure of transition metal ion complexes. The spin Hamiltonian parameters obtained from EPR experiments, namely the g matrix for systems with S =1/2 and the g and D (zero-field splitting) matrices for systems with S > 1/2 provide information on d orbital energy levels. This information can be combined with ligand-field theory (LFT) to provide information on the overall electronic structure of the paramagnetic transition metal complex. As has been discussed by others, LFT is still useful in providing such a quantitative understanding of these complexes, even in the day of advanced computational methods, such as density functional theory (DFT). The discussion is illustrated by examples across the d n configuration.

An NMR Study of Solvent Interactions in a Paramagnetic System

This study explores and interprets in a new way the complex solvent and the temperature dependence of the NMR shifts for the N-<TEX>$CH_2$</TEX> protons in tris(N,N-diethyldithiocarbamato) iron(III) in acetone, benzene, carbon disulfide, chloroform, dimethylformamide and pyridine. The NMR shifts are interpreted in terms of the Fermi contact interaction and the dipolar term from the multipole expansion of the interaction of the electron orbital angular momentum and the electron spin dipolar-nuclear spin angular momentum. This analysis yields a direct measure of the effect of the solvent system on the environment of the transition metal ion. The results are analysed in terms of the crystal field environment of the transition metal ion with contributions from (a) the dithiocarbamate ligand (b) the solvent molecules and (c) the interaction of the effective dipole moment of the polar solvent molecule with the transition metal ion complex.

Metal ion retention from aqueous solution using the ultrafiltration technique: preparation, retention capacity of copolymers of N‐maleimide derivatives with β‐methylhydrogen itaconate and metal complexes

AbstractChlorophenylmaleimide (Cl‐PhMI) and N‐maleoylglycine (N‐MG) with β‐methylhydrogen itaconate (β‐MHI) were copolymerized by radical polymerization, and their metal ion retention capacity (MRC) and thermal behavior were studied. The copolymers were obtained by varying the mole fraction of Cl‐PhMI or N‐MG in the feed from 0.25 to 0.75. The monomer reactivity ratios, r1 and r2, were determined using the Kelen–Tüdös method. The molecular weight and polydispersity were also determined. The capacity to remove several metal ions, such as Cu(II), Cr(III), Co(II), Zn(II), Ni(II), Pb(II), and Fe(III), in aqueous phase was determined using the liquid‐phase polymer‐based retention technique. Inorganic ion interactions with the hydrophilic polymer were determined as a function of pH and the filtration factor. The MRC depends strongly on the pH. Metal ion retention increased with increases in pH and the content of β‐MHI units in the macromolecular backbone. The copolymers and polymer–metal complexes of transition metal ions were characterized using elemental analysis, Fourier transform infrared spectroscopy, 1H NMR, and electron paramagnetic resonance spectroscopy. The maximum MRC of Cu(II) ions of poly(Cl‐PhMI‐co‐β‐MHI) varied from 240 to 260 mg g−1, while the MRC of Cu(II) ions of poly(N‐MG‐co‐β‐MHI) varied from 270 to 318 mg g−1 at pH 5 and pH 7. The thermal behavior of the copolymers and polymer–metal complexes was studied using differential scanning calorimetry and thermogravimetry techniques under nitrogen atmosphere. The copolymers have a lower thermal decomposition temperature than the polymer‐metal complex for the same copolymer composition. The thermal behavior may be correlated with the copolymer composition. Copyright © 2006 Society of Chemical Industry