Gold(I) and gold(III) complexes with anionic oxygen donor ligands: hydroxo, oxo and alkoxo complexes

The chemistry of gold(I) and gold(III) hydroxo, oxo and alkoxo complexes containing organic co-ligands is reviewed. Due to the high reactivity of the gold-oxygen bond most of these species can be employed as useful intermediates in many important processes. Alkoxides are by far the most numerous class among these species, and both gold(I) and gold(III) complexes are known with a variety of alkoxides. The recent discovery of the catalytic activity of some gold(I) and gold(III) fluoroalkoxides has enlivened the interest towards this class of compounds leading to new applications for previously known complexes, as is the case for a gold(III) siloxo complex which has found use as a precursor for CVD, as well as for the synthesis of new alkoxo derivatives. Another well represented and well known class of compounds are the gold(I) oxo complexes [O(AuPR₃)₃]⁺ which are the most effective aurating reagents. Gold(III) oxo complexes have been synthesized only recently and much of their chemistry is still largely to be explored. Preliminary studies suggest their potential in the transfer of oxygen atoms. Finally, some cationic gold(III) hydroxo complexes are found to display significant,and in some cases relevant, cytotoxic effects on cancer cell lines.     

Theoretical study on the second-order nonlinear optical properties of gold (III) alkyl complexes

The equilibrium geometries of gold (III) alkyl complexes are optimized by DFT/B3LYP method. On the basis of the optimized structures, the electronic structures and second-order nonlinear optical properties are calculated by using time-dependent density-functional theory (TDDFT) combined with the sum-over-states (SOS) method. The results show that these complexes possess remarkably larger molecular second-order polarizabilities compared with the typical organometallic and organic complexes. The analysis suggests that charge transfer from the z-axis directions plays a key role in the second-order nonlinear optical response. Moreover, different ancillary ligands can substantially adjust the second-order nonlinear optical response. Thus, it can be concluded that these complexes will be hopeful candidates for the second-order nonlinear optical materials from the standpoint of high transparency, relatively large β values and small dispersion behaviors.     

Photoluminescence of some aluminum(III) complexes

The spectroscopic properties of seven aluminum(III) complexes (including AlQ₃) are examined. The ligands of the aluminum complexes are 2,2′-biphenol, 1,1′-bi-2-naphthol and 8-hydroxyquinoline. The effect of the aromatic ligands 2,2′-biphenol and 1,1′-bi-2-naphthol, on the photoluminescence of 8-hydroxyquinoline aluminum(III) complexes was studied. The λ_max (nm) of the emission spectra was measured in solution (with THF as the solvent) and in the solid state. The results show that some energy is transferred between the aromatic ligand and 8-hydroxyquinoline in aluminum(III) complexes, according to emission spectra of the complex obtained using a photoluminescence emission spectroscope. But the mechanisms of energy-transfer are not clear now.     

Excited state calculations of Europium(III) complexes

A new theoretical methodology developed to guide the design of light-conversion molecular devices is applied to the complex tris(3-aminopyrazine-2-carboxylate)(1,10-phenanthroline) of Eu(III), and the results are compared to the experimental data obtained in our laboratory. The calculations have shown that there are two triplet states at 363 and 377 nm localized on the 1,10-phenanthroline, which are quasi-resonant with the ⁵G₆ (374 nm) and ⁵L₆ (395 nm) energy levels of the Eu(III) ion, respectively. The 3-aminopyrazine-2-carboxylate anion ligands have a richer quasi-resonant energy level structure, namely, three singlet states (344, 323 and 377 nm) and their corresponding triplet states (498, 509 and 530 nm), which are near-resonant to the ⁵D₄ and ⁵D₀ Eu(III) energy levels, respectively. These ligand and metal ion energy levels were used in the dipole–dipole and dipole-2^ℓ-pole models for energy transfer rate calculations. Thus, the high quantum yield observed for this complex (28% in DMSO solution) seems to be due to the calculated high yield energy transfer from these several ligand states to the quasi-resonant Eu(III) energy levels.     

Spectroscopic studies of the Eu(III) and Gd(III) tris(3-aminopyridine-2-carboxylic acid) complexes

The synthesis and spectroscopic studies of the complexes of Eu(III) and Gd(III) with 3-aminopyridine-2-carboxylic acid (3-NH₂pic) are described. An experimental and theoretical analysis of the intensities of the ⁵D₀→⁷F_0,1,2,4 transitions of the Eu(III) ion is presented. An approximate structure for the Eu(III) complex is assumed and the theoretical calculations are based on a model, previously described, which takes into account the forced electric dipole and dynamic coupling mechanisms.     

Perfluorinated oxygen- and sulfur-containing compounds as extractants for gold(III)

A series of highly fluorinated compounds of the type {CF₃(CF₂)₅CH₂CH₂}₃P=O, [{CF₃(CF₂)₅CH₂CH₂}₂P(E)CH₂CH₂P(E){CH₂CH₂(CF₂)₅CF₃}] and {CF₃(CF₂)₅CH₂CH₂}₂C=E (E = O or S) have been examined for their ability to extract gold(III) from aqueous solutions. The phosphine oxides have been studied under liquid–liquid extraction conditions from water into perfluorohexane and found to give poor distribution ratios. The bidentate phosphine oxide, ketone and thioketone were studied under solid–liquid extraction conditions and were substantially better with extraction of up to 80% of Au(III). In addition, the crystal structure of {CF₃(CF₂)₅CH₂CH₂}₃P=O has been determined.     

Processing of residual gold (III) solutions via ion exchange

The processing of gold (III)-hydrochloric acid solutions by the anionic ion exchange Lewatit MP-64_resin has been investigated. The influence of several variables such as the temperature, the hydrochloric acid and metal concentrations in the aqueous solution and the variation of the amount of resin added has been studied. Moreover, a kinetic study performed in the uptake of gold (III) by Lewatit MP-64_shows that either the film-diffusion and the particle-diffusion models fit the adsorption process on the resin. Results obtained from batch experiments were applied to a continuous system using a vertical column. The loaded resin could be eluted by an acidic thiourea solution at 20°C. Various systems were investigated to precipitate gold from eluants, only the use of sodium borohydride allowed to accomplish the recovery of the metal from the pregnant solutions. Gold was recovered as fine particles, which were characterised by means of optical and scanning electron microscopy.     

Novel phosphinoxide-bearing ligands and their photoluminescent complexes: Spectroscopic studies

Several novel phosphinoxide ligands have been prepared, based on molecular frameworks: pyridine, 2,2′-bipyridine, cavitands, cyclotriphosphazene and 1,3,5-triazine. These compounds form highly luminescent complexes with Eu(III) and Tb(III). Excellent luminescent properties were observed in case of pyridine and 2,2′-bipyridine ligands with photoluminescence quantum yields approaching 25%. Cavitand-based phosphinoxides turned out to be rather poor sensitisers for the lanthanide ion emission. Particularly long emission lifetime was observed in case of pyridine P-oxide complexes of Eu(III) and Tb(III), exceeding 3 ms.     

Recovery of gold(III) ions by a chitosancoated magnetic nano-adsorbent

The monodisperse chitosan-coated Fe₃O₄ nanoparticles with a mean diameter of 13.5 nm and 4.92 wt% chitosan were used as an anionic magnetic nano-adsorbent for the recovery of Au(III) ions from aqueous solutions. It was found that Au(III) ions could be fast and efficiently adsorbed, and the adsorption capacity increased with the decrease in pH due to the protonation of the amino groups of chitosan. The adsorption data obeyed the Langmuir equation with a maximum adsorption capacity of 59.52 mg/g (1210 mg/g based on the weight of chitosan) and a Langmuir adsorption equilibrium constant of 0.066 l/mg. From the studies on the adsorption kinetics and thermodynamics of Au(III) ions, it was found that the adsorption process obeyed the pseudo-second-order kinetic model. Furthermore, the time required to reach the equilibrium was significantly shorter than those using the micro-sized adsorbents due to the large available surface area.     

Synthesis of 8-hydroxyquinoline functionalised DO3A ligand and Eu(III) and Er(III) complexes: Luminescence properties

The synthesis of a new DO3A-based macrocyclic ligand bearing a 8-hydroxyquinoline residue together with the preparation of its Eu³⁺ and Er³⁺ neutral complexes are described. In a previous report [F. Rizzo, A. Papagni, F. Meinardi, R. Tubino, M. Ottonelli, G.F. Musso, G. Dellepiane, Synth. Met. 147 (2004) 143], we have shown that lanthanide complexes display very high stability combined with a good luminescence in aqueous solution under UV radiation, which indicate an energy transfer process from the excited 8-hydroxyquinoline moiety to the metal. In this work, we correlate the ability to transfer the energy from the sensitizer to lanthanide ion with pH behaviour of the antenna. Furthermore, the variation of pH in Eu³⁺ complex supports the hypothesis of presence of charge-transfer transitions. The good solubility and sensitized emission in different solvents (organic and water) are very important aspects for their technologic applications as luminescent probes or NIR-emitting devices.     

Design of luminescent sulfur-containing polynuclear gold(I) complexes for advanced nanomaterials and chemosensors

A series of high-nuclearity gold(I) sulfido complexes with bridging diphosphine ligands have been synthesized and isolated, with the general formulae of [Au₁₀(μ-P^P)₄(μ₃-S)₄]X₂ and [Au₁₂(μ-P^P)₄(μ₃-S)₄]X₄ (P^P = diphosphine; X = PF₆ or ClO₄). Intense green and orange emissions were observed upon excitation at λ > 350 nm both in the solid state and in solutions. The green emission has been attributed to originate from excited states derived from the metal-perturbed intraligand (IL) transition while the orange emission arises from the ligand-to-metal-metal bond charge-transfer (LMMCT; S(Au...Au) states. The switching on and off of the LMMCT emission in a series of dinuclear gold(I) thiolate complexes with crown ether pendants induced by ion-binding has been demonstrated, and this provides a new strategy for the design of luminescence signalling and chemosensing devices in optoelectronics and sensor technology.     

Fluorescence enhancement and cofluorescence in complexes of terbium（Ⅲ） with trimellitic acid

The fluorescence of terbium (III) was enhanced by about three orders of magnitude in the presence of trimellitic acid (benzene-1, 2, 4-tricarboxylic acid (TLA)) in aqueous solution at pH 6. The fluorescence intensity could be greatly increased when the system of Tb³⁺-TLA was treated with La³⁺(or Gd³⁺) and TritonX-100. The addition of La³⁺(or Gd³⁺⁾ enhances the fluorescence of the system by about two orders of magnitude due to cofluorescence, and the TritonX-100 micellar medium plays an important role for stabilization of the system. Both the intermolecular energy transfer mode and intramolecular energy transfer mode are responsible for the mechanism of fluorescence enhancement. In the optimum conditions, the fluorescence intensity is a linear function of Tb³⁺ concentration in the range of 7.8 × 10⁻⁹-3.6 × 10⁻⁶ mol/L for the system Tb³⁺-La³⁺-TLA and 1.0 × 10⁻⁸-4.7 × 10⁻⁶ mol/L for the system Tb³⁺-Gd³⁺-TLA, and the limits of detection are 4.6 × 10⁻¹⁰ mol/L and 6.0 × 10⁻¹⁰ mol/L, respectively.     

Fluorescence enhancement and cofluorescence in complexes of terbium(III) with trimellitic acid

1. Introduction Rare earth elements have an important function inlife process. The fluorescence enhancement of lan-thanides in aqueous solutions has therefore becomean area of active study in trace-level estimation oflanthanides using spectrofluorimetry [1]. Its possiblemechanism and application as fluorescence probesin biological systems have also attracted attention inrecent years [2]. Generally, fluorescence enhance-ment can be achieved through ligand sensitization.Various ligands have bee…     

Circularly polarized luminescence and enantiomeric energy transfer discrimination of chiral Tb(III)–Nd(III) EDDS and related complexes

Total luminescence (TL), circularly polarized luminescence (CPL), luminescence dissymmetry factor g_lum and lifetimes of optical active Tb(III)– , -EDDS complexes are measured in solution in order to investigate enantiomeric discrimination of energy transfer processes in the presence of quenchers: Nd(III)– , -EDDS or (+),(−)-[Co(en)₃]I₃ complexes. The spectroscopic differences for the chiral complex pairs are discussed in terms of the Stern–Volmer luminescence quenching mechanism. The quenching rate constants give evidence of the fact that a homochiral-pair is lower in energy in the excited states than a heterochiral-pair. The TL and CPL spectral patterns and fine structures in high resolutions are discussed at 10 K of Tb(III)– , -EDDS and Tb(III)–(R),(S)-cyclene derivative complex nanocrystals in xerogel. The crystal field splitting and the structural anomaly are found in the axial CPL/TL spectra of trigonal dihedral Tb(ODA)₃ single crystals in the temperature range between 300 and 10 K.     

A series of water soluble RE(III) complexes: Synthesis,characterization, photophysical property and sensing activity towards Cr(III)

In this paper, four water soluble rare-earth(III) fluorescent chemosensors, Na₃RE(PDA)₃ (PDA = pyridine-2,6-dicarboxylic acid, and RE = Sm, Eu, Tb, Dy), are synthesized and characterized. Their excitation and emission spectra, fluorescence responses towards Cr(III), quenching mechanism, oxygen and thermal sensitivity of the complexes are systemically studied. The emission intensity and the excited state lifetimes of the four complexes decrease with increasing concentration of trivalent chromium (Cr(III)). Their sensing behavior towards Cr(III) is investigated by fluorescence spectroscopy. Results suggest that Na₃Dy(PDA)₃ exhibits highest sensitivity and linear spectral response towards Cr(III) (Stern–Volmer constant = 0.461 × 10⁷ L/mol, linearity = 0.996). It is note worthy that oxygen has little effect on the emission of Na₃RE(PDA)₃ complexes. These important advantages make themselves promising candidates to be utilized in actual applications.     

Conjugated complexes via oxidative complexation of polyaniline derivatives to vanadium(III)

The emeraldine base of poly(o-toluidine) and N,N′-bis(4′-dimethylaminophenyl)-1,4-quinonediimine were demonstrated to undergo oxidative complexation to VCl₃, affording the corresponding conjugated complexes. The complexation proceeds via reduction of the quinonediimine moiety with oxidation of V(III)–V(IV), in which the vanadium species is considered to play an important role in both the complexation and reduction.     

Syntheses and cofluorescence of complexes of Eu（Ⅲ）/Y（Ⅲ） with terephthalic acid, 2-thenoyltrifluoroacetone and trioctylphosphine oxide

A series of Eu（ Ⅲ）/Y（Ⅲ） complexes of terephthalic acid（TPA） with 2-thenoyltrifluoroacetone（HTTA） and trioctylphosphine oxide（TPPO） were synthesized. Compositions of these complexes are revealed to be Eu2（1-x）Y2x（TPA）（TTA）4- （TPPO）4 or EU1-xYx（TPA）（TTA）（TPPO）2. Their 1R spectra, fluorescent spectra and the thermal and optical stability were studied. The fluorescent excitation spectra of these complexes show more broad excitation bands than those of Eu2（TPA）3（TPPO）4 and Eu（TTA）3（TPPO）2 corresponding to their formations. In addition, both the binuclear complex EuY（TPA）（TTA）4（TPPO）4 and the chain complex EU0.4Y0.6（TPA）（TTA）（TPPO）2 present higher thermal stability and better optical stability than the mononuclear complex Eu（TTA）3（TPPO）2 does. And their thermal and optical stabilities are preferably interpreted from the binuclear structure together with the chain polynuclear structure of the complexes. The fluorescence enhancement of cofluorescence Y^3＋ ions to the Eu（Ⅲ） complexes is clear. The optimum content of Y^3＋ is 0.6 （molar fraction） for the chain complexes Eu1-xYx（TPA）（TTA）- （TPPO）2 and 0.5 for the binuclear complexes Eu^2（1-x）Y2x（TPA）（TTA）4（TPPO）4. The formation of polynuclear structure of the complex Eu1-xYx（TPA）（TTA）（TPPO）2 appears to be responsible for the good cofluorescence effect of Y^3＋ ions.     

Water-soluble and water-stable Gold(I), Gold(II) and Gold(III) phosphine complexes: The early years

This article briefly reviews the still rather limited knowledge of the chemistry, structures, reactions and applications of gold complexes containing water-soluble phosphine ligands sorted by gold oxidation state.     

Optical and electronic properties of phosphorescent iridium(III) complexes with phenylpyrazole and ancillary ligands

Phosphorescent Ir(III) complexes Ir(ppz)₃, Ir(ppz)₂(acac), Ir(ppz)₂(pic) and Ir(ppz)₂(dbm) (here ppz = phenylpyrazole, acac = acetylacetonate, dbm = dibenzoylmethane, and pic = picolinate) have been synthesized and investigated by optical spectroscopy, electrochemistry as well as density functional theory (DFT) calculations. These complexes show either no emission or medium intensity emission in solution or solid state at room temperature, but exhibit very strong emission from blue (422 nm) to orange-red (587 nm) at low temperature (77 K). Combined experimental and theoretical study, we reveal that replacing one of ppz ligand by ancillary ligand acac, dbm, and pic is a feasible way to alter the electronic structures of complexes resulting in changing emission colors. Both the cyclic voltammetry and DFT study testify that ancillary ligands have little influence on the highest occupied molecular orbital (HOMO) but great effect on lowest unoccupied molecular orbital (LUMO) by lowering the LUMO levels dramatically. The decreased LUMO level induced by the ancillary ligand makes the excited state of the complex far from the non-radiative states, which might enhance the quantum efficiency.     

Spectral properties of Eu(III) complexes with heteropolyanions immobilised in xerogel matrices

Eu³⁺ complexes with two heteropolymetalates (HPMs) were entrapped in various xerogel matrices by the sol-gel process. The spectral behaviour of these complexes in the rigid xerogel was studied by means of absorption and emission spectra. The luminescence emission experiments prove that photoexcitation of the HPM lattices (tungstate and molybdate) induced the energy transfer from the oxygen-to-metal charge transfer {O→M (= W, Mo)} triplet states to Eu³⁺ (⁷F_0,1,2→⁵D_0,1). Among the studied matrices with the Eu(III) complexes the best results, i.e. highest relative intensity and longest lifetime, were observed for methylated silicate (SiO₂-polydimethylsiloxane) and silica. In both the cases intensity of the emission could be improved by drying at elevated temperature. The studied materials consisting of complexes Eu³⁺ with the HPMs exhibit in practice stable emission intensity during UV irradiation.