The excited states of bipyridyl and phenanthroline complexes of Fe(III), Ru(II) and Ru(III): A molecular orbital study

The semiempirical zero-differential-overlap molecular orbital model which was shown in earlier papers in this series to give a good account of the charge transfer and -* spectra of Fe(II) complexes with conjugated ligands such as 2,2-bipyridyl and 1,10-phenanthroline is extended to complexes having openshell ground states, such as those of Fe(III), and to complexes of Ru(II) and Ru(III). The results are used to assign the observed charge transfer and intra-ligand absorption bands to specific orbital transitions. Observed and calculated intensities are in good agreement: reasons are advanced for the much lower intensity of the charge transfer bands in Ru(III) compared to Ru(II) complexes.     

Thermal Analysis of Fe(III) Complexes with Salicylaldehyde Semi-, Thiosemi- and S-methylisothiosemi-carbazones

The paper describes the results of differential thermal analysis of the octahedral Fe(III) complexes of the general formula [Fe(HLⁿ)₂]Cl and Fe(HL³)L³, as well as of the corresponding ligands H₂Lⁿ (H₂Lⁿ — tridentate salicylaldehyde semi thiosemi- and S-methylisothiosemi-carabazones with n=1, 2 and 3 respectively). The decomposition of the complexes involving sulphur-containing ligands (H₂L² and H₂L³) starts with sulphur elimination. In case of the complexes [Fe(HL²)]Cl and [Fe(HL³)]Cl sulphur evolves independently, whereas with Fe(HL³)L³ it is eliminated within the SCH₃ group. In the former case, sulphur elimination takes place at the same temperature for both complexes. The change in the coordination mode, being a consequence of the replacement of O by S, has no essential effect on thermal stability of the coordination polyhedron. The complexes involving ONN coordination, realized with the H₂L³ ligand, exhibit a comparatively highest thermal stability of the coordination polyhedron.This revised version was published online in November 2005 with corrections to the Cover Date.     

Fe(III)-pyruvate and Fe(III)-citrate induced photodegradation of glyphosate in aqueous solutions

The photolysis of Fe(III)-pyruvate and Fe(III)-citrate complexes in water produces hydroxyl radicals in the presence of dissolved oxygen, and can promote the oxidation of organic compounds. The photodegradation of glyphosate with Fe(III)-pyruvate and Fe(III)-citrate complexes was investigated under irradiation at λ?≥?365?nm. The effect of initial concentration of glyphosate, the initial pH value, and the Fe(III)/carboxylate ratio were examined. Upon irradiation of glyphosate aqueous solution with the complexes in the acidic range of natural waters, the bioavailable orthophosphate could be released from degradation of glyphosate. The amount of orthophosphate increased with increasing Fe(III)/carboxylate ratio.     

Mononuclear gallium(III) complexes based on salicylaldoximes: Synthesis,structure and spectroscopic characterization

The reactions of Ga(acac)₃ with salicylaldoxime (saoH₂) and methyl-salicylaldoxime (Me-saoH₂) in dichloromethane/hexane afforded the complexes [Ga(acac)(saoH)₂] (1) and [Ga(acac)₃][Ga(acac)(MesaoH)₂] (2), respectively, in high yields. The crystal structures of 1 and 2 have been determined by single-crystal X-ray crystallography. Both complexes are mononuclear with the Ga(III) atoms being in octahedral environments surrounded by two bidentate chelate R-saoH⁻ and one bidentate chelate acac⁻ ligands. A [Ga(acac)₃] moiety has co-crystallized along with the methylsalicylaldoximato complex. Characteristic IR as well as NMR data are discussed in terms of the nature of bonding in the structures of the two complexes. ¹H and ¹³C NMR data in CDCl₃ indicate that the salicylaldoximato complexes isomerize in solution.     

A Review on Coordination Properties of Al(III) and Fe(III) toward Natural Antioxidant Molecules: Experimental and Theoretical Insights

This review focuses on the ability of some natural antioxidant molecules (i.e., hydroxycinnamic acids, coumarin-3-carboxylic acid, quercetin, luteolin and curcumin) to form Al(III)- and Fe(III)-complexes with the aim of evaluating the coordination properties from a combined experimental and theoretical point of view. Despite the contributions of previous studies on the chemical properties and biological activity of these metal complexes involving such natural antioxidants, further detailed relationships between the structure and properties are still required. In this context, the investigation on the coordination properties of Al(III) and Fe(III) toward these natural antioxidant molecules might deserve high interest to design water soluble molecule-based metal carriers that can improve the metal’s intake and/or its removal in living organisms.     

Ru(III), Cr(III), Fe(III) complexes of Schiff base ligands bearing phenoxy Groups: Application as catalysts in the synthesis of vitamin K3

Two polydentade Schiff base ligands and their Ru(III), Cr(III) and Fe(III) complexes were synthesized and characterized by elemental analysis (C, H, N), UV/Vis, FT IR, ¹H and ¹³C NMR, LC–MS/MS, molar conductivity and magnetic susceptibility techniques. The absorption bands in the electronic spectra and magnetic moment measurements verified an octahedral environment around the metal ions in the complexes. The thermal stabilities were investigated using TGA. The synthesized complexes were used in the catalytic oxidation of 2-methyl naphthalene (2MN) to 2-methyl-1,4-naphthoquinone; vitamin K₃, menadione, 2MNQ; using hydrogen peroxide, acetic acid and sulfuric acid. L₁-Fe(III) complex showed very efficient catalytic activity with 58.54% selectivity in the conversions of 79.11%.     

Complex-Forming Properties of Ceftazidime with Fe(III) Ions in an Aqueous Solution

In the present study, the complexing properties of ceftazidime with Fe(III) ions in aqueous solutions were characterized by UV-vis spectrophotometric and potentiometric methods. Using the UV-vis spectrophotometric method, the absorbance values for Fe(III) ions, a third-generation cephalosporin antibiotic (ceftazidime), and the Fe(III)-ceftazidime system were determined. Based on pH-metric studies, the value of the stability constant for the Fe(III)-ceftazidime complex was calculated.     

Mononuclear Fe(III) and tetranuclear [Fe(III)Gd(III)]2 complexes with a Schiff-base ligand derived from the o-vanillin: Synthesis, crystal structures and magnetic properties

The mononuclear high-spin iron(III) complexes [Fe(3-MeOsalpn)Cl(H₂O)] (1) and [Fe(3-MeOsalpn)(NCS)(H₂O)]·0.5CH₃CN (2) and the tetranuclear oxo-bridged compound [{Fe(3-MeOsalpn)Gd(NO₃)₃}₂(μ-O)]·CH₃CN (3) [3-MeOsalpn²⁻ = N,N′-propylenebis(3-methoxysalicylideneiminate)] have been prepared and magneto-structurally characterised. The iron(III) ion in 1 and 2 is six-coordinated in a somewhat distorted octahedral surrounding with the two phenolate-oxygens and two imine-nitrogens from the Schiff-base building the equatorial plane and a water (1 and 2) and a chloro (1)/thiocyanate-nitrogen (2) in the axial positions. The neutral mononuclear units of 1 and 2 are assembled into centrosymmetric dinuclear motifs through hydrogen bonds between the axially coordinated water molecule of one iron centre and methoxy-oxygen atoms from the Schiff-base of the adjacent iron atom. The values of the intradimer metal-metal distance within the supramolecular dimers are 4.930 (1) and 4.878 Å (2). The tetranuclear of 3 can be described as two {Fe^III(3-MeOsalpn)} units connected through an oxo-bridge, each one hosting a [Gd^III(NO₃)₃] entity in the outer cavity defined by the two phenolate- and two methoxy-oxygen atoms. The values of the intramolecular Fe?Fe and Fe?Gd distances in 3 are 3.502 and 3.606 Å, respectively. The analysis of the magnetic data of 1-3 in the temperature range 1.9-300 K shows the occurrence of weak intermolecular antiferromagnetic interactions in 1 and 2 [J = −0.76 (1) and −0.75 cm⁻¹ (2) with the Hamiltonian defined as H = −JS_Fe1·S_Fe1] whereas two intramolecular antiferromagnetic interactions coexist in 3, one very strong between the two iron(III) ions (J₁) through the oxo bridge and the other much weaker between the iron(III) and the Gd(III) ions (J₂) across the double phenoxo oxygens [J₁ = −275 cm⁻¹ and J₂ = −3.25 cm⁻¹, the Hamiltonian being defined as H=-J₁S_Fe1·S_Fe1^′-J₂(S_Fe1·S_Gd1+S_Fe1^′·S_Gd1^′)]. These values are analysed in the light of the structural data and compared with those of related systems.     

Synthesis, structures and properties of hydrolytic Al(III) aggregates and Fe(III) analogues formed with iminodiacetate-based chelating ligands

Both Al(III) and Fe(III) display a rich hydrolytic chemistry which can lead to the formation of a variety of aggregated oxo and hydroxo-bridged aggregates. The formation, structures and properties of these species are important in defining the availability and reactivity of these species in aqueous environments such as are found in biological systems and the environment. Although there are many similarities in the behaviour of the Al³⁺ and Fe³⁺ ions there are also some important differences between these two metal ions which can lead to a divergence in their chemistries. These considerations are discussed and illustrated with reference to 16 Al(III) and Fe(III) compounds, which have been crystallographically characterised, and which form in aqueous environments in the presence of chelating ligands containing the iminodiacetate functionality.     

Efficient Aerobic Oxidative Synthesis of Benzimidazoles with Fe(III) based PEG1000 Dicationic Imidazolium Ionic Liquid/toluene Temperature‐dependent Biphasic System

A green protocol for the synthesis of benzimidazoles with Fe(III) based PEG1000 dicationic imidazolium ionic liquid ([PEG₁₀₀₀mim₂][FeCl₄]₂)/toluene temperature‐dependent biphasic system was described. Conformed by IR analysis, FeCl₄⁻ is the dominating anion species. It could be seen that aldehydes aryla mines and aromatic aldehydes bearing electron‐deficient group ( Cl,  Br,  NO₂) and electron‐rich groups ( OH,  N(CH₃)₂) on the aromatic rings gave good yields (78–96 %). Moreover, the Fe(III) based PEG1000 dicationic imidazolium ionic liquid could be recycled and reused without significant loss of catalytic activity after seven runs.     

Thermogravimetric and spectroscopic studies on La(III) and Ce(III) complexes with some thio-schiff bases

Solid complexes of five derivatives of thio-Schiff bases with La(III) and Ce(III) ions were prepared and characterized by elemental and thermogravimetric analyses. The suggested general formula of the solid complexes is [ML₂(H₂O)X]·2H₂O, whereM=trivalent lanthanide ion,L=Schiff base andX=Cl^? or ClO ₄ ^? . Information about the water of hydration, the coordinated water molecules, the coordination chemistry and the thermal stability of these complexes was obtained and is discussed. Additionally, a general scheme of thermal decomposition of the lanthanide-Schiff base complexes is proposed.     

Group III quinaldates: synthesis,structure and photoluminescence

The reactions of Al(III), Ga(III) and In(III) nitrates with 2-quinaldic acid (qaH) afforded [Al₂(OH)₂(qa)₄]·2H₂O (1), [Ga(qa)₂(H₂O)₂]NO₃ (2) and [In(qa)₂(NO₃)(H₂O)] (3), respectively, in high yields. The crystal structures of 1, 2 and 3 have been determined by single-crystal X-ray crystallography. The structure of 1 features a di-hydroxo bridged [Al₂(μ-OH)₂]⁴⁺ dimer in which each Al(III) is further ligated by two bidentate chelate qa^? ligands. Complexes 2 and 3 are mononuclear with the M(III) ions in octahedral environments surrounded by two bidentate chelate qa^? and two H₂O in 2 or one H₂O and a terminal NO₃^? in 3. Characteristic IR as well as thermal analysis and solid-state fluorescence are discussed.     

Studies of the catalytic activity of Fe(III)(salen) complexes as epoxidation catalysts

Two new Fe(III)(salen) complexes, FeL¹ClO₄·2H₂O (1) and FeL²ClO₄ (2) [L¹ = N,N′-ethylenebis(3-formyl-5-methylsalicylaldimine) and L² = N,N′-cyclohexenebis(3-formyl-5-methylsalicylaldimine)], have been synthesized and characterized. The catalytic activity of the complexes for epoxidation of alkenes has been investigated in the presence of two terminal oxidants PhIO and NaOCl, with two solvents CH₃CN and CH₂Cl₂. As alkenes styrene and (E)-stilbene have been chosen for investigation; styrene is a better substrate than electron-rich (E)-stilbene. The study also suggests that unlike their Mn(III) counterparts, 1 and 2 are poor epoxidation catalysts; catalysis proceeds with formation of one intermediate, rather than forming more than one intermediate depending on the terminal oxidant used. Use of exogenous neutral donor ligands such as Py, PyNO and 1-MePy is effective to improve catalytic behavior.     

Simple flow injection method for simultaneous spectrophotometric determination of Fe(II) and Fe(III)

The method is based on spectrophotometric determination of Fe(II) and Fe(III) at a single wavelength (530 nm) with the use of a dedicated reversed-flow injection system. In the system, EDTA solution is injected into a carrier stream (HNO₃) and then merged with a sample stream containing a mixture of sulfosalicylic acid and 1,10-phenanthroline as indicators. In an acid environment (pH ≅ 3) the indicators form complexes with both Fe(III) and Fe(II), but EDTA replaces sulfosalicylic acid, forming a more stable colourless complex with Fe(III), whereas Fe(II) remains in a complex with 1,10-phenenthroline. As a result, the area and minimum of the characteristic peak can be exploited as measures corresponding to the Fe(III) and Fe(II) concentrations, respectively. The analytes were not found to affect each other's signals, hence two analytical curves were constructed with the use of a set of standard solutions, each containing Fe(II) and Fe(III). Both analytes were determined in synthetic samples within the concentration ranges of 0.05–4.0 and 0.09–6.0 mg L⁻¹, respectively, with precision less than 1.5 and 2.6% (RSD) and with accuracy less than 4.3 and 5.6% (RE). The method was applied to determination of the analytes in water samples collected from artesian wells and the results of the determination were consistent with those obtained using the ICP-OES technique.     

Solution-Processed Yellow Organic Light-Emitting Diodes Based on Two New Ionic Ir (III) Complexes

Two new and efficient cationic yellow-emissive Ir (III) complexes (Ir1 and Ir2) are rationally designed by using 2-(4-chloro-3-(trifluoromethyl)phenyl)-4-methylquinoline as the main ligand, and, respectively, 4,4′-dimethyl-2,2′-bipyridyl and 4,4′-dimethoxy-2,2′-bipyridyl as the ancillary ligands. Both complexes show enhanced phosphorescence (546 nm with 572 nm as shoulder and high phosphorescent quantum efficiency in solution, which is in favor of efficient solution-processed phosphorescent organic light-emitting diodes. Compared with Ir2, the Ir1-based device displays excellent device performance, with maximum external quantum efficiency, current efficiency, and power efficiency of up to 7.92%, 26.32 cd/A and 15.31 lm/W, respectively, thus proving that the two new ionic Ir (III) complexes exhibit great potential for future solution-processed electroluminescence.     

Chalcone-derived thiosemicarbazones and their zinc(II) and gallium(III) complexes: spectral studies and antimicrobial activity

Chalcone-derived 3-phenyl-1-pyridin-2-ylprop-2-en-1-one thiosemicarbazone (HPyCTPh) (1), 3-(4-chlorophenyl)-1-pyridin-2-ylprop-2-en-1-one thiosemicarbazone (HPyCT4ClPh) (2), 3-(4-bromophenyl)-1-pyridin-2-ylprop-2-en-1-one thiosemicarbazone (HPyCT4BrPh) (3), and 3-(4-nitrophenyl-1-pyridin-2-ylprop-2-en-1-one thiosemicarbazone (HPyCT4NO₂Ph) (4) were obtained as well as their gallium(III) and zinc(II) complexes [Ga(PyCTPh)₂]NO₃ (Ga1), [Ga(PyCT4ClPh)₂]NO₃ (Ga2), [Ga(PyCT4BrPh)₂]NO₃ (Ga3), [Ga(PyCT4NO₂Ph)₂]NO₃ (Ga4), [Zn(PyCTPh)₂] (Zn1), [Zn(PyCT4ClPh)₂] (Zn2), [Zn(PyCT4BrPh)₂] (Zn3), and [Zn(PyCT4NO₂Ph)₂] (Zn4). The chalcones, thiosemicarbazones, and zinc(II) complexes were not active against Pseudomonas aeruginosa. The thiosemicarbazones proved to be more active than the parent chalcones against Staphylococcus aureus and Candida albicans. Coordination to zinc(II) resulted in activity improvement of most thiosemicarbazones against S. aureus. Coordination to gallium(III) significantly improved the antimicrobial activity of all thiosemicarbazones against the studied micro-organisms, suggesting this to be an effective strategy for antimicrobial activity enhancement.     

On-line solid-phase extraction and multisyringe flow injection analysis of Al(III) and Fe(III) in drinking water

A new analytical method was developed for on-line monitoring of residual coagulants (aluminium and iron salts) in potable water. The determination was based on a sequential procedure coupling an extraction/enrichment step of the analytes onto a modified resin and a spectrophotometric measurement of a surfactant-sensitized binary complex formed between eluted analytes and Chrome Azurol S. The optimization of the solid phase extraction was performed using factorial design and a Doehlert matrix considering six variables: sample percolation rate, sample metal concentration, flow-through sample volume (all three directly linked to the extraction step), elution flow rate, concentration and volume of eluent (all three directly linked to the elution step). A specific reagent was elaborated for sensitive and specific spectrophotometric determination of Al(III) and Fe(III), by optimizing surfactant and ligand concentrations and buffer composition. The whole procedure was automated by a multisyringe flow injection analysis (MSFIA) system. Detection limits of 4.9 and 5.6 μg L⁻¹ were obtained for Al(III) and Fe(III) determination , respectively, and the linear calibration graph up to 300 μg L⁻¹ (both for Al(III) and Fe(III)) was well adapted to the monitoring of drinking water quality. The system was successfully applied to the on-site determination of Al(III) and Fe(III) at the outlet of two water treatment units during two periods of the year (winter and summer conditions).     

Novel drug‐based Fe(III) heterochelates: synthetic,spectroscopic, thermal and in‐vitro antibacterial significance

A series of novel heterochelates of the type [Fe(Aⁿ)(L)(H₂O)₂]^?mH₂O [where H₂Aⁿ = 4,4′‐(arylmethylene)bis(3‐methyl‐1‐phenyl‐4,5‐dihydro‐1H‐pyrazol‐5‐ol); aryl = 4‐nitrophenyl, m = 1 (H₂A¹); 4‐chlorophenyl, m = 2 (H₂A²); phenyl, m = 2 (H₂A³); 4‐hydroxyphenyl, m = 2 (H₂A⁴); 4‐methoxyphenyl, m = 2 (H₂A⁵); 4‐hydroxy‐3‐methoxyphenyl, m = 1.5 (H₂A⁶); 2‐nitrophenyl, m = 1.5 (H₂A⁷); 3‐nitrophenyl, m = 0.5 (H₂A⁸); p‐tolyl, m = 1 (H₂A⁹) and HL = 1‐cyclopropyl‐6‐fluoro‐4‐oxo‐7‐(piperazin‐1‐yl)‐1,4‐dihydroquinoline‐3‐carboxylic acid] were investigated. They were characterized by elemental analysis (FT‐IR, ¹H‐ & ¹³C‐NMR, and electronic) spectra, magnetic measurements and thermal studies. The FAB‐mass spectrum of [Fe(A³)(L)(H₂O)₂]^?2H₂O was determined. Magnetic moment and reflectance spectral studies revealed that an octahedral geometry could be assigned to all the prepared heterochelates. Ligands (H₂Aⁿ) and their heterochelates were screened for their in‐vitro antibacterial activity against Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Serratia marcescens bacterial strains. The kinetic parameters such as order of reaction (n), the energy of activation (E_a), the pre‐exponential factor (A), the activation entropy (ΔS^#), the activation enthalpy (ΔH^#) and the free energy of activation (ΔG^#) are reported. Copyright © 2009 John Wiley & Sons, Ltd.