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.     

Darstellung,Eigenschaften und elektronische Raman-Spektren von Bis(chloro)phthalocyaninatoferrat(III), -ruthenat(III) und -osmat(III)

Preparation, Properties and Electronic Raman Spectra of Bis(chloro)-phthalocyaninatoferrate(III), -ruthenate(III) and -osmate(III) Bis(chloro)phthalocyaninatometalates of Fe^III, Ru^III and Os^III [MCl₂Pc(2-)]^?, with an electronic low spin ground state are formed by the reaction of [FeClPc(2-)] resp. H[MX₂Pc(2?)] (M = Ru, Os; X = Cl, I) with excess chloride in weakly coordinating solvents (DMF, THF) and are isolated as (n-Bu₄N) salts. The asym. M? Cl stretch (ν_as(MCl)) is observed in the f.i.r. at 288 cm^?1 (Fe), 295 cm^?1 (Ru), 298 cm^?1 (Os), ν_as(MN) at 330 cm^?1 (Fe), 327 cm^?1 (Ru), and 317 cm^?1 (Os); only ν_s(OsCl) at 311 cm^?1 is resonance Raman (r.r.) enhanced with blue excitation. The m.i.r. and FT-Raman spectra are typical for hexacoordinated phthalocyanines of tervalent metal ions. The UV-vis spectra show besides the characteristic π-π* transitions (B, Q, N, L band) of the Pc ligand a number of extra bands at 12–15 kK and 18–24 kK due to trip-doublet and (Pc→M)CT transitions. The effect of metal substitution is discussed. The r.r. spectra obtained by excitation between the B and Q band (λ₀ = 476.5 nm) are dominated by the intraconfigurational transition Γ₇ Γ ₈ arrising from the spin-orbit splitting of the electronic ground state for Fe^III at 536 cm^?1, for Ru^III at 961 cm^?1 and Os^III at 3 028 cm^?1. Thus the spin-orbit coupling constant increases very greatly down the iron group: Fe^III (357 cm^?1)< Ru^III (641 cm^?1)< Os^III (2 019 cm^?1). The Γ₇ Γ ₈-transition is followed by a very pronounced vibrational finestructure being composed in the r.r. spectra by the coupling with ν_s(MCl), δ(MClN) and the most intense fundamental vibrations of the Pc ligand. In absorption only vibronically induced transitions are observed for the Ru and Os complex at 1 700-2800 rsp. 3100-5800 em^?1 instead of the 0-0 phonon transitions. The most intense lines are attributed to combinations of the intense odd vibrational mo-des at ≈ 740 and 1120 cm^?1 with ν₅(MCI), δ(MClN).     

Intercalation of hydrotalcites with hexacyanoferrate(II) and (III)—a thermoRaman spectroscopic study

Raman spectroscopy using a hot stage indicates that the intercalation of hexacyanoferrate(II) and (III) in the interlayer space of a Mg, Al hydrotalcites leads to layered solids where the intercalated species is both hexacyanoferrate(II) and (III). Raman spectroscopy shows that depending on the oxidation state of the initial hexacyanoferrate partial oxidation and reduction takes place upon intercalation. For the hexacyanoferrate(III) some partial reduction occurs during synthesis. The symmetry of the hexacyanoferrate decreases from O_h existing for the free anions to D_3d in the hexacyanoferrate interlayered hydrotalcite complexes. Hot stage Raman spectroscopy reveals the oxidation of the hexacyanoferrate(II) to hexacyanoferrate(III) in the hydrotalcite interlayer with the removal of the cyanide anions above 250 °C. Thermal treatment causes the loss of CN ions through the observation of a band at 2080 cm⁻¹. The hexacyanoferrate (III) interlayered Mg, Al hydrotalcites decomposes above 150 °C.     

Detection of cationic guest molecules by quenching of luminescence of a self-assembled host molecule consisting of terbium(III) and calix[4]arene-p-tetrasulfonates

By self-assembly in aqueous solution, calix- (CAS) and thiacalix[4]arene-p-tetrasulfonate (TCAS) formed luminescent complexes Tb^III·(CAS)₂ and Tb^III·TCAS, respectively, which were utilized as a host for cationic guests. Addition of 1-ethylpyridinium guest quenched luminescence of Tb^III·(CAS)₂ in accordance with the Stern-Volmer (SV) relation with a low detection limit (D.L.) of 5.94 × 10⁻⁸ M (S/N = 3, M ≡ mol dm⁻³). On the other hand, 1-ethylquinolinium quenched luminescence of Tb^III·TCAS most efficiently, affording a very low D.L. (6.71 × 10⁻¹⁰ M). The agreement of the SV coefficients obtained with luminescent intensity (K_SV,all = 6.74 × 10⁶ M⁻¹) and lifetime (K_SV,Tb = 6.50 × 10⁶ M⁻¹) implied that dynamic quenching of ⁵D₄ excited state of Tb^III was predominant in the quenching processes. The quenching rate was estimated to be k_q,Tb = 9.94 × 10⁹ M⁻¹ s⁻¹, which was as fast as diffusion-limited rate. Quenching of Tb^III·(CAS)₂ was also applied to detection of NAD⁺, with a D.L. of 2.78 × 10⁻⁷ M.     

Benefits of near-infrared spectroscopy for characterization of selected organo-montmorillonites

The potential of near infrared (NIR) spectroscopy in characterization of organically modified clay minerals is introduced. Selected organo-clays, possibly perspective fillers in clay polymer nanocomposites, were prepared from Na-montmorillonite and different surfactants containing octylammonium chain(s), hexadecylammonium chain(s) or a benzene ring with or without a reactive double bond. Based on the stretching (ν) and bending (δ) vibrations observed in the middle IR (MIR) region, the first overtone (2νXH) and combination (ν + δ)XH modes of XH groups (X = O, C, N) are identified. The effect of larger alkylammonium cations on the vibrations of Si-O and OH bonds in montmorillonite layers is observed. The changes in the intensity of the (ν + δ)H₂O band near 5250 cm⁻¹ allows for comparison of the amount of water adsorbed on the montmorillonite surface. The water content decreases with the size of the organic cation reflecting increasing hydrophobicity of the montmorillonite surface. The NIR region shows the 2νCH₃ and 2νCH₂ bands in the 5900-5500 cm⁻¹ region, an upward shift is observed for the complex band due to 2νCH(Ar) of aromatic benzene ring. The NIR spectra are extremely useful in identification of NH₂⁺, NH⁺ and vinyl groups, which are difficult to recognize in the MIR spectra of organo-clays due to overlapping with other absorption bands. The intense bands corresponding to overtones and combination vibrations of NH₃⁺ and NH₂⁺ groups are found in the 6600-6050 cm⁻¹ and 5000-4600 cm⁻¹ regions, the (ν + δ)NH⁺ is unambiguously identified near 4750 cm⁻¹. The characteristic band assigned to 2νCH₂ in H₂CC is detected near 6130 cm⁻¹.     

Synthesis,structure, and electrochemistry of pyridinecarboxamide cobalt(III) complexes; the effect of bridge substituents on the redox properties

Two series of complexes of the types trans-[Co^III(Mebpb)(amine)₂]ClO₄ {Mebpb²⁻ = N,N-bis(pyridine-2-carboxamido)-4-methylbenzene dianion, and amine = pyrrolidine (prldn) (1a), piperidine (pprdn) (2a), morpholine (mrpln) (3a), benzylamine (bzlan) (4a)}, and trans-[Co^III(cbpb)(amine)₂]X {cbpb²⁻ = N,N-bis(pyridine-2-carboxamido)-4-chlorobenzene dianion, and amine = pyrrolidine (prldn), X = PF₆ (1b), piperidine (pprdn), X = PF₆ (2b), morpholine (mrpln), X = ClO₄ (3b), benzylamine (bzlan), X = PF₆ (4b)} have been synthesized and characterized by elemental analyses, IR, UV–Vis, and ¹H NMR spectroscopy. The crystal structure of 1a has been determined by X-ray diffraction. The electrochemical behavior of these complexes, with the goal of evaluating the effect of axial ligation and equatorial substitution on the redox properties, is also reported. The reduction potential of Co^III, ranging from −0.53 V for (1a) to −0.31 V for (3a) and from −0.48 V for (1b) to −0.22 V for (3b) show a relatively good correlation with the σ-donor ability of the axial ligands. The methyl and chloro substituents of the equatorial ligand have a considerable effect on the redox potentials of the central cobalt ion and the ligand-centered redox processes.     

Ruthenium(III) mediated C-H activation of azonaphthol: Synthesis, structural characterization and transfer hydrogenation of ketones

Treatment of [RuCl₃(PPh₃)₃] with 1-(arylazo)naphthol ligands in benzene under reflux afford air-stable new organoruthenium(III) complexes with general composition [Ru(an-R)Cl(PPh₃)₂] (where, R = H, Cl, CH₃, OCH₃, OC₂H₅) in fairly good yield. The 1-(arylazo)naphtholate ligands behave as dianionic tridentate C, N, O donors and coordinates to ruthenium through phenolic oxygen, azo nitrogen and ortho carbon generate two five-membered chelate rings. The composition of the complexes have been established by analytical (elemental analysis and magnetic susceptibility measurement) and spectral (FT-IR, UV-Vis, EPR) methods. The complexes are paramagnetic (low-spin, d⁵) in nature and in dichloromethane solution show intense d-d transitions and ligand-to-metal charge transfer (LMCT) transitions in the visible region. The solution EPR spectrum of complex [Ru(an-CH₃)Cl(PPh₃)₂] (3) in dichloromethane at 77 K shows rhombic distortion around the ruthenium ion with three different ‘g’ values (g_x ≠ g_y ≠ g_z). The single crystal structure of the complex [Ru(an-OCH₃)Cl(PPh₃)₂] (4) has been characterised by X-ray crystallography, indicates the presence of a distorted octahedral geometry in these complexes. All the complexes exhibit one quasi-reversible oxidative response in the range 0.60-0.79 V (Ru^IV/Ru^III) and two quasi-reversible reductive responses (Ru^III/Ru^II; Ru^II/Ru^I) within the range −0.50 to −0.62 V and −0.93 to −0.98 V respectively. The formal potential of all the couples correlate linearly with the Hammett constant of the para substituent in arylazo fragment of the 1-(arylazo)naphtholate ligand. Further, the catalytic efficiency of one of the ruthenium complexes (4) was determined for the transfer hydrogenation of ketones with an excellent yield up to 99% in the presence of isopropanol/KOH.     

Two novel rhenium complexes derived from [ReO(OMe)Cl2(dpphen)] - Synthesis, crystal structure, spectroscopic and magnetic properties

The reaction of [ReO(OMe)Cl₂(dpphen)] (dpphen = 4,7-diphenyl-1,10-phenanthroline) with triphenylphosphine has been examined and two novel rhenium complexes - [Re^IIICl₃(dpphen)(PPh₃)]·Me₂CO (1) and [Re^IVCl₄(dpphen)]·CHCl₃ (2) - have been obtained. The compounds have been characterised by elemental analysis, IR, UV-Vis spectroscopy, magnetic measurements and X-ray crystallography. The electronic structures of [ReCl₃(dpphen)(PPh₃)] and [ReCl₄(dpphen)] have been studied by DFT/B3LYP level calculations, and TD-DFT calculations have been employed for discussion of the electronic spectra in more detail. The magnetic behaviour of 1 is characteristic of mononuclear complexes with d⁴ low-spin octahedral Re(III) complexes (³T_1g ground state) and arise because of the large spin-orbit coupling (ζ = 2500 cm⁻¹), which gives diamagnetic ground state. For complex 2 the results of calculations revealed value of zero-field splitting parameter D = 10.8 cm⁻¹, g_|| = 2.49 and g_⊥ = 1.51.     

Resonance Raman spectra of tris(acetylacetonato)iron(III) and ruthenium(III) complexes and their solvent effect

The resonance Raman spectra of tris(acetylacetonatoiron(III)) and ruthenium(III) complexes in various solvents and in water-acetonitrile (W-AN) mixtures were measured. The resonance Raman spectra of both complexes indicated peaks near 460 and around 1580 cm^–1. Thev(C-O) peak (around 1580 cm^–1) is shifted to low frequency with an increase in the dielectric constant _T of the solvents, whereas thev(M-O) (M=Fe and Ru, near 460 cm^–1) are constant, independent of _T. It implies that the C-O bond in the acac^– ligand is lengthened by the polarizability effect of the solvents, while both the Fe-O and Ru-O bonds, which are located in the inside of the complexes, are not influenced by the solvents indicating that the interaction does not depend on the properties of individual solvent molecules but on those of the aggregate.     

Facilitated transport of Am(III) through a flat-sheet supported liquid membrane (FSSLM) containing tetra(2-ethyl hexyl) diglycolamide (TEHDGA) as carrier

Facilitated transport of Am(III) in nitric acid medium using tetra(2-ethyl hexyl) diglycolamide (TEHDGA) in n-dodecane as carrier was studied. It was aimed at finding out the physico-chemical model for the transport of Am(III) using TEHDGA/n-dodecane as carrier under various experimental parameters like feed acidity, carrier concentration, varying strippant, varying membrane pore size, etc. The feed acidity and carrier concentrations were varied from 1 M to 6 M HNO₃ and 0.1 M to 0.3 M TEHDGA/n-dodecane, respectively. The transport of Am(III) increased with increase in feed acidity and carrier concentration reaching maximum at 3 M HNO₃ and 0.2 M TEHDGA/n-dodecane, respectively. Several stripping agents were tested and 0.1 M HNO₃ was found to be the most suitable stripping agent for this system. Almost quantitative transport of Am(III) was observed at about 180 min with feed acidity of 3 M HNO₃, 0.1 M HNO₃ as strippant and 0.2 M TEHDGA/n-dodecane as carrier. The pore size of the membrane support was varied from 0.20 μm to 5 μm and the permeation coefficient increased with increase in pore size up to 0.45 μm (2.43 × 10⁻³ cm/s), and then decreased with further increase in pore size. The plot between permeation coefficient vs. (membrane thickness)⁻¹ was linear which showed that the Am(III) transport was membrane diffusion limited. The membrane diffusion coefficient calculated from the graph was found to be 1.27 × 10⁻⁶ cm²/s and its theoretical value was 1.22 × 10⁻⁶ cm²/s. The stability of the carrier against leaching out of the membrane support as well as the integrity of membrane support was studied over a period of 30 days and was found to be satisfactory within the studied time period.     

Syntheses and investigation of the effects of position and nature of substituent on the spectral,electrochemical and spectroelectrochemical properties of new cobalt phthalocyanine complexes

The syntheses of new cobalt phthalocyanine (CoPc) complexes, tetra-substituted with diethylaminoethanethio at the peripheral (complex 3a) and non-peripheral (complex 3b) positions, and with benzylmercapto at the non-peripheral position (complex 5), are reported. The effects of the nature and position of substituent on the spectral, electrochemical and spectroelectrochemical properties of these complexes are investigated. Solution electrochemistry of complex 3a showed three distinctly resolved redox processes attributed to Co^IIIPc⁻²/Co^IIPc⁻² (E_½ = +0.64 V versus Ag|AgCl), Co^IIPc⁻²/Co^IPc⁻² (E_½ = −0.24 V versus Ag|AgCl) and Co^IPc⁻²/Co^IPc⁻³ (E_½ = −1.26 V versus Ag|AgCl) species. No ring oxidation was observed in complex 3a. Complex 3b showed both ring-based oxidation, attributed to Co^IIIPc⁻¹/Co^IIIPc⁻² species (E_p = +0.86 V versus Ag|AgCl), and ring-based reduction associated with Co^IPc⁻²/Co^IPc⁻³ species (E_½ = −1.46 V versus Ag|AgCl), with the normal metal-based redox processes in CoPc complexes: Co^IIIPc⁻²/Co^IIPc⁻² (E_p = +0.41 V versus Ag|AgCl) and Co^IIPc⁻²/Co^IPc⁻² (E_½ = −0.38 V versus Ag|AgCl). Solution electrochemistry of complex 5 showed the same type and number of species observed in complex 3a: Co^IIIPc⁻²/Co^IIPc⁻² (E_p = +0.59 V versus Ag|AgCl), Co^IIPc⁻²/Co^IPc⁻² (E_½ = −0.26 V versus Ag|AgCl) and Co^IPc⁻²/Co^IPc⁻³ (E_½ = −1.39 V versus Ag|AgCl) species. These processes were confirmed using spectroelectrochemistry.     

Effects of chloride ions on electrochemical reactions of manganese(III) complexes

Electrochemical reactions of manganese(III) complexes, Mn^III(L)X (L; salen, salpn, 5-NO₂–salen or 5-NO₂–salpn, X; Cl, Br or NO₂) and Mn^III(L’)₂X (L’; N-Bu-sal, N-Oct–sal, N-Oct–5-Br–sal or N-Oct–5-NO₂–sal, X; Cl or Br), were investigated by voltammetry at a glassy carbon electrode in the absence/presence of Cl⁻ in acetonitrile solution. By the addition of Cl⁻, oxidation processes of Mn^III(L)X and Mn^III(L’)₂X have been found to be improved from quasi-reversible to reversible, and their oxidation products, [Mn^IV(L)X]⁺ and [Mn^IV(L’)₂X]⁺, were stabilized by the combination with Cl⁻ resulting in [Mn^IV(L)Cl₂] and [Mn^IV(L’)₂Cl₂], respectively. On the other hand, the reduction processes of Mn^III(L)X and Mn^III(L’)₂Cl were not so significantly affected by Cl⁻ as those observed for their oxidation. Other types of manganese(III) complexes and iron(III) complex were also investigated. The present study may clarify the role of Cl⁻ being involved in OEC (oxygen-evolving center) in photosystem II.     

Raman spectroscopic characteristics of octa-substituted bis(phthalocyaninato) rare earth complexes peripherally substituted with (4-methoxy)phenoxy derivatives

The Raman spectroscopic data in the range 500-1800 cm⁻¹ for a series of 15 rare earth double-deckers with tervalent rare earths M^III[Pc(MeOPhO)₈]₂ (M = Y, La, …, Lu, except Ce, Pr and Pm), reduced state HPr[Pc(MeOPhO)₈]₂ and intermediate-valent cerium Ce[Pc(MeOPhO)₈]₂ have been collected using laser excitation source emitting at 632.8 nm. With excitation at 632.8 nm, which is in close resonance with the main Q absorption band of the phthalocyanine ligand, typical Raman marker bands of the monoanion radical [Pc(MeOPhO)₈]⁻ were observed at 1500-1528 cm⁻¹ as very strong bands resulting from the coupling of pyrrole CC and aza CN stretchings. For Ce[Pc(MeOPhO)₈]₂ and HPr[Pc(MeOPhO)₈]₂, a very strong band at 1499 cm⁻¹ with contributions from both pyrrole CC and aza CN stretchings and also isoindole stretching was the marker Raman band of [Pc(MeOPhO)₈]²⁻. In addition, the influence of ionic radius of the rare earth metal and substituent species on the Raman scatting characteristics of sandwich-type compounds has also been tentatively studied.     

Infrared and Raman studies of the anion ordering transitions in paramagnetic organometallic radical cation salts [Cp2Mo(dmit)]X (X = PF6, SbF6)

Temperature dependence of infrared and Raman spectra of the two isostructural salts [Cp₂Mo(dmit)]PF₆ and [Cp₂Mo(dmit)]SbF₆ is studied. At room temperature the physical properties of both compounds are very similar but at lower temperatures they undergo phase transitions associated with anion ordering, which are surprisingly different. The phase transitions in [Cp₂Mo(dmit)]PF₆ salt at T₁ = 120 K and T₂ = 89 K have no important influence on infrared and Raman spectra, while the phase transition in [Cp₂Mo(dmit)]SbF₆ salt at T₁ = 175 K causes a splitting of Raman bands assigned to the CC stretching at about 1334 cm⁻¹ and the in-plane Mo(dmit) ring deformation at about 353 cm⁻¹, and also an infrared band at about 939 cm⁻¹ related to the C-S stretching. The splitting of vibrational bands demonstrates a clear distortion of [Cp₂Mo(dmit)]⁺ cations in the [Cp₂Mo(dmit)]SbF₆ salt. This molecular distortion is related to a lattice distortion providing thus a good argument for applicability of the compressible model of the anion ordering transition.     

Synthesis, characterization, and structure of a new N-nitrosamine of cyclam (1,4,8,11-tetraazacyclotetradecane)

A novel N-nitrosamine of cyclam has been synthesized. The N-N bond lengths values, as determined from the X-ray crystal structure, fall in the 1.318(2) and 1.320(2) Å range, smaller than the ones expected for the N-N single bond. The N-NO bond angles are in the 115.0(1)° and 114.8(1)° range. The νNO, νNN, and δN-NO vibrational modes were observed in the infrared spectrum at 1454, 1139, and 555 cm⁻¹, respectively. The photolysis of the cyclam(NO)₄ compound gives rise to the nitrosyl release through an heterolytic cleavage of the N-NO bonds, as indicated by the appearance of the νNO⁺ band at 2228 cm⁻¹ at the expense of decreasing the νNO, νNN, and δN-NO bands.     

Temperature dependence on recrystallisation of the magnesium phthalocyanine (MgPc) in triethylamine

Three complexes of magnesium phthalocyaninato(2−) derivatives in the crystalline form, MgPc(H₂O)·(C₂H₅)₃N – (I), MgPc(H₂O)₂·2(C₂H₅)₃N – (II) and MgPc(H₂O)₂ – (III), depending on the thermal recrystallisation conditions were obtained and structurally characterised. In complex I, the Mg center exhibits square-pyramidal (4 + 1) coordination environment, whereas in II and III the Mg center of MgPc the biaxial (4 + 2) coordination. Owing to the interaction of the positively charged Mg center with oppositely charged oxygen atom of water molecule in an axial position in I, the Mg atom is significantly displaced (0.451(2) Å) from the plane defined by four isoindole N atoms and leads to distortion of the planar Pc(2−) macrocycle to the saucer-shape form. In II and III due to the biaxial (4 + 2) coordination of the Mg center of MgPc, the Mg atom lies on a N₄-isoindole plane. The triethylamine solvent molecules in I and II interact with mono or bis(aqua)magnesium phthalocyanine via   O–H?$?$N hydrogen bonds. The axial Mg–O bond in I is significantly shorter than that in the II and III complexes. The strength of the Mg–O bond in these complexes is correlated with their thermal stability. From among the complexes only complex I exhibits an intense near-IR absorption band in the solid-state. The spectra of I, II and III in solution are very similar.     

Chemical speciation of chromium(III,VI) employing extractive spectrophotometry and tetraphenylarsonium chloride or tetraphenylphosphonium bromide as ion-pair reagent

A simple and accurate extractive spectrophotometric procedure for the chemical speciation of chromium(III,VI) species in aqueous media has been developed. The method is based upon the extraction of the complex ion-associate formed between the chloro chromate (CrO₃Cl⁻) anion and the ion-pair reagent tetraphenylarsonium chloride (TPAs⁺Cl⁻) or tetraphenylphosphonium bromide (TPP⁺Br⁻) at pH ≤ 0 in chloroform followed by direct spectrophotometric measurement at 355 nm. The optimum concentration range evaluated by Beer-Lambert's law, Ringbom's plot, the molar absorptivity, the Sandell's sensitivity, the extraction and stability constants (K_D, K_ex and β), the stoichiometry and the extraction equilibria of the produced complex ion-associates have been determined and gave a convenient applications of the investigated system for analytical purposes. Chromium(III) was also determined by the proposed procedure after prior oxidation to chromate with H₂O₂ in alkaline solution. The method has been applied successfully for the analysis of chromium(VI) and total chromium(III,VI) in industrial wastewater of electroplating plant.     

Iron(III) complexes of the tris-(3-aminopropyl) derivative of a 14-membered tetraazamacrocycle: Potentiometric,spectroscopic and electrochemical studies

The properties of the iron(III) complexes of the ditopic macrocyclic ligand with three aminopropyl pendant arms, L¹ = 3,7,11-tris-(3-aminopropyl)-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene were investigated in aqueous solution. Potentiometric studies indicated the presence of mononuclear [FeH_hL¹]^h+3 (h = 0–3), and dinuclear [Fe₂L¹]⁶⁺, [Fe₂L¹(OH)]⁵⁺ and [Fe₂L¹(OH)₂]⁴⁺ complexes, and their stability constants were determined at 298.2 K and ionic strength 0.10 mol dm⁻³ in KNO₃. The log K values of mononuclear protonated species indicated the consecutive deprotonation of the aminopropyl arms, suggesting the nitrogen donor atoms from the macrocycle as the preferred coordination environment for the first metal centre, and the amines from the pendant arms for the second one. The dinuclear complex is formed at about 85% of the total amount of the metal ion for 2:1 Fe:L¹ ratio solutions at pH 4.0–4.5. The log K values of the deprotonation of dinuclear hydrolysed species are consistent with the presence of two water molecules directly bound to the metal centres. Spectroscopic UV–Vis and IR data for 2:1 Fe³⁺:L¹ ratio samples confirmed the existence of dinuclear and hydroxo dinuclear species. EPR spectra of these solutions were interpreted by an equilibrium of two high-spin d⁵ state of iron(III) species with different rhombic E/D distortions. Electrochemical studies also established the formation of mono- and dinuclear complexes, showing irreversible redox behaviour. The two metal centres on the dinuclear complexes have only weak interactions.     

Simultaneous capillary electrophoretic determination of Sc(III) and Y(III) based on the complex-formation with a lacunary Keggin-type [PW11O39] complex

Trace amounts of Sc(III) and Y(III) can react with [PW₁₁O₃₉]⁷⁻ to form the ternary Keggin-type complexes: [P(Sc^IIIW₁₁)O₄₀]⁶⁻ and [P(Y^IIIW₁₁)O₄₀]⁶⁻ having high molar absorptivities in the UV region. Since the rate of the complex-formation was very rapid and the kinetically stable ternary anions migrated in the capillary with different electrophoretic mobilities, the complex-formation reaction was applied to the simultaneous CE determination of Sc(III) and Y(III) with direct UV detection at 250 nm. For both Sc(III) and Y(III), the pre-column method provided linear calibration curves in the range of 2 × 10⁻⁷ to 1 × 10⁻⁵ M; the respective detection limits were 1 × 10⁻⁷ M (the signal-to-noise ratio = 3). The proposed method was successfully applied to the determination of Sc(III) and Y(III) in river water.     

Backscattering light detection of nucleic acids with tetraphenylporphyrin-Al(III)-nucleic acids at liquid/liquid interface

A backscattering light (BSL) detection assembly is constructed and applied to the determination of nucleic acids with high sensitivity and selectivity based on the measurements of BSL signals at water/tetrachloromethane (H₂O/CCl₄) interface. In aqueous medium of pH 3, the binary complex of of Al(III)-DNAs could be formed by the interaction of Al(III) with the phosphate group of DNAs, which then could interact with tetraphenylporphyrin (TPP) in tetrachloromethane through liquid/liquid interaction, forming a ternary complex of TPP-Al(III)-DNAs at the interface. It was observed that greatly enhanced BSL signals occurred with maximum peak at 469 nm when the ternary complex of TPP-Al(III)-DNAs were absorbed to the liquid/liquid interface. The enhanced backscattering light intensity (I_BSL) is in proportion to the concentration of calf thymus DNA (ctDNA) and fish sperm DNA (fsDNA) in the range of 0.6-1200 ng ml⁻¹ and 1.1-1200 ng ml⁻¹, respectively. The limits of determination (3σ) are 60 pg ml⁻¹ and 110 pg ml⁻¹, correspondingly. Artificial samples with highly interference backgrounds were determined with the recovery ranging from 94.5 to 106.7%, and relative standard deviation (R.S.D.) less than 2.40%.