Kinetics and mechanism of uncatalysed and ruthenium(III) catalysed oxidation of allyl alcohol by diperiodatoargentate(III) in aqueous alkaline medium

The oxidation of allyl alcohol by diperiodatoargentate(III) (DPA) is carried out both in the absence and presence of ruthenium(III) catalyst in alkaline medium at 298 K and a constant ionic strength of 1.1 mol dm^?3 was studied spectrophotometrically. The oxidation products in both the cases were acrolein and Ag(I), identified by spectral studies. The stoichiometry is same in both the cases, that is, [AA]/[DPA] = 1:1. The reaction shows first order in [DPA] and has less than unit order dependence each in both [AA] and [Alkali] and retarding effect of [IO] in both the catalysed and uncatalysed cases. The order in [Ru(III)] is unity. The active species of DPA is understood to be as monoperiodatoargentate(III) (MPA) in both the cases. The uncatalysed reaction in alkaline medium has been shown to proceed via a MPA–allyl alcohol complex, which decomposes in a rate determining step to give the products. In catalysed reaction, it has been shown to proceed via a Ru(III)‐allyl alcohol complex, which further reacts with one molecule of MPA in a rate determining step to give the products. The reaction constants involved in the different steps of the mechanisms were calculated for both reactions. The catalytic constant (K_c) was also calculated for catalysed reaction at different temperatures. The activation parameters with respect to slow step of the mechanisms were computed and discussed for both the cases. The thermodynamic quantities were also determined for both reactions. Copyright © 2007 John Wiley & Sons, Ltd.     

Ru(III), Os(VIII), Pd(II) and Pt(IV) catalysed oxidation of glycyl–glycine by sodium N‐chloro‐p‐toluenesulfonamide: comparative mechanistic aspects and kinetic modelling

The Ru(III)/Os(VIII)/Pd(II)/Pt(IV)‐catalysed kinetics of oxidation of glycyl–glycine (Gly‐Gly) by sodium N‐chloro‐p‐ toluenesulfonamide (chloramine‐T; CAT) in NaOH medium has been investigated at 308 K. The stoichiometry and oxidation products in each case were found to be the same but their kinetic patterns observed are different. Under comparable experimental conditions, the oxidation‐kinetics and mechanistic behaviour of Gly‐Gly with CAT in NaOH medium is different for each catalyst and obeys the underlying rate laws:

• Rate = k [CAT]_t [Gly‐Gly]⁰ [Ru(III)][OH^?]^x
• Rate = k [CAT]_t[Gly‐Gly]^x [Os(VIII)]^y[OH^?]^z
• Rate = k [CAT]_t[Gly‐Gly]^x [Pd(II)][OH^?]^y
• Rate = k [CAT]_t[Gly‐Gly]⁰ [Pt(IV)]^x[OH^?]^y

Here, and x, y, z < 1 in all the cases. The anion of CAT, CH₃C₆H₄SO₂NCl^?, has been postulated as the common reactive oxidising species in all the cases. Under comparable experimental conditions, the relative ability of these catalysts towards oxidation of Gly‐Gly by CAT are in the order: Os(VIII) > Ru(III) > Pt(IV) > Pd(II). This trend may be attributed to the different d‐electronic configuration of the catalysts. Further, the rates of oxidation of all the four catalysed reactions have been compared with uncatalysed reactions, under identical experimental conditions. It was found that the catalysed reaction rates are 7‐ to 24‐fold faster. Based on the observed experimental results, detailed mechanistic interpretation and the related kinetic modelling have been worked out for each catalyst. Copyright © 2008 John Wiley & Sons, Ltd.     

Photoinduced electron‐transfer reactions of tris(2,2′‐bipyridine)ruthenium(II)‐based carbonic anhydrase inhibitors tethering plural binding sites

Tris(2,2′‐bipyridine)ruthenium(II) complex‐based carbonic anhydrase (CA) inhibitors, [Ru(bpy)₂(bpydbs)]²⁺ {bpy = 2,2′‐bipyridine and bpydbs = 2,2′‐bipyridinyl‐4,4′‐dicarboxilic acid bis[(2‐{2‐[2‐(4‐sulfamoylbenzoylamino)ethoxy]ethoxy}ethyl)amide]} and [Ru(bpydbs)₃]²⁺, tethering plural benzenesulfonamide groups have been prepared. The CA catalytic activity was effectively suppressed by these synthetic [Ru(bpy)₂(bpydbs)]²⁺ and [Ru(bpydbs)₃]²⁺ inhibitors, and their dissociation constants at pH = 7.2 and at 25°C were determined to be K_I = 0.93 ± 0.02 μM and K_I = 0.24 ± 0.03 μM, respectively. Next, 2 photoinduced electron‐transfer (ET) systems comprising a Ru²⁺‐CA complex and an electron acceptor, such as chloropentaamminecobalt(III) ([CoCl(NH₃)₅]²⁺) or methylviologen (MV²⁺) were studied. In the presence of CA and a sacrificial electron acceptor, such as pentaamminechlorocobalt(III) complex, the photoexcited triplet state of ³([Ru(II)]²⁺)* was quenched through an intermolecular photoinduced ET mechanism. In case of the [Ru(bpydbs)₃]²⁺‐CA‐MV²⁺ system, the photoexcited triplet state of ³([Ru(bpydbs)₃]²⁺)* was quenched by sacrificial quencher through an intermolecular photoinduced ET mechanism, giving the oxidized [Ru(bpydbs)₃]³⁺. Then the following intramolecular ET from the amino acid residue, Tyr6, near the active site of CA proceeded. We observed a transient absorption around at 410 nm, arising from the formation of a Tyr^?+ in the [Ru(bpydbs)₃]²⁺‐CA‐MV²⁺ system. These artificial Ru(II)‐CA systems may clearly demonstrate both intermolecular and intramolecular photoinduced ET reactions of protein and could be one of the interesting models of the ET proteins. Their photophysical properties and the detailed ET mechanisms are discussed in order to clarify the multistep ET reactions.     

IR Spectra of Be(IO3)2.nH2O (n = 4, O) and of the Deuterated Analogue

Abstract

The compounds of beryllium - Be(IO₃)₂.4H₂O, its deuterated analogue and Be(IO₃)₂ were studied by IR-spectroscopy over the range of 200 to 4000 cm^?1.     

Investigation of Europium (III)-Rutin Complex in Water-Ethanolic Solution

Abstract

The composition and the stability constant of Eu(III)-rutin complex were determined by suitable spectrophotometric methods and pH-metric measurements. The formation of a (Eu(C₂₇H₂₆O₁₆H₃)₂)⁺ complex whose concentration stability constant β₂ ranged from 10.59 at pH=5.0 to 7.21 at pH=8.0, was established. Spectrophotometric determination of Eu(III) by means of the reaction of complex formation with rutin, was investigated. It was found that Eu(III) can be determined in the range from 5×10^?6 to 7.5×10^?5M. All investigations were carried out with 70% ethanolic solutions at room temperature (20°C), whereas spectrophotometric investigations were performed in the presence of a buffer, at constant pH values and ionic strength (0.015). The determination of the complex composition was done at pH=5.6, and that of Eu(III) at pH=6.3.     

Mössbauer studies of photochemical reaction products of Ru(bpy)3 2+ iron cyanide double complexes

The reductive and the oxidative electron-transfer photochemical reaction system of light-irradiated the mix solutions of Ru(bpy)₃ ²⁺ with [Fe(CN)₆]^4–, [Fe(CN)₆]^3–, [Fe(CN)₅NO]^2– and PB (Prussian Blue) have been studied. The double complexes which isolated from the precipitates of the photochemical reaction have been identified by means of Mössbauer spectroscopy. In order to clarify the chemical states of these isolated double complexes, we have (prepared and) studied Mössbauer spectra of the double complexes such as [Ru(bpy)₃]₃[Fe(CN)₆]₂.14H₂O, [Ru(bpy)₃]₂[Fe(CN)₆].10H₂O, [Ru(bpy)₃][Fe(CN)₅NO].4H₂O, and [Ru(bpy)₃][PB]₂.xH₂O.     

Synthesis,Characterization, DNA Binding Studies,Photocleavage, Cytotoxicity and Docking Studies of Ruthenium(II) Light Switch Complexes

A new ligand 3-(1H-imidazo[4,5-f][1,10]phenanthrolin-2yl)phenylboronic acid and its (IPPBA) three ruthenium(II) complexes [Ru(phen)₂(IPPBA)](ClO₄)₂ (1), [Ru(bpy)₂(IPPBA)](ClO₄)₂ (2) and [Ru(dmb)₂(IPPBA)](ClO₄)₂ (3) have been synthesized and characterized by elemental analysis, UV/VIS, IR, ¹H-NMR,¹³C-NMR and mass spectra. The binding behaviors of the three complexes to calf thymus DNA were investigated by absorption spectra, emission spectroscopy, viscosity measurements, thermal denaturation and photoactivated cleavage. The DNA-binding constants for complexes 1, 2 and 3 have been determined to be 7.9?×?10⁵ M^?1, 6.7?×?10⁵ M^?1 and 2.9?×?10⁵ M^?1. The results suggest that these complexes bound to double-stranded DNA in an intercalation mode. Upon irradiation at 365 nm, three ruthenium complexes were found to promote the cleavage of plasmid pBR322 DNA from super coiled form ? to nicked form ??. Further in the presence of Co²⁺, the emission of DNA–Ru(ΙΙ) complexes can be quenched. And when EDTA was added, the emission was recovered. The experimental results show that all three complexes exhibited the “on–off–on” properties of molecular “light switch”. The highest Cytotoxicity potential of the complex1 was observed on the Human alveolar adenocarcinoma (A549) cell line. Good agreement was generally found between the spectroscopic techniques and molecular docked model which provides further evidence of groove binding.     

Luminescence properties of lanthanide(III) ions in concentrated carbonate solution

Luminescence properties of lanthanide(III) ions (Ln = Nd, Sm, Eu, Gd, Tb, Dy and Tm) were investigated by measuring the excitation and emission spectra, and emission lifetimes in H₂O and D₂O solutions of 3 moll^?1 K₂CO₃, where anionic tetra-carbonate complexes, [Ln(CO₃)₄]^5- were the predominant species.

Electronic transitions of the carbonato complex corresponding to both the excitation and emission spectra were assigned from the energy level diagrams of Ln(III) and compared with those of the aqua ion. Enhancement of emission intensity of the complex was observed at particular excitation transitions of Eu(III), Gd(III) and Tb(III), and at particular emission transitions of Sm(III), Eu(III), Dy(III) and Tm(III). The enhancement at the emission transition was estimated quantitatively as a branching ratio from the lowest emitting state of Ln(III), and discussed in terms of hypersensitivity.

Emission lifetimes of the carbonato complexes were all longer than those of aqua ions in H₂O solution, while the lifetimes of the complexes for Eu(III) and Tb(III) shorter than those in D₂O solution. The difference in non-radiative decay constants for the excited complex in H₂O and D₂O solutions was found to be proportional to an exponential of the energy gap of Ln(III). The lifetime ratio between the H₂O and D₂O solutions showed the order of Sm > Dy > Eu > Tb, corresponding to the opposite order of the energy gap. These were discussed in terms of an energy gap law, i.e. a relationship between the energy gap of Ln(III) and vibration energies of the ligand or water molecules.     

Self‐assembly of a [2]pseudorotaxane complex by the threading of a nitrobenzimidazol‐based guest on dibenzo‐24‐crown ether host

A new derivative of the previously reported 1,2‐bis(benzimidazol‐2‐yl)ethane motif, cation [1H₂]²⁺, was synthesized under microwave irradiation and fully characterized by solution NMR, high‐resolution mass spectrometry, cyclic voltammetry and X‐ray crystallography. This cation presents a linear geometry and incorporates nitro substituents as electrochemical handles. In solution, cation [1H₂]²⁺, is capable of threading the cavity of dibenzo‐24‐crown‐8 ether host (DB24C8) giving rise to a [2]pseudorotaxane complex [1H₂?DB24C8]²⁺, regardless of the counterion, [CF₃SO₃]^? or [CF₃COO] ^?. The interpenetrated structure of [1H₂?DB24C8]²⁺ was proven by solution NMR and X‐ray crystallography. This host–guest complex is held together by several non‐covalent interactions, such as hydrogen bonding and ion‐dipole. An electrochemical study of [1H₂]²⁺ in the presence of variable amounts of DB24C8 was performed; due to the irreversible redox behavior of cation [1H₂]²⁺, it was not possible to electrochemically control the association/dissociation process with DB24C8. Copyright © 2014 John Wiley & Sons, Ltd.     

Chemical tuning of high-spin complexes based on 3- and 4-hydroxy-pentadentate-Fe (III) complex-units investigated by Mössbauer spectroscopy

The pentadentate ligands 3-OH-⁵L?=?[N,N′-Bis(1,3-dihydroxy-2-benzylidene)-1,7-diamino-4-azaheptane] and 4-OH-⁵L?=?[N,N′-Bis(1,4-dihydroxy-2-benzylidene)-1,7-diamino-4-azaheptane] has been prepared by a Schiff base condensation between 1,7-diamino-4-azaheptane and the dihydroxybenzaldehyde. Complexation with Fe(III) yields high-spin (S?=?5/2) complexes of [Fe^III(3-OH-⁵L)Cl] and [Fe^III(4-OH-⁵L)Cl]. These precursors were combined with [M(CN) _x ] ^y? (M?=?W(IV), Mo(IV), Ru(II), Co(III)) and heptanuclear and nonanuclear clusters of [M{(CN-Fe^III(3-OH-⁵L)} _x ]Cl _y and [M{(CN-Fe^III(4-OH-⁵L)} _x ]Cl _y resulted. Such starshaped hepta- and nonanuclear compounds are high-spin systems at room temperature. On cooling to 10 K some of the iron(III) centers switch to a second high-spin state as proven by Mössbauer spectra, i.e. multiple electronic transitions. Parts of the compounds perform a high-spin to high-spin transition.     

Calix Receptor Edifice; Scrupulous Turn Off Fluorescent Sensor for Fe(III), Co(II) and Cu(II)

Novel Supramolecular fluorescence receptor derived from calix-system i.e. calix[4]resorcinarene bearing dansylchloride as fluorophore was designed and synthesized. The compound was purified by column chromatography and characterized by elemental analysis, NMR and Mass spectroscopy. Tetradansylated calix[4] resorcinarene (TDCR) shows a boat conformation with C₂v symmetry. The complexation behaviour of metal cations [Ag(I), Cd(II), Co(II), Fe(III), Hg(II), Cu(II), Pb(II), Zn(II), U(VI) (1?×?10^-4?M)] with tetra dansylated calix[4]resorcinarene (1?×?10^-6?M) was studied by spectophotometry and spectrofluorometry. Red shift in the absorption spectra led us to conclude that there is strong complexation Fe(III), Co(II) and Cu(II) with TDCR. These metal cations also produce quenching with red shifts in the emission spectra. The maximum quenching in emission intensity was observed in the case of Fe(III) and its binding constant was also found to be significantly higher than that of Co(II) and Cu(II). Quantum yield of metal complexes of Fe(III) was found to be lower in comparison with Co(II) and Cu(II) complexes. Stern Volmer analysis indicates that the mechanism of fluorescence quenching is either purely dynamic, or purely static.     

Characterization of Ir(ppy)3 and [Ir(ppy)2 bpy]+ by infrared,Raman spectra and surface‐enhanced Raman scattering

The Raman and infrared spectra of fac ‐tris(2‐phenylpyridinato‐N,C2′)iridium(III), Ir(ppy)₃ and surface‐enhanced resonance Raman spectra of bis(2‐phenyl pyridinato‐) (2,2′bipyridine) iridium (III), [Ir(ppy)₂ (bpy)]⁺ cation were recorded in the wavenumber range 150–1700 cm⁻¹, and complete vibrational analyses of Ir(ppy)₃ and [Ir(ppy)₂ (bpy)]⁺ were performed. Most of the vibrational wavenumbers were calculated with density‐functional theory agree with experimental data. On the basis of the results of calculation and comparison of the spectra of both complexes and their analogue [Ru(bpy)₃]²⁺, we assign the vibrational wavenumbers for metal–ligand modes; metal–ligand stretching wavenumbers are 277/307 and 261/236 cm⁻¹ for Ir(ppy)₃, and 311/324, 257/270, 199/245 cm⁻¹ for [Ir(ppy)₂ bpy]⁺. Surface‐enhanced Raman scattering spectra of [Ir(ppy)₂ bpy]²⁺ were measured at two wavelengths on the red and blue edges of the low‐energy metal‐to‐ligand charge‐transfer band. According to the enhanced Raman intensities for the vibrational modes of both ligands ppy and bpy, the unresolved charge‐transfer band is deduced to consist of charge‐transfer transitions from the triplet metal to both ligands ppy and bpy. Copyright © 2010 John Wiley & Sons, Ltd.     

Structural Investigation and Photoluminescent Properties of Gadolinium(III), Europium(III) and Terbium(III) 3-Mercaptopropionate Complexes

This work reports on the synthesis, crystallographic determination and spectroscopic characterization of gadolinium(III), terbium(III) and europium(III) 3-mercaptopropionate complexes, aqua-tris(3-mercaptopropionate)lanthanide(III) - [Ln(mpa)₃(H₂O)]. The Judd-Ofelt intensity parameters were experimentally determined from emission spectrum of the [Eu(mpa)₃(H₂O)]complex and they were also calculated from crystallographic data. The complexes are coordination polymers, where the units of each complex are linked together by carboxylate groups leading to an unidimensional and parallel chains that by chemical interactions form a tridimensional framework. The emission spectrum profile of the [Eu(mpa)₃(H₂O)] complex is discussed based on point symmetry of the europium(III) ion, that explains the bands splitting observed in its emission spectrum. Photoluminescent analysis of the [Gd(mpa)₃(H₂O)] complex show no efficient ligand excitation but an intense charge transfer band. The excitation spectra of the [Eu(mpa)₃(H₂O)] and [Tb(mpa)₃(H₂O)] complexes do not show evidence of energy transfer from the ligand to the excited levels of these trivalent ions. Therefore the emission bands are originated only by direct f-f intraconfigurational excitation of the lantanide(III) ions.     

Complexes based on ethylene- and propylene-bridged-pentadentate-Fe(III)-units allow interplay between magnetic centers and multistability investigated by Mössbauer spectroscopy

The propylene-based ⁵3,3-L?=?[N,N′-Bis(1-hydroxy-2-benzylidene)-1,7-diamino-4-azaheptane] and ethylene-based pentadentate ligand ⁵2,2-L?=?[N,N′-Bis(1-hydroxy-2-benzylidene)-1,5-diamino-3-azapentane] has been prepared. Complexation with Fe(III) yields high-spin (S?=?5/2) complexes of [Fe^III(⁵2,2-L)Cl] and [Fe^III(⁵3,3-L)Cl]. Such precursors were combined with [M(CN) _x ] ^y? (M?=?W(IV), Mo(IV), Ru(II), Co(III)) and heptanuclear and nonanuclear clusters of [M{(CN-Fe^III(⁵2,2-L)} _x ]Cl _y and [M{(CN-Fe^III(⁵3,3-L)} _x ]Cl _y resulted. Such starshaped hepta- and nonanuclear compounds are high-spin systems at room temperature. On cooling to 20 K in all presented ethylene compounds the iron(III) centers switch to a second high-spin state as proven by Mössbauer spectra with a yield of about 30%, i.e., multiple electronic transitions. The propylene compounds, however, perform a high-spin to low-spin transition. Mössbauer spectra taken during green light irradiation indicate changes in the population of the different electronic states, i.e. concerted inorganic reaction.     

Synthesis,characterization, luminescence properties and antioxidant activity of Ln(III) complexes with a new aryl amide bridging ligand

A novel Aryl amide ligand H₂L and its eight complexes, [LnH₂L(NO₃)₂·H₂O]NO₃ [Ln=Sm(III), Er(III), Tb(III), Dy(III), La(III), Gd(III), Nd(III), and Pr(III)], are presented. The ligand and complexes were synthesized and characterized based on elemental analyses, molar conductance, IR, ¹H and ¹³C-NMR, UV–VIS., and TGA studies. The conductivity data show a 1:1 electrolytic nature with a general formula [LnH₂L(NO₃)₂·2H₂O]NO₃ The IR spectra reveal coordination of the ligand through the azomethine nitrogen and the phenolic hydroxyl of the ligand to the lanthanide ion. The coordinated nitrate ions behave in a bidentate fashion. The thermal decomposition studies indicate the presence of two water molecules in the inner coordination sphere. Under the excitation at 319 nm, the luminescence emission properties for Sm, Tb, and Dy complexes are observed. These observations show that the ligand favors energy transfers to the emitting energy level of these lanthanide ions. Furthermore, the antioxidant activity of the ligand and its Ln(III) complexes was determined by DPPH radical scavenging method, which indicates that the Ln(III) complexes exhibit more effective antioxidant activity than the ligand alone.     

High-frequency and -field electron paramagnetic resonance of high-spin manganese(III) in axially symmetric coordination complexes

High-frequency and -field electron paramagnetic resonance (HFEPR) has been used to study several complexes of high-spin manganese(III) (3d⁴,S = 2): [Mn(Me₂dbm)X] and [Mn(OEP)X] (X = Cl^?, Br^?), where Me₂dbm^? is the anion of 4,4′-dimethyldibenzoylmethane and OEP^2? is the dianion of 2,3,7,8,12,13,17,18-octaethylporphine. These non-Kramers (integer spin) systems are not EPR-active with conventional magnetic fields and microwave frequencies. However, use of fields up to 15 T in combination with multiple frequencies in the range of 95–550 GHz allows observation of richly detailed EPR spectra. Analysis of the field- and frequency-dependent HFEPR data allows accurate determination of the following spin Hamiltonian parameters for these complexes: [Mn(Me₂dbm)Cl],D = ?2.45(3) cm^?1; [Mn(Me₂dbm)Br],D = ?1.40(2) cm^?1; [Mn(OEP)Cl],D = ?2.40(1) cm^?1; [Mn(OEP)Br],D = ?1.07(1) cm^?1 (E ≈ 0, andg ≈ 2.0 in all cases). Comparison of structural data with the electronic parameters for these and related complexes shows quantitatively the effects of axial and equatorial ligation on the electronic structure of Mn(III). These high-spin complexes can be employed as building blocks in the construction of single-molecule magnets. Thus the accurate determination and understanding of the electronic properties, best obtainable by HFEPR, of these monomeric units is important in understanding and improving the properties of the polynuclear single-molecule magnets which can be formed from them.     

Luminescent Sensor for Carbonate Ion Based on Lanthanide(III) Complexes of 1,4,7,10-Tetraazacyclododecane-1,4,7-Triacetic Acid (DO3A)

Lanthanide(III) complexes of 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (H₃DO3A) are suggested as sensors for sensitive luminescence-based determination of a carbonate anion. Thermodynamic study of association of [Eu(H₂O)₂(DO3A)] with bidentate anionic ligands using luminescence spectroscopy reveals an affinity order CO ₃ ^2? > oxalate^2? > picolinate^? > phthalate^2? ≈ citrate^3?; presumably as a consequence of an increasing chelate ring size. The ternary [Eu(DO3A)(picolinate)]^? and [Tb(DO3A)(picolinate)]^? complexes show improved photophysical properties due to the antenna effect of the picolinate anion. High quenching effect of carbonate anion and, to a lesser extent also oxalate, enables construction of a linear calibration plot utilizing optimized experimental conditions (e.g. c _LnL?=?0.1 mM, c _picolinate?=?2–5 mM, pH?=?7.4, λ _exc?=?286 nm, etc.) for carbonate determination in solution. Both sensors show a comparable sensitivity and the detection limit of about 0.4 mM. In order to improve the photophysical properties of Ln(III) sensor by shift of excitation wavelength about 40 nm to VIS range, the isoquinoline-3-carboxylic acid (IQCA) as antenna ligand was employed instead of picolinic acid. The analysis of commercial samples of European mineral waters was carried out and they were compared to the results obtained by capillary isotachophoresis to confirm there is no inherent (systematic) error to the present analysis. The Ln(III) sensor with IQCA is recommended since it has a better robustness than that with picolinate. The present analytical method is simple and rapid, and it is useful for sensitive determination of bicarbonate/carbonate concentration in water samples under aerobic conditions.     

EPR investigation of the spin-spin interactions in a Cu(II)-Gd(III)-Fe(III) heterospin system

The spin-spin interactions in a system that contains three different spin carriers, [{LCu}Gd(H₂O)₃×{Fe(CN)₆}] _n ·4nH₂O (1) [L²⁻, N,N-propylenedi(3-methoxysalicylideneiminato)], were investigated by electron paramagnetic resonance spectroscopy. Additional information was obtained by analyzing the discrete heterobinuclear system [LCu(OH₂)Gd(O₂NO)₃] (2), which contains the Cu(II)-Gd(III) pair also existing in the structure of 1, and the compounds [{LCu}Gd(H₂O)₃{Co(CN)₆}] _n ·3.5nH₂O and [{LCu}La(H₂O)₃×{Fe(CN)₆}] _n ·4nH₂O, which are isostructural with 1 and in which the paramagnetic low-spin Fe(III) and Gd(III) ions were replaced by diamagnetic low-spin Co(III) and La(III), respectively. The investigations were carried out in the temperature range of 293–4 K in both X- and Q-bands and also using a dual-mode X-band. The experimental spectra of the Cu(II)-Gd(III) pairs in 2 were interpreted as the sum of spectra of the ground spin state with total S = 4 and the excited state with S = 3 appearing due to the ferromagnetic exchange interaction between Cu(II) and Gd(III) ions. By fitting the experimental and simulated spectra, the zero-field splitting parameters of the Gd(III) ion are estimated and it is shown that no influence of the anisotropic interaction is detected. The magnetic properties of 1 are discussed from the perspective of the interaction of the Cu(II)-Gd(III) binuclear fragments with the Fe(III) ions.     

The nature of the effect of Gd(III) on fluorescence of Ln(III) chelates in water solutions

The intensity of fluorescence of Eu(III) and Sm(III) ions sensitized by molecules of n-benzoyltrifluoroacetone and 1,10-phenanthroline introduced in a water solution in a ratio of 3: 1 is studied as a function of the ion concentration in the solution. The comparison of the fluorescence decay curves of Eu(III) and Sm(III) in D₂O and H₂O (pH≥7) solutions containing 10^?4 M of n-Cl-BTFA and 3×10^?5 M of 1,10-phen and the values of τ_fl of Sm(III) in themselves (51–90 μs) are indicative of an insignificant content of water molecules in the first coordination sphere of ions. The effect of other ions on I _fl and τ_fl of Eu(III) ions is studied under these conditions. The intensity of fluorescence of Eu(III) in solutions of 10^?4 M Cl-BTFA and 3×10^?5 H 1,10-phen is found to increase by 1–2 orders of magnitude in the presence of Y(III) and Gd(III) ions, and the magnitude of this effect is unaffected by deoxygenation of the solution. The introduction of a third ion Nd(III) in the solution is shown to attenuate the influence of Gd(III) on I _fl of Eu(III) for Nd(III) concentrations commensurable with the Eu(III) concentration in the solution. The strength of the influence of Gd(III) ions on I _fl of Eu(III) is found to depend on the method of preparation of the solution. The analysis of the results obtained testifies that inhomogeneities consisting of chelates of lanthanide ions displaced from the water structure appear in water. The presence of these inhomogeneities results in efficient energy transfer from ligands of Gd(III) chelates to Eu(III) chelates, which is the reason for the increasing I _fl of Eu(III). The possibility of using data on the enhancement of I _fl of Eu(III) in the presence of Gd(III) and on the reduction of τ_fl of Eu(III) in the presence of Nd(III) for estimating dimensions and structures of displaced systems is discussed.     

A Mechanism of the influence of Gd(III) and other Ln(III) ions on sensitized luminescence of Eu(III) and Tb(III) ions in aqueous and ethanol solutions: The role of hydroxyl bridges

We studied sensitization of Eu(III) and Tb(III) ions by molecules of 1,10-phenanthroline and 2,2-bipyridil in D₂O and d ₆-ethanol and the influence of Nd(III), Pr(III), Sm(III), Gd(III), and Ho(III) ions on the luminescence intensity I _lum and lifetime τ_lum of Eu(III) and Tb(III) in solutions. The stability constants of complexes of Eu(III) and Gd(III) with 2,2′-bipyridil are measured by spectrophotometric and luminescence methods. It is shown that luminescence of Eu(III) is quenched by Gd(III) ions at the ion concentration equal to 10^?2–10^?1 M, which is caused by competing between these ions for a sensitizer. At the concentration of Ln(III) ions equal to 10^?6?10^?3 M, the sensitized luminescence of Eu(III) and Tb(III) was quenched and τ_lum decreased in the presence of Nd(III) ions, whereas in the presence of Gd(III) the luminescence intensity increased. It is proved that a bridge that connects the two ions upon energy transfer is formed by hydroxyl groups. The intensity of luminescence of Eu(III) and Tb(III) in aqueous solutions and its lifetime decreased in the presence of hydroxyl groups, while upon addition of Gd(III) to these solutions these quantities were restored. We also found that the addition of Gd(III) to deoxygenated ethanol solutions of 2,2′-bipyridil and Eu(III) slows down photochemical and thermal reactions between bipyridil and Eu(III), resulting in the increase in the luminescence intensity of Eu(III).