Spectroscopic Investigation on Sonocatalytic Damage of BSA Molecules by FeIII Complexes with Binary Organic Acid Ligands Under Ultrasonic Irradiation

The interaction between bovine serum albumin (BSA) and Fe^III complexes with three binary organic acid (biorga) ligands, [Fe^III(oxa)(H₂O)₄]⁺ (oxa = oxalic acid), [Fe^III(pra)(H₂O)₄]⁺ (pra = propanedioic acid) and [Fe^III(sua)(H₂O)₄]⁺ (sua = succinic acid), as well as the sonocatalytic damage of BSA in the presence of these three Fe^III–biorga complexes under ultrasonic irradiation, were studied by UV–vis and fluorescence spectra. The experimental results show that the fluorescence quenching process of BSA caused by three Fe^III–biorga complexes are all static quenching and the corresponding quenching rate constants (K _q), equilibrium constants (K _A) and the binding site numbers (n) were calculated. The results reveal that, under ultrasonic irradiation, the BSA molecules were obviously damaged by these Fe^III–biorga complexes. In addition, the effects of several factors on the damage of BSA molecules were examined. The experimental results demonstrate that the damage degree of BSA increased with an increase of ultrasonic irradiation time, Fe^III–biorga complex concentration, and ionic strength. In comparison, [Fe^III(pra)(H₂O)₄]⁺ exhibited higher sonocatalytic activity than [Fe^III(oxa)(H₂O)₄]⁺ and [Fe^III(sua)(H₂O)₄]⁺. Finally, the extent of generation of $ \cdot {\text{O}}_{2}^{ - } $ · O 2 ? and ·OH during sonocatalytic processes was estimated. Perhaps, the results will be significant for promoting sonodynamic treatment (SDT) of tumors at the molecular level.     

The Effect of Concentration Parameters on Complexation in the Iron(0)–Iron(II)–Glycine–Water System

The processes of formation of iron(II) complexes in aqueous glycine solutions in the pH range of 1.0–8.0 at 298 K and ionic strength of 1 mol/L (NaClO₄) are studied using Clark and Nikolskii’s oxidation potential method. The type and number of coordinated ligands, the nuclearity, and the total composition of the resulting complexes are determined. The following complex species are formed in the investigated system: [Fe(OH)(H₂O)₅]⁺, [FeHL(H₂O)₅]²⁺, [Fe(HL)(OH)(H₂O)₄]⁺, [Fe(OH)₂(H₂O)₄]⁰, [Fe₂(HL)₂(OH)₂(H₂O)₈]²⁺, and [Fe(HL)₂(H₂O)₄]²⁺. Their formation constants are calculated by the successive iterations method using Yusupov’s theoretical and experimental oxidation function. The model parameters of the resulting coordination compounds are determined.     

Solution equilibria and antitumor activities of pentamethylcyclopentadienyl rhodium complexes of picolinic acid and deferiprone

Complex formation processes of rhodium(III)-η⁵-pentamethylcyclopentadienyl cation [RhCp*(H₂O)₃]²⁺ with 1,2-dimethyl-3-hydroxy-pyridin-4(1H)-one (deferiprone, dhp) and pyridine-2-carboxylic acid (pic) were studied with the aid of pH-potentiometry, ¹H NMR, and UV–Visible spectrophotometry in aqueous solution in the presence and absence of chloride ions. Stoichiometry and overall stability constants of the complexes formed were determined. Formation of mononuclear, monoligand complexes such as [RhCp*(L)Z] (where L = dhp or pic; Z = Cl^? or H₂O) and mixed hydroxido species [RhCp*(L)(OH)] were found. Relatively high pK_a values (9.32–11.90) were determined for the hydrolysis of the [RhCp*(L)Z] complexes. [RhCp*(L)Z] species predominate at physiological pH and negligible decomposition is probable only at low micromolar concentrations. More favored complex formation was found in the case of pic. Stability of the studied organorhodium complexes was compared with analogous Ru(II)(η⁶-p-cymene) compounds. In addition, the aqua/chlorido ligand replacement reaction in [RhCp*(L)(H₂O)]⁺ of dhp and pic was monitored to provide equilibrium constants with which the extent of aquation at various chloride concentrations can be estimated. Single crystals of [RhCp*(dhp)Cl] suitable for X-ray diffraction analysis were also obtained. The [RhCp*(L)Cl] complexes of dhp and pic were tested for cytotoxicity in various human cancer cell lines where they showed activity depending on the attached ligand scaffold.     

Kinetics and mechanism of the oxidation of tris(2,2′-bipyridine)iron(II) and tris(1,10-phenanthroline)iron(II) complexes by nitropentacyanocobaltate(III) in acidic aqueous medium

The kinetics of the oxidation of tris(2,2′-bipyridyl)iron(II) and tris(1,10-phenanthroline)iron(II) complexes ([Fe(LL)₃]²⁺, LL = bipy, phen) by nitropentacyanocobaltate(III) complex [Co(CN)₅NO₂]^3? was investigated in acidic aqueous solutions at ionic strength of I = 0.1 mol dm^?3 (HCl/NaCl). The reactions were carried out at fixed acid concentration ([H⁺] = 0.01 mol dm^?3) and the temperature maintained at 35.0 ± 0.1 °C. Spectroscopic evidence is presented for the protonated oxidant. Protonation constants of 360.43 and 563.82 dm³ mol^?1 were obtained for the monoprotonated and diprotonated Co(III) complexes respectively. Electron transfer rates were generally faster for [Fe(bipy)₃]²⁺ than [Fe(phen)₃]²⁺. The redox complexes formed ion-pairs with the oxidant with increasing concentration of the oxidant over that of the reductant. Ion-pair constants for these reaction were 160.31 and 131.9 dm³ mol^?1 for [Fe(bipy)₃]²⁺ and [Fe(phen)₃]^2+, respectively. The activation parameters measured for these systems have values as follows: ?H ^≠ (kJ K^?1 mol^?1) = +113.4 ± 0.4 and +119 ± 0.3; ?S ^≠ (J K^?1) = +107.6 ± 1.3 and 125.0 ± 1.6; ?G ^≠ (kJ K^?1) = +81 ± 0.4 and +82.4 ± 0.4; and E _a (kJ mol^?1) = 115.9 ± 0.5 and 122.3 ± 0.6 for LL = bipy and phen, respectively. Effect of added anions (Cl^?, $ {\text{SO}}_{4}^{2 - } $ and $ {\text{ClO}}_{4}^{ - } $ ) on the systems showed decrease in the electron transfer rate constant. An outer-sphere mechanism is proposed for the reaction.     

DNA Binding and Equilibrium Investigation of the Interaction of a Model Pd(II) Complex with Some Selected Biorelevant Ligands

The Pd(DAP)Cl₂ complex, where DAP is 2,6-diaminopyridine, was synthesized and characterized. The stoichiometries and stability constants of the complexes formed between various biologically relevant ligands (amino acids, amides, DNA constituents, and dicarboxylic acids) and [Pd(DAP)(H₂O)₂]²⁺ were investigated at 25 °C and at constant 0.1 mol·dm^?3 ionic strength. The concentration distribution diagrams of the various species formed were evaluated. A further investigation of the binding properties of the diaqua complex [Pd(DAP)(H₂O)₂]²⁺ with calf thymus DNA (CT-DNA) was investigated by UV–Vis spectroscopy. The intrinsic binding constants (K _b) calculated from UV–Vis absorption studies is 1.04 × 10³ mol·dm^?3. The calculated (K _b) value was found to be of lower magnitude than that of the classical intercalator EB (ethidium bromide) (K _b = 1.23 (±0.07) × 10⁵ mol·dm^?3), suggesting an electrostatic and/or groove binding mode for the interaction with CT-DNA.     

Complex formation of iron (III) with chrome azurol s

The complex formation of iron(IIl) with 3”-sulpho-2”,6”-dichloro-3,3'-dimethyl-4'-hydroxy-fuchson-5,5'-dicarboxylic acid (chrome azurol S) was studied by spectrophotometric, conductometric and potentiometric methods. The pure tetrabasic acid of the ligand was prepared from the impure trisodium salt (commercially availalile), and the dissociation constants of the ligand were redetermined. At 20° ± 1° and in the presence of 0.10 M potassium chloride the dissociation constants were: pk₁ < 0.0, pk₂ = 2.25 ± 0.05, pk₃ = 4.71 ± 0.03 and pk₄ = 11.81 ± 0.03.In the pH range 2–4, four complexes were detected (the absolute stability constants at 20° ± 5° and at an ionic strength of 0.10 M are given in parentheses) : a ring-formed dimer complex [Fe(H₂O)₂]₂Ch₂^2- (log k_2,2 = 36.2); a monomer of composition [Fe(H₂O)₄]HCh or [Fe(H₂O)₄]HCh^- (the absolute stability constant was calculated as log k_1,1 = 15.6 for the latter composition); a complex [Fe(H₂O)₄]₂Ch²⁺ (log k_3.1=20.2) and, finally, a complex of composition [Fe(H₂O)₂]H_xCh₂^x-5 (the value of x being unknown). In addition, hydroxo complexes of the dimer were formed at higher pH values.     

Speciation studies of mono- and binuclear Pd(II) complexes involving mixed nitrogen–sulfur donor ligand and 4,4′-bipiperidine as a linker

Pd(MME)Cl₂ complex, where MME = methionine methyl ester, was synthesized and characterized by elemental analysis and spectroscopic techniques. [Pd(MME)(H₂O)₂]²⁺ interacts with some DNA constituents giving 1 : 1 and 1 : 2 complexes. The binuclear complexes having 4,4′-bipiperidine as a linker and involving [Pd(MME)(H₂O)₂]²⁺ and DNA constituents were investigated. The results show formation of [(H₂O)(MME)Pd(Bip)Pd(MME)(H₂O)]⁴⁺. Inosine, uracil, and thymine interact with the previously mentioned complex by substitution of the two coordinated water molecules. Formation constants of all possible mono- and binuclear complexes were determined and their speciation diagrams were evaluated.     

Electron transfer mechanism for the oxidation of ternary N-(2-acetamido)iminodiacetatocobaltate(II) complexes involving succinate and maleate as secondary ligands by periodate

The kinetics of oxidation of the ternary complexes [Co^II(ADA)(Su)(H₂O)]^2? and [Co^II(ADA)(Ma)(H₂O)]^2? (ADA?=?N-(2-acetamido)iminodiacetate, Su?=?succinate and Ma?=?maleate) by periodate have been investigated spectrophotometrically at 580?nm under pseudo-first-order conditions in aqueous medium over 30?C50?°C range, pH 3.72?C4.99, and I?=?0.2?mol?dm^?3. The kinetics of the oxidation of [Co^II(ADA)(Su)(H₂O)]^2? obeyed the rate law d[Co^III]/dt?=?[Co^II(ADA)(Su)(H₂O)]^2?[H₅IO₆] {k ₄ K ₅?+?(k ₅ K ₆ K ₂/[H⁺)}, and the kinetics oxidation of [Co^II(ADA)(Ma)(H₂O)]^2? obeyed the rate law d[Co^III]/dt?=?k ₁ K ₂[Co^II] _T [I^VII] _T /{1?+?([H⁺]/K ₇)?+?K ₂[I^VII] _T }. The pseudo-first-order rate constant, k _obs, increased with increasing pH, indicating that the hydroxo form of maleate complex, [Co^II(ADA)(Ma)(OH)]^3?, is the reactive species. The initial Co(III) products were slowly converted to the final products, fitting an inner-sphere mechanism. Thermodynamic activation parameters were calculated using the transition state theory equation. The initial cobalt(II) complexes were characterized by physicochemical and spectroscopic methods.     

Investigation on sonocatalytic damage of BSA under ultrasonic irradiation by Fe<Superscript>III</Superscript> complexes with some aminocarboxylic acid

The interaction of BSA and Fe^III complexes ([Fe^III(gly)(H₂O)₄]²⁺, [Fe^III(ida)(H₂O)₃]⁺, and [Fe^III(nta)(H₂O)₂], gly—glyane, ida—iminodiacetic acid, nta—triglycolamic acid) as well as the sonocatalytic damage to BSA was studied by UV-vis and fluorescence spectra. In addition, the influences of ultrasonic irradiation time and Fe^III complex concentration were also examined on the sonocatalytic damage to BSA. The results showed that the fluorescence quenching of BSA solution caused by the Fe^III complexes belonged to the static quenching process. The BSA and Fe^III complexes interacted with each other mainly through weak interaction and coordinate actions. The binding association constants (K) and binding site numbers (n) were calculated. The results were as follows: K ₁ = 0.5353 × 10⁴ l mol⁻¹ and n ₁ = 0.9812 for [Fe^III(gly)(H₂O)₄]²⁺, K ₂ = 1.4285 × 10⁴ l mol⁻¹ and n ₂ = 1.0899 for [Fe^III(ida)(H₂O)₃, and K ₃ = 0.4411 × 10⁴ l mol⁻¹ and n ₃ = 0.9471 for [Fe^III(nta)(H₂O)₂]. Otherwise, under ultrasonic irradiation the BSA were obviously damaged by the Fe^III complexes. The damage degree rose up with the increase of ultrasonic irradiation time and Fe^III complex concentration. And that, [Fe^III(nta)(H₂O)₂] exhibited in a way higher sonocatalytic activity than [Fe^III(gly)(H₂O)₄]²⁺ and [Fe^III(ida)(H₂O)₃]⁺.     

Synthesis and spectroscopic studies of 2,5-hexanedione bis(isonicotinylhydrazone) and its first raw transition metal complexes

New VO²⁺, Mn²⁺, Co²⁺, Ni²⁺ Cu²⁺ and Zn²⁺ complexes of 2,5-hexanedione bis(isonicotinylhydrazone) [H₂L] have been synthesized and characterized. The analyses confirmed the formulae: [VO(L)]·H₂O, [Mn₂(H₂L)Cl₂(H₂O)₆]Cl₂, [Co(L)(H₂O)₂]·2H₂O, [Ni(HL)(OAc)]·H₂O, [Cu(L)(H₂O)₂]·2H₂O, [Cu(L)]·2H₂O and [Zn(L)(H₂O)₂]. The formulae of [Ni(HL)(OAc)]·H₂O, [Zn(L)(H₂O)₂] and [Mn₂(H₂L)Cl₂(H₂O)₆]Cl₂, are supported by mass spectra. The molecular modeling of H₂L is drawn and showed intramolecular hydrogen bonding. The ligand releases two protons during reaction from the two amide groups (NHCO) and behaves as a binegative tetradentate (N₂O₂); good evidence comes from the ¹H NMR spectrum of [Zn(L)(H₂O)₂]. The ligand has a buffering range 10–12 and pK's of 4.62, 7.78 and 9.45. The magnetic moments and electronic spectra of all complexes provide a square-planar for [Cu(L)]·2H₂O, square-pyramidal for [VO(L)]·H₂O and octahedral for the rest. The ESR spectra support the mononuclear geometry for [VO(L)]·H₂O and [Cu(L)(H₂O)₂]·2H₂O. The thermal decomposition of the complexes revealed the outer and inner solvents where the end product in most cases is metal oxide.     

Synthesis,X-ray structure,DFT and thermodynamic studies of mono- and binuclear palladium(II) complexes involving 1,4-bis(2-hydroxyethyl)piperazine,bio-relevant ligands and 4,4′-bipiperidine

[Pd(BHEP)Cl₂] (BHEp = 1,4-bis(2-hydroxyethyl)piperazine) was synthesized and characterized. The palladium center has a typical square-planar geometry with a tetrahedral distortion. The alcohol groups of the ligand do not participate in binding to Pd(II). The DFT/B3LYP method was used for geometric optimization of the ligand and the complex using the Gaussian 09 program and compared with experimental results. The stoichiometry and stability constants of the complexes formed between [Pd(BHEP)(H₂O)₂]²⁺ and some selected amino acids, peptides, and DNA constituents were investigated at 25 °C and 0.1 M ionic strength. The binuclear complex [(H₂O)(BHEP)Pd(Bip)Pd(BHEP)(H₂O)]⁴⁺ was detected, where Bip = 4,4′-bipiperidine. Inosine, uracil, and thymine interact with the binuclear complex via substitution of both coordinated water molecules. The potentiometric results were complimented by spectroscopic measurements. The concentration distribution diagrams of the various species formed were evaluated.     

Thermal decomposition and biological activity studies of some transition metal complexes derived from mixed ligands sparfloxacin and glycine

The synthetic method of novel ternary M(II)/(III)/(IV) complexes, with fluoroquinolone drug sparfloxacin (HSFX) and glycine (HGly) containing nitrogen and oxygen donor ligand have been synthesized and characterized. The prepared complexes fall into stoichiometric formulae of [M(SFX)(Gly)(H₂O)₂]Cl (M = Cr(III) and Fe(III), [M(SFX)(Gly)(H₂O)₂] (M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and UO₂(II) and [Th(SFX)(Gly)(H₂O)₂]Cl₂. The chelate rings are six-membered and six coordinate with 1:1:1 [M]:[SFX]:[Gly]. The important bands in the IR Spectra and main ¹H NMR signals are tentatively assigned and discussed in relation to the predicted molecular structure. The IR data of the HSFX and HGly ligands suggested the existing of a bidentate binding involving carboxylate O and carbonyl O for HSFX ligand and amino N and carboxylate O atoms for HGly ligand. The coordination geometries and electronic structures are determined from the diffused reflectance spectra and magnetic moment measurements. The complexes exist in octahedral form. The complexes decomposed in four to six steps within the temperature range 30–1,000 °C with metal oxides as residues of decomposition. The decomposition steps are accompanied by endothermic or exothermic peaks in the DTA. The HSFX drug, HGly and metal complexes have been screened for their in vitro antibacterial activities against Staphylococcus aureus and Escherichia coli, and antifungal activities against Aspergillus niger and Candida albicans by MIC method. The metal complexes were found to have higher antimicrobial activity than the HSFX drug and HGly ligand and their activity are comparable with the antibacterial and antifungal standards.     

Kinetics and mechanism of oxidation of iodide with a (μ‐oxo)diiron(III,III) complex in weakly acidic media

The complex ion [Fe^III₂(μ‐O)(phen)₄(H₂O)₂]⁴⁺ ( 1 ) (phen = 1,10‐phenanthroline) and its hydrolytic derivatives [Fe^III₂(μ‐O)(phen)₄(H₂O)(OH)]³⁺ ( 1a ) and [Fe^III₂(μ‐O)(phen)₄‐ (OH)₂]²⁺ ( 2a ) coexist in rapid equilibria in the range pH 4.23–5.35 in the presence of excess phenanthroline (pK_a1 = 3.71±0.03, pK_a2 = 5.28± 0.07). The solution reacts quantitatively with I⁻ to produce [Fe(phen)₃]²⁺ and I₂. Only 1 but none of its hydrolytic derivatives is kinetically active. Both inner and outer sphere pathways operate. The observed rate constants show second‐order dependence on the concentration of iodide, while the dependence on [H⁺] is complex in nature. Added Cl⁻ inhibits the formation of adduct with I⁻ and thus retards the rate of inner sphere path, leading to a rate saturation at high [Cl⁻], where only the outer sphere mechanism is active. Kinetic data indicate that simultaneous presence of two I⁻ in the vicinity of diiron core is necessary for the reduction of 1 . © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 737–743, 2005     

Mixed Ligand Complex Formation of Cetirizine Drug with Bivalent Transition Metal(II) Ions in the Presence of 2-Aminomethylbenzimidazole: Synthesis,Structural, Biological,pH-Metric and Thermodynamic Studies

Mononuclear copper(II), cobalt(II) and nickel(II) complexes of cetirizine (CTZ = 2-[2-[4-[(4-chlorophenyl)phenyl methyl]-piperazine-1-yl]-ethoxy]acetic acid) in the presence of 2-aminomethyl-benzimidazole·2HCl (AMBI), as a representative example of heterocyclic bases, were synthesized and studied by different physical techniques. All mixed-ligand complexes have been fully characterized with the help of elemental analyses, molecular weight determinations, molar conductance, magnetic moments and spectroscopic data. The formulae of the isolated complexes are [M(AMBI)(CTZ)(NO₃)(H₂O)₂]·nH₂O where AMBI is the neutral bidentate 2-aminomethylbenzimidazole, CTZ the deprotonated cetirizine and n = 1 for Co(II) or 0 for Cu(II) and Ni(II) complexes. The measured molar conductance values in DMSO indicate that the complexes are non-electrolytes. The formation equilibria of the ternary complexes have been investigated. Ternary complexes are formed by a simultaneous mechanism. Stoichiometry and stability constants for the complexes formed are reported. The concentration distribution of the complexes in solution was evaluated as a function of pH. The thermodynamic parameters were calculated from the temperature dependence of the equilibrium constants and are discussed. The synthesized metal chelates have been screened for their antimicrobial activities against the selected types of Gram-positive (G⁺) and Gram-negative (G^?) bacteria. They were found to be more active against Gram positive than Gram negative bacteria. The antimicrobial activity in terms of metal ions obeys this order: Cu(II) > Ni(II) > Co(II).     

Kinetics and Mechanism of the Formation of (1,5)bis(2-hydroxybenzamido)3- azapentaneiron(III) and its Reactions with Thiocyanate,Azide, Acetate,Sulfur(IV) and Ascorbic Acid in Solution,and the Synthesis and Characterization of (nitrato)bis- (2-hydroxybenzamido)3-azapentaneiron(III). The Role of Phenol–amide–amine Coordination

The complexation of iron(III) with (1,5)bis(2-hydroxybenzamido)3-azapentane (H₂L) under varying [H⁺]_T (0.01–0.1 mol dm^?3) and [Fe^III]_T (3.0 × 10^?4–1.7 × 10^?2, [L]_T=(0.5 - 1.0) × 10^-4 mol dm^?3) (I=0.3 mol dm^?3, 10% v/v, MeOH  + H₂O, 25.0 °C) was reversible and displayed monophasic kinetics; the dominant path involved FeOH²⁺ and H₃L⁺. The mechanism is essentially a dissociative interchange (I_d) and dissociation of the aqua ligand from the encounter complex, [Fe(OH₂)₅OH²⁺, H₃L⁺] is rate-limiting. Equilibrium measurements indicated that the ligand binds iron(III) in a bidentate, tetradentate and pentadentate fashion under varying pH conditions. Iron(III) promoted deprotonation of the phenol moieties, and sec-NH ₂ ⁺ of the dien unit are in tune with this proposition. The octahedral coordination of [Fe(HL/L})(OH₂)]^2+/+ is further supported by the aqua ligand substitution by AcO^?, NCS^?, N ₃ ^- /N₃H, SO ₃ ^2- /HSO ₃ ^- . However, marked pK perturbation of the bound ascorbate in [Fe(L)(HAsc/Asc)]^0/? (ΔpK_{{[Fe(L)(HAsc)] ? HAsc?}}=6) is compelling evidence for chelation of HAsc^?/Asc^2? leading to unusual hepta coordination of iron(III) in the ascorbate complexes. Despite the multidentate nature of the ligand, its iron(III) complexes remain sensitive to reduction by S^IV and ascorbic acid. The complex (nitrato){(1,5)bis(2-hydroxybenzamido)3-azapentane}iron(III) has been synthesised and characterised by elemental analysis, i.r. and u.v.–vis spectral measurements. The room temperature magnetic moment (μ_eff=4.2 BM) conforms to the intermediate spin state of iron(III) (S=3/2) which is further supported by e.s.r. measurements (77 K, g=4.2, 8.1) and the ⁵⁷Fe Mössbauer spectrum (δ=0.41 mm s^?1; ΔE_Q=0.78 mm/s). The cyclic voltametry (MeOH, TEAP as background electrolyte) display only one quasi-reversible peak in the ?0.254 to ?0.4 V range (vs. SCE), the irreversibility being due to the formation of an iron(II) complex which dissociates under the experimental conditions.     

Crystallization method controlled trinuclear or ion-pair Manganese(III)-porphyrin-based heterobimetallic complexes: Synthesis,spectra characterization,and crystal structure

Cyanide-bridged trinuclear heterometallic Ag(I)-Mn(III) complex {[Mn(TClPP)(H₂O)]₂[Ag(CN)₂]}₂ · 2Br · 2C₃H₆O · 3H₂O (I) and ion-pair complex {[Mn(TClPP)(CH₃OH)₂][Ag(CN)₂]} · 0.5H₂O (II) have been synthesized with [Mn(TClTPP)(H₂O)₂]Br (H₂TClTPP = meso-tetra(4-chlorophenyl)porphyrin) as assembling segment and K[Ag(CN)₂] as building block by using different crystallization method. These two complexes have been characterized by elemental analysis, IR spectroscopy and X-ray structure determination. In the trinuclear complex I, [Ag(CN)₂]^? as bidentate ligand coordinates with the two central Mn(III) atom of [Mn(TClPP)(H₂O)₂]⁺ through its two trans cyanide groups to form the complex cation of [Mn(TClPP)(H₂O)]₂[Ag(CN)₂]⁺, which further constructs the neutral complexes with the help of one Br^? as balanced anion. For the ion-pair complex II composed by free [Mn(TClPP)(CH₃OH)₂]⁺ cation and free [Ag(CN)2]^? anion, it can be linked into one-dimensional supramolecular structure with the dependence of the intermolecular O-H...N and O-H...O hydrogen bond interactions.     

Inner-sphere oxidation of ternary nitrilotriacetatocobalt(II) complexes involving oxalate and phthalate by periodate

The oxidation of [Co^II(nta)(ox)(H₂O)₂]³⁻ and [Co^II(nta)(ph)(H₂O)₂]³⁻ (nta = nitrilotriacetate, ox = oxalic acid and ph = phthalic acid) by periodate have been studied kinetically in aqueous solution over 20–40 °C and a variety of pH ranges. The rate of oxidation of [Co^II(nta)(ox)(H₂O)₂]³⁻ by periodate, obeys the following equation: d[Co^III]/dt = [Co^II(nta)(ox)(H₂O)₂³⁻][H₅IO₆] {k ₄ K ₅ + (k ₅ K ₆ K ₂/[H⁺]} while the reaction of [Co^II(nta)(ph)(H₂O)₂]³⁻ with periodate in aqueous acidic medium obeys the following rate law: d[Co^III]/dt = k ₆ K ₈[Co^II]_T [I^VII]_T/{1 + [H⁺]/K ₇ + K ₈[I^VII] _T }. Initial cobalt(III) products were formed and slowly converted to final products, fitting an inner-sphere mechanism. Thermodynamic activation parameters have been calculated. A common mechanism for the oxidation of ternary nitrilotriacetatocobalt(II) complexes by periodate is proposed and supported by an excellent isokinetic relationship between ΔH* and ΔS* values for these reactions.     

COMPLEXES OF MOLYBDENUM(V) AND LANTHANUM(III) WITH 2′,2″′-(2,6-PYRIDINEDIYLDIETHYLIDENE)-DIOXAMOHYDRAZIDE (H2DAPSOX)

Abstract

In a template synthesis from ethanolic solution of MoOCl₃, 2,6-diacetylpyridine (dap), and semioxamazide (sox), in the molar ratio 1:1:2, a dimeric molybdenum(V) complex [Mo₂O₂(H₂dapsox)₂]Cl₆ · 4H₂O (where H₂dapsox = 2′,2″′-(2,6-pyridinediyldiethylidenedioxa-mohydrazide) was obtained. In a similar reaction, starting from La(NO₃)₃ · 6H₂O, the complex [La(H₂dapsox)(NO₃) _x ](NO₃)_3-x · 1/2EtOH (x = 1,2), having coordination number 9, was obtained. In the latter complex two NO₃ Groups were bidentately coordinated in the solid state, but only one in the solution.

Besides [Mo₂O₂(TPP)₂] (TPP = tetraphenylporphyrin), the molybdenum(V) complex [Mo₂O₂ (H₂dapsox)₂]Cl₆ · 4H₂O is the only other known example of a dimeric μ-oxodimolybdenum(V) species that is paramagnetic (μ = 0.95 BM). One of the Mo atoms has pentagonal bipyramidal coordination, and the other pentagonal pyramidal coordination. In aqueous solution a rare example of a pentagonal pyramidal ion [MoO(dapsox)]⁺ is presumably present. Solution EPR spectra (at 77K) cannot be related to either of the two known types of Mo(V) species based on the extent of g anisotropy. The substances also were characterized by IR and electronic spectroscopy, and by thermal analysis.     

Complex Formation Equilibria of Unusual Seven-Coordinate Fe(EDTA) Complexes with DNA Constituents and Related Bio-relevant Ligands

Seven-coordinate Fe(EDTA)?CL complexes, where L represents a DNA constituent (uracil, uridine, thymine, thymidine and inosine), methylamine, ammonium chloride or imidazole, were investigated to resolve the solution chemistry of this system. The results show formation of 1:1 complexes with DNA constituents and the other ligands, supporting the hepta-coordination mode of Fe(III) ion. Stability constants of the complexes were measured by potentiometric titration at 25?°C and ionic strength 0.1 mol?L^?1 NaNO₃. The hydrolysis constant of [Fe(EDTA)(H₂O)]^? and the formation constants of the complexes formed in solution were calculated using the non-linear least-squares program MINIQUAD-75. The concentration distributions of the various complex species were evaluated as a function of?pH. The thermodynamic parameters ??H ⁰ and ??S ⁰, calculated from the temperature dependence of the equilibrium constants, were determined for the Fe(EDTA)?Curacil complex. The effect of dioxane as a solvent on the protonation constant of uracil, hydrolysis constants of [Fe(EDTA)(H₂O)]^?, and the formation constants of the Fe(EDTA)?Curacil complex are discussed.     

Mössbauer effect studies on alkali tris(maleato) ferrates(III)

Mössbauer spectra of alkali tris(maleato) ferrates(III), i.e., M₃[Fe(C₂H₂C₂O₄)₃]·nH₂O [M=Li, Na, K, Cs] at 300 K display a doublet. The Mössbauer parameters indicate these complexes to be high spin with octahedral symmetry. The isomer shift shows a decreasing trend with the increase in electronegativity/polarizing power of the substituent cation (Li⁺, Na⁺, K⁺, Cs⁺). A linear correlation between isomer shift values and the (Fe?O) stretching frequencies has also been observed.