Synthesis and characterization of solid molybdenum(VI) complexes with glycolic,mandelic and tartaric acids. Photochemistry behaviour of the glycolate molybdenum complex

The complexes (NH₄)₂[MoO₂(C₂H₂O₃)₂]·H₂O, (NH₄)₂[MoO₂(C₈H₆O₃)₂] and (NH₄)₂[MoO₃(C₄H₄O₆)]·H₂O were prepared by reaction of MoO₃ with glycolic, mandelic and tartaric acids, respectively. The complexes were characterized by elemental and thermal analysis, IR spectroscopy and X-ray diffraction. Crystals of the glycolate and tartarate complexes are orthorhombic and the mandelate complex is monoclinic. Elemental and thermal analysis data showed that the glycolate and tartarate complexes are monohydrated. Hydration water is not present in the structure of the mandelate complex. IR spectra showed COO^? is involved in coordination as well as the oxygen atom of the deprotonated hydroxyl group of the α-carbon. The glycolate molybdenum complexes with general formula M₂[MoO₂(C₂H₂O₃)₂]·nH₂O, where M is an alkali metal and n?=?1 or ½, were also prepared and characterized. Aqueous solutions of the glycolate complex become blue and mandelate and tartarate complexes change to yellow or brown when exposed to UV-radiation.     

Potentiometric and Conductometric Studies on the Complexes of Some Rare Earth Metals with Rhodanine Azosulfonamide Derivatives, XII

Stability constants for La³⁺, Ce³⁺, UO₂ ²⁺, and Th⁴⁺ metal ion complexes with rhodanine azosulfonamide derivatives have been determined potentiometrically in 0.1 M KCl in a 30% (v/v) ethanol–water mixture. The order of the stability constants of the complexes found was to La³⁺ < Ce ²⁺ < UO ₂ ²⁺ < Th ⁴⁺. The influence of substituents on the stability of the complexes was examined on the basis of electron-repelling property of the substituent. The effect of temperature on the stability constants was studied and the Gibbs energy, the enthalpy, and entropy of complexation thermodynamic parameters were derived and are discussed. The stoichiometries of these complexes were determined conductometrically and the results indicated the formation of 1:1 and 1:2 (metal:ligand) complexes.     

Stability constants of Np(V) complexes with fluoride and sulfate at variable temperatures

Summary A solvent extraction method was used to determine the stability constants of Np(V) complexes with fluoride and sulfate in 1.0M NaClO₄ from 25 to 60 °C. The distribution ratio of Np(V) between the organic and aqueous phases was found to decrease as the concentrations of fluoride and sulfate were increased. Stability constants of the 1 : 1 Np(V)-fluoride complexes and the 1 : 1 Np(V)-sulfate and 1 : 2 Np(V)-sulfate complexes, dominant in the aqueous phase under the experimental conditions, were calculated from the effect of [F^-] and [SO₄^2-] on the distribution ratio. The enthalpy and entropy of complexation were calculated from the stability constants at different temperatures by using the Van't Hoff equation.     

Mercaptokomplexe von Indium(III)

The complexes of In(III) with thioglycolate (HO? CH₂? CH₂? S^?) have been investigated by pH-metric methods. Only the mononuclear species In(SR)_n(3-n)+ (n = 1, 2, 3, 4) are formed (Fig. 1): It was difficult to obtain an accurate value for the first stability constant K₁ because of the high stability of the 1:1-complex and therefore mixtures of KCl-KNO₃ were used to keep up the ionic strength of μ = 0.1. In presence of chloride, the constants K_n are smaller because of the formation of chloro complexes and mixed complexes In(SR)_nCl_i(3-n-1)+ and the stability constants of these have also been determined. The constants for the complexes without coordinated chloride can finally be obtained by an extrapolation (Fig. 2). The problem of the influence of increasing charge on the stability of various complexes of the isoelectronic 4d¹⁰ cations is discussed (Fig. 3).     

Dissociation constants of some Schiff bases and stability constants of their copper,cobalt, nickel and zinc complexes

The stoichiometry and stability constant of metal complexes with 4-(3-methoxy-salicylideneamino)-5-hydroxynaphthalene-2,7-disulfonic acid monosodium salt (H₂L) and 4-(3-methoxysalicylideneamino)-5-hydroxy-6-(2,5-dichlorophenylazo)-2,7-naphthalene disulfonic acid monosodium salt (H₂L¹) were studied by potentiometric titration. The stability constants of H₂L and H₂L¹ Schiff bases have been investigated by potentiometric titration and u.v.–vis spectroscopy in aqueous media. The dissociation constants of the ligand and the stability constants of the metal complexes were calculated pH-metrically at 25 °C and 0.1 m KCl ionic strength. The dissociation constants for H₂L were obtained as 3.007, 7.620 and 9.564 and for H₂L¹, 4.000, 6.525, 9.473 and 10.423, respectively. The complexes were found to have the formulae [M(L)₂] for M = Co(II), Ni(II), Zn(II) and Cu(II). The stability of the complexes follows the sequence: Zn(II) < Co(II) < Cu(II) < Ni(II). The high stability of H₂L¹ towards Cu(II) and Ni(II) over the other ions is remarkable, in particular over Cu(II), and may be of technological interest. Concentration distribution diagram of various species formed in solution was evaluated for ligands and complexes. The formation of the hydrogen bonds may cause this increased stability of ligands. The pH-metric data were used to find the stoichiometry, deprotonation and stability constants via the SUPERQUAD computer program.     

Study of acidic and complexing properties of tetraphenylporphyrazine and octa(4-bromophenyl)porphyrazine in DMSO at 298 K

The acid dissociation of tetraphenylporphyrazine (H₂PA(Ph)₄) and octa(4-bromophenyl)porphyrazine (H₂PA(4-BrPh)₈) and their reactions with Cd²⁺ ions were studied in DMSO at 298 K. The equilibrium formation constants of the complexes and the acid dissociation constants of porphyrins were calculated; their relationship with the stability constants of the complexes was analyzed. The acidity sequence for porphyrazine derivatives was established.     

Stability of bismuth(III), indium(III), lead(II), and cadmium(II) monocomplexes with selenourea and thiourea

The stability constants of the bismuth(III), indium(III), lead(II), and cadmium,(II) monocomplexes with selenourea (seu) and thiourea (tu) were determined spectrophotometrically at the ionic strength 1 (0.5 mol/L HClO₄ + NaClO₄) or 2 (1 mol/L HClO₄ + NaClO₄) and 276 and 298 K. For all metals, the stability constants (β₁) of the complexes with seu were higher than those of the complexes with tu and changed in the series Bi³⁺ > Cd²⁺ ≈ In³⁺ > Pb²⁺. A correlation between logβ₁(S) and logβ₁(Se) was established.     

Differential Pulse Voltammetric Study of Complexes of Rare Earth Ion(Eu3+) with Glutarate and 1,2-Diminopropane

Abstract

The mixed complexes of Eu (III) with glutarate (Gluta) and 1,2-diaminopropane (DMPA) have been studied at 25°C, μ=0.12(NaClO₄) by differential pulse voltammetry(DPV). The reduction process in each case appears to be quasi-reversible and diffusion-controlled. The stability constants have been measured by Schaap and McMasters′ method. The stability constants of three mixed complexes formed are logβ₁₁=7. 414 for [Eu(Gluta) (DMPA)]⁺, logβ₂₁ = 8. 506 for [Eu(Gluta)₂ (DMPA)]^? and logβ₁₂ = 9. 984 for [Eu(Gluta) (DMPA)₂]⁺.     

The Complexes of Holmium with Methylenediphosphonate and 1-Hydroxyethylidenephosphonate

The composition and stability of holmium methylenediphosphonate (MDP) and 1-hydroxyethylidenephosphonate (HEDP) complexes were studied by potentiometric titration methods in 0.1M NaCl at 25 °C. It was found that besides L^4– anions the protonated H _n L^(4–n)– species (n = 1–3 for MDP and n = 1–4 for HEDP) are present in the pH region 3 to 10. The presence of the undissociated acids (H₄L) has not been unambiguously proved for MDP. The complexes of the composition HoH _n L (n varies from 1 to –2 for MDP and from 1 to –1 for HEDP) have been found if the concentration of the ligand is higher than the concentration of holmium. The protonation constants of both acids and the stability constants of the complexes discussed were determined and the comparison with literature data of analogical complexes of other lanthanides was performed.     

Methylmercury(II) complexes with 2-mercaptopyridinecarboxylic acids

The stability constants of the complexes [MeHgL]^?(H₂L = 2-mercaptopyridine-3-carboxylic acid, 2-mercaptopyridine-4-carboxylic acid, 2-mercaptopyridine-5-carboxylic acid and 2-mercaptopyridine-6-carboxylic acid) have been obtained by differential pulse polarography. The values of log β₁ are in the range 14.14–14.96 at 20°C and ionic strength 0.1 mol dm^?3. The complexes MeHgHL have been isolated and characterized by chemical analysis and mass and IR spectrometry.     

Effect of ionic strength on the stabilities of ciprofloxacin – Metal complexes

Proton–ligand dissociation constant of 1-cyclopropyl-1,4-dihydro-4-oxo-7-(1-piperazinyl) quinolone-3-carboxylic acid is ciprofloxacin and metal–ligand stability constants of its complexes with some metal ions have been determined potentiometrically in the presence of (0.01, 0.02 and 0.03 mol/dm³) NaClO₄. The order of the stability constants of the formed complexes increases in the sequence Cu²⁺, Fe³⁺, Ni²⁺ and Zn²⁺ and decreases with increase in the concentration of ionic strength.     

Complexation of 4′-nitrobenzo-15-crown-5 with Li+, Na+, K+, and NH 4 + cations in acetonitrile–methanol binary solutions

The complexation processes between Li⁺, Na⁺, K⁺ and NH ₄ ⁺ cations with macrocyclic ligand, 4′-nitrobenzo-15C5, were studied in acetonitrile–methanol (AN–MeOH) binary mixtures at different temperatures using conductometric method. The conductance data show that the stoichiometry of the complexes formed between the ligand and Li⁺, Na⁺, K⁺ and NH ₄ ⁺ cations is 1:1(M:L). Addition of 4′-nitrobenzo-15C5 to these cations solution, causes a continuous increase in the molar conductivities which indicates that the mobility of the complexed cations is more than the uncomplexed ones. The values of stability constants of the complexes were determined from conductometric data using GENPLOT computer program. The obtained results show that the selectivity order of the ligand for Li⁺, Na⁺, K⁺ and NH ₄ ⁺ cations changes with the nature and composition of the binary mixed solvent. The values of thermodynamic parameters (ΔH°_c, ΔS°_c) for formation of the complexes were obtained from temperature dependence of the stability constants using the van’t Hoff plot. The results show that the complexes are both enthalpy and entropy stabilized. A non-linear behavior was observed between the stability constants (log K _f ) of the complexes and the composition of the AN–MeOH binary solution.     

Coordination properties of bidentate (N,O) and tridentate (N,O,O) heterocyclic alcohols with dimethyltin(IV)

The complex-formation equilibria of dimethyltin(IV) (DMT) with 4-hydroxymethyl imidazole (HMI) and 2,6-dihydroxymethyl pyridine (PDC) have been investigated. Stoichiometry and stability constants for the complexes formed were determined at different temperatures and 0.1?mol?L^?1 NaNO₃ ionic strength. The concentration distribution of the complexes in solution was evaluated as a function of pH. The effect of dioxane as a solvent on both protonation constants and formation constants of DMT complexes with HMI and PDC are discussed. The thermodynamic parameters ΔH° and ΔS° calculated from the temperature dependence of the equilibrium constants were investigated.     

Dissociation constants of phosphoric acid at 25°C and the ion pairing of sodium with orthophosphate ligands at 25°C

The first and second acidity constants of phosphoric acid were determined in a 0.70 ionic strength solution of both a sodium and a potassium ion background salt at 25°C. These experimentally determined constants were compared to literature values as well as values calculated from a theoretical model. Assuming negligible ion pairing of the phosphate ligand with the potassium ions, the stability constants of the NaHPO ₄ ^- and NaH₂PO ₄ ⁰ complexes were determined to be 1.3±0.3 and 0.49±0.07 (mol-L^–1), respectively. These constants were used to model the speciation of orthophosphate in a background of a sodium salt from pH 3 to 10.     

Heteroligand polynuclear nickel(II) complexonates in aqueous solutions of 2,2′-dipyridyl

Formation of nickel(II) complexes with ethylenediaminetetraacetic acid (Edta) and 2,2′-dipyridyl (Dipy) has been studied by electronic absorption spectroscopy. Mathematical modeling has demonstrated that the most probable mathematical models to describe the experimental dependences of absorption on the medium acidity and concentration of solution components relies on the dissociation constants of the ligands (K _i ) and stability constants (β) of homoligand, heteroligand, and polynuclear complexes of general composition [Ni _m Dipy _n Edta _r ]^{2m ? 4r} (m = 1–4, n = 0–8, r = 0–1) as parameters. The reaction equilibrium constants and stability constants of the resulting complexes have been calculated. The structures of these complexes have been suggested.     

A combined experimental and density functional theory study on the complexation ability of 15-crown-5 with Li+, Na+, K+, and NH4 + cations

The complexation processes among Li⁺, Na⁺, K⁺, and NH₄ ⁺ cations with the macrocyclic ligand, 15-crown-5 (15C5) have been studied in acetonitrile–methanol binary mixtures at different temperatures using conductometric method. The stability constants of the resulting 1:1 complexes were calculated from the computer fitting of the molar conductance–mole ratio data at various temperatures. The values of thermodynamic parameters ( $ \Updelta H_{\text{c}}^{^\circ } $ and $ \Updelta S_{\text{c}}^{^\circ } $ ) for the formation of the complexes were obtained from temperature dependence of the stability constants of complexes using van’t Hoff plots. In addition, a theoretical study has been carried out using density functional theory to obtain the stability of the complexes and the geometrical structure of the 15C5 and its complexes with Li⁺, Na⁺, K⁺ and NH₄ ⁺ cations in the gas phase. We compared the experimental data with those obtained by quantum chemistry calculations to investigate the effect of the solvent on complexation process.     

Stability of crown-ether complexes with alkali-metal ions in ionic liquid-water mixed solvents

Stability constants of sodium and cesium ion complexes with 18-crown-6 (18C6) and dibenzo-18-crown-6 (DB18C6) in N-butyl-4-methyl-pyridinium tetrafluoroborate [BMP][BF₄] aqueous solutions were measured using the ²³Na and ¹³³Cs NMR technique at 23 °C. To the best of our knowledge, the estimated values of stability constants reported in this study are the first such values given for ionic liquid solutions. The cationic exchange between the free and complexed species is rapid, and only formation of the 1:1 complexes [M(18C6)]⁺ and [M(DB18C6)]⁺ (M = Na⁺, Cs⁺) were observed. The complex formation constants demonstrated a strong dependence on the [BMP][BF₄] concentration. For [M(18C6)]⁺, in solutions with a 0.33–0.70 mole fraction of water in [BMP][BF₄], lg K values are found to be more than one unit higher than the lg K values measured in pure aqueous solutions, although no information concerning the influence of [BMP][BF₄] on the complex formation selectivity could be observed. DB18C6 complexes revealed significantly lower stability under the same conditions. An extrapolation to zero water content gave the lg K = 2.42 for [Cs(18C6)]⁺ in [BMP][BF₄]. It was discovered that when added to water, [BMP][BF₄] increases the solubility of crown ethers and decreases the solubility of alkali metal nitrates. Complex formation with crown ethers enhances the solubility of alkali metal salts in [BMP][BF₄].     

Constantes d'acidite de l'acide pyrophosphorique et constantes de stabilite des complexes avec le potassium et le sodium: en|The acidity constants of pyrophosphoric acid and the stability constants of complexes with potassium and sodium ions

(The acidity constants of pyrophosphoric acid and the stability constants of complexes with potassium and sodium ions)The effect of potassium and sodium ions on the acidity constants of pyrophosphoric acid is studied by potentiometry at 25°C and at an ionic strength of 0.5 mol l^-1. Comparison of the results obtained in potassium chloride or sodium chloride medium with those found in tetramethylammonium chloride medium provides evidence of the formation of potassium and sodium complexes of the type MHP₂O^2-₇ and MP₂O^3-₇. Stability constants of these complexes are calculated and distribution diagrams of the species as a function of pH are given for the three different media utilized.     

Mononuclear and Dinuclear Cobalt Complexes and its Dioxygen Adduct with a New 24-membered Hexaaza Macrocyclic Ligand

Abstract

Dinucleating 24-membered hexaazadiphenol macrocyclic ligand 3,6,9,17,20,23-hexaaza-29,30-dihydroxy-13,27-dimethyl-tricyclo[23,3,1,1^11,15] triaconta-1(29), 11,13,15(30),25,27-hexaene (L or BDBPH), is prepared by the NaBH₄ reduction of the Schiff base obtained from [2+2] template condensation of 2,6-diformyl-p-cresol with diethylenetriamine. The ligand maintains dinuclear integrity for cobalt (II) while facilitating the formation of bridging phenolate dicobalt cores. Potentiometric equilibrium studies indicate that a variety of protonated, mononuclear and dinuclear cobalt (II) complexes form from p[H] 2 through 11 in aqueous solution. The protonation constants of this ligand and stability constants of the 1:1, 1:2 ligand: cobalt(II) complexes were determined in KCl supporting electrolyte (μ = 0.100 M) at 25°C. The mechanism for the formation of dinuclear dioxygen cobalt(II) complexes is also described. The stability constants of mononuclear and dinuclear cobalt complexes were determined under nitrogen. Preliminary results show that the dinuclear dioxygen cobalt (II) complexes do not catalyze hydroxylation of adamantane in the presence of H₂S as two-electron reductant.     

Synthesis of Two N,N′-bis(N,N-dialkylamide) Derivatives of Diethylenetriaminepentaacetic Acid and the Stabilities of Their Complexes with Gd3+, Ca2+, Cu2+, and Zn2+

Two bis(N,N-dialkylamide) derivatives of DTPA [(carboxymethyl)iminobis (ethylenenitrilo) tetraacetic acid], DTPA-BDMA = the bis(N,N-dimethylamide) and DTPA-BDEA = the bis(N,N-diethylamide) were synthesized. Their protonation constants were determined by potentiometric titration in 0.10 M Me₄NNO₃ and by NMR pH titration at 25.0 ± 0.1 °C. Stability and selectivity constants were measured to evaluate the possibility of using the corresponding gadolinium(III) complexes for magnetic resonance imaging contrast agents. The stability constants of gadolinium(III), copper(II), zinc(II), and calcium(II) complexes with DTPA-BDMA and DTPA-BDEA were investigated quantitatively by potentiometry. The stability constant for gadolinium(III) complexes is larger than those for Ca(II), Zn(II), and Cu(II) complexes. The selectivity constants and modified selectivity constants of the amides for Gd³⁺ over endogenously available metal ions were calculated. Effectiveness of these two ligands in binding divalent and trivalent metal ions in biological media is assessed by comparing pM values at physiological pH 7.4. Spin-lattice relaxivity values R₁ for Gd(III) complexes were also determined. The observed relaxivity values were found to decrease with increasing pH in the acid range below pH 4 and relaxivity values became invariant with respect to pH changes over the range of 4–10. ¹⁷O NMR shifts showed that the [Dy(DTPA-BDMA)] and [Dy(DTPA-BDEA)] complexes had one inner-sphere water molecule. Water proton spin-lattice relaxation rates for the [Gd(DTPA-BDMA)] and [Gd(DTPA-BDEA)] complexes were also consistent with one inner-sphere gadolinium(III) coordination position.