Complexation of Ni (II) and Zn(II) ions by 3-(1-naphthyI)-2-mercaptopropenoic acid

The complexation equilibria between Ni(II) and Zn(II) metal ions with 3-(1-naphthyl)-2-mercaptopropenoic acid (H₂NMP) were studied by glass electrode potentiometry, at 25 °C and 1.0 mol·dm^–3 in NaClO₄ as constant ionic medium in 50% (v/v) water-ethanol solutions. Formation constants for the complexes Ni(NMP), Ni(NMP) ₂ ^2– , Zn(NMP) and Zn(NMP) ₂ ^2– , refined by the MINIGLASS program, are reported.     

Complexation of Co(II) with phosphonomethylaminosuccinic acid in solutions

Complexation in the Co(II)-phosphonomethylaminosuccinic acid (H₄L) system in aqueous solutions at component ratios of 1 : 1 and 1 : 2 and c _Co(II) = 1 × 10^?2 mol/L was studied by electronic absorption spectroscopy. The formation of various protonated complexes of the general formula Co(H _n L) _m (OH) _q (n = 3?0; m = 1?C2; q = 0?C2) was found, and their stability constants and distribution diagrams were calculated. It was demonstrated that the bis complexes have the structure of a distorted octahedron, and the octahedron ?? tetrahedron rearrangement of the coordination polyhedron occurs in the equimolar complexes at pH > 8.     

Supramolecular structure of calcium(II) based on chelidamic acid: An agreement between theoretical and experimental studies

A novel supramolecular structure of an s-Block metal ion, Ca(II) atom, formulated as (pnH₂)₂au][Ca₂(H₂O)₂(Hhypydc)₄]·4H2O (1), was synthesized and characterized by elemental analysis, IR, 1H and 13C NMR spectroscopies and single crystal X-ray diffraction. Compound 1 is a member of a large family of supramolecular metallic compounds recently derived from a proton transfer ion pair, (pnH2)(Hhypydc), where pn is propane-1,3-diamine and (Hhypydc)^2-is 4-hydroxypyridine-2,6-dicarboxylate ion. Based upon the molecular structure analysis of the binuclear anionic complex, the coordination environment around each Ca(II) atom is pentagonal bipyramidal with seven-coordination number. The strong hydrogen bonding between hydroxyl groups of two neighboring anionic complexes produce the nice tape as X-like supramolecular structure. Optimization was carried out using two standard basis sets of 6-31G (d,p) for the single anionic complex (S) and LanL2MB basis set for the double anionic complexes (D) which describe the electrons of all atoms. As an interesting finding from our theoretical calculations, when we reoptimized the double complexes in the presence of strong hydrogen bond interaction between two hydroxyl groups, O3-H3A??O8ⁱⁱ (ii = x-1, y, z-1), it was revealed that the parallel position of ligands to each other was exactly like that of the solid state. The complexation reaction of H3hypydc with Ca²⁺ in aqueous solution was investigated by potentiometric pH titrations, the equilibrium constants and species distribution in various pHs. The for major complexes formed are described.     

A theoretical and experimental study of lead substitution in calcium hydroxyapatite

Characterization of lead substitution for calcium in hydroxyapatite (CaHA) is carried out, using experimental techniques and Density Functional theoretical (DFT) analyses. Theoretical modeling is used to obtain information of the Pb chemical environment for occupancy at either Ca(I) or Ca(II) sites of CaHA. Effects of the larger ionic radius of Pb(+2) compared to Ca(+2) are apparent in embedded cluster calculations of local chemical bonding properties. DFT periodic planewave pseudopotential studies are used to provide first-principles predictions of local structural relaxation and site preference for Pb(x)Ca(10-x)HA over the composition range x< or = 6. General characteristics of the polycrystalline material are verified by X-ray diffraction and FTIR analysis, showing the presence of a single phase of CaHA structure. A short range structure around lead is proposed in order to interpret the Pb L-edge EXAFS spectrum of the solid solution Ca(6.6)Pb(3.4)HA. In this concentration we observe that lead mainly occupies Ca(II) sites; the EXAFS fit slightly favors Pb clustering, while theory indicates the importance of Pb-Pb avoidance on site (II).     

Potentiometric stripping analysis and anodic stripping voltammetry for measurement of copper(II) and lead(II) complexation by fulvic acid: A comparative study

The utility of potentiometric stripping analysis (PSA) for studying the interaction of fulvic acid with Cu^II and Pb^II at pH 1.8 and 4.8 was assessed. The impact of fulvic acid on both the deposition and stripping steps was considered. In contrast to results obtained by anodic stripping voltammetry, fulvic acid influenced both these steps in PSA, and to different degrees. Surface active substances have been claimed to have self-compensatory effects in PSA; this work shows that this is not valid for heterogenous natural complexants such as fulvic acid.     

Complexation of iron(III) by pimelyldihydroxamic acid

Pimelyldihydroxamic acid forms strong complexes with iron(III) in aqueous solution at pH 2–9. Plots of n? and proton liberation against pH show plateaux regions at values of 1.5 and 3.0, respectively, over the pH range 4.0–8.0 supporting a formulation of Fe₂L₃ (logβ = 41.06). The orage-red complex exhibits maximum absorbance at 420 nm, and a well-defined peak at 0.6 V vs. SCE in differential pulse polarography.     

Spectrophotometric study of the complexes of hydroxyethylethylenediaminetriacetic acid with bismuth(III), copper(II) and lead(II)

The bismuth(III), copper(II) and lead(II) hydroxyethylethylenediaminetriacetic acid systems were investigated in detail. Evidence for the formation of species BiX, Bi(OH)X⁻, CuHX, CuX⁻, PbHX and PbX⁻ is presented and their stability constants given.     

The mechanism of the (bispidine)copper(II)-catalyzed aziridination of styrene: a combined experimental and theoretical study

Experimental and DFT-based computational results on the aziridination mechanism and the catalytic activity of (bispidine)copper(I) and -copper(II) complexes are reported and discussed (bispidine=tetra- or pentadentate 3,7-diazabicyclo[3.1.1]nonane derivative with two or three aromatic N donors in addition to the two tertiary amines). There is a correlation between the redox potential of the copper(II/I) couple and the activity of the catalyst. The most active catalyst studied, which has the most positive redox potential among all (bispidine)copper(II) complexes, performs 180 turnovers in 30 min. A detailed hybrid density functional theory (DFT) study provides insight into the structure, spin state, and stability of reactive intermediates and transition states, the oxidation state of the copper center, and the denticity of the nitrene source. Among the possible pathways for the formation of the aziridine product, the stepwise formation of the two N-C bonds is shown to be preferred, which also follows from experimental results. Although the triplet state of the catalytically active copper nitrene is lowest in energy, the two possible spin states of the radical intermediate are practically degenerate, and there is a spin crossover at this stage because the triplet energy barrier to the singlet product is exceedingly high.     

Synthesis and oxygenation of a nickel(II) and zinc(II) dithiolate: an experimental and theoretical comparison

The diamino-dithiolato N2S2 ligand N,N'-bis-2-methyl-mercaptopropyl-N,N'-dimethylethylenediamine, H2bmmp-dmed), and its nickel (1) and zinc (2) complexes have been prepared and their reactivities with hydrogen peroxide investigated. Complex 1 yields a mixture of sulfenato (RSO-), 4, sulfinato (RSO2-), 3, and sulfonato (RSO3-), 5, products upon addition of H2O2. Products are separable by column chromatography. Stoichiometric addition of H2O2 to 2 yields an inseparable mixture. Excess peroxide addition results in oxygenation of the ligand to the disulfonate, 6, and decomplexation of zinc. Complexes 1, 2, and 3 and compound 6 have been investigated by X-ray crystallography, and their structures are reported. Density functional theory (DFT) calculations of 1 and 2 reveal significant sulfur p character in the HOMO of each complex. However, 1 also shows significant metal d character that is pi-antibonding with respect to the sulfur p orbitals. Complex 2 shows little metal character in the HOMO. Implications of the HOMO with respect to S-centered reactivity and metal ligand distances in S-oxygenated products are provided.     

Complexation of lanthanides(III), americium(III), and uranium(VI) with bitopic N,O ligands: an experimental and theoretical study

New functionalized terpyridine-diamide ligands were recently developed for the group actinide separation by solvent extraction. In order to acquire a better understanding of their coordination mode in solution, protonation and complexation of lanthanides(III), americium(III), and uranium(VI) with these bitopic N,O-bearing ligands were studied in homogeneous methanol/water conditions by experimental and theoretical approaches. UV-visible spectrophotometry was used to determine the protonation and stability constants of te-tpyda and dedp-tpyda. The conformations of free and protonated forms of te-tpyda were investigated using NMR and theoretical calculations. The introduction of amide functional groups on the terpyridine moiety improved the extracting properties of these new ligands by lowering their basicity and enhancing the stability of the corresponding 1:1 complexes with lanthanides(III). Coordination of these ligands was studied by density functional theory and molecular dynamics calculations, especially to evaluate potential participation of hard oxygen and soft nitrogen atoms in actinide coordination and to correlate with their affinity and selectivity. Two predominant inner-sphere coordination modes were found from the calculations: one mode where the cation is coordinated by the nitrogen atoms of the cavity and by the amide oxygen atoms and the other mode where the cation is only coordinated by the two amide oxygen atoms and by solvent molecules. Further simulations and analysis of UV-visible spectra using both coordination modes indicate that inner-sphere coordination with direct complexation of the three nitrogen and two oxygen atoms to the cation leads to the most likely species in a methanol/water solution.     

o-Iminobenzosemiquinonato(1-) and o-amidophenolato(2-) complexes of palladium(II) and platinum(II): a combined experimental and density functional theoretical study

From the reaction mixture of [M(II)(bpy)Cl(2)], the ligand 2-anilino-4,6-di-tert-butylphenol, H[L(AP)], and 2 equiv of a base (NaOCH(3)) in CH(3)CN under anaerobic conditions were obtained the blue-green neutral complexes [M(II)(L(AP)-H)(bpy)] (M = Pd (1), Pt (2)). (L(AP)-H)(2)(-) represents the o-amidophenolato dianion, (L(AP))(1)(-) is the o-aminophenolate(1-), (L(ISQ))(1)(-) is its one-electron-oxidized, pi-radical o-iminobenzosemiquinonate(1-), and (L(IBQ))(0) is the neutral quinone. Complexes 1 and 2 can be oxidized by ferrocenium hexafluorophosphate, yielding the paramagnetic salts [M(II)(L(ISQ))(bpy)]PF(6) (S = (1)/(2)) (M = Pd (1a), Pt (2a)). The reaction of PtCl(2), 2 equiv of H[L(AP)], and 4 equiv of base in CH(3)CN in the presence of air yields diamagnetic [Pt(L(ISQ))(2)] (3), which is shown to possess an electronic structure that is best described as a singlet diradical. Complexes 1, 1a, 2, 2a, and 3 have been structurally characterized by X-ray crystallography at 100 K. It is clearly established that O,N-coordinated (L(AP)-H)(2)(-) ligands have a distinctly different structure than the corresponding O,N-coordinated (L(ISQ))(1)(-) radicals. It is therefore possible to unambiguously assign the protonation and oxidation level of o-aminophenol derived ligands in coordination compounds. All complexes have been investigated by cyclic voltammetry, spectroelectrochemistry, EPR, and UV-vis spectroscopy. Complexes 1 and 2 can be reversibly oxidized to the [M(II)(L(ISQ))(bpy)](+) and [M(II)(L(IBQ))(pby)](2+) mono- and dications, respectively, and reduced to the [M(L(AP)-H)(bpy(*))](-) anion, where (bpy(*))(1)(-) is the radical anion of 2,2'-bipyridine. Complex 3 exhibits four reversible one-electron-transfer waves (two oxidations and two reductions) which are all shown to be ligand centered. The EPR spectra of the one-electron-reduced species [Pt(L(AP)-H)(L(ISQ))](-) (S = (1)/(2)) and of the one-electron-oxidized species [Pt(L(ISQ))(L(IBQ))](+) (S = (1)/(2)) in CH(2)Cl(2) solutions have been recorded. To gain a better understanding of the electronic structure of 3 and its monooxidized and reduced forms, relativistic DFT calculations have been carried out. Magnetic coupling parameters and hyperfine couplings were calculated and found to be in very good agreement with experiment. It is shown that both the one-electron oxidation and reduction of 3 are ligand centered. A simple MO model is developed in order to understand the EPR properties of the monocation and monoanion of 3.     

Carbon-carbon bond activation of 2,2,6,6-tetramethyl-piperidine-1-oxyl by a Rh(II) metalloradical: a combined experimental and theoretical study

Competitive major carbon-carbon bond activation (CCA) and minor carbon-hydrogen bond activation (CHA) channels are identified in the reaction between rhodium(II) meso-tetramesitylporphyrin [Rh(II)(tmp)] (1) and 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO) (2). The CCA and CHA pathways lead to formation of [Rh(III)(tmp)Me] (3) and [Rh(III)(tmp)H] (5), respectively. In the presence of excess TEMPO, [Rh(II)(tmp)] is regenerated from [Rh(III)(tmp)H] with formation of 2,2,6,6-tetramethyl-piperidine-1-ol (TEMPOH) (4) via a subsequent hydrogen atom abstraction pathway. The yield of the CCA product [Rh(III)(tmp)Me] increased with higher temperature at the cost of the CHA product TEMPOH in the temperature range 50-80 degrees C. Both the CCA and CHA pathways follow second-order kinetics. The mechanism of the TEMPO carbon-carbon bond activation was studied by means of kinetic investigations and DFT calculations. Broken symmetry, unrestricted b3-lyp calculations along the open-shell singlet surface reveal a low-energy transition state (TS1) for direct TEMPO methyl radical abstraction by the Rh(II) radical (SH2 type mechanism). An alternative ionic pathway, with a somewhat higher barrier, was identified along the closed-shell singlet surface. This ionic pathway proceeds in two sequential steps: Electron transfer from TEMPO to [Rh(II)(por)] producing the [TEMPO]+ [RhI(por)]- cation-anion pair, followed by net CH3+ transfer from TEMPO+ to Rh(I) with formation of [Rh(III)(por)Me] and (DMPO-like) 2,2,6-trimethyl-2,3,4,5-tetrahydro-1-pyridiniumolate. The transition state for this process (TS2) is best described as an SN2-like nucleophilic substitution involving attack of the d(z)2 orbital of [Rh(I)(por)]- at one of the C(Me)-C(ring) sigma* orbitals of [TEMPO]+. Although the calculated barrier of the open-shell radical pathway is somewhat lower than the barrier for the ionic pathway, R-DFT and U-DFT are not likely comparatively accurate enough to reliably distinguish between these possible pathways. Both the radical (SH2) and the ionic (SN2) pathway have barriers which are low enough to explain the experimental kinetic data.