Aquo Complexes Research Articles

Effect of Low Spin Excited States for Magnetic Anisotropy of Transition Metal Mononuclear Single Molecule Magnets

Rational, fine tuning of magnetic anisotropy is critical to obtain new coordination compounds with enhanced single molecule magnet properties. For mononuclear transition metal complexes, the largest contribution to zero-field splitting is usually related to the excited states of the same spin as the ground level. Thus, the contribution of lower multiplicity roots tends to be overlooked due to its lower magnitude. In this article, we explore the role of lower multiplicity excited states in zero-field splitting parameters in model structures of Fe(II) and Co(II). Model aquo complexes with coordination numbers ranging from 2 to 6 were constructed. The magnetic anisotropy was calculated by state of the art ab initio methodologies, including spin-orbit coupling effects. For non-degenerate ground states, contributions to the zero-field splitting parameter (D) from highest and lower multiplicity roots were of the same sign. In addition, their relative magnitude was in a relatively narrow range, irrespective of the coordination geometry. For degenerate ground states, the contribution from lower multiplicity roots was significantly smaller. Results are rationalized in terms of general expressions for D and are expected to be reasonably transferable to real molecular systems.

Thermodynamic Evaluation of Trace-Amount Transition-Metal-Ion Doping in NiOOH Films

In aqueous solution, NiOOH has a strong tendency to spontaneously incorporate various transition-metal ions. These impurities dramatically affect the properties of NiOOH and may have been present unknowingly in NiOOH systems throughout the past several decades. A better understanding of this tendency of NiOOH to spontaneously incorporate possible contaminants therefore is of great interest. In this work, we calculated the free energies of adsorption and incorporation of Fe3+, Co3+, and Mn4+ dopants in β-NiOOH using ab initio thermodynamics. We define the aqueous phase energies for these dopants using both calculated solid phase bulk energies and their corresponding experimental solubilities. We then demonstrate that only a weak driving force exists for adsorption of Fe3+ and Co3+ complexes on the surface of β-NiOOH and no tendency at all for the adsorption of Mn4+ aquo and hydroxo complexes. We predict a strong thermodynamic driving force for bulk incorporation of Fe3+ and Co3+, even at trace concentrations (ppb to ppm levels) under ambient and basic aqueous conditions, but no such tendency for Mn4+. These results provide a thermodynamic explanation for the scavenging and doping behavior of NiOOH observed experimentally and highlight the importance of careful control of the experimental conditions when studying this material.

Ruthenium Water Oxidation Catalysts based on Pentapyridyl Ligands.

Ruthenium complexes containing the pentapyridyl ligand 6,6''-(methoxy(pyridin-2-yl)methylene)di-2,2'-bipyridine (L-OMe) of general formula trans-[RuII (X)(L-OMe-κ-N5 )]n+ (X=Cl, n=1, trans-1+ ; X=H2 O, n=2, trans-22+ ) have been isolated and characterized in solution (by NMR and UV/Vis spectroscopy) and in the solid state by XRD. Both complexes undergo a series of substitution reactions at oxidation state RuII and RuIII when dissolved in aqueous triflic acid-trifluoroethanol solutions as monitored by UV/Vis spectroscopy, and the corresponding rate constants were determined. In particular, aqueous solutions of the RuIII -Cl complex trans-[RuIII (Cl)(L-OMe-κ-N5 )]2+ (trans-12+ ) generates a family of Ru aquo complexes, namely trans-[RuIII (H2 O)(L-OMe-κ-N5 )]3+ (trans-23+ ), [RuIII (H2 O)2 (L-OMe-κ-N4 )]3+ (trans-33+ ), and [RuIII (Cl)(H2 O)(L-OMe-κ-N4 )]2+ (trans-42+ ). Although complex trans-42+ is a powerful water oxidation catalyst, complex trans-23+ has only a moderate activity and trans-33+ shows no activity. A parallel study with related complexes containing the methyl-substituted ligand 6,6''-(1-pyridin-2-yl)ethane-1,1-diyl)di-2,2'-bipyridine (L-Me) was carried out. The behavior of all of these catalysts has been rationalized based on substitution kinetics, oxygen evolution kinetics, electrochemical properties, and density functional theory calculations. The best catalyst, trans-42+ , reaches turnover frequencies of 0.71 s-1 using CeIV as a sacrificial oxidant, with oxidative efficiencies above 95 %.

Inclusion and exclusion complexes of cucurbit[7]uril with silver cations

We describe a strategy to prepare cucurbit [7]uril(Q [7])-Mn+ complexes in an ammonia medium, in which a competitive coordination of metal ions to ammonia molecules or Q [7] molecules occurs. Using this strategy, a novel compound consisting of Q [7] and a metal Ag+ ion was obtained. The X-ray crystal structure of this compound showed an infinite 2D network comprising three-Q [7] units and with a cavity size of around 11.0Å×5.5Å. Moreover, a Q [7]-based host-guest inclusion Ag+ aquo complex was observed. Considering the generality of the behavior shown in the complexes described, this phenomenon may well deserve further study.

Metal ion complexation by tetraphosphonate cavitands: The influence of the ionic radius

Two new complexes formed by tetraphosphonate cavitands with lead and copper salts, respectively, have been prepared and characterized in the solid state through X-ray diffraction analysis. In both cases, dimeric capsules are obtained, whose architecture depends on the cation dimensions: the coordination of the phosphonate groups to the metal center is direct in the case of lead, but it is mediated by an aquo complex through a second-coordination sphere in the copper compound.

Two new cocrystals of lanthanide aquo complexes with aromatic molecules

Two new cocrystals of lanthanide aquo complexes with aromatic molecules

An NMR relaxivity and ESR study of the interaction of the paramagnetic manganese(II) and gadolinium(III) ions with anionic, cationic and neutral water-soluble polymers and their mixtures

Solutions of the series of polymers (sodium polystyrene sulfonate, polyethyleneimine, and poly-N-vinylpyrrolidone) and certain mixtures thereof were studied by NMR relaxation and ESR spectroscopy using manganese(II) and gadolinium(III) ions as paramagnetic probes. The growth of the NMR-relaxation efficiency (relaxivity, R1,2) is observed in solutions of the anionic polymer, as well as the decrease of R1,2 - in the case of the cationic polymer. For mixtures of polymers, the dependent on the solution composition non-monotonic changes of R1,2 are caused either by a formation of metal-interpolymer complexes or by a competitive cation/polymer substitution. For both ions, the changes in the ESR spectra of their polyelectrolyte solutions were analyzed. In case of sodium polystyrene sulfonate and blends thereof, the ESR spectra parameters are only slightly broadened compared to the pure metal aqua ion's, whereas for the polyethyleneimine solution the ESR spectra lines broaden greatly at pH>7 up to their disappearance. All these effects were explained by the distinction of ion probes' binding mode to polyelectrolytes of different nature. Addition of NaCl to manganese(II) solutions containing polystyrene sulfonate, or mixtures thereof with PVP or PEI, lead to recovery of R1,2 values, close to the probes' aqua ions relaxivities due to the release of the latter from the polymer/medium interface into the bulk water, while no changes were detected for PEI solutions.

Photoisomerization of ruthenium(ii) aquo complexes: mechanistic insights and application development.

Ruthenium(ii) complexes with polypyridyl ligands have been extensively studied as promising functional molecules due to their unique photochemical and photophysical properties as well as redox properties. In this context, we report the photoisomerization of distal-[Ru(tpy)(pynp)OH2]2+ (d-1) (tpy = 2,2';6',2''-terpyridine, pynp = 2-(2-pyridyl)-1,8-naphthyridine) to proximal-[Ru(tpy)(pynp)OH2]2+ (p-1), which has not been previously characterized for polypyridyl ruthenium(ii) aquo complexes. Herein, we review recent progress made by our group on the mechanistic insights and application developments related to the photoisomerization of polypyridyl ruthenium(ii) aquo complexes. We report a new strategic synthesis of dinuclear ruthenium(ii) complexes that can act as an active water oxidation catalyst, as well as the development of unique visible-light-responsive giant vesicles, both of which were achieved based on photoisomerization.

Rates of Water Exchange in 2,2′-Bipyridine and 1,10-Phenanthroline Complexes of CoII and MnII

The rates and activation parameters of water exchange at pH 3.0 have been determined using variable temperature 17O NMR spectroscopy for four CoII complexes and one MnII complex: [Co(bpy)(H2O)4]2+, [Co(bpy)2 (H2O)2]2+, [Co(phen)-(H2O)4]2+, [Co(phen)2 (H2O)2]2+, and [Mn(bpy)(H2O)4]2+ (bpy = 2,2′-bipyridyl and phen = 1,10-phenanthroline). Substitution of aquo ligands with 1,10-phenanthroline or 2,2′-bipyridyl leads to an increase in the rate of exchange in the manganese complexes, from k298 (1.8 ± 0.1) × 107 s−1 for [Mn(H2O)6]2+ to (7.2 ± 0.3) × 107 s−1 for [Mn(phen)2 (H2O)2]2+, whereas the trends are more complex for the cobalt complexes. We have used the new data in conjunction with literature data for similar complexes to analyse the effect of M–OH2 distance and degree of substitution.

Paramagnetism of Aqueous Actinide Cations. Part II: Theoretical Aspects and New Measurements on An(IV).

The magnetic properties of actinide(IV) (An(IV)) cations are investigated in various solutions (HClO4, HCl, and HNO3) by the Evans NMR method. The magnetic susceptibilities measured in noncomplexing medium are compared with the previous studies, and the influence of the medium is verified with new measurements in complexing solutions. To rationalize these results, spin-orbit complete active space perturbation theory at second order calculations are performed on the free ions and on the aquo complexes to determine the nature of electronic states, the magnetic susceptibility, and the UV-visible-near-IR spectra. The different factors contributing to the An(IV) magnetic properties were identified. The ligand field effect on the magnetic behavior (Curie constant and temperature-independent susceptibilities) was analyzed by considering different solvation environments. These results indicate a significant effect of the zero-field splitting of the ground J manifold on the An(IV) magnetic susceptibility.

Identifying Coordination Geometries of Metal Aquaions in Water: Application to the Case of Lanthanoid and Actinoid Hydrates.

The angular distribution function (ADF) associated with the oxygen-metal ion-oxygen angle (OMO) of several trivalent lanthanoid and actinoid aquaions has been used to identify the most probable coordination geometry of these aquaions in aqueous solutions. The ADFs extracted from the molecular dynamics trajectories have been compared with continuous distribution functions corresponding to the geometry of a reference polyhedron pattern. The procedure incorporates specific quantum-mechanical information on the aquaion under study. The new method is applied to the analysis of four M(H2O)n3+ aquaions in water, M = Lu and Cf for n = 8, and M = La and Ac for n = 9. For those that are 8-coordinated, the square antiprism (SA) coordination geometry is preferred. For the 9-fold coordination, the simulation ADFs are more similar to the continuous ADF derived from a Gyro-elongated-SA rather than to the usually proposed trigonal tricapped prism. Advantages of these continuous distributions with respect to the usually employed discrete distributions are emphasized as well as further applications are suggested.

Synthesis of Ag nanoparticles on oxide and carbon supports from Ag diammine precursor

To determine whether the method of “strong electrostatic adsorption” (SEA) can be extended to the preparation of uniform and highly dispersed supported Ag catalysts, the adsorption of silver diammine, Ag(NH3)2+, also known as Tollen’s reagent, has been examined over five supports (i.e., SiO2, γ-Al2O3, ZrO2, Nb2O5, and carbon) with different surface areas and PZCs. The speciation of Ag in solution was followed by UV–vis spectroscopy, Ag uptake as a function of the solution pH was determined by atomic absorption, and Ag particle size was determined by powder XRD and STEM.At the Ag concentrations, pH, and surface loadings employed, silver diammine complexes convert into soluble Ag(H2O)2+ aquo complexes below pH 11 and hydrolyze to insoluble Ag2O above pH 11. The deposition of either Ag species over carbon at any pH appears to be reactive and results in large particles. The silver aquo complexes appear to adsorb via ion exchange near the PZC of alumina, zirconia, and niobia but not silica, while the silver diammine complexes appear to adsorb electrostatically at high pH over all the oxides tested - niobia, silica, zirconia, and alumina in the order of ascending PZC. Niobia, which has the lowest PZC, adsorbs the highest surface density of Ag via both mechanisms. The particles obtained via electrostatic adsorption of Ag(NH3)2+ at high pH are somewhat smaller than those formed from Ag(H2O)2+ ions at the lower pH values. In the absence of ammonia in solution at high pH, deposition of Ag aquo complexes occurs via surface precipitation and gives large particles. In sum, SEA of silver ammine is demonstrated to be a simple, reproducible way to synthesize small particles on all supports but carbon.

The secondary coordination sphere and axial ligand effects on oxygen reduction reaction by iron porphyrins: a DFT computational study.

Oxygen reduction reaction (ORR) catalyzed by a bio-inspired iron porphyrin bearing a hanging carboxylic acid group over the porphyrin ring, and a tethered axial imidazole ligand was studied by DFT calculations. BP86 free energy calculations of the redox potentials and pK a's of reaction components involved in the proton coupled electron transfer (PCET) reactions of the ferric-hydroxo and -superoxo complexes were performed based on Born-Haber thermodynamic cycle in conjunction with a continuum solvation model. The comparison was made with iron porphyrins that lack either in the hanging acid group or axial ligand, suggesting that H-bond interaction between the carboxylic acid and iron-bound hydroxo, aquo, superoxo, and peroxo ligands (de)stabilizes the Fe-O bonding, resulting in the increase in the reduction potential of the ferric complexes. The axial ligand interaction with the imidazole raises the affinity of the iron-bound superoxo and peroxo ligands for proton. In addition, a low-spin end-on ferric-hydroperoxo intermediate, a key precursor for O-O cleavage, can be stabilized in the presence of axial ligation. Thus, selective and efficient ORR of iron porphyrin can be achieved with the aid of the secondary coordination sphere and axial ligand interactions.

PICVib: an accurate, fast and simple procedure to investigate selected vibrational modes at high theoretical levels and evaluate Raman intensities

Raman intensities and depolarization ratios are important properties to assign the vibrational spectrum and thus to characterize substances and materials. Practical and reliable computational methods are relevant to guide and aid the assignment and interpretation of Raman spectra. The procedure for investigating categories of vibrations (PICVib) approach is generalized for the Raman intensity calculations, and it is shown to be successful and to preserve all interesting features of the procedure such as easiness of implementation, parallelization, flexibility and treatment of large systems at high theoretical levels. The PICVib method involves calculations of the polarizability tensors at the displaced structures to provide the Raman intensities of selected normal modes, in addition to their vibrational wavenumbers and infrared intensities. It was validated for very diverse molecular systems: XH3 (D3h), YH4 (D4h), conformers of 1,3,5-trinitro-1,3,5-triazacyclohexane, SN2 and E2 product complexes, fullerene C60, lanthanide ion aquo complexes and hydrogen-bonded complexes (water–water, water–methanol and methanol–methanol) including the guanine-cytosine pair. This assessment shows an excellent overall performance of the PICVib method for calculating Raman intensities of localized normal modes and even mixed vibrations. For vibrations involving intermolecular complexes, the choice of the lower level method (e.g. density functionals and semiempiricals) is crucial. This makes the PICVib procedure practically complete for vibrational analysis of molecular systems and should now be generalized for extended and periodic systems. Copyright © 2016 John Wiley & Sons, Ltd.

Topological Study of Bonding in Aquo and Bis(triazinyl)pyridine Complexes of Trivalent Lanthanides and Actinides: Does Covalency Imply Stability?

The geometrical and electronic structures of Ln[(H2O)9]3+ and [Ln(BTP)3]3+, where Ln = Ce-Lu, have been evaluated at the density functional level of theory using three related exchange-correlation (xc-)functionals. The BHLYP xc-functional was found to be most accurate, and this, along with the B3LYP functional, was used as the basis for topological studies of the electron density via the quantum theory of atoms in molecules (QTAIM). This analysis revealed that, for both sets of complexes, bonding was almost identical across the Ln series and was dominated by ionic interactions. Geometrical and electronic structures of actinide (An = Am, Cm) analogues were evaluated, and [An(H2O)9]3+ + [Ln(BTP)3]3+ → [Ln(H2O)9]3+ + [An(BTP)3]3+ exchange reaction energies were evaluated, revealing Eu ↔ Am and Gd ↔ Cm reactions to favor the An species. Detailed QTAIM analysis of Eu, Gd, Am, and Cm complexes revealed increased covalent character in M-O and M-N bonds when M = An, with this increase being more pronounced in the BTP complexes. This therefore implies a small electronic contribution to An-N bond stability and the experimentally observed selectivity of the BTP ligand for Am and Cm over lanthanides.

Kinetico-mechanistic Studies on the Substitution Reactivity on the {Ru(II)(bpy)2} Core with Nucleosides and Nucleotides at Physiological pH.

The kinetico-mechanistic study of the substitution reactions of the aquo ligands in cis-[Ru(bpy)2(H2O)2](2+) by different nucleotides and nucleosides has been conducted at pH close to the physiological value. The concentration dependence and thermal and pressure activation parameters have been measured to ascertain the activation via which reactions take place. Substitution processes are found associatively activated for nitrogen-bonded nucleosides or nucleotides, with outer-sphere hydrogen-bonded aggregates being determinant. For reactions leading to oxygen-bonded nucleotides, the process is clearly dissociatively activated. A selectively induced lability of the inert {Ru(II)(bpy)2} core is observed on the formation of nitrogen(amide)-bonded complexes at relatively low pH values, which might be relevant for the effective intercalation of designed, ruthenium(II)-bonded, aromatic rings.

Zinc Coordination Polymers Containing the m-(2-thiazolyl)benzoic Acid Spacer: Synthesis, Characterization and Luminescent Properties in Aqueous Solutions

Four 1D coordination polymers have been prepared, starting from ZnII salts and the organic linker m-(2-thiazolyl)benzoic acid (HL), also combined with auxiliary ligands: [Zn2(L)4(H2O)⋅2(MeCN)]∞ (1), [Zn2(L)3(NO3)(bipy)]∞ (2; bipy = 4,4′-dipyridyl), [Zn2(L)4(bipy)]∞ (3), [Zn2(L)4(PyEtPy)]∞ [4; PyEtPy = 1,2-bis(4-pyridyl)ethane]. In all species, the Zn2(carboxylate)4 “paddle-wheel” dimer is the constituting inorganic node, where the carboxylate groups from L- are bridging two adjacent metal centers. The square pyramidal metal coordination environment is completed by aquo ligands and the N(thiazole) atoms (in 1) or by the N donors from auxiliary bridging spacers like bipy (in 2 and 3) or PyEtPy (in 4). The luminescent properties in aqueous solutions of 3 and 4 have been examined. The N and S donors dangling from the thiazole rings in these polymers can engage into further supramolecular interactions with (acidic) metal cations, inducing a luminescence quenching after complexation. The interaction of 3 and 4 with HgII (in the form of its chloride salt HgCl2) has been analyzed as a representative example of this behaviour.

Exploring the Potential of (99m)Tc(CO)3-Labeled Triazolyl Peptides for Tumor Diagnosis.

In recent years the authors have reported on (99m)Tc(CO)3-labeled peptides that serve as carriers for biomolecules or radiopharmaceuticals to the tumors. In continuation of that work they report the synthesis of a pentapeptide (Met-Phe-Phe-Gly-His; pep-1), a hexapeptide (Met-Phe-Phe-Asp-Gly-His; pep-2), and a tetrapeptide (Asp-Gly-Arg-His; pep-3) and the attachment of 3-amino-1,2,4-triazole to the β carboxylic function of the aspartic acid unit of pep-2 and pep-3. The pharmacophores were radiolabeled in high yields with [(99m)Tc(CO)3(H2O)3](+) metal aqua ion, characterized for their stability in serum and saline, as well as in His solution, and found to be substantially stable. B16F10 cell line binding studies showed favorable uptake and internalization. In vivo behavior of the radiolabeled triazolyl peptides was assessed in mice bearing induced tumor. The (99m)Tc(CO)3-triazolyl pep-3 demonstrated rapid urinary clearance and comparatively better tumor uptake. Imaging studies showed visualization of the tumor using (99m)Tc(CO)3-triazolyl pep-3, but due to high abdominal background, low delineation occurred. Based on the results further experiments will be carried out for targeting tumor with triazolyl peptides.

Speciation and thermodynamic properties of zinc in sulfur-rich hydrothermal fluids: Insights from ab initio molecular dynamics simulations and X-ray absorption spectroscopy

Chlorine and sulfur are the main elements involved in the complexing of metals in ore-forming fluids. The nature and thermodynamic properties of the Zn(II)–Cl complexes have been investigated by previous experimental and theoretical studies and are now well established up to high temperatures (600°C). In contrast, the role of bisulfide complexes for zinc speciation in sulfur-bearing fluids remains poorly known, and a better understanding of Zn(II)–HS complexation is required for modeling zinc transport in magmatic and metamorphic fluids and for optimizing the hydrometallurgical processing of sulfide ores.We have conducted ab initio molecular dynamics (MD) simulations to calculate the speciation of Zn(II)–HS complexes from ambient to hydrothermal-magmatic conditions (25–600°C, up to 2000bar). These theoretical calculations were complemented by X-ray absorption spectroscopy (XAS) measurements of Zn(II) in HS−-rich solutions at 200–500°C and 600–1000bar. The speciation and geometrical properties predicted by the ab initio MD simulations and the in situ XAS data are in excellent agreement. Upon heating from room temperature to 250°C, Zn(II) speciation in HS−-rich solutions shows a transition from the sixfold octahedral hexaaquo complex [Zn(H2O)6]2+ to fourfold tetrahedral [Zn(HS)n(H2O)4−n]2−n complexes (n=1–4). Ab initio MD simulations also show that at temperatures>250°C, the threefold trigonal-planar [Zn(HS)3]− complex becomes increasingly stable, and predominates in S-rich solutions; in contrast, chloro-complexes display a tetrahedral geometry at 25–500°C, while trigonal planar ZnCl3− predominates at temperatures>500°C. The stability constants of Zn(II)–HS complexes were calculated by thermodynamic integration of constrained ab initio MD simulations at 200, 350 and 600°C. The stability constants generated from this study predict that zinc can be transported by HS− at high temperature in reduced, neutral to alkaline solutions, while Zn chloride complexes dominate in acidic fluids.

Know-how and Know-why Nutrients may be Less Bioaccessible and Less Bioavailable due to Proton Pump Inhibitor - Food Interactions and Incompatibilities Involving Metal-Aquo Complexes

Background: Proton pump inhibitors change gastric pH from around 2.0 to 2.5 to more than 4.0 for up to 16 hours per day and suppress gastric function widely. Risk factors assigned to long-term inhibition of gastric acidity arise from cleavage-resistance of peptides and glycosides, mucosal degeneration and leak, loss of bactericidal action, and modification of absorption kinetics of medicines and nutrients. This article aims to contribute to wisely use of proton pump inhibitors and to recommend nutritional options. Methods: A systematic online literature research was performed on usual platforms. Recommendations rely on a multidisciplinary focus group assessment. Explanations arising from the retrieved references were tested for consistency by titration of iron solution from acidic to basic pH while observing precipitation. Results and discussion: Literature describes bacterial overgrowth, community and hospital-acquired pneumonia, childhood asthma related to PPI treatments of mothers in pregnancy, sensitization to food allergens in the elderly and in pregnant women (as progesterone slows down gastric emptying), deterioration of intolerances, and various diseases such as celiac and inflammatory diseases. In addition to pathologies, bioavailability of medicines may be modified dramatically. For micronutrients, aquo-complexes of metal ions revealed to be a neglected issue in research of food-drug interactions arising from PPI treatments. To prevent these complications, a focus group from a clinical support team recommends intermittent and ondemand strategies, alternative antacids, avoidance of high allergenic food, buffering, pepsin replacement, stimulation of digestion and peristalsis, and physical activity, and medicines review and reconciliation. Conclusion: Proton pump inhibitor safety profiles are troubled by risk factors arising from inappropriate longterm use. Drugs’ bioavailability may increase as a result of mucosal hyperpermeability, or decrease as a result of altered dissociation. Care should be given to substrates with pKa<4.5 as well as to micronutrient supply. At least children and pregnant women should prefer alternative antacids.