Environment Of Metal Ions Research Articles

Host-Guest-Induced Environment Tuning of 3d Ions in a Polyoxopalladate Matrix.

A series of unprecedented supramolecular associates of phenylarsonate-capped {MII PdII 12 O8 }-type (M=Co, Ni and Zn) polyoxopalladates with α-cyclodextrins (α-CD) was obtained and characterized in the solid state (single-crystal X-ray diffraction (XRD), FT-IR spectroscopy, elemental and thermogravimetric (TGA) analyses), in aqueous solution (1 H and 13 C NMR) and in the gas phase (ESI-MS). The non-covalent host-guest interactions between the organopolyoxoanions and α-CD rings alter the O8 coordination environment of a 3d transition metal ion (MII ) situated at the center of a cuboid polyoxododecapalladate shell. This synthetically controlled "chemical pressure" effectively induces axial distortion of the otherwise cubic polyoxopalladate environment between two trans-positioned α-CD moieties. Its effect on the magnetic properties and the electronic structure of the CoII derivative was assessed in a combined SQUID magnetometry, EPR, X-ray magnetic circular/linear dichroism (XMCD/XMLD), and X-ray absorption near-edge structure (XANES) spectroscopy study.

Three hybrid tungstosilicates: Confinement of SiW12O404− anions in rigid concave surfaces with excellent nonlinear optical performance and interesting magnetic properties

Three novel polyoxoanion-based organic–inorganic compounds confined by the conjugate organic ligand tris(2-benzimidazylmethyl)amine (NTB) [Co(NTB)]2(SiW12O40)·4H2O (1) [Zn(NTB)]2(SiW12O40)·4H2O (2) and [Ni(NTB)(H2O)]2(SiW12O40)(C2H5OH)2·12H2O (3) have been synthesized successfully by using of hydrothermal synthesis. The penta-coordinate environment of metal ions for compound 1 and compound 2 leads to the formation of trigonal bipyramid, which was less to see in other polyoxoanion-based compounds. All three compounds are constituted of the [SiW12O40]4− unit and M(NTB) unit. The two-photon absorption (TPA) cross section σ value of three compounds are calculated as 1826, 2253 and 1470 GM (1 GM = 10−50 cm4 s/photon), respectively. The compound 2 reveals the biggest σ value among the NTB-modified POMs. Furthermore, the compounds 1 and 3 show intriguing paramagnetic performance. The effect of different metal ions on optical property would also be investigated.

Crystal Chemistry of Zinc Quinaldinate Complexes with Pyridine-Based Ligands

Substitution of methanol in [Zn(quin)2(CH3OH)2] (quin− denotes an anionic form of quinoline-2-carboxylic acid, also known as quinaldinic acid) with pyridine (Py) or its substituted derivatives, 3,5-lutidine (3,5-Lut), nicotinamide (Nia), 3-hydroxypyridine (3-Py-OH), 3-hydroxymethylpyridine (3-Hmpy), 4-hydroxypyridine (4-Py-OH) and 4-hydroxymethylpyridine (4-Hmpy), afforded a series of novel heteroleptic complexes with compositions [Zn(quin)2(Py)2] (1), [Zn(quin)2(3,5-Lut)2] (2), [Zn(quin)2(Nia)2]·2CH3CN (3), [Zn(quin)2(3-Py-OH)2] (4), [Zn(quin)2(3-Hmpy)2] (5), [Zn(quin)2(4-Pyridone)] (6) (4-Pyridone = a keto tautomer of 4-hydroxypyridine), and [Zn(quin)2(4-Hmpy)2] (7). In all reactions, the {Zn(quin)2} structural fragment with quinaldinate ions bound in a bidentate chelating manner retained its structural integrity. With the exception of [Zn(quin)2(4-Pyridone)] (6), all complexes feature a six-numbered coordination environment of metal ion that may be described as a distorted octahedron. The arrangement of ligands is trans. The coordination sphere of zinc(II) in the 4-pyridone complex consists of only three ligands, two quinaldinates, and one secondary ligand. The metal ion thereby attains a five-numbered coordination environment that is best described as a distorted square-pyramid (τ parameter equals 0.39). The influence of substituents on the pyridine-based ligand over intermolecular interactions in the solid state is investigated. Since pyridine and 3,5-lutidine are not able to form hydrogen-bonding interactions, the solid state structures of their complexes, [Zn(quin)2(Py)2] (1) and [Zn(quin)2(3,5-Lut)2] (2), are governed by π···π stacking, C–H∙∙∙π, and C–H∙∙∙O intermolecular interactions. With other pyridine ligands possessing amide or hydroxyl functional groups, the connectivity patterns in the crystal structures of their complexes are governed by hydrogen bonding interactions. Thermal decomposition studies of novel complexes have shown the formation of zinc oxide as the end product.

Syntheses, crystallization and selective dye adsorption of three Co(II) coordination polymers via one-pot reaction

Three novel Co(II) coordination polymers, namely [Co(HL)(4,4′-bibp)]n (1), [Co(HL)(4,4′-bibp)]n (2) and {[Co2(L)(4,4′-bibp)2(H2O)3(HCOO)]·2H2O·HCOOH}n (3) (H3L=5-(2′′-carboxylphenoxy)isophthalic, 4,4′-bibp=4,4′-bis(imidazol-1-yl)biphenyl) were synthesized through one-pot reaction under co-crystallization conditions. These complexes were characterized by elemental analysis, IR spectra, powder X-ray diffraction (PXRD), thermogravimetric (TG) analysis and single-crystal X-ray diffraction. Complexes 1 and 2 were supramolecular isomers with different 2D configurations. Complex 1 shows a sql 2D-network with a [Co(HL2−)]n single-strand helix chain and another [Co(4,4′-bibp)]n single-strand helix chain, which are further assembled into 3D supramolecular architectures through H-bonds and C–H⋯N bonds. While complex 2 exhibits another 2D-network with two different [Co(HL2−)]n helix chains (left and right) and one [Co(4,4′-bibp)]n zigzag chain, which further constructing a 3D supramolecular structure through H-bonds. Compared with 1 and 2, 3 also shows a sql 2D-network with a bigger channel which influenced by the coordination environment of metal ions. Furthermore, the selective dye adsorption studies indicate that complex 1 can highly and selectively adsorb Methyl Orange (MO) in a short time, and complex 2 shows a highly adsorption activity for Alizarin Red S (ARS) than Methyl Orange, and complex 3 can selectively adsorb Methyl Orange.

Thiophene-thiazole functionalized oligomers-excellent fluorescent sensing and selective probe for copper and iron ion

This paper reports the fluorescent and colorimetric sensing of Cu2+ and Fe2+ using thiophene-thiazole functionalized conjugated oligomers from water samples. Oligomers namely, oligo-4,5-bis-{2-[5-(2-thiophene-2-yl-vinyl)thiophene-2-yl]-vinyl}-thiazole (OBTV-TZ) and oligo-2,4,5-tris-{2-[5-(2-thiophene-2-yl-vinyl) thiophene-2-yl]-vinyl}-thiazole (OTTV-TZ) were synthesized through Wittig condensation and confirmed from FT-IR, 1H NMR and LCMS analysis. The effects of the thiophene and thiazole rings in the oligomer towards metal ion sensing applications were systematically investigated. The color of both oligomers was changed from pale yellow to pale green and dark yellow by the addition of Cu2+ and Fe2+ ions respectively. Upon adding Cu2+ and Fe2+, both sensors displayed a new absorption peak at around 207nm which forms hyper and hypochromic effects. The detection limit (LOD) of Cu2+ for OBTV-TZ and OTTV-TZ was 1.04 and 0.988×10−5M respectively. Both oligomers were successfully regained from the Fe2+ coordinated system by adding of EDTA. A high selectivity of Cu2+ and Fe2+ using these oligomers in a competent environment of several other metal ions was successfully observed. The electrochemical studies revealed that HOMO and LUMO values of the oligomers increased after mixing with Cu2+ and Fe2+. The LUMO value of the oligomer (OTTV-TZ) was sensed to −3.35 and −3.15eV after incorporating Cu2+ and Fe2+. Both oligomers exhibited wide pH response in absorbance (pH=5–10) and fluorescence intensities (pH=2–9).

Highly efficient bio-sorption of trivalent f-elements using wild type Rhizopus arrhizus dead fungus

Wild type Rhizopus arrhizus biomass was demonstrated as highly efficient bio-sorbent for trivalent f-elements. Both Am3+ and Eu3+ were found to follow the Fruendlich isotherm through chemi-sorption. The sorption for Am3+ was found be faster compared to Eu3+ while both proceeded via pseudo-second order reaction. EDTA was found to be effective strippant whereas up to 500 kGy, the bio-sorbent showed high radiolytic stability. Luminescence employed for probing the local environment of metal ion on sorption which revealed the presence of single adsorbed species with no inner sphere water molecules. The covalency of metal–ligand bond enhanced on complexation with the bio-sorbent.

Polymorphism in a Cobalt-Based Single-Ion Magnet Tuning Its Barrier to Magnetization Relaxation.

A large barrier to magnetization reversal, a signature of a good single-molecule magnet (SMM), strongly depends on the structural environment of a paramagnetic metal ion. In a crystalline state, where SMM properties are usually measured, this environment is influenced by crystal packing, which may be different for the same chemical compound, as in polymorphs. Here we show that polymorphism can dramatically change the magnetic behavior of an SMM even with a very rigid coordination geometry. For a cobalt(II) clathrochelate, it results in an increase of the effective barrier from 109 to 180 cm-1, the latter value being the largest one reported to date for cobalt-based SMMs. Our finding thus highlights the importance of identifying possible polymorphic phases in search of new, even more efficient SMMs.

Modifying magnetic properties and dispersity of few-layer MoS2 particles by 3d metal carboxylate complexes

The interaction of MoS2 sheets produced by chemical exfoliation of LiMoS2 in liquid media with trinuclear metal carboxylate complexes of the general formula [M3(O2CR)6L3]n+ (M = Fe, Co; R = CH3, C(CH3)3, CH2N+(CH3)3; L = H2O or pyridine) was studied. The composition, structure and dispersity of the obtained materials as well as the distribution of magnetically active metal cations within their particles were analyzed on the basis of PXRD, SEM, TEM, HAADF-STEM, TGA-MS and magnetic measurements data. The interaction process was found to result in the displacement of the important part of carboxylate ligands from coordination environment of metal ions and formation of metal oxide-like nanoclusters. These nanoclusters are distributed within the surface of MoS2 sheet packets of the thickness of 4–6 nm, which are formed due to restacking of exfoliated MoS2. The metal complexes strongly influence sheet restacking, leading to a significantly lower (up to ∼ 1.5 times) thickness of the sulfide packets than in their absence. The metal atoms constituting oxide nanoclusters exhibit strong antiferromagnetic interactions.

The role of metals in protein conformational disorders - The case of prion protein and Aβ -peptide

Protein conformational disorders are members of a vast class of pathologies in which endogenous proteins or peptides undergo a misfolding process by switching from the physiological soluble configuration to a pathological fibrillar insoluble state. An important, but not yet fully elucidated, role in the process appears to be played by transition metal ions, mainly copper and zinc. X-ray absorption spectroscopy is one of the most suitable techniques for the structural characterization of biological molecules in complex with metal. Owing to its chemical selectivity and sensitivity to the local atomic geometry around the absorber, it can be successfully used to study the environment of metal ions in complex with proteins and peptides in physiological conditions. In this paper we present X-ray absorption spectroscopy studies of the metal ions coordination modes in systems where metals are complexed with specific amyloidogenic proteins and peptides. In particular, we show results concerning the Amyloid β peptide, that is involved in Alzheimer's disease, and the Prion protein, that is responsible for the Transmissible Spongiform Encephalopathy. Our findings suggest that the copper and zinc ions may play a crucial role in the aggregation and fibril formation process of these two biomolecules. Elucidating this kind of interaction could be a key preliminary step before any viable therapy can be conceived or designed.

Local environment of metal ions in phthalocyanines: K-edge X-ray absorption spectra.

We report a detailed study of the K-edge X-ray absorption spectra of four transition metal phthalocyanines (MPc, M = Fe, Co, Cu and Zn). We identify the important single and multiple scattering contributions to the spectra in the extended energy range and provide a robust treatment of thermal damping; thus, a generally applicable model for the interpretation of X-ray absorption fine structure spectra is proposed. Consistent variations of bond lengths and Debye Waller factors are found as a function of atomic number of the metal ion, indicating a variation of the metal-ligand bond strength which correlates with the spatial arrangement and occupation of molecular orbitals. We also provide an interpretation of the near edge spectral features in the framework of a full potential real space multiple scattering approach and provide a connection to the local electronic structure.

Migration and transformation rule of heavy metals in sludge during hydrolysis for protein extraction.

The content and speciation of heavy metals can fundamentally affect the hydrolysis of sludge. This research study investigates the migration and transformation rule of heavy metals during the hydrolysis process by measuring the content of exchangeables (F1), bound to carbonates (F2), bound to Fe-Mn oxides (F3), bound to organic matter (F4), and residuals (F5) under different periods of time undergoing hydrolysis. The results show that the hydrolysis process generally stabilized Cu, Zn, Mn, Ni, Pb, Cr, and As by transforming the unstable states into structurally stable states. Such transformations and stabilization were primarily caused by the changes in local metal ion environment and bonding structure, oxidation of sulfides, pyrolyzation of organic matter, and evaporation of resulting volatile materials. An X-ray diffractometry (XRD) of the residuals conducted after hydrolysis indicated that hydrolysis did have a significant influence on the transportation and transformation of heavy metals.

The Leaching of Valuable Metal from Mine Waste Rock by the Adaptation Effect and the Direct Oxidation with Indigenous Bacteria

The aim of this study was leaching valuable metal ions from mine waste rocks which were abandoned mine site using indigenous aerobic bacteria. In order to tolerate the the indigenous aerobic bacteria to the heavy metal ions they were repeatedly adapted in environment. As the repeated generation-adaptation progressed, the pH values of the growth-medium were gradually decreased. During bio-leaching experiments with indigenous aerobic bacteria raised in a heavy metal ion environment for 42 days, the pH of the leaching solution was decreased while increasing the adaptation period. The indigeous bacteria were much more active on the surface of Younhwa waste rocks which contained relatively few the chalcopyrite and Cu content than the Goseong mine waste rocks, and also the amount of Cu and Fe ions were leached more in the Younhwa sample(leaching rate of 92.79% and 55.88%, respectively) than the Goseong sample(leaching rate of 66.77% and 21.83%, respectively). Accordingly, it is confirmed that valuable metal ions can be leached from the mine waste rocks, if any indigenous bacteria which inhabits a mine environment site for a long time with heavy metal ions can be used, and these bacteria can be progressively adapted in the growth-solutions containing the target heavy metals.

Dioxygen Activation by an in situ Reduced Cu II Hydrazone Complex

A CuII hydrazone complex has been synthesized that can be reduced in situ in boiling methanol to give the corresponding CuI complex. The latter complex readily activates dioxygen under ambient conditions, as was unambiguously shown by isotopic labeling studies. As a consequence of the dioxygen activation, the thienyl moiety appended to the hydrazone ligand is easily oxidized in β position (C–H C–O), finally leading to a change in the coordination environment of the central metal ion. All relevant complexes have been structurally characterized by single-crystal X-ray diffraction analyses. The hydrazone ligand applied in this study does not mimic a biologically relevant coordination motif in copper-containing oxygenases. Nonetheless, the reactivity of the CuI complex resembles that found in many oxygenases, indicating that hydrazone ligands may be well-suited for the generation of novel bioinspired oxidation catalysts.

Complexes of 2,6-diacetylpyridine dihydrazone with middle and late first row transition metals

A study of the transition metal chemistry with the planar tridentate ligand 2,6-diacetylpyridine dihydrazone (1, DAPH) is presented, expanding the chemistry of this ligand across the first row of the transition metals. Ligand 1 forms both 1:1 and homoleptic 2:1 complexes with transition metal ions, depending on the metal salt used and reaction conditions, and seven new complexes with Mn, Fe, Co, Cu and Zn are presented. All compounds, including the ligand, have been characterized by X-ray crystallography. DAPH (1) binds to metal ions in an asymmetric fashion, with a M–Npyr bond that is shorter than the flanking M–Nimine bonds. Additionally, the Nimine–M–Nimine bonds form acute angles ranging from ~140 to 160°, depending on the identity of the metal ion and ligand environment. All compounds are compared with previously elucidated DAPH structures from the literature.

Near-UV and blue wavelength excitable Mg0.6Ca2.16Mo0.2W0.8O6: Eu0.123+/Na0.12+ high efficiency red phosphors

Red phosphors with narrow emission around 615nm (with FWHM~5–10nm) having chemical compositions of A0.6Ca2.16Mo0.2W0.8O6: Eu0.123+/Na0.12+ (A=Mg, Sr) have been found to exhibit the highest luminescence amongst the molybdate–tungstate family when excited by sources in the 380–420nm wavelength range. Thus they are most suitable for enhancing color rendering index and lowering color temperature in phosphor converted white LEDs (pc-WLEDs) with near-UV/blue LED excitation sources. The excitation band edge in the near UV/blue wavelength in the reported phosphor has been attributed to the coordination environment of the transition metal ion (Mo6+, W6+) and host crystal structure. Furthermore the quantum efficiency of the phosphors has been enhanced by adjusting activator concentration, suitable compositional alloying using substitutional alkaline earth metal cations and charge compensation mechanisms.

Evolutionary implications of metal binding features in different species' prion protein: an inorganic point of view.

Prion disorders are a group of fatal neurodegenerative conditions of mammals. The key molecular event in the pathogenesis of such diseases is the conformational conversion of prion protein, PrPC, into a misfolded form rich in β-sheet structure, PrPSc, but the detailed mechanistic aspects of prion protein conversion remain enigmatic. There is uncertainty on the precise physiological function of PrPC in healthy individuals. Several evidences support the notion of its role in copper homeostasis. PrPC binds Cu2+ mainly through a domain composed by four to five repeats of eight amino acids. In addition to mammals, PrP homologues have also been identified in birds, reptiles, amphibians and fish. The globular domain of protein is retained in the different species, suggesting that the protein carries out an essential common function. However, the comparison of amino acid sequences indicates that prion protein has evolved differently in each vertebrate class. The primary sequences are strongly conserved in each group, but these exhibit a low similarity with those of mammals. The N-terminal domain of different prions shows tandem amino acid repeats with an increasing amount of histidine residues going from amphibians to mammals. The difference in the sequence affects the number of copper binding sites, the affinity and the coordination environment of metal ions, suggesting that the involvement of prion in metal homeostasis may be a specific characteristic of mammalian prion protein. In this review, we describe the similarities and the differences in the metal binding of different species’ prion protein, as revealed by studies carried out on the entire protein and related peptide fragments.

Role of Crystal Field in Mixed Alkali Metal Effect: Electron Paramagnetic Resonance Study of Mixed Alkali Metal Oxyfluoro Vanadate Glasses

The mixed alkali metal effect is a long-standing problem in glasses. Electron paramagnetic resonance (EPR) is used by several researchers to study the mixed alkali metal effect, but a detailed analysis of the nearest neighbor environment of the glass former using spin-Hamiltonian parameters was elusive. In this study we have prepared a series of vanadate glasses having general formula (mol %) 40 V2O5-30BaF2-(30 - x)LiF-xRbF with x = 5, 10, 15, 20, 25, and 30. Spin-Hamiltonian parameters of V(4+) ions were extracted by simulating and fitting to the experimental spectra using EasySpin. From the analysis of these parameters it is observed that the replacement of lithium ions by rubidium ions follows a "preferential substitution model". Using this proposed model, we were able to account for the observed variation in the ratio of the g parameter, which goes through a maximum. This reflects an asymmetric to symmetric changeover of the alkali metal ion environment around the vanadium site. Further, this model also accounts for the variation in oxidation state of vanadium ion, which was confirmed from the variation in signal intensity of EPR spectra.

Synthesis and structural characterisation of iron(II) and copper(II) diphosphates containing flattened metal oxotetrahedra

Single crystal and bulk polycrystalline forms of K2MP2O7 (M=Fe(II), Cu(II)) have been synthesised and their structures determined from single crystal X-ray diffraction data. Both compounds crystallize in the tetragonal system, space group P-421m. Their structures are formed from infinite sheets of linked oxopolyhedra of the stoichiometry [MP2O7]2− with potassium cations situated between the layers. The MO4 tetrahedra share oxygen atoms with [P2O7]4− diphosphate groups and the potassium ions have KO8 square prismatic geometry. In both compounds the M(II) centre has an unusual strongly flattened, tetrahedral coordination to oxygen, as a result of the Jahn–Teller (JT) effect for the high spin d6 Fe(II) and p-orbital mixing or a second order JT effect for d9 Cu(II) centres in four fold coordination. The uncommon transition metal ion environments found in these materials are reflected in their optical absorption spectra and magnetism data.

Synthesis, spectroscopy and magnetic properties of transition-metal complexes with imidazol-2-yl-methyl[N-(n-butyl)amino]-diphenylphosphine oxide (2-izmape) – Structure of [Cu(2-izmape)2](BF4)2 complex

A series of three tetrafluoroborate coordination compounds of bioactive imidazol-2-yl-methyl[N-(n-butyl)amino]-diphenylphosphine oxide (2-izmape) ligand, with the following stoichiometries [Cu(2-izmape)2](BF4)2 and [M(2-izmape)2(BF4)2], M=Ni and Co, were obtained and studied. Stoichiometry and geometry of the compounds was confirmed by spectroscopic and magnetic studies as well as by elemental analyses. In particular, the crystal structures of the copper(II) compound was determined by X-ray diffraction method. The 2-izmape ligand has a potential capacity to coordinate to metal ions by following atoms: phosphoryl oxygen, amino nitrogen and imidazolyl nitrogen. In studied compounds, 2-izmape adopts the didentate N,N-coordination mode, bonding metal centers through the imidazolyl and amino nitrogen atoms. Phosphoryl oxygen atom does not participate in coordination. All complexes are monomeric with square planar (Cu) or octahedral (Ni, Co) environment of metal ions. The magnetic studies (1.8–300K) suggest the possibility of very weak antiferromagnetic (Co) and ferromagnetic (Ni) interaction between paramagnetic centers in crystal lattice. Copper centers are magnetically isolated.

Preparation of Iodide-Thiolate Bridged Binuclear Ni-Ni Complexes via Versatile Reaction of Labile Ni(II)-S(thiolate) Bond

The reaction between Fe(CO)4I2and Ni(SR)2(dppe) affords NiI2(dppe) due to the nucleophilic attack of iodide on the labile Ni-S(thiolate) bonds. The iodide-dithiolate-bridged binuclear Ni-Ni complexes [(dppe)Ni(µ-I)(µ-pdt)Ni(dppe)]I is readily prepared from the reaction between [NiI2(dppe)] and [Ni(pdt)(dppe)] [dppe = 1,2-bis(diphenyl phosphino)-ethane; pdt = 1,3-propane-dithiolate] in CH2Cl2as a result of attack on Ni-I bond by the lone pairs of electrons on thiolato sulfur donors. The reaction between [FeCp(CO)2I] and [Ni(pdt)(dppe)] in CH2Cl2processes extremely slowly. However, upon metathesis with NH4PF6, the iodide-thiolate bridged binuclear Ni-Ni complexes [(dppe)Ni(µ-I)(µ-pdt)Ni(dppe)]PF6is formed from the reaction of iodide and the Ni(II)-S bonds. The reaction between [NiCl2(dppe)] and NH4PF6and [Ni(pdt)(dppe)] gives a binuclear complex [(dppe)Ni(µ-pdt)Ni(dppe)]PF6without a halide-bridge. These results suggest that the reactivity of Ni-SR bonds in the Ni-thiolate-phosphine complexes is tunable with regard to the electronic environment of second metal ion and the different reactivity of iodide moiety. Electrochemical and crystallographic results are also analyzed for relevant compounds.