Properties Of Transition Metal Ions Research Articles

Tuning Transition Metal‐Containing Molecular Magnets by On‐Surface Polymerization

AbstractPorphyrins are promising multifunctional units particularly interesting for the realization of molecular nanodevices. Their structural variety allows to create precursors suitable for the on‐surface polymerization of porphyrin blocks. The corresponding increased stability and improved transport properties of the formed polymerized molecular nanostructures make them practically worthwhile. For the case of 2D porphyrin materials, the effect of polymerization on the magnetic properties of transition metal ions has not been reported yet. Therefore, details on the properties of an extended covalent nickel tetraphenylporphyrin network formed via Ullmann coupling on the Cu(111) surface are reported. By using photoelectron and absorption spectroscopies together with density functional theory calculations, it is systematically evolving how the functional properties of the Ni centers are changed within a polymerized molecular structure in comparison to single‐molecule nickel tetraphenylporphyrin derivatives that build the 2D molecular network. A model that explains the differences in the electronic and magnetic properties observed for the Ni centers in both structures based on the additional rigidity characteristic of the molecular layer after polymerization is drawn.

4-[(E)-2-(1-Pyrenyl)Vinyl]Pyridine Complexes: How to Modulate the Toxicity of Heavy Metal Ions to Target Microbial Infections.

Pyrene derivatives are regularly proposed for use in biochemistry as dyes due to their photochemical characteristics. Their antibacterial properties are, however, much less well understood. New complexes based on 4-[(E)-2-(1-pyrenyl)vinyl]pyridine (PyPe) have been synthesized with metal ions that are known to possess antimicrobial properties, such as zinc(II), cadmium(II), and mercury(II). The metal ion salts, free ligand, combinations thereof, and the coordination compounds themselves were tested for their antibacterial properties through microdilution assays. We found that the ligand is able to modulate the antibacterial properties of transition metal ions, depending on the complex stability, the distance between the ligand and the metal ions, and the metal ions themselves. The coordination by the ligand weakened the antibacterial properties of heavy metal ions (Cd(II), Hg(II), Bi(III)), allowing the bacteria to survive higher concentrations thereof. Mixing the ligand and the metal ion salts without forming the complex beforehand enhanced the antibacterial properties of the cations. Being non-cytotoxic itself, the ligand therefore balances the biological consequences of heavy metal ions between toxicity and therapeutic weapons, depending on its use as a coordinating ligand or simple adjuvant.

Structural analysis and electronic properties of transition metal ions (Ni2+, Fe2+, Mn+ and Co+) with psoralen biomolecule as an anticancer drug

In the current research, the density functional theory (DFT) method is used to investigate the effects of cation-π interaction on complexes formed by psoralen drug with metal cations (Ni2+, Fe2+, Mn+ and Co+). The calculations are performed in the gas phase and the water and carbon tetrachloride (CCl4) solvents. The interactions generated in the complexes are analyzed using the atoms in molecules (AIM) and the natural bond orbital (NBO) approaches. The results indicate that the absolute amount of the binding energy of complexes in the polar solvent is less than the non-polar solvent while in the gas phase it is more than solution. The obtained data also show that with increasing polarity of the solvent, the stabilization energy of the complexes increases. To gain a better insight into the mentioned interactions, the descriptors of chemical reactivity such as energy gap, hardness, softness and electronic chemical potential are also explored. Our findings display that the studied complexes have high chemical stability and low chemical reactivity in the solution relative to the gas phase.

Strong two-photon absorption of Mn-doped CsPbCl3 perovskite nanocrystals

Emerging CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals (NCs) have been demonstrated to be efficient emitters with a high fluorescence quantum yield, making these materials interesting for optical applications as well as for fundamental physics. Interestingly, doping with transition metal ions has been extensively explored as a way of introducing new optical, electronic, and magnetic properties, making perovskite NCs much more functional than their undoped counterparts. However, there have been no reports regarding the nonlinear optical properties of transition metal ion doped perovskite NCs. Herein, by using femtosecond-transient absorption spectroscopy, we have determined the one-photon linear absorption cross-section (∼1.42 × 10−14 cm2) of Mn-doped CsPbCl3 NCs (∼11.7 ± 1.8 nm size, ∼0.2% doping concentration, and ∼600 nm emission wavelength). More importantly, their nonlinear optical properties—in particular, the two-photon absorption (TPA) and resultant emission—were investigated. Notably, the NCs exhibit wavelength-dependent TPA with a maximum value up to ∼3.18 × 105 GM at a wavelength of 720 nm. Our results indicate that Mn-doped CsPbCl3 NCs show promise in nonlinear optical devices and multiphoton fluorescence lifetime imaging.

Photoluminescence properties of transition metal-doped Zn–In–S/ZnS core/shell quantum dots in solid films

The photoluminescence (PL) properties of transition metal ion (Mn2+ or Cu+) doped Zn–In–S/ZnS core/shell quantum dots (QDs) in solution and solid films were investigated by using steady-state and time-resolved PL spectra.

Study of Photocatalytic Activity and Properties of Transition Metal Ions Doped Nanocrystalline TiO2Prepared by Sol-Gel Method

Transition metal (Mn, Fe, Co,) doped TiO2nanoparticles were synthesized by the sol-gel method. All the prepared samples were calcined at different temperatures like 200°C to 800°C and characterized by X-ray diffraction (XRD) and energy dispersive X-ray (EDX) analysis. The studies revealed that transition metal (TM) doped nanoparticles have smaller crystalline size and higher surface area than pure TiO2. Dopant ions in the TiO2structure caused significant absorption shift into the visible region. The results of photodegradation of formaldehyde in aqueous medium under UV light showed that photocatalytic activity of TiO2nanoparticles was significantly enhanced by the presence of some transition metal ions. Chemical oxygen demand (COD) of formaldehyde solutions done at regular intervals gave a good idea about mineralization of formaldehyde.

Transition Metal Complexes Coupled to Vacancies in Oxides: Origin of Different Properties of Cr3+in MgO Bounded to a ⟨100⟩ or ⟨110⟩ Mg2+Vacancy

Despite the importance of vacancies over the properties of insulating oxides its influence on neighboring transition metal ions is far from being understood. This work is devoted to find the origin of various up to now unexplained properties of chromium bounded either to a <100> or a <110> Mg(2+) vacancy in MgO. In these model systems particular attention is paid to understand, by means of ab initio calculations, why the cubic field splitting parameter, 10Dq, is surprisingly 1600 cm(-1) higher for a <100> than for a <110> vacancy, a fact behind the suppression of the sharp (2)E → (4)A2 luminescence in the latter case. Our calculations, which reproduce the main experimental facts, prove that the average Cr(3+)-O(2-) distance is the same within 0.8% for both systems, and thus, the low 10Dq value for a <110> vacancy is shown to be due mainly to the electrostatic potential from the missing Mg(2+) ion, which increases the energy of antibonding t(2g) (∼xy, xz, yz) levels. By contrast, for a <100> Mg(2+) vacancy that potential provides a supplementary increase of the e(g) (∼x(2) - y(2), 3z(2 )- r(2)) level energy and thus of 10Dq. The existence of the (2)E → (4)A2 luminescence for Cr(3+)-doped MgO under perfect cubic symmetry or with a <100> vacancy is shown to be greatly helped by the internal electric field created by the rest of the lattice ions on the CrO6(9-) unit, whose importance is usually ignored. The present results underline the role of ab initio calculations for unveiling the subtle effects induced by a close vacancy on the properties of transition metal ions in oxides. At the same time they stress the failure of the empirical superposition model for deriving the equilibrium geometry of C4v and C2v centers in MgO:Cr(3+).

RETRACTED: The structural, optical, magnetic and photocatalytic properties of transition metal ions doped TiO2 nanoparticles

Metal-ions doped TiO2 (M–TiO2) have been synthesized using a hydrothermal method at 100 °C with a post-annealing temperature process at 500 °C, including individual Co2+, and Mn2+ ions. Furthermore, effects of these doping metals ions on the crystallization and phase transition of the TiO2 nanoparticles were discussed by XRD, TEM/HRTEM, BET specific surface area (SBET), pore-size distribution by BJH, UV–vis Spectroscopy, photoluminescence (PL), FTIR, VSM as well as photocatalytic measurements. The presence of anatase type structure in TiO2 nanopowders with high crystallinity and high phase stability even after annealing at 500 °C substantially indicated that the dopants might inhibit densification and crystallite growth in TiO2 nanophase by providing dissimilar boundaries. Moreover, with a suitable amount (ca. 0.2, 0.3 mol%), the Mn, Co dopants reduces anatase grain size and increases the specific surface area of TiO2 powders. The band gap energy values of Mn2+ and Co2+ ions doped nano-TiO2 were higher than the pure nano-TiO2 and they showed a blue shift to the visible region. Furthermore, the obtained experimental results revealed that all the samples exhibited the paramagnetic behavior at room temperature. The paramagnetic order was increased with increasing the (Mn, Co) content, whereas the coercivity force Hc was decreased. Photocatalytic degradation of methylene blue (MB) under UV lights indicated that the meso-TiO2 exhibited enhanced activity under UV lights. However, photodegradation of the MB under UV light was enhanced with the presence of Mn and Co with TiO2.

Studies on structural and electrical properties of transition metal ions (Mn, Co and Cu) co-doped Bi0.9Dy0.1FeO3 thin films

Effects of rare earth Dy and transition metal (TM = Cu, Co and Mn) ions co-doping on the structural, electrical and ferroelectric properties of the BiFeO3 thin films prepared on Pt(111)/Ti/SiO2/Si(100) substrates by using a chemical solution deposition method were investigated. All thin films formed as randomly oriented polycrystalline, with no detectable impurity or secondary phases. Among the thin films, the (Bi0.9Dy0.1)(Fe0.975Mn0.025)O3 thin film exhibited well saturated hysteresis loops with remnant polarization (2P r ) of 51 μC/cm2 and low coercive electric field (2E c ) of 685 at 935 kV/cm and low leakage current density of 1.4 × 10−5 A/cm2 at 100 kV/cm. The enhanced properties observed in the co-doped thin films could be considered as being the results of the suppression of ionic defects and of the modified microstructure.

Structural, magnetic and XPS studies of Sn0.95Co0.05O2-0.05 and Sn0.95Fe0.05O2-0.05 nanoparticles

Structural, microstructural, X-ray photoemission spectra (XPS) and magnetic properties of transition metal ion [5 mol% of Co (SC5) and Fe (SF5)]-doped SnO2 nanoparticles have been studied. The SC5 and SF5 nanoparticles were synthesized by a chemical route using polyvinyl alcohol as surfactant. The doped SnO2 crystallites were found to exhibit a tetragonal rutile structure and the average grains size was measured by the Scherer relation of X-ray diffraction. Transmission electron micrographs showed that the average grain size of SC5 is smaller than SF5. SC5 nanoparticles showed strong ferromagnetic behaviour but SF5 exhibited an F-centre exchange (FCE) mechanism. Temperature-dependent magnetization showed the values of phase transition temperature. XPS confirmed the presence of Sn–O–Co and Sn–O–Fe bonds in these SC5 and SF5 nanoparticles. The oxidation states of Sn, Co and Fe were found to be +4, +2 and +2, respectively, while the core level XPS peaks of Sn 3d, O 1s, Co 2p and Fe 2p were analyzed.

Preparation and photodegradation properties of transition metal ion–poly-o-phenylenediamine/TiO2/fly-ash cenospheres by ion imprinting technology

Transition metal ions have been immobilized on TiO2/fly-ash cenospheres (TiO2/FACs) with poly-o-phenylenediamine (OPD). The as-prepared ion imprinting photocatalyst (M-POPD/TiO2/FACs) has been characterized by SEM, XRD, FT-IR, UV-vis DRS and ICP-AES. The results demonstrated that the polymer and mental ions existed in the M-POPD/TiO2/FACs. The photocatalytic activity of M-POPD/TiO2/FACs was studied by the degradation of tetracycline, oxytetracycline, ciprofloxacin, tetracycline hydrochloride and chloromycetin in simulated wastewater under visible light irradiation. The results showed that the M-POPD/TiO2/FACs could effectively increase the separation rate of photoelectrons and holes in the cycling system and improve the photocatalytic activity for the degradation of antibiotics in solution. Experimental data showed that the as-prepared M-POPD/TiO2/FACs were more suitable for degradation of tetracycline (5 mg L−1), and the photodegradation rate could reach 71.7%. In addition, possible formation and photocatalytic mechanisms were proposed.

Matrix Method for Analysis the Effect of the Crystal Field on the Magnetic Moment of Co&lt;sup&gt;2&lt;/sup&gt;&lt;sup&gt;+&lt;/sup&gt; Ion

This paper introduces the common principals of theoretical matrix method for the direct determination of magnetic properties of transition metal ions, which is based on calculation of the full matrix of all the interactions. In this work this method was used to calculating, study and analysis the magnitude of magnetic moment of Co2+ ion in crystal fields with different symmetry.

Emission properties of Mn doped ZnO nanoparticles prepared by mechanochemical processing

Mechanochemical processing was reported to introduce lot of crystal defects which can significantly influence emission properties. Nevertheless, to the best of our knowledge, there are no reports on effect of mechanochemical processing on emission properties of transition metal ion doped ZnO. In this study, Zn1−xMnxO nanoparticles with different Mn content (x=0, 0.02, 0.04, 0.06, 0.08, and 0.1) were prepared by mechanochemical processing to study the effect of Mn doping and processing on emission properties. Confirmation of nanoparticles size and nanocrystalline nature of hexagonal wurtzite ZnO structure is carried out using transmission electron microscopy (TEM) and selected area electron diffraction (SAED), respectively. The samples were also characterized using Fluorescence Spectroscope before and after heat-treatment. The emission studies revealed that blue emission intensity is stronger compared to UV and green emission in contrast to the earlier reports, where other synthesis routes were employed for the ZnO nanoparticles' preparation. The blue emission originates from the zinc interstitial (Zni) and oxygen interstitial (Oi) defects, which indicate that the mechanochemical route resulted in more interstitial defects compared to oxygen substitution (OZn) and oxygen vacancy (Vo) defects which otherwise would give green emission. Mn doping resulted in shifting of near-band-edge (NBE) emission and the reduction in the intensities of NBE, blue and green emissions. The initial red shift at lower Mn content could be due to s–d and p–d exchange interactions as well as band tailing effect where as the blue shift at higher Mn content can be attributed to the Burstein-Moss shift. The reduction in emission intensity could be due to non-radiative recombination processes promoted by Mn ions with increasing Mn content.

Synthesis of functionalized silica gel with poly(diethylenetriamine bis(methylene phosphonic acid)) and its adsorption properties of transition metal ions

A novel functionalized silica gel with poly(diethylenetriamine bis(methylene phosphonic acid)) (SH–DETA–PDBMPA) was synthesized in order to improve the adsorption for transition metal ions from aqueous solutions. The material was characterized using infrared spectra (IR), X-ray diffractometry (XRD), scanning electron microscope (SEM), Brunauer–Emmett–Teller (BET) surface area measurement, porous analysis, thermogravimetric analysis (TG) and 29Si Magic Angle Spinning Nuclear Magnetic Resonance ( 29Si MAS NMR). The application of this material in adsorption of transition metal ions revealed that SH–DETA–PDBMPA had excellent adsorption amount and high selectivity for Au(III), which provided a novel material for adsorbing this specious metal ions from aqueous solutions.

Influence of physicochemical–electronic properties of transition metal ion doped polycrystalline titania on the photocatalytic degradation of Indigo Carmine and 4-nitrophenol under UV/solar light

To understand the role of dopant inside TiO2 matrix, anatase TiO2 was doped with transition metal ions like Mn2+, Fe3+, Ru3+ and Os3+ having unique half filled electronic configuration and their photocatalytic activity was probed in the degradation of Indigo Carmine (IC) and 4-nitrophenol (NP) under UV/solar light. For comparison, TiO2 was also doped with V5+, Ni2+ and Zn2+ metal ions having d0, d8 and d10 electronic configuration respectively. Irrespective of excitation source UV/solar light and nature of the organic pollutant, photocatalytic activities of doped photocatalysts followed the order: Mn2+-TiO2>Fe3+-TiO2>Ru3+-TiO2≥Os3+-TiO2>Zn2+-TiO2>V5+-TiO2>Ni2+-TiO2 at an optimum concentration of dopant. Based on the experimental results obtained, it is proposed that the existence of dopant with half filled electronic configuration in TiO2 matrix which is known to enhance the photocatalytic activity is not universal! Rather it is a complex function of several physicochemical–electronic properties of doped titania. Enhanced photocatalytic activity of Mn2+ (0.06at.%)-TiO2 was attributed to the combined factors of high positive reduction potential of Mn2+/Mn3+ pairs, synergistic effects in the mixed polymorphs of anatase and rutile, smaller crystallite size with high intimate contact between two phases and favorable surface structure of the photocatalyst. Despite the intense research devoted to transition metal ion doped TiO2, it is rather difficult to make unifying conclusion which is highlighted in this study.

Liquid phase catalytic oxidation of isophorone with tert-butylhydroperoxide over Cu/Co/Fe–MgAl ternary hydrotalcites

Abstract Liquid phase catalytic oxidation of isophorone was carried out over M–MgAl ternary hydrotalcites, where M is Cu, Co or Fe, using tert -butylhydroperoxide (TBHP) as an oxidant. The influence of various reaction parameters, namely, substrate/catalyst mass ratio, substrate:oxidant mole ratio, nature of oxidant, solvent, reaction temperature and reaction time on the activity and selectivity for the desired reaction, were studied. The catalysts were synthesized by the coprecipitation technique using metal nitrates and a NaOH/Na 2 CO 3 mixture. Powder X-ray diffraction and thermal analysis of these samples confirmed the presence of hydrotalcite like layered network. Oxidation of isophorone over these catalysts resulted mainly in the formation of ketoisophorone (KIP). A maximum isophorone conversion of 74% with 100% selectivity to KIP was observed over CuMgAl-13 at 333 K up to 48 h using acetonitrile as a solvent, followed by CoMgAl-13 (36%) and FeMgAl-13 (25%). The redox properties of transition metal ions played an important role in driving the reaction and a reaction mechanism involving predominantly free radicals were proposed. An increase in the conversion of isophorone was observed with decreasing substrate/catalyst mass ratio down to 20. With respect to the influence of reaction temperature, the conversion increased up to 333 K and decreased when the temperature was further increased. Among the solvents studied acetonitrile showed maximum conversion and selectivity to KIP, where as methanol showed minimum conversion. An increase in the conversion of isophorone was observed with decreasing molar ratio of isophorone to TBHP. A gradual increase in the conversion of isophorone was observed with reaction time and the maximum conversion was observed at 48 h. Reusable studies showed that the catalysts were stable and reusable up to three cycles without substantial loss of activity.

Correlation between electrical transport, optical, and magnetic properties of transition metal ion doped ZnO

We report on the transport and optical properties of transition metal ions, namely Ti, V, Fe, Co and Ni doped ZnO samples. Diffuse reflectance spectroscopy of doped ZnO showed the existence of absorption bands which were attributed to the d-d transitions of respective dopants. Resistivity was found to decrease in the case of Ti, V, Fe, and Ni dopings. Correlation between the electrical resistivity and magnetic properties of the samples has been explained on the basis of impurity d-band splitting model.

Structural State and Redox Behavior of Framework Co(II) in CoIST-2: A Novel Cobalt-Substituted Aluminophosphate with AEN Topology

A highly crystalline cobalt-substituted aluminophosphate with an AEN topology, labeled CoIST-2, has been synthesized and characterized by powder XRD, TG/DSC, diffuse reflectance UV−vis spectroscopy, FTIR, EPR spectroscopy, and cyclic voltammetry. Both water and methylamine were shown to play a complementary role as dual template and space-filling agents during the hydrothermal synthesis of this material. The spectroscopic (EPR, UV−vis, and FTIR) and electrochemical characterization of the as-synthesized and calcined CoIST-2 material revealed the presence of two structurally different Co(II) species incorporated in its crystalline framework. The redox behavior and acidity was found to be different for these two Co(II) species. While one of these cobalt species corresponded to Brönsted Co(OH)P acid sites, the other seemed to be associated with the presence of Lewis acid sites (Co□P type species). UV−vis spectra, typical of divalent cobalt in tetrahedral coordination, along with FTIR, demonstrated that only a fraction of the Co(II) ions undergo a reversible oxidative process after calcination in air and that some extraframework CoxOy type species are also generated through oxidation. The presence of divalent Co(II) in a slightly distorted tetrahedral coordination, both in the as-synthesized and calcined phase, was also detected with use of EPR data. The electrochemical oxidation of the two different framework Co(II) species and their further reduction could be evaluated semiquantitatively by cyclic voltammetry. The redox ability of CoIST-2 was also compared with that of two other cobalt-substituted aluminophosphates involving different pore structures, namely CoAPO-40 and CoAPO-37, by using FTIR of adsorbed NO. It was found that the most readily oxidized ions were present in the more dense AEN topology, followed by the more open AFR and FAU structures, thereby emphasizing how the redox properties of transition metal ions in porous aluminophosphates are intimately linked to both the structure type/density of the host lattice and framework positions of the heteroelement.

Toward a Molecular Description of Heterogeneous Catalysis: Transition Metal Ions in Zeolites

AbstractFor Abstract see ChemInform Abstract in Full Text.

Toward a molecular description of heterogeneous catalysis: transition metal ions in zeolites

Quantum mechanical modeling of the properties of transition metal ions (TMI) in zeolites gives a picture of the material which corresponds to that of a large organometallic system in which the zeolite framework behaves as a multidentate ligand. The electron density is distributed among the whole system with highly delocalized frontier orbitals. Analyses of the electron density changes in CuZSM-5 and CuFAU models upon adsorption and desorption of donor or acceptor ligands point to a supermolecular behavior of the whole system where the zeolite framework acts as a reservoir of electronic charge. This molecular description of TMI-zeolites provides a rational explanation of various aspects of their catalytic behavior in the decomposition and selective catalytic reduction (SCR) of nitrogen oxides, such as the nature of the rate determining step and the positive influence of protons in the SCR of NO by NH3.