Octahedral Cr Research Articles

Effect of chromium substitution on structural and optical properties of Ca3(VO4)2 for laser and SRS applications

Crystal structures of Czochralski-grown Ca3(VO4)2 single crystals doped with over-stoichiometric 0.01, 0.05, and 0.1 wt% Cr2O3 (CVO:Cr) are solved and refined. A whitlockite-like structure with five Ca sites, two-capped (Ca1 and Ca3) and mono-capped (Ca2) trigonal prisms, distorted octahedron (Ca4) and tetrahedron (Ca5), is determined for CVO:Cr. Single-crystal synchrotron X-ray diffraction analysis revealed the presence of chromium in Ca2, Ca3, Ca4 sites. In CVO:Cr, chromium has octahedral (Cr3+) and tetrahedral (Cr4+) coordination, which suggests structural superpositions of CaO8, CaO7, CaO6 and Cr3+O6 or Cr4+O4 polyhedra. X-ray diffraction, EPR and spectroscopic studies showed that green or yellow color of CVO:Cr is related to chromium valence state, Cr3+ or Cr4+, respectively. An increase in the Cr4+ concentration is accompanied by increased vacancy content in two of three vanadium sites. Structural behavior of transition metal ions with a variable formal charge (Co, Mn, Cr) in CVO structure is summarized, analyzed and discussed. Three absorption bands around 23900, 16300 and 14000 cm−1, typical for Cr3+ ions, are revealed in the UV-VIS spectra of green samples. An additional broad band with a maximum at 21254 cm−1 refers to Cr4+ ions, the appearance of which after annealing in air was established by X-ray diffraction analysis.

Luminescence enhancement of Cr3+ doped garnet phosphor for high-performance LED towards smart NIR light source

Cr3+ doped phosphor shows great potential for near-infrared (NIR) light-emitting diodes (LED), but it suffers from low quantum efficiency and poor thermal stability. Herein, a novel Cr3+ doped broadband NIR garnet Ca3Sc2Ge3O12 phosphor was developed. The multisite structure of the emission band is investigated by site-selective spectroscopy and is attributed to the octahedral Cr3+ perturbed by defects. Moreover, we propose different strategies to enhance the luminescence of the phosphor, including enhancement of crystallinity and elimination of defects. Compared with the initial sample, the emission intensity of the optimized phosphor is improved for 8.6 times. The optimal Ca3Sc2Ge3O12: 0.06Cr3+ phosphor exhibits excellent thermal stability. At 423 K, the integral emission intensity of the optimal sample remains 94.7% of that at room temperature. Finally, high-performance NIR LED was fabricated using a blue LED and the title phosphor. The packaged LED lamp has high radiance (109.3 mW@300 mA) and photoelectric efficiency (15.96%@40 mA). Our study not only provides a boulevard for enhancing the luminescence of Cr doped NIR phosphor, but also gives a new perspective for understanding the multisite luminescence of Cr3+ in garnet host.

UV/blue/green converted efficient red-NIR photoluminescence in Cr incorporated MgAl2O4 nanocrystals: Site selective emission tailored through cation inversion and intrinsic defects

The UV/visible activated near-infrared (NIR) phosphors have many applications in solid state lighting, night vision devices and bio-imaging. The early research reported the red-NIR emitting phosphors doped with Cr3+ centers upon visible light excitation. Here, in this work the intense red-NIR emission and color tuning is achieved for broad excitation range (UV/blue/green) through Cr dopant induced defect centers and cation inversion in MgCr Al2O4 ( = 0.5, 1, 3, 5 and 10 mol%) nanocrystals. The Cr3+ doped MgAl2O4 nanocrystals were synthesized by combustion method through stoichiometric substitution of Mg by Cr, while most of the Cr3+ ions occupied the octahedral sites of spinel host with the formation of antisite defects, Cr3+ clusters, magnesium and oxygen vacancies. These defect centers were probed through Rietveld refinement, photoluminescence (PL), x-ray photoelectron and nuclear magnetic resonance spectra analyses. At UV excitation, the intrinsic defects played an interesting role in exhibiting the blue-violet emission attributed to host lattice defects and red-NIR emission attributed to strong/weak ligand field octahedral Cr3+ sites, via charge transfer to Cr3+ ions. The PL spectra evinced the enhanced red-NIR emission intensity upon 266 nm excitation than upon blue and green light excitation. Further, the weak ligand field site emission is found to be dominating with increase in doping concentration. Thus, Cr doped MgAl2O4 nanocrystals showed their potency of exhibiting the intense red-NIR emission and color tuning (from red purple to bluish purple and then to red color) upon UV/blue/green excitation.

Synthesis and Characterization of New Mixed-Ligand Complexes; Density Functional Theory, Hirshfeld, and In Silico Assays Strengthen the Bioactivity Performed In Vitro.

N'-Acetyl-2-cyanoacetohydrazide (H2L1) and 2-cyano-N-(6-ethoxybenzo thiazol-2-yl) acetamide (HL2) ligands were used to synthesize [Cr(OAc)(H2L1)(HL2)]·2(OAc) and [Mn(H2L1)(HL2)]·Cl2·2H2O as mixed ligand complexes. All new compounds were analyzed by analytical, spectral, and computational techniques to elucidate their chemical formulae. The bidentate nature was suggested for each coordinating ligand via ON donors. The electronic transitions recorded are attributing to 4A2g(F) → 4T2g(F)(υ2) and 4A2g(F) → 4T1g(F)(υ3) types in the octahedral Cr(III) complex, while 6A1 → 4T2(G) and 6A1 → 4T1(G) transitions are attributing to the tetrahedral Mn(II) complex. These complexes were optimized by the density functional theory method to verify the bonding mode which was suggested via N(3), O(8), N(9), and N(10) donors from the mixed-ligands. Hirshfeld crystal models were demonstrated for the two ligands to indicate the distance between the functional groups within the two ligands and supporting the exclusion of self-interaction in between. Finally, the biological activity of the two mixed ligand complexes was tested by in silico ways as well as in vitro ways for confirmation. Three advanced programs were applied to measure the magnitude of biological efficiency of the two complexes toward kinase enzyme (3nzs) and breast cancer proliferation (3hy3). All in silico data suggest the superiority of the Mn(II) complex. Moreover, the in vitro assays for the two complexes that measure their antioxidant and cytotoxic activity support the distinguished activity of the Mn(II) complex.

Cr3+-Sphere Effect on the Whitlockite-Type NIR Phosphor Sr9Sc(PO4)7 with High Heat Dissipation for Digital Medical Applications.

The analysis of human body composition and food composition requires high-efficiency broadband near-infrared (NIR) lighting sources to achieve a portable, appropriately sized equipment. Herein, we develop a whitlockite-type NIR phosphor Sr9Sc(PO4)7:Cr3+ with an emission centered at 860 nm and full width at half-maximum of 147 nm. Due to the structural characteristics of the matrix, the 60 mol % Cr3+ substitution at the Sc3+ sites gives an internal quantum efficiency up to 56.5%. By replacing Sr with Ba and Ca, we observe a nontypical spectral shift phenomenon and discuss the influence of the second-sphere effect on octahedral Cr3+ ions. To evaluate the diagnostic application, we design a NIR ceramic device with a high optical power of 27.38 mW and high heat dissipation, which can decrease surface working temperature by nearly 50 °C for digital intraoral application. This study provides the research of the second-sphere coordination effect for selective octahedral sites such as Ca, Sr, and Ba coordinated by O atoms on a whitlockite-type crystal. Furthermore, the device promotes a nonionizing solution for detecting dental caries, tooth calcification, and diagnostic application.

Synthesis and optical properties of Ni/Co/Cr doped BaMg6Ti6O19

Novel green and blue chromophores based on Ni/Co/Cr doped BaMg6Ti6O19 solid solutions are successfully synthesized through a solid-state reaction. The crystal structure of all the samples belongs to the magnetoplumbite structure with the space group of P63/mmc. The BaMg6-x/2Ti6-x/2NixO19 (0 ≤ x ≤ 0.3) compounds exhibit a light green (x = 0.1) to yellow-green (x = 0.3) color. The oxidation state of Ni is confirmed to be +2 valence and the d-d transition of Ni2+ in octahedral sites is responsible for color. BaMg6-x/2Ti6-x/2CoxO19 (0 ≤ x ≤ 0.3) series show a blue color and the intensity of blueness is increasing with the increase of Co content. The blue color is due to d-d transitions within Co2+ present in the tetrahedral sites. For BaMg6-x/2Ti6-x/2CrxO19 (0 ≤ x ≤ 2) phases the color varies from light green (x = 0.2) to green (x = 2). Chromium exists in +3 and + 6 oxidation states and the observed color is due to charge transfer transition between Cr3+–Ti4+ and d-d transitions within octahedral Cr3+ sites resulting in strong absorption in the visible region. The synthesized colored oxides are mixed with PMMA to prepare novel green and blue PMMA polymer composites to evaluate their compatibility in plastics.

Crystal and Substituent Effects on Paramagnetic NMR Shifts in Transition-Metal Complexes.

Nuclear magnetic resonance (NMR) spectroscopy of paramagnetic molecules provides detailed information about their molecular and electron-spin structure. The paramagnetic NMR spectrum is a very rich source of information about the hyperfine interaction between the atomic nuclei and the unpaired electron density. The Fermi-contact contribution to ligand hyperfine NMR shifts is particularly informative about the nature of the metal–ligand bonding and the structural arrangements of the ligands coordinated to the metal center. In this account, we provide a detailed experimental and theoretical NMR study of compounds of Cr(III) and Cu(II) coordinated with substituted acetylacetonate (acac) ligands in the solid state. For the first time, we report the experimental observation of extremely paramagnetically deshielded 13C NMR resonances for these compounds in the range of 900–1200 ppm. We demonstrate an excellent agreement between the experimental NMR shifts and those calculated using relativistic density-functional theory. Crystal packing is shown to significantly influence the NMR shifts in the solid state, as demonstrated by theoretical calculations of various supramolecular clusters. The resonances are assigned to individual atoms in octahedral Cr(acac)3 and square-planar Cu(acac)2 compounds and interpreted by different electron configurations and magnetizations at the central metal atoms resulting in different spin delocalizations and polarizations of the ligand atoms. Further, effects of substituents on the 13C NMR resonance of the ipso carbon atom reaching almost 700 ppm for Cr(acac)3 compounds are interpreted based on the analysis of Fermi-contact hyperfine contributions.

A combined Fourier transform infrared and Cr K-edge X-ray absorption near-edge structure spectroscopy study of the substitution and diffusion of H in Cr-doped forsterite

Abstract. Single crystals of synthetic Cr-doped forsterite (Cr:Mg2SiO4) containing both Cr3+ and Cr4+ were partially hydroxylated in piston-cylinder apparatuses at 750–1300 ∘C and pressures from 0.5 to 2.5 GPa, with p(H2O) ≈Ptotal. The oxygen fugacity (fO2) was buffered by graphite-water, Ni–NiO, Re–ReO2, Fe2O3–Fe3O4 or Ag–Ag2O, and the silica activity (aSiO2) was buffered by powdered forsterite plus either enstatite (Mg2Si2O6), periclase (MgO) or zircon–baddeleyite (ZrSiO4–ZrO2). Profiles of OH content versus distance from the crystal edge were determined using Fourier transform infrared (FTIR) spectroscopy, and profiles of the oxidation state and coordination geometry of Cr were obtained, at the same positions, using K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The techniques are complementary – FTIR spectroscopy images the concentration and nature of O–H bonds, where Cr K-edge XANES spectroscopy shows the effect of the added H on the speciation of Cr already present in the lattice. Profiles of defect-specific absorbance derived from FTIR spectra were fitted to solutions of Fick's second law to derive diffusion coefficients, which yield the Arrhenius relationship for H diffusion in forsterite: log⁡10D̃[001]=-2.5±0.6+-(224±12+4.0±2.0P)2.303RT, where D̃ is the measured diffusion coefficient in m2 s−1, valid for diffusion parallel to [001] and calibrated between 1000 and 750 ∘C, P and T are in GPa and K, and R is 0.008314 kJK−1 mol−1. Diffusivity parallel to [100] is around 1 order of magnitude lower. This is consistent with previous determinations of H diffusion associated with M-site vacancies. The FTIR spectra represent a variety of Cr-bearing hydrous defects, along with defects associated with the pure Mg–Si–O–H system. It is proposed that all of the defects can form by interaction between the dry lattice, including Cr3+ and Cr4+, and fully hydroxylated M-site vacancies. The initial diffusive wave of hydroxylation is associated with neither reduction nor oxidation of Cr but with Cr4+ changing from tetrahedral to octahedral coordination. Superimposed on the H diffusion and concomitant change in Cr4+ site occupancy, but at a slower rate, producing shorter profiles, is reduction of Cr4+ to Cr3+ and potentially of Cr4+ and Cr3+ to Cr2+. In addition, by comparing FTIR data to trace element contents measured by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), constraints can be placed on absorption coefficients used for converting absorbance to H2O contents – our data support either wavenumber- or defect-dependent values of absorption coefficients. We estimate absorption coefficients of between 60 200 and 68 200 L mol−1 cm−1 for OH− associated with octahedral Cr3+ and an M-site vacancy and 18 700 to 24 900 L mol−1 cm−1 for two OH− associated with octahedrally coordinated Cr4+ and a Si vacancy (i.e. a “clinohumite-type” point defect).

Conductometric pulse radiolysis study of the interconversion Cr(III)/Cr(VI) redox reactions in acidic solution: Atmospheric pollution relevance

ABSTRACT Hexavalent chromium (VI) is a potent carcinogen for humans, while trivalent chromium (III) is an important element in glucose metabolism. In atmospheric water droplets, oxidation of Cr(III) to Cr(VI) by free radicals is a major environmental issue. Laboratory simulation studies of the aqueous phase oxidation-reduction of the couple Cr(III)/Cr(VI) by OH• and HO2 •/O2 •− by applying conductometric pulse radiolysis techniques were carried out in the pH range 3.5–5.5 chosen as characteristic values of atmospheric water droplets acidity. A pKa of 3.9 was found for the first hydrolysis of Cr(IV). The bimolecular second-order decay of the Cr(V) transient species shows a strong pH dependency consequence of the change of the coordination sphere of the tetrahedral Cr(VI) to the octahedral Cr(III).

X-ray scattering reveals ion clustering of dilute chromium species in molten chloride medium.

Enhancing the solar energy storage and power delivery afforded by emerging molten salt-based technologies requires a fundamental understanding of the complex interplay between structure and dynamics of the ions in the high-temperature media. Here we report results from a comprehensive study integrating synchrotron X-ray scattering experiments, ab initio molecular dynamics simulations and rate theory concepts to investigate the behavior of dilute Cr3+ metal ions in a molten KCl–MgCl2 salt. Our analysis of experimental results assisted by a hybrid transition state-Marcus theory model reveals unexpected clustering of chromium species leading to the formation of persistent octahedral Cr–Cr dimers in the high-temperature low Cr3+ concentration melt. Furthermore, our integrated approach shows that dynamical processes in the molten salt system are primarily governed by the charge density of the constituent ions, with Cr3+ exhibiting the slowest short-time dynamics. These findings challenge several assumptions regarding specific ionic interactions and transport in molten salts, where aggregation of dilute species is not statistically expected, particularly at high temperature.

Preparation and characterization of green glazes using ferrochromium slag waste

Green glazes were successfully prepared using ferrochromium slag waste as chromium and iron precursors by introducing Co2O3 as coloring agent. The performance of the glazes was investigated by XRD, EDS, FT-IR, and UV-vis. A chromatic mechanism was proposed to explain the variation of glaze colors with the increase of Co2O3 content. The results showed that the Co-doped glazes had Co-Fe-Cr mixed spinel-type structures when Co-doped contents were 0.5–1.5 wt%. Green glazes could be prepared by adjusting the blue component (Co2+) proportion, which was achieved with different amounts of Co2O3, to balance the color proportion of blue and yellow in glazes according to subtractive color process. The intensity of green color in glaze samples was related to the presence of d-d transitions of tetrahedral Fe3+, 4A2(F) → 4T(P) of tetrahedral Co2+, and 4A2g → 4T2g of octahedral Cr3+ in spinel structures. These results indicated that environment-friendly, Co-doped, spinel-type structured, coloring agents, prepared using ferrochromium slag waste, can be applied to produce green glazes or inkjet printer ink as well as to provide a means for preparing green glaze using ferrochromium slag waste.

CrI3 magnetic nanotubes: A comparative DFT and DFT+U study, and strain effect

Abstract In this paper, structural and electronic properties of CrI3 magnetic nanotubes (NTs) are studied using density functional theory. Both armchair and zigzag CrI3 nanotubes demonstrate a high correlation in strain energy between each other independently on accounting the Hubbard correction. The strain energies decrease with expansion of the tube diameter making the tubes’ synthesis with a diameter larger than 45 A to be energetically possible. The nanotubes of both zigzag and armchair chirality are ferromagnetic semiconductors with band gaps close to that of the CrI3 monolayer. The band gaps are suppressed by reducing the tube diameters due to the structural stress leading to deformation of the Cr–I crystal field and changes in the bond lengths. The external strain can be utilized to flexibly tune the electronic properties of CrI3 nanotubes with the desired spin-up/spin-down band gap ratio. Strong distortion of the octahedral Cr–I crystal field under compression results in nontrivial behavior in the spin-up band gap of (4, 4) tube. Stretching of tubes leads to the enhancement of the exchange energy that should result in higher Curie temperature, therefore providing a good platform for potential applications in spintronic nanodevices.

Chromate removal by electrospun PVA/PEI nanofibers: Adsorption, reduction, and effects of co-existing ions

Chromium (Cr(VI)) is one of the most toxic heavy metals threatening humans’ health and the environment. Water-stable poly(vinyl alcohol)/polyethylenimine (PVA/PEI) nanofibers were fabricated through electrospinning and evaluated for Cr(VI) removal from water in batch experiments. The adsorption behavior and removal mechanisms of Cr(VI) by PVA/PEI nanofibers were systematically investigated through a combination of batch experiments and spectroscopic characterizations. The Cr(VI) removal by PVA/PEI nanofibers showed a pH-dependent behavior, and the maximum removal was achieved at pH 4.0. The optimum adsorption capacity for Cr(VI) was found to be 150 mg/g by fitting the Langmuir model. Removal of Cr(VI) by the nanofibers is fast (<3 h), and they could be regenerated without reducing the removal capacity. Electrostatic attraction between negatively charged Cr(VI) and positively charged nanofiber surfaces is the major mechanism for Cr(VI) adsorption. Most of the adsorbed Cr(VI) was reduced to Cr(III), showing an octahedral Cr(III) oxide structure. Amine groups in the nanofibers act as both reducing and binding sites for Cr(VI) removal. Among commonly coexisting anions, only sulfate and nitrate decreased the Cr(VI) removal by nanofibers, but did not affect the structure of adsorbed Cr. Copper could compete with Cr(VI) for complexing with amine groups, and consequently attenuate the reduction of Cr(VI). This study evaluated the application of electrospun PVA/PEI nanofibers on Cr(VI) removal in complex water matrices and provided comprehensive evidence regarding the adsorption and reduction mechanisms. Such information improves the understanding of Cr(VI) removal by electronspun PVA/PEI nanofibers, and is helpful to predict its performance in dynamic environments.

Site-related broadband sensitization in La3Ga5.5Nb0.5O14: Cr3+, Ln3+(Ln=Yb, Er) phosphors.

Yb3+ 1000nm and Er3+ 1536nm emission can be efficiently sensitized by broadband absorption of Cr3+ in almost the whole visible region in La3Ga5.5Nb0.5O14(LGNO): Cr3+, Ln3+ (Ln=Yb, Er) phosphor. Between the two kinds of Cr3+ sites, tetrahedral Cr(II) mainly behaves as the broadband sensitizer for Er3+ or Yb3+. Meanwhile octahedral Cr(I) may energy transfer (ET) to Cr(II), thereby influences the luminescence decay of Cr(II) as increasing Er3+ or Yb3+ content. This kind of site-related broadband sensitization may propose a strategy of designing tunable ET process between transition metal ions and rare earth ions.

Enhancement of red emission assigned to inversion defects in ZnAl2O4:Cr3+ hollow spheres

ZnAl2O4:Cr3+ hollow spheres composed of secondary nanoparticles with single spinel phase were fabricated using carbon templets. Monitoring the emission of 687 nm, two wide excitation bands attributed to the electrons of Cr3+ transiting from 4A2g (4F) → 4T1g (4F) and 4A2g (4F) → 4T2g (4F) were observed. The broad excitation band at about 397 nm was asymmetric and consisted of two peaks, indicating that there was a trigonal distortion existing in the lattices. The intensity of all emitting peaks revealed sharp increasing trend with the sintering temperature increase, and the intensity of emission at 698 nm assigned to inversion defects was more intense than that of emission at 687 nm assigned to octahedral Cr3+ ions in the undistorted spinel lattice. The samples with higher synthesized temperature revealed longer decay time, and the relative weightage of shorter decay time component decreased with the increase of sintering temperature, indicating that the surface defects decreased.

Zn2TiO4 photoluminescence enhanced by the addition of Cr3+

In this work, the photoluminescent properties of Zn2TiO4:Cr3+ are presented. Samples were prepared from ZnO, TiO2 and Cr2O3 by solid-state reaction. The compound formation was confirmed by X-ray diffraction. Emissions were obtained using photoluminescence spectroscopy at room temperature. The system crystallizes in the space group $$Fd\overline{3} m$$ with an inverse spinel structure. The emission spectrum presents a broad and intense band in the near-infrared region. Photoluminescence excitation shows two bands in the visible frequency range assigned to octahedral Cr3+ transitions. Cr3+-doped and undoped sample emissions were compared. Optical spectra were analyzed and interpreted according to the crystal field theory and the Tanabe–Sugano energy matrices for the d3 configuration by calculating the Dq and B parameters. This work is a follow-up of the previous research on transition metal cations used as dopants in a Zn2TiO4 lattice, and the current results suggest that the system might be a promising luminescence source at room temperature.

Synthesis, crystal structure, hirshfeld surface analysis, spectroscopic, optical and thermal behavior of new organic-inorganic hybrid material (C7H11N2)2[CrCl2(H2O)4]Cl3·2H2O

(C7H11N2)2[CrCl2(H2O)4]Cl3·2H2O has been obtained by slow evaporation method at room temperature. The single crystal X–ray diffraction proves that it crystallizes in the P2/c monoclinic space group with a = 8.384(2)Å, b = 7.495(6)Å, c = 21.868(5)Å, β = 98.49(2)°, V = 1359(12)Å3. The structure is built up by (C7H11N2)+ organic cation, an octahedral Cr(III) inorganic cluster [CrCl2(H2O)4], two other free chlorine anions and a water molecule. The structure exhibits an alternate organic-inorganic layered stacking along c-axis. The isolated octahedra are building a zero-dimensional anionic network. The crystal structure is stabilized by NH⋯Cl, OH⋯Cl, OH⋯O and offset cycle stacking interactions. The powder X-ray diffraction confirms the phase purity. Hirshfeld surface projections elucidate the contribution of the H⋯Cl, H⋯H, H⋯O intermolecular interactions. The UV–visible, the photoluminescence (PL), the observed/calculated infrared, the electronic transition and the crystal shape morphology as well as the thermal behaviour of the studied compound have been discussed.

Synthesis and Characterizations of s-Triazine Polymeric Complexes Including Epoxy Groups: Investigation of Their Magnetic and Thermal Properties

We aimed to synthesize and characterize novel salen/salophen capped polymeric complexes including oxirane groups. For this purpose, we used 2,4,6-trichloro-1,3,5-triazine (I) as starting material. 2,4-dichloro,6-(3,4-dihydroxyphenylethylamino)-1,3,5-triazine (II) was synthesized by the reaction of an equivalent (I) and an equivalent dopamine. 2-(3,4-bis(oxiran-2-ylmethoxy)phenethyl)amine,4,6-dichloro-1,3,5-triazin (III) was synthesized by the reaction of two equivalents of epichlorohydrin and an equivalent of (II). [(Salen/Salophen) (Cr(III)/Fe(III))] capped complexes of (III) were synthesized by reaction of the reactants, codded as IV, V, VI and VII. Then, these monomeric complexes were polymerized by using ethylenediamine and o-phenylenediamine in 1,4-dioxane media, codded as VIII, IX, X, XI, XII, XIII, XIV and XV. II and III, monomeric and polymeric complexes were characterized by means of elemental analyses, 1H-NMR (spectrometry) and 13C-NMR (spectrometry), FT-IR spectrometry, ESI-MS and thermal analyses. Metal content in the prepared polymeric complexes was determined by inductively coupled plasma atomic emission spectrophotometer (ICPAES). We also synthesized novel polymeric complexes and investigated their effects on magnetic behaviors of [Cr(III)/Fe(III)(salen/salophen)] capped complexes. The complexes were determined to be low-spin distorted octahedral Fe(III) and distorted octahedral Cr(III).

Nanocrystalline Transition-Metal Gallium Oxide Spinels from Acetylacetonate Precursors via Solvothermal Synthesis.

The synthesis of mixed-metal spinels based on substituted γ-Ga2O3 is reported using metal acetylacetonate precursors in solvothermal reactions with alcohols as solvents at 240 °C. New oxides of Cr, Mn and Fe have been produced, all of which are formed as nanocrystalline powders, as seen by high-resolution transmission electron microscopy (HR-TEM). The first chromium-gallium mixed oxide is thus formed, with composition 0.33Ga1.87Cr0.8O4 ( = vacant site). X-ray absorption near-edge spectroscopy (XANES) at the chromium K-edge shows the presence of solely octahedral Cr3+, which in turn implies a mixture of tetrahedral and octahedral Ga3+, and the material is stable on annealing to at least 850 °C. An analogous manganese material with average chemical composition close to MnGa2O4 is shown to contain octahedral Mn2+, along with some Mn3+, but a different inversion factor to materials reported by conventional solid-state synthesis in the literature, which are known to have a significant proportion of tetrahedral Mn2+. In the case of iron, higher amounts of the transition metal can be included to give an Fe:Ga ratio of 1:1. Elemental mapping using energy dispersive X-ray spectroscopy on the TEM, however, reveals inhomogeneity in the distribution of the two metals. This is consistent with variable temperature 57Fe Mössbauer spectroscopy that shows the presence of Fe2+ and Fe3+ in more than one phase in the sample. Variable temperature magnetisation and electron paramagnetic resonance (EPR) indicate the presence of superparamagnetism at room temperature in the iron-gallium oxides.

Transition metal complexes of nano bidentate organometallic Schiff base: Preparation, structure characterization, biological activity, DFT and molecular docking studies

An organometallic NO‐bidentate Schiff base, (2‐(1‐((1‐carboxyethyl)imino)ethyl) cyclopenta‐2,4‐dien‐1‐yl)(cyclopenta‐2,4‐dien‐1‐yl) iron (HL) was synthesized by condensation of 2‐acetylferrocene with amino acid alanine. Then its octahedral Cr (III), Mn (II), Fe (III), Co (II), Ni (II), Cu (II), Zn (II) and Cd (II) complexes were synthesized. All compounds were characterized on the basis of elemental analysis (C, H, N and M), molar conductivity, FT‐IR, UV–Vis, 1H‐NMR, SEM, mass analysis and thermal studies. Furthermore, computational studies of HL ligand have been carried out by DFT/B3LYP method. HOMO and LUMO energy values, chemical hardness‐softness, electronegativity, electrophilic index and other parameters were calculated. SEM micrographs of HL ligand and its [Cd (HL)(H2O)2Cl2].2H2O complex, showed that they were prepared in nano‐structure forms with particle size 54 and 41 nm, respectively. Antifungal and antibacterial activities of HL ligand and its metal complexes have been screened in vitro against different species such as Aspergillus fumigatus, Candida albicans, Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Salmonella typhimurium. The synthesized compounds were evaluated for their anticancer activities against breast cancer cell line (MCF‐7) and normal melanocytes cell line (HFB‐4). It was found that [Co (HL)(H2O)2Cl2].3H2O complex had the lowest IC50 value (10.9 μg/ml) and hence was the most active one. Finally, the optimized structures of the Schiff base and its Co (II) complex have been used to accomplish molecular docking studies with receptors of 3HB5, 3MIW, 5IBV and 4WM8 to determine the most preferred mode of interaction.