A simple solvothermal synthesis of MFe2O4 (M=Mn, Co and Ni) nanoparticles

Nanoparticles of MFe₂O₄ (M=Mn, Co and Ni), with diameters ranging from 5 to 10 nm, have been obtained through a solvothermal method. In this synthesis, an alcohol (benzyl alcohol or hexanol) is used as both a solvent and a ligand; it is not necessary, therefore, to add a surfactant, simplifying the preparation of the dispersed particles. We have studied the influence of the synthetic conditions (temperature, time of synthesis and nature of solvent) on the quality of the obtained ferrites and on their particle size. In this last aspect, we have to highlight that the solvent plays an important role on the particle size, obtaining the smallest diameters when hexanol was used as a solvent. In addition, the magnetic properties of the obtained compounds have been studied at room temperature (RT). These compounds show a superparamagnetic behaviour, as was expected for single domain nanoparticles, and good magnetization values. The maxima magnetization values of the MFe₂O₄ samples are quite high for such small nanoparticles; this is closely related to the high crystallinity of the particles obtained by the solvothermal method.     

Anchored Ni-dimethylglyoxime complex on Fe3O4@SiO2 core/shell nanoparticles for the clean catalytical synthesis of dicoumarols

Ni-Dimethylglyoxime complex immobilized on functionalized Fe₃O₄ was synthesized by a post-grafting way and utilized as a novel, thermally stable, recoverable, and efficient for green synthesis of dicoumarols through reaction of 4-hydroxycoumarin with various aldehydes in excellent yields and higher rate. Fe₃O₄@SiO₂-silylcyclopropyl-dimethylglyoxime-Ni superparamagnetic nanoparticles (MNP_s) were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, vibrating sample magnetometer, and Brunauer–Emmett–Teller technique. This nanocatalyst could be conveniently recovered via the use of an external magnetic field and reused for subsequent reactions for at least 7 times without any remarkable change and decrease in catalytic activity.     

Synthesis of Various Metal/TiO2 Core/shell Nanorod Arrays

We present a general approach to fabricate metal/TiO₂ core/shell nanorod structures by two-step electrodeposition. Firstly, TiO₂ nanotubes with uniform wall thickness are prepared in anodic aluminum oxide (AAO) membranes by electrodeposition. The wall thickness of thenanotubes could be easily controlled by modulating the deposition time, and their outer diameter and length are only limited by the channel diameter and the thickness of the AAO membranes, respectively. The nanotubes' tops prepared by this method are open, while the bottoms are connected directly with the Au film at the back of the AAO membranes. Secondly, Pd, Cu, and Fe elements are filled into the TiO₂ nanotubes to form core/shell structures. The core/shell nanorods prepared by this two-step process are high density and free-standing, and their length is dependent on the deposition time.     

Inorganic-organic hybrid structure: Synthesis, structure and magnetic properties of a cobalt phosphite-oxalate, [C4N2H12][Co4(HPO3)2(C2O4)3]

A hydrothermal reaction of a mixture of cobalt (II) oxalate, phosphorous acid, piperazine and water at 150 °C for 96 h followed by heating at 180 °C for 24 h gave rise to a new inorganic-organic hybrid solid, [C₄N₂H₁₂][Co₄(HPO₃)₂(C₂O₄)₃], I. The structure consists of edge-shared CoO₆ octahedra forming a [Co₂O₁₀] dimers that are connected by HPO₃ and C₂O₄ units forming a three-dimensional structure with one-dimensional channels. The amine molecules are positioned within these channels. The oxalate units have a dual role of connecting within the plane of the layer as well as out of the plane. Magnetic susceptibility measurement shows the compound orders antiferromagnetically at low temperature (). Crystal data: I, monoclinic, space group=P2₁/c (No. 14). a=7.614(15), b=7.514(14), , β=97.351(3)°, , Z=2, , , R₁=0.0310 and wR₂=0.0807 data [I>2σ(I)].     

Preparation and mechanism of Fe3O4/Au core/shell super-paramagnetic microspheres

In the presence of Fe₃O₄ nano-particles, a new type of super-paramagnetic Fe₃O₄/Au microspheres with core/shell structures was prepared by reduction of Au³⁺ with hydroxylamine. The formation mechanism of the core/shell microspheres was studied in some detail. It was shown that the formation of the complex microspheres can be divided into two periods, that is, surface reaction-controlled process and diffusion-controlled process. The relative time lasted by either process depends upon the amount of Fe₃O₄ added and the initial concentration of Au³⁺. XPS analysis revealed that along with increasing in coating amount, the strength of the characteristic peaks of Au increased, and the Auger peaks of Fe weakened and even disappeared. Size distribution analysis showed that the core/shell microspheres are of an average diameter of 180 nm, a little bit larger than those before coating.     

Synthesis and characterisation of [(C5Me4R)2NbS2]2M complexes (M = Fe, Co; R = Me, Et) : organometallic tetrathiometalates with niobocene ligands

Irradiation of Cp₂^* Nb(η²---S₂)H (Cp^* = C₅Me₅) 1a in the presence of Fe(CO)₅ gives the CO-free complex [Cp₂^*NbS₂]₂Fe 2a. The core of 2a contains an FeS₄ tetrahedron which is ligated by two niobocene ligands as shown by X-ray diffraction analysis. In the reaction of 1a or Cp₂^xNb(η²---S₂)H (CP^x = C₅Me₄Et) 1b with Co₂(CO)₈, compounds 3a and 3b of the same type are formed. Electrochemical studies of 2a and 3a,b show that they undergo three reversible 1e⁻ steps. The oxidation of 3b exerts a considerable influence on its absorption spectrum. A qualitative EHMO analysis is in agreement with a strong delocalisation of electron density over the whole NbS₂MS₂Nb system.     

MGe(PO4)2 (M=Ca, Sr, Ba): Crystal structure, phase transitions and thermal expansion

Three earth alkali-germanium monophosphates M^IIGe(PO₄)₂ (M=Ca, Sr, Ba) were prepared by solid state reaction and their structures, previously unknown, studied by Rietveld analysis. BaGe(PO₄)₂ and high-temperature β-SrGe(PO₄)₂ (space group C2/m, Z=2) are fully isotypic with yavapaiite, whereas CaGe(PO₄)₂ and low-temperature α-SrGe(PO₄)₂ (C2/c, Z=4) are distorted derivatives. The phase transition between the two forms is observed for the first time. The thermal expansion, resulting from several structural mechanisms, is very anisotropic.     

Two isotypic diphosphates LiM2H3(P2O7)2 (M=Ni, Co) containing ferromagnetic zigzag MO6 chains

Two new isotypic phosphates LiNi₂H₃(P₂O₇)₂ (1) and LiCo₂H₃(P₂O₇)₂ (2) have been hydrothermally synthesized and structurally characterized by the single-crystal X-ray diffraction technique. They crystallize in the monoclinic space group C2/c with the lattice: a=10.925(2) Å, b=12.774(3) Å, c=8.8833(18) Å, β=123.20(3)° for 1 and a=10.999(2) Å, b=12.863(3) Å, c=8.9419(18) Å, β=123.00(3)° for 2. The transition metal atoms are octahedrally coordinated, whereas the lithium and phosphorus atoms are all tetrahedrally coordinated. As the lithium-induced derivatives of MH₂P₂O₇ (M=Ni, Co), 1 and 2 possess the same structure with MH₂P₂O₇ in terms of topology, comprising the MO₆ zigzag chains and P₂O₇ as the interchain groups. The magnetisms of 1 and 2 could be interpreted by adopting a quasi-one-dimensional (1D) zigzag chain model as that in their parent compounds: both 1 and 2 have ferromagnetic (FM) NiO₆/CoO₆ chains; 1 shows a FM cluster glass behavior at low temperatures, which is originated from the possible antiferromagnetic (AFM) next-nearest-neighbour intrachain interactions; 2 shows a AFM ordering at T_N=2.6 K and a metamagnetic transition at H_C=4.2 kOe at 1.8 K.     

Synthesis and structural characterization of two cobalt phosphites: 1-D (H3NC6H4NH3)Co(HPO3)2 and 2-D (NH4)2Co2(HPo3)3

Two new cobalt phosphites, (H₃NC₆H₄NH₃)Co(HPO₃)₂ (1) and (NH₄)₂Co₂(HPO₃)₃ (2), have been synthesized and characterized by single-crystal X-ray diffraction. All the cobalt atoms of 1 are in tetrahedral CoO₄ coordination. The structure of 1 comprises twisted square chains of four-rings, which contain alternating vertex-shared CoO₄ tetrahedra and HPO₃ groups. These chains are interlinked with trans-1,4-diaminocyclohexane cations by hydrogen bonds. The 2-D structure of 2 comprises anionic complex sheets with ammonium cations present between them. An anionic complex sheet contains three-deck phosphite units, which are interconnected by Co₂O₉ to form complex layers. Magnetic susceptibility measurements of 1 and 2 showed that they have a weak antiferromagnetic interaction.     

Synthesis and characterization of Na5[Co(CO)3(P{(CH2)nC6H4-P-SO3}3)2], n = 1, 2, 3, and 6. Novel zwitterion

The electron donating water soluble phosphines, P{(CH₂)nC₆H₄-p-SO₃Na}₃,n = 1, 2, 3 and 6, react rapidly with Co₂(CO)₈ under two phase reaction conditions to yield the disproportionation products, [Co(CO)₃(P{(CH₂)nC₆H₄-p-SO₃Na₃}₂] [Co(CO)₄]. Selective precipitation yields the formally zwitterionic complex anions as the sodium salt, [Co(CO)₃(P{(CH₂)nC₆H₄-p-SO₃} ₃)₂]⁵⁻. The anions can be used as precursors to water soluble cobalt hydroformylation catalysts under two phase and supported aqueous phase conditions. The tendency to form alcohol products is low with these complexes. The behavior of the catalysts is consistent with an active species that remains water soluble during the reaction and is not leached into the nonaqueous phase.     

Synthesis, structure, and characterization of a new one-dimensional tellurite phosphate, Ba2TeO(PO4)2

A new one-dimensional tellurite phosphate, Ba₂TeO(PO₄)₂ has been synthesized by standard solid-state reaction techniques using BaCO₃, TeO₂, and (NH₄)H₂PO₄ as reagents. The structure of Ba₂TeO(PO₄)₂ was determined by single-crystal X-ray diffraction. Ba₂TeO(PO₄)₂ crystallizes in the triclinic space group P-1 (No. 2), with , , , α=76.843(4)°, β=79.933(4)°, γ=75.688(4)°, , and Z=2. Ba₂TeO(PO₄)₂ has a novel one-dimensional chain structure that is composed of PO₄ tetrahedra and TeO₅ polyhedra. Te⁴⁺ cations are in asymmetric coordination environments attributable to their lone pairs. The lone pairs on the Te⁴⁺ cations point in the [100] and [−100] direction and interact with the Ba²⁺ cations. Infrared, Raman, and UV-Vis diffuse reflectance spectroscopy, thermogravimetric analysis, and dipole moment calculations are also presented.     

A novel three-dimensional cobalt (III) complex via hydrogen bonds: [Co(tacn)2] (ClO4)3 (tacn=1,4,7-triazacyclononane)

A novel cobalt (III) complex has been synthesized and its structure was determined. The structure consists of Co(tacn)₂³⁺ ions and ClO₄⁻, each cobalt (III) ion was six-coordinated with six nitrogen atoms of two tacns. Hydrogen bonds widely exist between the oxygen atoms of ClO₄⁻ and the nitrogen and carbon atoms of tacn, resulting in a unique three-dimensional network. The electronic spectra were measured and assigned in the strong-field approximation, giving the values of the parameter: Δ, B and C.     

Effect of formation conditions on the structure, morphology and magnetic properties of nanosized MIIFe 2III O4 ferrites (M = Mn, Co, Ni) and Fe2O3

A study was carried out on the conditions of formation of highly crystalline, superparamagnetic, nanosized oxides, M^II Fe ₂ ^III O₄ and γ-Fe₂O₃ (4.9–11.7 nm) by the thermal decomposition of complexes [MFe₂O(CH₃CO₂)₆(H₂O)₃] (M = Mn, Fe, Co, Ni) in tetraethylene glycol. The presence of surfactants leads to a decrease in the size and size distribution of the nanoparticles formed, while the use of microwave radiation significantly reduces the time for formation of the nanocrystalline oxides. The magnetic measurements showed ferrimagnetic ordering in the nanoparticles studied and their superparamagnetic behavior. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 5, pp. 323–329, September–October, 2007.     

Synthesis of highly fluorescent LaF3:Ln/LaF3 core/shell nanocrystals by a surfactant-free aqueous solution route

A surfactant-free aqueous solution route has been established for the synthesis of LaF₃:Ln³⁺/LaF₃ core/shell nanocrystals (Ln=Ce, Tb, Nd) heated at 75 °C at ambient pressure. All the as-prepared nanocrystals with spherical shape have an average size around 20 nm, and consist of well crystallized hexagonal phases. The X-ray photoelectron spectra was used to confirm that the LaF₃ shells have coated the LaF₃:Ce³⁺, Tb³⁺ cores. Compared with that of the original cores under the same conditions, the emission intensity of the LaF₃:Ce³⁺, Tb³⁺/LaF₃ and LaF₃:Nd³⁺/LaF₃ core/shell nanocrystals increased significantly of 120% and 60%, respectively. The quantum yield of the LaF₃:Ce³⁺, Tb³⁺/LaF₃ core/shell nanocrystals reached about 27% in aqueous solution. These results indicate that a significant reduction of the quenching from the surface of the core nanocrystals can be obtained by the synthesis of the core/shell structures, and this method can provide more desirable lanthanide-doped nanocrystals for potential biological applications.     

Potassium-conductive solid electrolytes in systems K2 ? 2 x M2 ? x V x O4(M = Al, Fe)

New high-conductivity solid electrolytes based on potassium monoaluminate and monoferrite are synthesized by partial substitution of V⁵⁺ for three-charged cations. In both systems, the introduction of vanadium cations leads to a substantial increase in the conductivity, with the maximum values corresponding to upper boundaries of the monophase solid solution regions. The principal factors responsible for the high conductivity are the formation of potassium vacancies at the substitutions M³⁺ → V⁵⁺ + 2V’ _K and the extension of the temperature range of existence of high-temperature modifications of KAl(Fe)O₂. Original Russian Text ? E.I. Burmakin, G.V. Nechaev, B.D. Antonov, G.Sh. Shekhtman, 2008, published in Elektrokhimiya, 2008, Vol. 44, No. 10, pp. 1261–1264.     

Double (n=2) and triple (n=3) [M4Bi2n−2O2n] polycationic ribbons in the new Bi∼3Cd∼3.72M∼1.28O5(PO4)3 oxyphosphate (M=Co, Cu, Zn)

The crystal structure of the new Bi_∼3Cd_∼3.72Co_∼1.28O₅(PO₄)₃ has been refined from single crystal XRD data, R₁=5.37%, space group Abmm, a=11.5322(28) Å, b=5.4760(13) Å, c=23.2446(56) Å, Z=4. Compared to Bi_∼1.2M_∼1.2O_1.5(PO₄) and Bi_∼6.2Cu_∼6.2O₈(PO₄)₅, this compound is an additional example of disordered Bi³⁺/M²⁺ oxyphosphate and is well described from the arrangement of double [Bi₄Cd₄O₆]⁸⁺ (=D) and triple [Bi₂Cd_3.44Co_0.56O₄]⁶⁺ (=T) polycationic ribbons formed of edge-sharing O(Bi,M)₄ tetrahedra surrounded by PO₄ groups. According to the nomenclature defined in this work, the sequence is TT/DtDt, where t stands for the tunnels created by PO₄ between two subsequent double ribbons and occupied by Co²⁺. The HREM study allows a clear visualization of the announced sequence by comparison with the refined crystal structure. The Bi³⁺/M²⁺ statistic disorder at the edges of T and D entities is responsible for the PO₄ multi-configuration disorder around a central P atom. Infrared spectroscopy and neutron diffraction of similar compounds (without the highly absorbing Cadmium) even suggests the long range ordering loss for phosphates. Therefore, electron diffraction shows the existence of a modulation vector q^*=1/2a^*+(1/3+ε)b^* which pictures cationic ordering in the (001) plane, at the crystallite scale. This ordering is largely lost at the single crystal scale. The existence of mixed Bi³⁺/M²⁺ positions also enables a partial filling of the tunnels by Co²⁺ and yields a composition range checked by solid state reaction. The title compound can be prepared as a single phase and also the M=Zn²⁺ term can be obtained in a biphasic mixture. For M=Cu²⁺, a monoclinic distortion has been evidenced from XRD and HREM patterns but surprisingly, the orthorhombic ideal form can also be obtained in similar conditions.     

Hydrothermal synthesis, crystal structure, and characterization of a new pseudo-two-dimensional uranyl oxyfluoride, [N(C2H5)4]2[(UO2)4(OH2)3F10]

A new uranyl oxyfluoride, [N(C₂H₅)₄]₂[(UO₂)₄(OH₂)₃F₁₀] has been synthesized by a hydrothermal reaction technique using (C₂H₅)₄NBr, UO₂(OCOCH₃)₂·2H₂O, and HF as reagents. The structure of [N(C₂H₅)₄]₂[(UO₂)₄(OH₂)₃F₁₀] has been determined by a single-crystal X-ray diffraction technique. [N(C₂H₅)₄]₂[(UO₂)₄(OH₂)₃F₁₀] crystallizes in the monoclinic space group P2₁/n (No. 14), with , , , β=98.88(3)°, , and Z=4. [N(C₂H₅)₄]₂[(UO₂)₄(OH₂)₃F₁₀] reveals a novel pseudo-two-dimensional crystal structure that is composed of UO₂F₅, UO₃F₄, and UO₄F₃ pentagonal bipyramids. Each uranyl pentagonal bipyramid shares edges and corners through F atoms to form a six-membered ring. The rings are further interconnected to generate infinite strips running along the b-axis. [N(C₂H₅)₄]₂[(UO₂)₄(OH₂)₃F₁₀] has been further characterized by elemental analysis, bond valence calculations, Infrared and Raman spectroscopy, and thermogravimetric analysis.     

Syntheses, structure and magnetic properties of pillared layered diphosphonates: M2(O3PC6H4PO3)(H2O)2 (M=Co, Ni)

This paper describes the hydrothermal syntheses of two isostructural metal bisphosphonates: M₂(O₃PC₆H₄PO₃)(H₂O)₂ [M=Co^II (1), Ni^II (2)]. Single-crystal structure determination of compound 1 revealed a pillared layered structure in which the phenyl groups connect the inorganic layers of cobalt phosphonate. Crystal data for 1: orthorhombic, space group Pnnm, a=19.306(5), b=4.8293(12), c=5.6390(14) Å, V=525.7(2) Å³, Z=2. Magnetic susceptibility data indicate that antiferromagnetic interactions are mediated in both cases.     

Synthesis and electrical properties of Li1+ x M x Ti2– x (PO4)3 (where M =Sc, Al, Fe, Y; x =0.3) superionic ceramics

Compounds of the system Li_{1+ x} M _x Ti_{2– x} (PO₄)₃ (where M=Sc, Al, Fe, Y; x=0.3) were synthesized by a solid-state reaction and studied by X-ray diffraction. The ceramic samples were sintered and investigated by complex impedance spectroscopy in the frequency range 10⁶–1.2×10⁹ Hz in the temperature range 300–600 K. Two relaxation dispersions related to the fast Li⁺ ion transport in bulk and grain boundaries were found. The activation energies of the bulk conductivity and relaxation frequency were obtained from the slops of Arrhenius plots. The values of the activation energies of the bulk ionic conductivity and relaxation frequency were found to be very similar in all the materials investigated. That can be attributed to the fact that the temperature dependences of the bulk conductivity are caused only by the mobility of the fast Li⁺ ions, while the number of charge carriers remains constant with temperature. Electronic Publication