A general method for preparing lanthanide oxide nanoparticles via thermal decomposition of lanthanide(III) complexes with 1-hydroxy-2-naphthoic acid and hydrazine ligands

Six new lanthanide(III) complexes (i.e., [Ln(L)₂(NA)_1.5]·3H₂O, where Ln=La(III), Pr(III), Nd(III), Sm(III), Gd(III), and Ce(III) and L and NA indicate N₂H₄ and C₁₀H₆(1-O)(2-COO), respectively) with 1-hydroxy-2-naphthoic acid [C₁₀H₆(1-O)(2-COOH)] and hydrazine (N₂H₄) as co-ligands were characterized by elemental, FTIR, UV-visible, and XRD techniques. In the FT-IR spectra, the N-N stretching frequency in the range of 981–949 cm⁻¹ demonstrates evidence of the presence of coordinated N₂H₄, indicating the bidentate bridging nature of hydrazine in the complexes. These complexes show symmetric and asymmetric COO⁻ stretching from 1444 to 1441 cm⁻¹ and 1582 to 1557 cm⁻¹, respectively, indicating bidentate coordination. TG-DTA studies revealed that the compounds underwent endothermic dehydration from 98 to 110 °C. This was followed by the exothermic decomposition of oxalate intermediates to yield the respective metal oxides as the end products. From SEM images, the average size of the metal oxide particles prepared by thermal decomposition of the complexes was determined to be 39–42 nm. The powder X-ray and SEM coupled with energy dispersive X-ray (EDX) studies revealed the presence of the respective nano-sized metal oxides. The kinetic parameters of the decomposition of the complexes were calculated using the Coats-Redfern equation.     

Synthesis of [Ru3(μ3-NPh)(Br)(CO)9] on self-assembled monolayers of di(3-aminopropyl)viologen/ITO surfaces and its application to photoelectrochemical cells

Triruthenium carbonyl clusters {[Ru₃(Br)(CO)₁₁]⁻ (denoted as Ru-1), [Ru₃(μ₂-Br)(CO)₁₀]⁻ (denoted as Ru-2), and [Ru₃(μ₃-NPh)(Br)(CO)₉]⁻ (denoted as Ru-3)} were synthesized on di(3-aminopropyl)viologen (DAPV)/indium tin oxide (ITO) using a surface reaction in a ruthenium (III) carbonyl [Ru₃(CO)₁₂] solution, and were applied to photoelectrochemical cells (PECs) at the molecular level. The formation of DAPV on ITO was realized in the form of self-assembled monolayers. Ru₃(CO)₁₂ then easily reacted with the Br⁻ of DAPV, and a mixture of Ru-1 and Ru-2 was formed on DAPV/ITO. Furthermore, Ru-3 was successfully anchored on DAPV/ITO by adding nitrosobenzene in order to react with Ru-2 on DAPV/ITO. The photocurrents of (Ru-1 and Ru-2)/DAPV/ITO and Ru-3/DAPV/ITO in PECs at the molecular level were 6.3 nA cm⁻² and 8.6 nA cm⁻², respectively. The quantum yield of Ru-3/DAPV/ITO was ∼0.8%. Time-resolved photoluminescence spectroscopy and emission spectroscopy were recorded to bring out the photoinduced charge transfer process from ruthenium clusters to DAPV.     

Solid state and sonochemical syntheses of nano lead(II) chloride and bromide coordination polymers from its nitrate analog via mechanochemical crystal to crystal transformations

Reversible crystal-to-crystal transformations of 3D lead(II) coordination polymers with the ligand 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene (4-bpdh), from nitrate analoge [Pb(4-bpdh)(NO₃)₂(H₂O)]_n (1) to [Pb(4-bpdh)(NO₃)(Br)]_n (2), [Pb(4-bpdh)(Br)₂]_n (3), [Pb(4-bpdh)(NO₃)(Cl)]_n (4) and [Pb(4-bpdh)(Cl)₂]_n (5) by solid state anion-replacement processes under mechanochemical reactions, have been studied. The reversible solid state structural transformations of compounds 1–5, by anion-replacement processes under mechanochemical reaction, have been verified by PXRD measurements. Nanoparticles of compounds were synthesized by sonochemical process and characterized by scanning electron microscopy (SEM), powder X-ray diffraction, IR spectroscopy and elemental analyses. The SEM images showed that morphology change occurs during solid state anion-replacements of nanocrystals.     

Trapping of metastable high-spin species and weak cooperativity in a mononuclear Fe(II) spin-crossover system

The magnetic and structural properties of three gradual spin transition monomeric compounds based on the cation [Fe(Hpt)₃]²⁺ (Hpt=3-(pyrid-2-yl)-1,2,4-triazole) are presented. The non-cooperative character of the spin-crossover in [Fe(Hpt)₃](BF₄)₂·2H₂O (I) is evaluated in light of its calorimetric properties, which yielded the thermodynamic values Δ_trsH=5.81 kJ mol⁻¹ and Δ_trsS=39.5 J mol⁻¹ K⁻¹. The light-induced excited spin-state trapping effect is performed on [Fe(Hpt)₃](BF₄)₂·2H₂O (I) and [Fe(Hpt)₃](SO₄)_0.4(BF₄)_1.2·3H₂O (II), and the subsequent HS→LS relaxations are studied. Their merely first-order kinetics are affected by disorder in the structure of both complexes, which appears in the presence of a distribution of activation energies. HS species can also be frozen-in in I by rapid cooling. Continuous irradiation is shown to induce only apparent light-induced thermal hysteresis effect in I and II, stemming from slow kinetics of relaxation with respect to the kinetics of measurement.     

Application of ultrasound to the synthesis of a new nanostructured Mn(II) supramolecular compound: A precursor for γ-Mn2O3 nanoparticles

A new nanostructured Mn(II) supramolecular compound [Mn(hpydcH₂)₂(H₂O)₄] (1) (hpydcH₃ = 4-hydroxy-2,6-pyridinedicarboxylic acid) has been synthesized using a sonochemical process. The structure of compound 1 was determined by single crystal X-ray diffraction and it was revealed that each hpydcH₂⁻ anionic ligand has been coordinated to Mn(II) ion in a novel monodentate fashion leaving another functional carboxylic acid group intact. Compound 1 was also characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRPD), FT-IR spectroscopy and elemental analysis. Thermal stability of compound 1 was studied by thermal gravimetric (TG) analysis and compared to that of its crystalline analogue. Subsequently, the role of concentration of the initial reactants on the size of nanostructures of compound 1, has been investigated. Compound 1 was proved to be a precursor for γ-Mn₂O₃ nanoparticles.     

Sonochemical synthesis,characterization, thermal and semiconducting behavior of nano-sized azidopentaamminecobalt(III) complexes containing anion,CrO42− or Cr2O72−

New nano-sized cobalt(III) coordination complexes, [Co(NH₃)₅N₃]CrO₄ (1N) and [Co(NH₃)₅N₃]Cr₂O₇ (2N) were synthesized using an innovative sonochemical methodology based on reaction between [Co(NH₃)₅N₃]Cl₂ and potassium salt of CrO₄²⁻ or Cr₂O₇²⁻ in aqueous medium. These complexes were also compared with their respective bulks which were synthesized under identical conditions in the absence of sonicaion. All the complexes were characterized by elemental analysis and spectroscopic techniques (UV–visible and IR). Morphology and particle size of nano-sized complexes was determined by SEM and Zeta-sizer respectively. TGA was used for comparative thermal stability and XRD to identify the phase difference between nano structures and bulk complexes. Furthermore, the electrical property was investigated and all complexes were found to be electrical semiconducting materials and 2N shows better result than others. The single crystals X-ray structure study of new [Co(NH₃)₅N₃]Cr₂O₇ revealed the presence of discrete ions, [Co(NH₃)₅N₃]²⁺ and Cr₂O₇²⁻, crystallizes in monoclinic, space group P_c, with R = 0.0636 in the solid state.     

Chemical tuning by 5-Methyl and N-Methyl-substitution in heptanuclear complexes effects multistability investigated by Mössbauer spectroscopy

The precursors [Fe^(III)(^N???R???L)Cl] (^N???R???LH₂=N,N′-bis(2′-hydroxy- 5′-methyl-benzyliden)-1,7-diamino-4-R-4-azaheptane, R ?=? H, methyl(Me)) are high-spin (S?=?5/2) complexes. The Lewis-acidic precursors are combined with Lewis- Base-bridging-units [M(CN) _x ] ^y??? (M = Fe^(II), Ru^(II), Co^(III)) to form heptanuclear star-shaped [M{CN-Fe^(III)(^N???R???L)} _x ]Cl _y molecular switches. The star-shaped compounds are high-spin systems at room temperature. On cooling to 20 K some of the compounds exhibit multistability, i.e. several iron(III) centers within a molecule switch to the low-spin state as shown by Mössbauer spectroscopy.     

3-Methyl and N-Methyl-substitution in heptanuclear complexes effects multistability investigated by Mössbauer spectroscopy

The precursors [Fe^(III)(^N???R???L)Cl] (^N???R???LH₂ = N,N ^′ -bis(2’-hydroxy-3’- methyl-benzyliden)-1,7-diamino-4-R-4-azaheptane, R = H, methyl(Me)) are high-spin (S?=?5/2) complexes. The Lewis-acidic precursors are combined with Lewis-Base-bridging-units [M(CN) _x ] ^y??? (M = Fe^(II), Ru^(II), Co^(III)) to form heptanuclear star-shaped [M{CN–Fe^(III)(^N???R???L)} _x ]Cl _y molecular switches. The starshaped compounds are high-spin systems at room temperature. On cooling to 20 K some of the compounds exhibit multistability, i.e. several iron(III) centers within a molecule switch the spin state as shown by Mössbauer spectroscopy.     

Phase stability and oxygen non-stoichiometry of SrCo0.8Fe0.2O3−δ measured by in situ neutron diffraction

The phase stability, oxygen stoichiometry and expansion properties of SrCo_0.8Fe_0.2O_3−δ (SCF) were determined by in situ neutron diffraction between 873 and 1173 K and oxygen partial pressures of 5 × 10^− 4 to 1 atm. At a pO₂ of 1 atm, SCF adopts a cubic perovskite structure, space group Pm3¯m, across the whole temperature range investigated. At a pO₂ of 10^− 1 atm, a two-phase region exists below 922 K, where the cubic perovskite phase coexists with a vacancy ordered brownmillerite phase, Sr₂Co_1.6Fe_0.4O₅, space group Icmm. A pure brownmillerite phase is present at pO₂ of 10^− 2 and 5 × 10^− 4 atm below 1020 K. Above 1020 K, the brownmillerite phase transforms to cubic perovskite through a two-phase region with no brownmillerite structure observed above 1064 K. Large distortion of the BO₆ (B = Co, Fe) octahedra is present in the brownmillerite structure with apical bond lengths of 2.2974(4) Å and equatorial bond lengths of 1.9737(3) Å at 1021 K and a pO₂ of 10^− 2 atm. SCF is highly oxygen deficient with a maximum oxygen stoichiometry, 3 − δ, measured in this study of 2.58(2) at 873 K and a pO₂ of 1 atm and a minimum of 2.33(2) at 1173 K and a pO₂ of 5 × 10^− 4 atm. Significant differences in lattice volume and expansion behavior between the brownmillerite and cubic perovskite phases suggest potential difficulties in thermal cycling of SrCo_0.8Fe_0.2O_3−δ membranes.     

Sonochemical syntheses of a new fibrous-like nano-scale manganese(II) coordination supramolecular compound; precursor for the fabrication of octahedral-like Mn3O4 nano-structure

Nanoparticles of a new three-dimensional Mn(II) coordination supramolecular compound, [Mn(L)₂(H₂O)₂] (1), (L⁻ = 1H-1,2,4-triazole-3-carboxylate), have been synthesized by a sonochemical process and characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRPD), FT-IR spectroscopy and elemental analyses. Structural determination of compound 1 reveals the Mn(II) ion is six coordinated, bonded to two nitrogen atoms, two oxygen atoms from the L⁻ ligand and two water molecules. The thermal stability of compound 1 both its bulk and nano-size has been studied by thermal gravimetric (TG) and differential thermal analyses (DTA) and compared each other. Concentration of initial reagents effects on size and morphology of nano-structured compound 1, have been studied and shows that low concentrations of initial reagents decreased particles size and also leaded to fibrous-like nanostructures morphology. Mn₃O₄ nano-structure with an octahedral-like morphology were simply synthesized by solid-state transformation of compound 1 at 650 °C.     

Influence of the orthorhombic distortion on the van Hove singularities in the DOS and ARPES spectra of layered cuprates

Four atom states Cu3d_{x² −  y²}, Cu4s, O_a2p_xare involved in a tight-binding model for the superconducting CuO₂plane. The orthorhombic distortion is taken into account by the differences of Cu–O hopping amplitudes and single-site oxygen energies ε_aand ε_bof two oxygen positions in the elementary cell as well. An effective ‘oxygen’ Hamiltonian including only the electron amplitudes at the oxygen ions is derived. Simple expressions for the constant energy contours and the Fermi surface are obtained and they qualitatively describe the photoemission spectra. Extended saddle points nearp = (π,0) andp = (0,π) are observed in qualitative agreement with the ARPES data. The van Hove singularities of the density of states (DOS) related to the extended saddle points are calculated by a Monte Carlo method. It is found that the splitting of the singularity of the DOS at the bottom of the conduction band is created by the energy difference ε_a −  ε_b = 2δ.     

Raman scattering study of IrxRu1−xO2 mixed metal oxide nanowires (0 ≤ x ≤ 1)

Recent interests in mixed metal oxide nanostructured materials especially Ir_xRu_1−xO₂ compounds have been mainly driven by the technological application as electrocatalyst and electrode materials. We present room temperature Raman scattering results of single crystalline Ir_xRu_1−xO₂ (0 ≤ x ≤ 1) nanowires grown by atmospheric pressure chemical vapor deposition. We observed that the E_g, the A_1g, and the B_2g phonon modes of a single Ir_xRu_1−xO₂ nanowire are blue-shifted linearly with respect to the Ir contents from which we could get stoichiometry information. We also observed that the asymmetric lineshape and the broadening of the full width at half maximum of the E_g mode that involves the out-of-plane oxygen vibration. The unusual asymmetric broadening of the E_g phonon can be explained by the activation of the non-zone-center phonons due to substitutional disorder present in the system. We also found that there is a mixed mode of the A_1g and the B_2g phonons due to the substitutional disorder, in the range of 630–750 cm⁻¹.     

Synthesis,crystal structure,spectroscopic characterization and optical properties of bis(4-acetylanilinium) tetrachlorocobalt (II)

The chemical preparation, crystal structure, spectroscopic investigations and optical features are given for a novel organic–inorganic hybrid material [C₈H₁₀NO]₂CoCl₄.The compound is crystallized in the orthorhombic space group Cmca, with the following unit cell parameters: a=19.461(2) Å, b=15.523(2) Å, c=13.7436(15) Å, and Z=8. The atomic arrangement shows an alternation of organic and inorganic layers along the b-axis. The cohesion between these entities is performed by N–H…Cl and N–H…O hydrogen bonds and π–π stacking interactions.Infrared and Raman spectra at room temperature are recorded in the 4000−400 and 4000−0 cm⁻¹ frequency regions, respectively and analyzed on the basis of literature data. This study confirms the presence of the organic cation [C₈H₁₀NO]⁺ and of the [CoCl₄]²⁻ anion. UV–vis spectroscopy results showed the indirect transition with band gap energy 2.98 eV.     

High temperature protonic conduction in Sr-doped LaP3O9

Electrical conduction of Sr-doped LaP₃O₉ ([Sr]/{[La] + [Sr]} = 2–10 mol%) was investigated under 0.4–5 kPa of p(H₂O) and 0.01–100 kPa of p(O₂) or 0.3–3 kPa of p(H₂) at 573–973 K. Sr-doped LaP₃O₉ showed apparent H/D isotope effect on conductivity regardless of the Sr-doping level under both H₂O/O₂ oxidizing and H₂/H₂O reducing conditions at investigated temperatures. Conductivities of the material were almost independent of p(O₂) and p(H₂O). These results demonstrated that the Sr-doped LaP₃O₉ exhibited protonic conduction under wide ranges of p(O₂), p(H₂O) and temperature. The conductivity of the Sr-doped LaP₃O₉ increased with increasing Sr concentration up to its solubility limit, ca. 3 mol%, while the further Sr-doping slightly degraded the conductivity. These indicate that Sr²⁺ substitution for La³⁺ leads to proton dissolution into the material and induced protonic conduction. Conductivities of the 3 mol% Sr-doped sample were 2 × 10^- 6–5 × 10^− 4 S cm^− 1 at 573–973 K.     

Relation between 2p X-ray photoelectron and Kα X-ray emission spectra of manganese and iron oxides

The high resolution Mn and Fe Kα X-ray emission spectra (XES), and Mn and Fe 2p X-ray photoelectron spectra (XPS) for manganese and iron oxides were measured. The spectra were compared with those of [MnO₄]⁻, [Fe(CN)₆]⁴⁻ and [Fe(CN)₆]³⁻ ions. As the electronic structure of the latter compounds do not change with electron hole creation in the core levels, satellite peaks due to charge transfer are not observed in the 2p XPS spectra, and the peak profiles of metal 2p XPS and Kα XES are governed by the exchange splitting between 2p and valence electrons. The metal 2p XPS spectra of the oxides had satellite peaks, but the XES spectra had no satellites. FWHMs of the metal 2p_3/2 main peaks of the compounds being low spin states are smaller than those of metal Kα₁ XES spectra. However, FWHMs of Mn 2p_3/2 of the manganese oxide were nearly equal to those of Mn Kα₁ XES spectra, and those of Fe 2p_3/2 XPS spectra of the iron oxides are greater than those of Fe Kα₁ XES spectra.     

Structural characterization of Sr–Ti and Ba–Ti catecholate complexes: single source precursors for SrTiO3 and BaTiO3 binary oxides

Titanium catecholate complex H₂Ti(cat)₃ (1) is synthesized from the direct reaction of Ti(OⁱPr)₄ with catechol (H₂cat). Treatment of 1 with NEt₃ gives ionic complex (HNEt₃)₂[Ti(cat)₃] (2). Reactions of 1 with SrCO₃ or with BaCO₃ afford the corresponding catecholate complexes with approximate composition Sr[Ti(cat)₃]3H₂O (3) and Ba[Ti(cat)₃]3H₂O (4), of which the formula was proposed according to the previous literature report and microanalytical data. Water soluble crystalline materials [Sr(H₂O)₅]₂[Ti₂O₂(cat)₄]6H₂O (5) and [Ba(H₂O)₄(C₃H₆O)]₂[Ti₂O₂(cat)₄]2C₃H₆O (6) are isolated in low yields by repeated recrystallization of 3 and 4 from a mixture of water and acetone at room temperature. The single crystal X-ray diffraction studies reveal that they fail to show the discrete Ti(cat)₃²⁻ unit as suggested previously, but they contain a dimeric [Ti₂O₂(cat)₄]⁴⁻ fragment with two bridging oxo ligands and two chelating catecholate ligands associated with each Ti atom. The latter is further linked to the hydrated Sr²⁺ or the Ba²⁺ counter cations through axial oxygen atoms of the catecholate ligands and the unique bridging oxo ligand. Crystal data for 5: a=7.8251(1), b=11.3739(2), c=11.4980(2) Å, α=91.942(1), β=100.441(1), γ=103.061(1)° with Z=1 in space group P1̄. For complex 6: a=9.6450(3), b=10.2092(3), c=13.3098(4) Å, α=18.192(1), β=85.876(1), γ=73.475(1)° with Z=1 in space group P1̄. Conversion to the respective SrTiO₃ and BaTiO₃ phases by calcination under oxygen atmosphere is confirmed by TG analysis and X-ray powder analysis.     

High-spin metal-cyanide clusters: species incorporating [Mn(salen)] complexes as a source of anisotropy

The use of N,N′-ethylenebis(salycylideneiminato) (salen) complexes of Mn^III in assembling high-spin metal-cyanide coordination clusters with significant magnetic anisotropy is demonstrated. The reaction of [Mn(salen)(H₂O)₂]⁺with [Cr(CN)₆]³⁻ in aqueous solution generates {Cr[CNMn(salen)(H₂O)]₆}[Cr(CN)₆]·6H₂O (1), a previously reported compound featuring a heptanuclear cluster with a distorted octahedral geometry. A fit to the variable-temperature magnetic susceptibility data for 1 revealed the presence of weak antiferromagnetic coupling of within the cluster, giving rise to an S=21/2 ground state. In addition, variable-field magnetization data collected at low temperatures revealed the presence of magnetic anisotropy in the ground state, with the best fit yielding zero-field splitting parameters of D=+0.19 cm⁻¹ and A reaction intended to produce a direct analogue of 1 by employing [Fe(CN)₆]³⁻ in place of [Cr(CN)₆]³⁻ instead gave an unusually complex compound of formula {Fe(CN)₄[CNMn(salen)(MeOH)]₂}{[Mn(salen)(H₂O)]₂}[Mn(salen)(H₂O)(MeOH)]₂[Fe(CN)₆]·4H₂O (2). The crystal structure and magnetic properties of this compound are reported.     

Synthesis, X-ray structure and magnetic properties of the quinone cobalt complexes [Co(3,5-DTBSQ)(bpy)2]x2 (x=BF4, ClO4)

Double oxidation of [Co^III(3,5-DTBCat)(3,5-DTBSQ)(bpy)] (1,ls-Co(III)) by AgBF₄ and of [Co^II(3,5-DTBSQ)₂(bpy)] (1,hs-Co(II)) by a mixture of HClO₄/H₂O₂ yielded [Co^III(3,5-DTBSQ) (bpy)₂]X₂, where X⁻=BF₄⁻ (4) and ClO₄⁻ (5), respectively. The mechanism for the double-oxidation process that leads to a loss of one of the quinone ligands and in some cases to a redistribution of the electronic charge is discussed here.     

Sonochemical synthesis and characterization of nano-sized lead(II) 3D coordination polymer: Precursor for the synthesis of lead(II) oxybromide nanoparticles

Nanoparticles of a three-dimensional coordination polymer, [Pb(L)(μ₂-Br)(H₂O)]_n (1), (L^? = 1H-1,2,4-triazole-3-carboxylate), have been synthesized by an ultrasonic method and characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analyses. The thermal stability of compound 1 both its bulk and nano-size has been studied by thermal gravimetric (TG) and differential thermal (DTA) analyses and compared each other. Concentration of initial reagents effects and the role of power ultrasound irradiation on size and morphology of nano-structured compound 1, have been studied. Calcination of the compound 1 at 500 °C under air atmosphere yields Pb₃O₂Br₂ nanoparticles.     

Electrochemical behavior of Li intercalation processes into a Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 cathode

Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂ (X=0.17, 0.25, 0.33, 0.5) compounds are prepared by a simple combustion method. The Rietvelt analysis shows that these compounds could be classified as having the α-NaFeO₂ structure. The initial charge-discharge and irreversible capacity increases with the decrease of x in Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂. Indeed, Li[Ni_0.50Mn_0.50]O₂ compound shows relatively low initial discharge capacity of 200 mAh/g and large capacity loss during cycling, with Li[Ni_0.17Li_0.22Mn_0.61]O₂ and Li[Ni_0.25Li_0.17Mn₀.₅₈]O₂ compounds exhibit high initial discharge capacity over 245 mAh/g and stable cycle performance in the voltage range of 4.8 -2.0 V. On the other hand, XANES analysis shows that the oxidation state of Ni ion reversibly changes between Ni²⁺ and about Ni³⁺, while the oxidation state of Mn ion sustains Mn⁴⁺ during charge-discharge process. This result does not agree with the previously reported ‘electrochemistry model’ of Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂, in which Ni ion changes between Ni²⁺ and NI⁴⁺. Based on these results, we modified oxidation-state change of Mn and Ni ion during charge-discharge process.