Impedance and modulus spectroscopic studies of lead free Na12 Dy12 TiO3 Ceramic

A lead-free perovskite ceramic, Na12Dy12TiO3 (NDT), was synthesized via the conventional solid state reaction method. The sample’s structural, microstructural, and electrical characterizations were performed over the varying range of frequency and temperature. The detailed electrical behavior of the samples has been analyzed and explored by applying impedance spectroscopy. The structural study confirmed the orthorhombic structure of NDT material, with the presence of a very small contribution of the impure pyrochlore phase. The dielectric permittivity of the sample as a function of temperature shows the ferroelectric to paraelectric phase transition temperature to be ∼94 °C, and the shift of phase transition temperature is attributed to its structure. The frequency and temperature-dependent electrical features are studied within the framework of impedance, modulus, and conductivity spectra. The Nyquist plots detect the contribution of grain/grain boundaries to the inclusive polarizations. The presence of two depressed semicircular arcs in the Nyquist Plots (both grain/grain boundaries contribute to electrical properties) was approached for higher temperatures (≥350 °C), suggesting the relaxation phenomena to be temperature dependent with a distribution of relaxation times. Also, the modulus spectra analysis confirms the temperature-dependent multiple relaxation phenomena to be of the Non-Debye type and is present in the sample at ≥350 °C. The conductivity spectra confirm the presence of dc conduction at ≥350 °C and a temperature-dependent polaron hoping conduction behavior with the validity of Johnscher’s universal law

Synthesis and chemistry of the open-cage cobaltaheteroborane cluster [\(η5-C5Me5)Co\2B2H2Se2]: a combined experimental and theoretical study

International audienceReaction of [(η5-C5Me5)CoCl]2 with a two-fold excess of [LiBH4·thf] followed by heating with an excess of Se powder produces the dicobaltaselenaborane species [\(η5-C5Me5)Co\2B2H2Se2], 1, in good yield. The geometry of 1 resembles a nido pentagonal [Co2B2Se2] bipyramid with a missing equatorial vertex. It can alternatively be seen as an open cage triple-decker cluster. Isolation of 1 permits its reaction with [Fe2(CO)9] to give heterometallic diselenametallaborane [\(η5-C5Me5)Co\Fe(CO)3B2H2Se2], 2. The geometry of 2 is similar to that of 1 with one of the [(η5-C5Me5)Co] groups replaced by the isolobal, two-electron fragment [Fe(CO)3]. Both new compounds have been characterized by mass spectrometry, and by 1H, 11B and 13C NMR spectroscopy. The structural architectures have been unequivocally established by crystallographic analysis. In addition, density functional theory calculations were performed to investigate the bonding and electronic properties. The large HOMO–LUMO gaps computed for both clusters are consistent with their thermodynamic stability. Natural bond order calculations predict the absence of metal–metal bonding interactio

Extended sandwich molecules displaying direct metal-metal bonds

Treatment of [Cp*IrCl₂]₂ (Cp* = pentamethylcyclopentadienyl) with Li[BH₃(SePh)] at room temperature led to the isolation of a dimetala analogue of hexaborane(10), nido-[(Cp*Ir)(µ-SePh)₂Ir{(Cp*Ir)SePh}B₄H₈] (1). Solid-state X-ray structure analysis of 1 showed an extended sandwich molecule with two iridium atoms between Cp* and a [B₄Ir] ring. Further, in an effort to synthesize the Rh analogue of 1 under similar reaction conditions, we isolated arachno-[{(Cp*Rh)(µ-SePh)₃}Rh(µ-SePh)B₃H₆] (2), a rhodium analogue of tetraboarane(10) in which the {RhB₃} unit shows geometric equivalence with a metal π-allyl {MC₃} species. Ir complex 1, having an Ir–Ir bond, can be considered similar to the dizinc sandwich complex [Cp*Zn-ZnCp*] in terms of the valence electron count at the metal centers

Triazolyl alkoxy fischer carbene complexes in conjugation with ferrocene/pyrene as sensory units: multifunctional chemosensors for lead(II), copper(II), and zinc(II) ions

The regioselective 1,3-dipolar cycloaddition reaction of alkoxy alkynyl Fischer carbene complex 1 with azidomethyl ferrocene 2 and with azidomethyl pyrene 4 under solvent-free conditions yielded the triazolyl Fischer carbene complexes 3 (C27H21O6N3FeW) and 5(C33H21O6N3W), respectively. The cation complexation properties of these receptors have been systematically studied using electrochemical and spectroscopic techniques. The exceptional structural feature existing in these receptors is the presence of a Fischer carbene moiety, connected to the ferrocene or pyrene moiety through a 1,2,3-triazole ring. Receptor 3 contains a redox-active ferrocene moiety and is highly selective toward Pb2+ ion, whereas receptor 5, having a fluorescent pyrene unit, selectively recognizes Zn2+ and Cu2+ ions. The binding ability of receptor 3 can be inferred either from the redox shift (the anodic shift ΔE1/2 = 55 mV) or the highly visual output response for Pb2+ ion. Receptor 5 displays considerable chelation-enhanced fluorescence (CHEF) upon binding with Zn2+ and Cu2+ ions in an aqueous environment. Further, the proposed binding modes of these receptors and their metal cation complexation properties have been supported by 1H NMR titration and MALDI-MS and a DFT study

Hypoelectronic metallaboranes: Synthesis, structural characterization and electronic structures of metal-rich cobaltaboranes

Reaction of [Cp∗CoCl]2 (Cp∗ = η5-C5Me5) with [LiBH4·THF] in toluene at −70 °C, followed by thermolysis with 2-mercaptobenzothiazole (C7H5NS2) in boiling toluene led to the isolation of a range of cobaltaborane clusters, [(Cp∗Co)2B7H6OMe], 1; [(Cp∗Co)3B8H7R], 2a, b (2a: R = H; 2b: R = Me); [(Cp∗Co) 3B8H8S], 3 and [(Cp∗Co)2B4H4RR′], 4a–d (4a: R, R′ = H; 4b: R = Me, R′ = H; 4c: R = H, R′ = Me and 4d: R, R′ = Me). In parallel to the formation of compounds 1–4, the reaction also yielded known [(Cp∗Co)3B4H4] in good yield. Compound 1 may be considered as 9-vertex hypoelectronic cluster with C1 symmetry, where cobalt atoms occupy the degree 5 vertices. All the dicobaltaboranes 4a–d contains two μ3-H protons and found to be very reactive. As a result, one of them (4a) when reacted with Fe2(CO)9 and sulfur powder yielded, almost immediately, [(Cp∗Co)2B4H5SFe3(CO)9], 5 and [(Cp∗Co)2B3H3(μ-CO)Fe(CO)3], 6. All the new compounds have been characterized in solution by mass, 1H, 11B, 13C NMR spectroscopy and elemental analysis. The structural types were unequivocally established by X-ray crystallographic analysis of compounds 1–6. Density functional theory (DFT) calculations on the model compounds 1′ and 2′ (1′, and 2′ are the Cp analog of 1, and 2a respectively, Cp = C5H5) yield geometries in agreement with the structure determinations. The existence of large HOMO–LUMO gap of these molecules rationalizes the isocloso description for 2a. Bonding patterns in the structure have been analyzed on the grounds of DFT calculations

New heteronuclear bridged borylene complexes that were derived from [{Cp*CoCl}₂] and mono-metal—carbonyl fragments

The synthesis, structural characterization, and reactivity of new bridged borylene complexes are reported. The reaction of [{Cp*CoCl}₂] with LiBH₄⋅THF at −70 °C, followed by treatment with [M(CO)₃(MeCN)₃] (M=W, Mo, and Cr) under mild conditions, yielded heteronuclear triply bridged borylene complexes, [(μ₃-BH)(Cp*Co)₂ (μ-CO)M(CO)₅] (1–3; 1: M=W, 2: M=Mo, 3: M=Cr). During the syntheses of complexes 1–3, capped-octahedral cluster [(Cp*Co)₂ (μ-H)(BH)₄{Co(CO)₂}] (4) was also isolated in good yield. Complexes 1–3 are isoelectronic and isostructural to [(μ₃-BH)(Cp*RuCO)₂ (μ-CO){Fe(CO)₃}] (5) and [(μ₃-BH)(Cp*RuCO)₂(μ-H)(μ-CO){Mn(CO)₃}] (6), with a trigonal-pyramidal geometry in which the μ₃-BH ligand occupies the apical vertex. To test the reactivity of these borylene complexes towards bis-phosphine ligands, the room-temperature photolysis of complexes 1–3, 5, 6, and [{(μ₃-BH)(Cp*Ru)Fe(CO)₃}₂(μ-CO)] (7) was carried out. Most of these complexes led to decomposition, although photolysis of complex 7 with [Ph₂P(CH₂)nPPh₂] (n=1–3) yielded complexes 9–11, [3,4-(Ph₂P(CH₂)nPPh₂)-closo-1,2,3,4-Ru₂Fe₂ (BH)₂] (9: n=1, 10: n=2, 11: n=3). Quantum-chemical calculations by using DFT methods were carried out on compounds 1–3 and 9–11 and showed reasonable agreement with the experimentally obtained structural parameters, that is, large HOMO–LUMO gaps, in accordance with the high stabilities of these complexes, and NMR chemical shifts that accurately reflected the experimentally observed resonances. All of the new compounds were characterized in solution by using mass spectrometry, IR spectroscopy, and ¹H, ¹³C, and ¹¹B NMR spectroscopy and their structural types were unequivocally established by crystallographic analysis of complexes 1, 2, 4, 9, and 10

Triazolyl Alkoxy Fischer Carbene Complexes in Conjugation with Ferrocene/Pyrene as Sensory Units: Multifunctional Chemosensors for Lead(II), Copper(II), and Zinc(II) Ions

The regioselective 1,3-dipolar cycloaddition reaction of alkoxy alkynyl Fischer carbene complex <b>1</b> with azidomethyl ferrocene <b>2</b> and with azidomethyl pyrene <b>4</b> under solvent-free conditions yielded the triazolyl Fischer carbene complexes <b>3</b> (C₂₇H₂₁O₆N₃FeW) and <b>5</b> (C₃₃H₂₁O₆N₃W), respectively. The cation complexation properties of these receptors have been systematically studied using electrochemical and spectroscopic techniques. The exceptional structural feature existing in these receptors is the presence of a Fischer carbene moiety, connected to the ferrocene or pyrene moiety through a 1,2,3-triazole ring. Receptor <b>3</b> contains a redox-active ferrocene moiety and is highly selective toward Pb²⁺ ion, whereas receptor <b>5</b>, having a fluorescent pyrene unit, selectively recognizes Zn²⁺ and Cu²⁺ ions. The binding ability of receptor <b>3</b> can be inferred either from the redox shift (the anodic shift Δ<i>E</i>_1/2 = 55 mV) or the highly visual output response for Pb²⁺ ion. Receptor <b>5</b> displays considerable chelation-enhanced fluorescence (CHEF) upon binding with Zn²⁺ and Cu²⁺ ions in an aqueous environment. Further, the proposed binding modes of these receptors and their metal cation complexation properties have been supported by ¹H NMR titration and MALDI-MS and a DFT study