π‑Back-Bonding Interaction Depending on the Bridging Chain Lengths of Chelated N‑Heterocyclic Carbene Platinum Units in Heterometallic Trinuclear Complexes Affecting Their Electrochemical Property

Newly synthesized heterometallic trinuclear M₂Pt complexes (M = Rh, Ir) containing a platinum moiety having a chelated bis-N-heterocyclic carbene (bisNHC) ligand with a variety of alkylene chain lengths of the bridging part showed two reversible reduction waves in cyclic voltammetry. Only the second reduction potentials were affected by the alkyl chain lengths, which afforded different dihedral angles between the imidazolylidene rings and the platinum coordination plane resulting in the variation of π-back-donation from the platinum center to the carbene carbon atoms

Carbon- and Sulfur-Bridged Diiron Carbonyl Complexes Containing N,C,S-Tridentate Ligands Derived from Functionalized Dibenzothiophenes: Mimics of the [FeFe]-Hydrogenase Active Site

Photochemical reactions of [Fe­(CO)₅] with dibenzothiophene (DBT) derivatives bearing a N-donor group produced a series of C,S-bridged diiron carbonyl complexes [{Fe­(μ-L′-κ³<i>N</i>,<i>C</i>,<i>S</i>)­(CO)₂}­Fe­(CO)₃], as previously reported for 4-(2′-pyridyl)­dibenzothiophene (L¹), where L′ represents the N,C,S-tridentate ligands L¹′–L⁵′, formed by C–S bond cleavage of L¹–L⁵, respectively. The DBT derivatives used in this study have Schiff base or oxazoline moieties at the 4-position: L² = PhCH₂NCH-DBT, L³ = 2-MeOC₆H₄CH₂NCH-DBT, L⁴ = (<i>S</i>)-PhC­(Me)­HNCH-DBT, L⁵ = (<i>R</i>)-4-isopropyl-2-oxazolinyl-DBT. The diiron complexes were characterized by NMR, absorption, and circular dichroism spectroscopy, and the dinuclear structures bridged by thiolate S and aryl C atoms were established by X-ray crystallography. The diiron complex [{Fe­(μ-L′-κ³<i>N</i>,<i>C</i>,<i>S</i>)­(CO)₂}­Fe­(CO)₃] consists of two units, Fe­(L′)­(CO)₂ and Fe­(CO)₃: the latter unit is located on a thiolate-containing metallacycle in the former one. The chiral Schiff base ligand precursor L⁴ gave a 55:45 mixture of two diastereomers for [{Fe­(μ-L⁴′-κ³<i>N</i>,<i>C</i>,<i>S</i>)­(CO)₂}­Fe­(CO)₃], while chiral L⁵ with an (<i>R</i>)-4-isopropyl-2-oxazolinyl group afforded [{Fe­(μ-L⁵′-κ³<i>N</i>,<i>C</i>,<i>S</i>)­(CO)₂}­Fe­(CO)₃] in a 9:1 diastereomeric ratio. The diiron carbonyl complexes of the N,C,S-tridentate ligands (L¹′L⁵′) showed two reversible redox couples for [Fe₂(μ-L′)­(CO)₅]^0/– and [Fe₂(μ-L′)­(CO)₅]^−/2–. The two-electron-reduced forms undergo protonation and act as electrocatalysts for proton reduction of acetic acid in acetonitrile

Chelated Bis-N-heterocyclic Carbene Platinum and Palladium Units as Tunable Components of Multinuclear Complexes

Heterometallic trinuclear M₂M′ complexes (M = Rh, Ir; M′ = Pt, Pd) containing a platinum or palladium moiety with chelated bis-N-heterocyclic carbene ligands, [(MCp*)₂­{M′(bisNHC-C<i>n</i>-R)}­(μ₃-S)₂]­(BPh₄)₂ (M = Rh, Ir; M′ = Pt, Pd; bisNHC-C<i>n</i>-R = methylene-, ethylene-, or propylene-bridged bis­(<i>N</i>-alkyl-imidazolylidene)), were synthesized by reacting bis­(hydrosulfido)­platinum­(II) or palladium­(II) complexs with bisNHC-C<i>n</i>-R and hydroxo-bridged dinuclear complexes [(MCp*)₂(μ-OH)₃]­(BPh₄), whose dinuclear structures remained intact during the formation of the trinuclear complexes, which was confirmed by using electrospray mass spectrometry and NMR spectroscopy. The heterometallic trinuclear M₂M′ complexes with a variety of alkylene bridges in bisNHC-C<i>n</i>-R showed two reversible reduction waves in the cyclic voltammogram, and the second reduction potentials were affected by the alkylene chain lengths, which caused different dihedral angles between the imidazolylidene rings and the coordination plane of the platinum or palladium center. The M₂M′ complexes, except for those containing the platinum unit with the ethylene-bridged bisNHC ligands, showed dynamic behavior in solution due to the flapping wing motion of the NHC ligand moieties. Although activation parameters obtained from line-shape analyses on variable-temperature NMR spectra of the complexes suggested that the flapping wing motion occurred without bond cleavage, large negative Δ<i><i>S</i></i>^‡ values were obtained for the complexes with the palladium unit with the ethylene-bridged ligand, suggesting that the Pd–C_carbene bond cleavage, accompanied by coordination of solvent molecules, occurred

π‑Back-Bonding Interaction Depending on the Bridging Chain Lengths of Chelated N‑Heterocyclic Carbene Platinum Units in Heterometallic Trinuclear Complexes Affecting Their Electrochemical Property

Newly synthesized heterometallic trinuclear M₂Pt complexes (M = Rh, Ir) containing a platinum moiety having a chelated bis-N-heterocyclic carbene (bisNHC) ligand with a variety of alkylene chain lengths of the bridging part showed two reversible reduction waves in cyclic voltammetry. Only the second reduction potentials were affected by the alkyl chain lengths, which afforded different dihedral angles between the imidazolylidene rings and the platinum coordination plane resulting in the variation of π-back-donation from the platinum center to the carbene carbon atoms

Der instationaere Kanalabfluss in der Schmutzfrachtmodellierung

SIGLETIB Hannover: RN 8701(42) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Stereocontrolled Total Synthesis of Fucoxanthin and Its Polyene Chain-Modified Derivative

Fucoxanthin exhibits high energy transfer efficiencies to Chlorophyll a (Chl a) in photosynthesis in the sea. In order to reveal how each characteristic functional group, such as the length of the polyene chain, allene, and conjugated carbonyl groups, of this marine natural product are responsible for its remarkably efficient ability, the total synthesis of fucoxanthin by controlling the stereochemistry was achieved. The method established for fucoxanthin synthesis was successfully applied to the synthesis of the C42 longer chain analogue

Stereocontrolled Total Synthesis of Fucoxanthin and Its Polyene Chain-Modified Derivative

Fucoxanthin exhibits high energy transfer efficiencies to Chlorophyll a (Chl a) in photosynthesis in the sea. In order to reveal how each characteristic functional group, such as the length of the polyene chain, allene, and conjugated carbonyl groups, of this marine natural product are responsible for its remarkably efficient ability, the total synthesis of fucoxanthin by controlling the stereochemistry was achieved. The method established for fucoxanthin synthesis was successfully applied to the synthesis of the C42 longer chain analogue

Preparation of Yellowish-Red Al-Substituted α‑Fe₂O₃ Powders and Their Thermostability in Color

Inspired by the traditional Japanese pigment Fukiya bengala, nanocomposite materials were synthesized using a polymer complex method, comprising Al-substituted α-Fe₂O₃ (hematite) particles with diameters ranging from 40 to 100 nm and ultrafine Fe-substituted α-Al₂O₃ (corundum) particles smaller than 10 nm in diameter. The obtained powders exhibited a vivid yellowish-red color and high thermostability, making them attractive as potential overglaze enamels on porcelain. Quantitative color measurements revealed that, when heated to 700, 800, and 900 °C, samples displayed high lightness (<i>L</i>*) and color-opponent dimensions (<i>a</i>* and <i>b</i>*) at 10 mol % Al. For the same particle size samples, <i>L</i>*, <i>a</i>*, and <i>b</i>* values increased with the Al molar ratio, revealing that Al substitution in the hematite structure intrinsically enhances lightness and chroma in hematite color. These samples mostly retained their color upon reheating at 900 °C, indicating their high thermostability. This thermostability should originate from the Al substitution-induced enhancement in lightness and chroma in hematite color, which should counter color fading caused by particle growth. These composite materials are expected to find application in the porcelain industry, cosmetics, and nanotechnology

Elucidation and Control of an Intramolecular Charge Transfer Property of Fucoxanthin by a Modification of Its Polyene Chain Length

Fucoxanthin is an essential pigment for the highly efficient light-harvesting function of marine algal photosynthesis. It exhibits excited state properties attributed to intramolecular charge transfer (ICT) in polar environments due to the presence of the carbonyl group in its polyene backbone. This report describes the excited state properties of fucoxanthin homologues with four to eight conjugated double bonds in various solvents using the femtosecond pump–probe technique. The results clarified that fucoxanthin homologues with longer polyene chains did not possess pronounced ICT spectroscopic signatures, while the shorter fucoxanthin homologues had a strong ICT character, even in a nonpolar solvent. On the basis of the observations, we quantitatively correlated the ICT character in the excited state to the conjugated polyene chain lengths of fucoxanthin molecules

Lithium Storage Properties of a Bioinspired 2‑Line Ferrihydrite: A Silicon-Doped, Nanometric, and Amorphous Iron Oxyhydroxide

Inspired by a nanometric iron-based oxide material of bacterial origin, silicon (Si)-doped iron oxyhydroxide nanoparticles or 2-line ferrihydrites (2Fhs) were prepared and their lithium (Li) storage properties were investigated. The structures of the Si-doped 2Fhs strongly depended on the Si molar ratio [<i>x</i> = Si/(Fe + Si)] whose long-range atomic ordering gradually vanished as the Si molar ratio increased, with a structural change from nanocrystalline to amorphous at <i>x</i> = 0.30. The most striking properties were observed for the sample with <i>x</i> = 0.30. Over the voltage range of 1.5–4.0 V at a current rate of 500 mA/g, this material exhibited a relatively high reversible capacity of ∼100 mAh/g, which was four times greater than that of the Si-free 2Fh and indicated a good rate capability and cyclability. The large capacity and good rate and cycle performances are presumably because of the amorphous structure and the strong and stabilizing covalent Si–O bonds, respectively. The minor amount of Si⁴⁺ in the structure of the iron oxyhydroxides is considered to improve the electrochemical properties. Use of more appropriate doping elements and fabrication of more appropriate nanostructures could drastically improve the Li storage properties of the developed bioinspired material