Syntheses and Properties of Dinuclear Group 6 Metal Complexes with the Zwitterionic Sulfur Donor Ligand Bis(<i>N</i>,<i>N</i>‑diethylamino)carbeniumdithiocarboxylate

A class of dinuclear group 6 metal complexes [{M⁰(CO)₅}₂(μ-<i>S</i>,<i>S′</i>-EtL)] (M = Cr, Mo, W) with the asymmetrically bridged zwitterionic sulfur donor bis­(<i>N,N</i>-diethylamino)­carbeniumdithiocarboxylate (EtL) was prepared by photoreaction of [M⁰(CO)₆] with EtL in hexane–CH₂Cl₂ for Cr and Mo or THF for W. The same structure in a <i>syn</i>–<i>anti</i> coordination mode was revealed by X-ray analyses for chromium(0) <i>and</i> tungsten(0) complexes, <b>1</b> and <b>3</b>, respectively, and speculated from various analytical data for the molybdenum(0) complex <b>2</b>. The pertinent criteria for the coordination mode are found to be the wavenumber of the asymmetric stretching vibration of the −CS₂ moiety in the solid state and the ligand-based reduction potential in solution. Complexes <b>1</b> and <b>3</b> showed quasi-reversible reduction waves, which are assigned to a two-step, one-electron reduction process derived from the bridging EtL. In a series of [Cr­(CO)₅L] complexes (L = monodentate ligand), the ¹³C NMR chemical shifts of the <i>trans</i>-to-L carbonyl group showed the order of increasing σ-donor/π-acceptor ratio of the ligands. The sulfur donor ligands, including EtL and thione, are positioned in the middle of this range. All complexes exhibited negative solvatochromism: the wavelength of the absorption maximum shifted to the blue side in the range 500–600 nm with an increase in the Reichardt solvent polarity parameters <i>E</i>_T(30), except for protic solvents. Quantum chemical calculations by time-dependent density functional theory–polarized continuum model were employed for understanding the excited states and solvatochromic properties of complex <b>3</b>. The calculated vertical excitation energies in solution are consistent with the experimental data, suggesting that the transition is a metal-to-ligand charge-transfer transition. In addition, UV–vis, NMR, and cyclic voltammetry data showed that complex <b>3</b> dissociates into two mononuclear species in polar solvents: [W­(CO)₅(EtL)] and [W­(CO)₅(solvent)]

Syntheses and Properties of Dinuclear Group 6 Metal Complexes with the Zwitterionic Sulfur Donor Ligand Bis(<i>N</i>,<i>N</i>‑diethylamino)carbeniumdithiocarboxylate

A class of dinuclear group 6 metal complexes [{M⁰(CO)₅}₂(μ-<i>S</i>,<i>S′</i>-EtL)] (M = Cr, Mo, W) with the asymmetrically bridged zwitterionic sulfur donor bis­(<i>N,N</i>-diethylamino)­carbeniumdithiocarboxylate (EtL) was prepared by photoreaction of [M⁰(CO)₆] with EtL in hexane–CH₂Cl₂ for Cr and Mo or THF for W. The same structure in a <i>syn</i>–<i>anti</i> coordination mode was revealed by X-ray analyses for chromium(0) <i>and</i> tungsten(0) complexes, <b>1</b> and <b>3</b>, respectively, and speculated from various analytical data for the molybdenum(0) complex <b>2</b>. The pertinent criteria for the coordination mode are found to be the wavenumber of the asymmetric stretching vibration of the −CS₂ moiety in the solid state and the ligand-based reduction potential in solution. Complexes <b>1</b> and <b>3</b> showed quasi-reversible reduction waves, which are assigned to a two-step, one-electron reduction process derived from the bridging EtL. In a series of [Cr­(CO)₅L] complexes (L = monodentate ligand), the ¹³C NMR chemical shifts of the <i>trans</i>-to-L carbonyl group showed the order of increasing σ-donor/π-acceptor ratio of the ligands. The sulfur donor ligands, including EtL and thione, are positioned in the middle of this range. All complexes exhibited negative solvatochromism: the wavelength of the absorption maximum shifted to the blue side in the range 500–600 nm with an increase in the Reichardt solvent polarity parameters <i>E</i>_T(30), except for protic solvents. Quantum chemical calculations by time-dependent density functional theory–polarized continuum model were employed for understanding the excited states and solvatochromic properties of complex <b>3</b>. The calculated vertical excitation energies in solution are consistent with the experimental data, suggesting that the transition is a metal-to-ligand charge-transfer transition. In addition, UV–vis, NMR, and cyclic voltammetry data showed that complex <b>3</b> dissociates into two mononuclear species in polar solvents: [W­(CO)₅(EtL)] and [W­(CO)₅(solvent)]

Recognition of d‑Glucose in Water with Excellent Sensitivity, Selectivity, and Chiral Selectivity Using γ‑Cyclodextrin and Fluorescent Boronic Acid Inclusion Complexes Having a <i>Pseudo</i>-diboronic Acid Moiety

Fluorescence recognition of d-glucose in water with excellent sensitivity, selectivity, and chiral selectivity is desired because d-glucose is an essential component in biological and pathological processes. We report an innovative approach that exploits the 1:2 stoichiometric inclusion complexes of γ-cyclodextrin (γ-CyD) with two molecules of fluorescent monoboronic acid-based receptors, which form a pseudo-diboronic acid moiety as the recognition site for d-glucose in water. Two monoboronic acids (1F and 2N) were easily synthesized without heating or column purification. The 1:2 stoichiometric inclusion complexes (1F/γ-CyD and 2N/γ-CyD) were prepared in a mixture of dimethyl sulfoxide/water (2/98 in v/v) by mixing γ-CyD and the corresponding monoboronic acids. Both 1F/γ-CyD and 2N/γ-CyD exhibited strong turn-on response to d-glucose with excellent selectivity over nine other saccharides in the water-rich solvent at pH 7.4 owing to the ditopic recognition of d-glucose by the pseudo-diboronic acid moieties. The limits of detection of 1F/γ-CyD and 2N/γ-CyD for d-glucose were 1.1 and 1.8 μM, respectively, indicating the remarkable sensitivity for the detection of d-glucose at μM levels. 1F/γ-CyD and 2N/γ-CyD also demonstrated chiral-selective recognition of d-glucose, which is apparent from the 2.0- and 6.3-fold enhancement of fluorescence by the addition of d-glucose relative to l-glucose addition, owing to the chiral pseudo-diboronic acid moieties produced by the chiral γ-CyD cavity. To the best of our knowledge, 2N/γ-CyD has the highest d/l selectivity among hitherto reported fluorescent diboronic acid-based receptors

Lattice Water-Induced Helical Stacking of Tartrate-Bridged Dinuclear Palladium(II) Complexes: The Role of Hydrogen Bonding

Hydrous crystals of [{Pd^II(bpy)}₂(μ-x-tart)]·<i>n</i>H₂O (bpy: 2,2′-bipyridine; tartH₂^2–: tartrate; <b>1a</b>: x = l, <i>n</i> = 6; <b>2a</b>: x = d, <i>n</i> = 6; <b>3a</b>: x = dl, <i>n</i> = 4; <b>4a</b>: x = <i>meso</i>, <i>n</i> = 4) and anhydrous crystals of [{Pd^II(bpy)}₂(μ-l-tart)] (<b>1b</b>) were isolated from aqueous and MeOH solutions, respectively. X-ray crystallography revealed the stacked structures of clamshell-like dinuclear units in <b>1a</b>–<b>3a</b> and <b>1b</b>, where intramolecular metal–metal and π–π stacking interactions were observed. Right- and left-handed helically stacked columns were formed in the <b>1a</b> and <b>2a</b> crystals, respectively. The significant role of hydrogen bonding among lattice water molecules and tartrate is suggested because <b>1b</b> exhibited a zigzag arrangement only through intermolecular metal–metal interactions. In <b>3a</b>, l- and d-tart units stacked alternately in a zigzag arrangement with intermolecular π–π interactions. In <b>4a</b>, dimeric aggregates of the twisted dinuclear units further formed a 2D sheet architecture