4 research outputs found
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 [{M<sup>0</sup>(CO)<sub>5</sub>}<sub>2</sub>(μ-<i>S</i>,<i>S′</i>-EtL)] (M = Cr, Mo, W) with the asymmetrically bridged zwitterionic
sulfur donor bisÂ(<i>N,N</i>-diethylamino)Âcarbeniumdithiocarboxylate
(EtL) was prepared by photoreaction of [M<sup>0</sup>(CO)<sub>6</sub>] with EtL in hexane–CH<sub>2</sub>Cl<sub>2</sub> 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 −CS<sub>2</sub> 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 [CrÂ(CO)<sub>5</sub>L] complexes
(L = monodentate ligand), the <sup>13</sup>C 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><sub>T</sub>(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: [WÂ(CO)<sub>5</sub>(EtL)] and [WÂ(CO)<sub>5</sub>(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 [{M<sup>0</sup>(CO)<sub>5</sub>}<sub>2</sub>(μ-<i>S</i>,<i>S′</i>-EtL)] (M = Cr, Mo, W) with the asymmetrically bridged zwitterionic
sulfur donor bisÂ(<i>N,N</i>-diethylamino)Âcarbeniumdithiocarboxylate
(EtL) was prepared by photoreaction of [M<sup>0</sup>(CO)<sub>6</sub>] with EtL in hexane–CH<sub>2</sub>Cl<sub>2</sub> 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 −CS<sub>2</sub> 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 [CrÂ(CO)<sub>5</sub>L] complexes
(L = monodentate ligand), the <sup>13</sup>C 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><sub>T</sub>(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: [WÂ(CO)<sub>5</sub>(EtL)] and [WÂ(CO)<sub>5</sub>(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<sup>II</sup>(bpy)}<sub>2</sub>(μ-x-tart)]·<i>n</i>H<sub>2</sub>O (bpy: 2,2′-bipyridine; tartH<sub>2</sub><sup>2–</sup>: 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<sup>II</sup>(bpy)}<sub>2</sub>(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