4 research outputs found
Room Temperature Stable Organocuprate Copper(III) Complex
The paramagnetic trigonal-planar
copper complexes {KÂ(18C6)}Â[Cu<sup>II</sup>(OCÂ(CH<sub>3</sub>)Â(CF<sub>3</sub>)<sub>2</sub>)<sub>3</sub>] (<b>2</b>) and KÂ[Cu<sup>II</sup>(OCÂ(C<sub>6</sub>H<sub>5</sub>)Â(CF<sub>3</sub>)<sub>2</sub>)<sub>3</sub>] (<b>3</b>) have
been prepared and characterized, including X-ray crystallography,
in 61% and 3% yields, respectively. The latter complex does not form
preferentially, because CuBr<sub>2</sub> and KOCÂ(C<sub>6</sub>H<sub>5</sub>)Â(CF<sub>3</sub>)<sub>2</sub>)<sub>3</sub> also form the diamagnetic
complexes {KÂ(18C6)}Â[K<sub>2</sub>{Cu<sup>I</sup>(OCÂ(C<sub>6</sub>H<sub>5</sub>)Â(CF<sub>3</sub>)<sub>2</sub>)<sub>2</sub>}<sub>3</sub>] (<b>4</b>) and {KÂ(18C6)}Â[Cu<sup>III</sup>(OCÂ(C<sub>6</sub>H<sub>4</sub>)Â(CF<sub>3</sub>)<sub>2</sub>)<sub>2</sub>] (<b>5</b>). These
species were characterized by X-ray crystallography, UV–vis
spectroscopy, <sup>1</sup>H, <sup>13</sup>CÂ{<sup>1</sup>H}, and <sup>19</sup>FÂ{<sup>1</sup>H} NMR spectroscopy, and elemental analysis.
The unique organocuprate CuÂ(III) species with {O<sub>2</sub>C<sub>2</sub>} coordination was formed by ortho metalation of two phenyl
rings, resulting in <i>trans</i>-{O<sub>2</sub>C<sub>2</sub>} coordination of CuÂ(III), and is stable at room temperature in the
solid state and in dark solutions of THF
Room Temperature Stable Organocuprate Copper(III) Complex
The paramagnetic trigonal-planar
copper complexes {KÂ(18C6)}Â[Cu<sup>II</sup>(OCÂ(CH<sub>3</sub>)Â(CF<sub>3</sub>)<sub>2</sub>)<sub>3</sub>] (<b>2</b>) and KÂ[Cu<sup>II</sup>(OCÂ(C<sub>6</sub>H<sub>5</sub>)Â(CF<sub>3</sub>)<sub>2</sub>)<sub>3</sub>] (<b>3</b>) have
been prepared and characterized, including X-ray crystallography,
in 61% and 3% yields, respectively. The latter complex does not form
preferentially, because CuBr<sub>2</sub> and KOCÂ(C<sub>6</sub>H<sub>5</sub>)Â(CF<sub>3</sub>)<sub>2</sub>)<sub>3</sub> also form the diamagnetic
complexes {KÂ(18C6)}Â[K<sub>2</sub>{Cu<sup>I</sup>(OCÂ(C<sub>6</sub>H<sub>5</sub>)Â(CF<sub>3</sub>)<sub>2</sub>)<sub>2</sub>}<sub>3</sub>] (<b>4</b>) and {KÂ(18C6)}Â[Cu<sup>III</sup>(OCÂ(C<sub>6</sub>H<sub>4</sub>)Â(CF<sub>3</sub>)<sub>2</sub>)<sub>2</sub>] (<b>5</b>). These
species were characterized by X-ray crystallography, UV–vis
spectroscopy, <sup>1</sup>H, <sup>13</sup>CÂ{<sup>1</sup>H}, and <sup>19</sup>FÂ{<sup>1</sup>H} NMR spectroscopy, and elemental analysis.
The unique organocuprate CuÂ(III) species with {O<sub>2</sub>C<sub>2</sub>} coordination was formed by ortho metalation of two phenyl
rings, resulting in <i>trans</i>-{O<sub>2</sub>C<sub>2</sub>} coordination of CuÂ(III), and is stable at room temperature in the
solid state and in dark solutions of THF
Serine–Lysine Peptides as Mediators for the Production of Titanium Dioxide: Investigating the Effects of Primary and Secondary Structures Using Solid-State NMR Spectroscopy and DFT Calculations
A biomimetic
approach to the formation of titania (TiO<sub>2</sub>) nanostructures
is desirable because of the mild conditions required
in this form of production. We have identified a series of serine–lysine
peptides as candidates for the biomimetic production of TiO<sub>2</sub> nanostructures. We have assayed these peptides for TiO<sub>2</sub>-precipitating activity upon exposure to titanium bisÂ(ammonium lactato)Âdihydroxide
and have characterized the resulting coprecipitates using scanning
electron microscopy. A subset of these assayed peptides efficiently
facilitates the production of TiO<sub>2</sub> nanospheres. Here, we
investigate the process of TiO<sub>2</sub> nanosphere formation mediated
by the S–K peptides KSSKK- and SKSK<sub>3</sub>SKS using one-dimensional
and two-dimensional solid-state NMR (ssNMR) on peptide samples with
uniformly <sup>13</sup>C-enriched residues. ssNMR is used to assign <sup>13</sup>C chemical shifts (CSs) site-specifically in each free peptide
and TiO<sub>2</sub>-embedded peptide, which are used to derive secondary
structures in the neat and TiO<sub>2</sub> coprecipitated states.
The backbone <sup>13</sup>C CSs are used to assess secondary structural
changes undergone during the coprecipitation process. Side-chain <sup>13</sup>C CS changes are analyzed with density functional theory
calculations and used to determine side-chain conformational changes
that occur upon coprecipitation with TiO<sub>2</sub> and to determine
surface orientation of lysine side chains in TiO<sub>2</sub>–peptide
composites
Structural and Electronic Properties of Old and New A<sub>2</sub>[M(pin<sup>F</sup>)<sub>2</sub>] Complexes
Seven
new homoleptic complexes of the form A<sub>2</sub>[MÂ(pin<sup>F</sup>)<sub>2</sub>] have been synthesized with the dodecafluoropinacolate
(pin<sup>F</sup>)<sup>2–</sup> ligand, namely (Me<sub>4</sub>N)<sub>2</sub>[FeÂ(pin<sup>F</sup>)<sub>2</sub>], <b>1</b>;
(Me<sub>4</sub>N)<sub>2</sub>[CoÂ(pin<sup>F</sup>)<sub>2</sub>], <b>2</b>; (<sup>n</sup>Bu<sub>4</sub>N)<sub>2</sub>[CoÂ(pin<sup>F</sup>)<sub>2</sub>], <b>3</b>; {KÂ(DME)<sub>2</sub>}<sub>2</sub>[NiÂ(pin<sup>F</sup>)<sub>2</sub>], <b>4</b>; (Me<sub>4</sub>N)<sub>2</sub>[NiÂ(pin<sup>F</sup>)<sub>2</sub>], <b>5</b>; {KÂ(DME)<sub>2</sub>}<sub>2</sub>[CuÂ(pin<sup>F</sup>)<sub>2</sub>], <b>7</b>; and
(Me<sub>4</sub>N)<sub>2</sub>[CuÂ(pin<sup>F</sup>)<sub>2</sub>], <b>8</b>. In addition, the previously reported complexes K<sub>2</sub>[CuÂ(pin<sup>F</sup>)<sub>2</sub>], <b>6</b>, and K<sub>2</sub>[ZnÂ(pin<sup>F</sup>)<sub>2</sub>], <b>9</b>, are characterized
in much greater detail in this work. These nine compounds have been
characterized by UV–vis spectroscopy, cyclic voltammetry, elemental
analysis, and for paramagnetic compounds, Evans method magnetic susceptibility.
Single-crystal X-ray crystallographic data were obtained for all complexes
except <b>5</b>. The crystallographic data show a square-planar
geometry about the metal center in all Fe (<b>1</b>), Ni (<b>4</b>), and Cu (<b>6</b>, <b>7</b>, <b>8</b>) complexes independent of countercation. The Co species exhibit
square-planar (<b>3</b>) or distorted square-planar geometries
(<b>2</b>), and the Zn species (<b>9</b>) is tetrahedral.
No evidence for solvent binding to any Cu or Zn complex was observed.
Solvent binding in Ni can be tuned by the countercation, whereas in
Co only strongly donating Lewis solvents bind independent of the countercation.
Indirect evidence (diffuse reflectance spectra and conductivity data)
suggest that <b>5</b> is not a square-planar compound, unlike <b>4</b> or the literature K<sub>2</sub>[NiÂ(pin<sup>F</sup>)<sub>2</sub>]. Cyclic voltammetry studies reveal reversible redox couples
for NiÂ(III)/NiÂ(II) in <b>5</b> and for CuÂ(III)/CuÂ(II) in <b>8</b> but quasi-reversible couples for the FeÂ(III)/FeÂ(II) couple
in <b>1</b> and the CoÂ(III)/CoÂ(II) couple in <b>2</b>.
Perfluorination of the pinacolate ligand results in an increase in
the central C–C bond length due to steric clashes between CF<sub>3</sub> groups, relative to perhydropinacolate complexes. Both types
of pinacolate complexes exhibit O–C–C–O torsion
angles around 40°. Together, these data demonstrate that perfluorination
of the pinacolate ligand makes possible highly unusual and coordinatively
unsaturated high-spin metal centers with ready thermodynamic access
to rare oxidation states such as NiÂ(III) and CuÂ(III)