Room Temperature Stable Organocuprate Copper(III) Complex

The paramagnetic trigonal-planar copper complexes {K­(18C6)}­[Cu^II(OC­(CH₃)­(CF₃)₂)₃] (<b>2</b>) and K­[Cu^II(OC­(C₆H₅)­(CF₃)₂)₃] (<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 CuBr₂ and KOC­(C₆H₅)­(CF₃)₂)₃ also form the diamagnetic complexes {K­(18C6)}­[K₂{Cu^I(OC­(C₆H₅)­(CF₃)₂)₂}₃] (<b>4</b>) and {K­(18C6)}­[Cu^III(OC­(C₆H₄)­(CF₃)₂)₂] (<b>5</b>). These species were characterized by X-ray crystallography, UV–vis spectroscopy, ¹H, ¹³C­{¹H}, and ¹⁹F­{¹H} NMR spectroscopy, and elemental analysis. The unique organocuprate Cu­(III) species with {O₂C₂} coordination was formed by ortho metalation of two phenyl rings, resulting in <i>trans</i>-{O₂C₂} coordination of Cu­(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 {K­(18C6)}­[Cu^II(OC­(CH₃)­(CF₃)₂)₃] (<b>2</b>) and K­[Cu^II(OC­(C₆H₅)­(CF₃)₂)₃] (<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 CuBr₂ and KOC­(C₆H₅)­(CF₃)₂)₃ also form the diamagnetic complexes {K­(18C6)}­[K₂{Cu^I(OC­(C₆H₅)­(CF₃)₂)₂}₃] (<b>4</b>) and {K­(18C6)}­[Cu^III(OC­(C₆H₄)­(CF₃)₂)₂] (<b>5</b>). These species were characterized by X-ray crystallography, UV–vis spectroscopy, ¹H, ¹³C­{¹H}, and ¹⁹F­{¹H} NMR spectroscopy, and elemental analysis. The unique organocuprate Cu­(III) species with {O₂C₂} coordination was formed by ortho metalation of two phenyl rings, resulting in <i>trans</i>-{O₂C₂} coordination of Cu­(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 (TiO₂) 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 TiO₂ nanostructures. We have assayed these peptides for TiO₂-precipitating activity upon exposure to titanium bis­(ammonium lactato)­dihydroxide and have characterized the resulting coprecipitates using scanning electron microscopy. A subset of these assayed peptides efficiently facilitates the production of TiO₂ nanospheres. Here, we investigate the process of TiO₂ nanosphere formation mediated by the S–K peptides KSSKK- and SKSK₃SKS using one-dimensional and two-dimensional solid-state NMR (ssNMR) on peptide samples with uniformly ¹³C-enriched residues. ssNMR is used to assign ¹³C chemical shifts (CSs) site-specifically in each free peptide and TiO₂-embedded peptide, which are used to derive secondary structures in the neat and TiO₂ coprecipitated states. The backbone ¹³C CSs are used to assess secondary structural changes undergone during the coprecipitation process. Side-chain ¹³C CS changes are analyzed with density functional theory calculations and used to determine side-chain conformational changes that occur upon coprecipitation with TiO₂ and to determine surface orientation of lysine side chains in TiO₂–peptide composites

Structural and Electronic Properties of Old and New A₂[M(pin^F)₂] Complexes

Seven new homoleptic complexes of the form A₂[M­(pin^F)₂] have been synthesized with the dodecafluoropinacolate (pin^F)^2– ligand, namely (Me₄N)₂[Fe­(pin^F)₂], <b>1</b>; (Me₄N)₂[Co­(pin^F)₂], <b>2</b>; (ⁿBu₄N)₂[Co­(pin^F)₂], <b>3</b>; {K­(DME)₂}₂[Ni­(pin^F)₂], <b>4</b>; (Me₄N)₂[Ni­(pin^F)₂], <b>5</b>; {K­(DME)₂}₂[Cu­(pin^F)₂], <b>7</b>; and (Me₄N)₂[Cu­(pin^F)₂], <b>8</b>. In addition, the previously reported complexes K₂[Cu­(pin^F)₂], <b>6</b>, and K₂[Zn­(pin^F)₂], <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 K₂[Ni­(pin^F)₂]. Cyclic voltammetry studies reveal reversible redox couples for Ni­(III)/Ni­(II) in <b>5</b> and for Cu­(III)/Cu­(II) in <b>8</b> but quasi-reversible couples for the Fe­(III)/Fe­(II) couple in <b>1</b> and the Co­(III)/Co­(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 CF₃ 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 Ni­(III) and Cu­(III)