Hosting Ability of Mesoporous Micelle-Templated Silicas toward Organic Molecules of Different Polarity

Spin probe water solutions were adsorbed onto differently treated micelle-templated silicas (MTS) of different pore sizes to analyze the hosting ability of the MTS surface toward different organic molecules. The MTS synthesis was performed at 388 K by self-assembly of inorganic silica and micelles of cetyltrimethylammonium bromide (CTAB) to which different amounts of 1,3,5 trimethylbenzene (TMB) were added at different TMB/CTAB ratios to modify the pore size:  40, 65, and 80 Å pore diameter were obtained for TMB/CTAB ratio = 0, 2.7, and 13, respectively. As-synthesized MTS, calcined MTS, and octyldimethyl(C8) grafted MTS were used. These MTS were characterized by means of nitrogen sorption isotherms and TEM as homoporous silica with regular and reproducible structure. Different spin probes (nitroxides) were taken as models for different types of organic molecules, namely, neutral and charged molecules and surfactants. The computer aided analysis of the electron paramagnetic resonance (EPR) spectra of these probes provided information on the hosting ability of the differently treated solid surface in respect of the different structure and hydrophilicity of the probes. The spectral analysis allowed the depiction of the probable distribution and location of the different probes at the differently treated silica surfaces. For the as-synthesized MTS, void space became available for the probe adsorption in vicinity of the surface when TMB was used in the synthesis and then evaporated. For the calcined MTSs, the hydrophobic sites at the solid surface, namely, siloxanes, increased by increasing the TMB content in the synthesis mixture. The binding of the EPR probe with the surface of these MTS is favored when both hydrophilic and hydrophobic interactions occur, as found with surfactant probes bearing both a hydrophilic and a hydrophobic moiety. For the C8-grafted MTSs, the results provided a proof of the quality of grafting:  the surface is largely hydrophobic and favors self-aggregation of the surfactant probes, led by chain−chain interactions

Electroabsorption of Dimers Containing MM (M = Mo, W) Quadruply Bonded Units: Insights into the Electronic Structure of Neutral Coupled Redox Centers and Their Relationship with Mixed Valence Ions

The electroabsorption spectra for the metal-to-ligand charge transfer transition in complexes containing oxalate and terephthalate bridged MM quadruply bonded units, [(MM)(pivalate)3]2-μ2-BR, where M = Mo or W and BR = oxalate or terephthalate, are reported. The measured magnitude of the change in dipole moment (|Δμ⃗|) and the change in polarizability (Δα) that accompany this electronic transition are found to be small and not to follow the behavior expected on the basis of the two-state model. In addition, the trend in the value of Δα for the neutral states is mirrored by the trend in the degree of electronic coupling (HAB) for the strongly coupled mixed valence states formed by the same complexes in their singly oxidized states

Electron Exchange Involving a Sulfur-Stabilized Ruthenium Radical Cation

Half-sandwich Ru(II) amine, thiol, and thiolate complexes were prepared and characterized by X-ray crystallography. The thiol and amine complexes react slowly with acetonitrile to give free thiol or amine and the acetonitrile complex. With the thiol complex, the reaction is dissociative. The thiolate complex has been oxidized to its Ru(III) radical cation and the solution EPR spectrum of that radical cation recorded. Cobaltocene reduces the thiol complex to the thiolate complex. The 1H and 31P NMR signals of the thiolate complex in acetonitrile become very broad whenever the thiolate and thiol complexes are present simultaneously. The line broadening is primarily due to electron exchange between the thiolate complex and its radical cation; the latter is generated by an unfavorable redox equilibrium between the thiol and thiolate complexes. Pyramidal inversion of sulfur in the thiol complex is fast at room temperature but slow at lower temperatures; major and minor conformers of the thiol complex were observed by 31P NMR at −98 °C in CD2Cl2

Electron Exchange Involving a Sulfur-Stabilized Ruthenium Radical Cation

Half-sandwich Ru(II) amine, thiol, and thiolate complexes were prepared and characterized by X-ray crystallography. The thiol and amine complexes react slowly with acetonitrile to give free thiol or amine and the acetonitrile complex. With the thiol complex, the reaction is dissociative. The thiolate complex has been oxidized to its Ru(III) radical cation and the solution EPR spectrum of that radical cation recorded. Cobaltocene reduces the thiol complex to the thiolate complex. The 1H and 31P NMR signals of the thiolate complex in acetonitrile become very broad whenever the thiolate and thiol complexes are present simultaneously. The line broadening is primarily due to electron exchange between the thiolate complex and its radical cation; the latter is generated by an unfavorable redox equilibrium between the thiol and thiolate complexes. Pyramidal inversion of sulfur in the thiol complex is fast at room temperature but slow at lower temperatures; major and minor conformers of the thiol complex were observed by 31P NMR at −98 °C in CD2Cl2

Electron Exchange Involving a Sulfur-Stabilized Ruthenium Radical Cation

Half-sandwich Ru(II) amine, thiol, and thiolate complexes were prepared and characterized by X-ray crystallography. The thiol and amine complexes react slowly with acetonitrile to give free thiol or amine and the acetonitrile complex. With the thiol complex, the reaction is dissociative. The thiolate complex has been oxidized to its Ru(III) radical cation and the solution EPR spectrum of that radical cation recorded. Cobaltocene reduces the thiol complex to the thiolate complex. The 1H and 31P NMR signals of the thiolate complex in acetonitrile become very broad whenever the thiolate and thiol complexes are present simultaneously. The line broadening is primarily due to electron exchange between the thiolate complex and its radical cation; the latter is generated by an unfavorable redox equilibrium between the thiol and thiolate complexes. Pyramidal inversion of sulfur in the thiol complex is fast at room temperature but slow at lower temperatures; major and minor conformers of the thiol complex were observed by 31P NMR at −98 °C in CD2Cl2

Electron Exchange Involving a Sulfur-Stabilized Ruthenium Radical Cation

Half-sandwich Ru(II) amine, thiol, and thiolate complexes were prepared and characterized by X-ray crystallography. The thiol and amine complexes react slowly with acetonitrile to give free thiol or amine and the acetonitrile complex. With the thiol complex, the reaction is dissociative. The thiolate complex has been oxidized to its Ru(III) radical cation and the solution EPR spectrum of that radical cation recorded. Cobaltocene reduces the thiol complex to the thiolate complex. The 1H and 31P NMR signals of the thiolate complex in acetonitrile become very broad whenever the thiolate and thiol complexes are present simultaneously. The line broadening is primarily due to electron exchange between the thiolate complex and its radical cation; the latter is generated by an unfavorable redox equilibrium between the thiol and thiolate complexes. Pyramidal inversion of sulfur in the thiol complex is fast at room temperature but slow at lower temperatures; major and minor conformers of the thiol complex were observed by 31P NMR at −98 °C in CD2Cl2

EPR Analysis and DFT Computations of a Series of Polynitroxides

Polynitroxides with varying numbers of nitroxide groups (one to four) derived from different aromatic core structures show intramolecular electron spin–spin coupling. The scope of this study is to establish an easy methodology for extracting structural, dynamical, and thermodynamical information from the EPR spectra of these polynitroxides which might find use as spin probes in complex systems, such as biological and host/guest systems, and as polarizing agents in dynamic nuclear polarization (DNP) applications. Density functional theory (DFT) calculations at the B3LYP/6-31G(d) level provided information on the structural details such as bond lengths and angles in the gas phase, which were compared with the single crystal X-ray diffraction data in the solid state. Polarizable continuum model (PCM) calculations were performed to account for solvent influences. The electron paramagnetic resonance (EPR) spectra of the polynitroxides in chloroform were analyzed in detail to extract information such as the percentages of different conformers, hyperfine coupling constants <i>a</i>, and rotational correlation times τ_c. The temperature dependence on the line shape of the EPR spectra gave thermodynamic parameters Δ<i>H</i> and Δ<i>S</i> for the conformational transitions. These parameters were found to depend on the number and relative positions of the nitroxide and other polar groups

Electron Exchange Involving a Sulfur-Stabilized Ruthenium Radical Cation

Half-sandwich Ru(II) amine, thiol, and thiolate complexes were prepared and characterized by X-ray crystallography. The thiol and amine complexes react slowly with acetonitrile to give free thiol or amine and the acetonitrile complex. With the thiol complex, the reaction is dissociative. The thiolate complex has been oxidized to its Ru(III) radical cation and the solution EPR spectrum of that radical cation recorded. Cobaltocene reduces the thiol complex to the thiolate complex. The 1H and 31P NMR signals of the thiolate complex in acetonitrile become very broad whenever the thiolate and thiol complexes are present simultaneously. The line broadening is primarily due to electron exchange between the thiolate complex and its radical cation; the latter is generated by an unfavorable redox equilibrium between the thiol and thiolate complexes. Pyramidal inversion of sulfur in the thiol complex is fast at room temperature but slow at lower temperatures; major and minor conformers of the thiol complex were observed by 31P NMR at −98 °C in CD2Cl2

Electron Exchange Involving a Sulfur-Stabilized Ruthenium Radical Cation

Half-sandwich Ru(II) amine, thiol, and thiolate complexes were prepared and characterized by X-ray crystallography. The thiol and amine complexes react slowly with acetonitrile to give free thiol or amine and the acetonitrile complex. With the thiol complex, the reaction is dissociative. The thiolate complex has been oxidized to its Ru(III) radical cation and the solution EPR spectrum of that radical cation recorded. Cobaltocene reduces the thiol complex to the thiolate complex. The 1H and 31P NMR signals of the thiolate complex in acetonitrile become very broad whenever the thiolate and thiol complexes are present simultaneously. The line broadening is primarily due to electron exchange between the thiolate complex and its radical cation; the latter is generated by an unfavorable redox equilibrium between the thiol and thiolate complexes. Pyramidal inversion of sulfur in the thiol complex is fast at room temperature but slow at lower temperatures; major and minor conformers of the thiol complex were observed by 31P NMR at −98 °C in CD2Cl2

Electron Exchange Involving a Sulfur-Stabilized Ruthenium Radical Cation

Half-sandwich Ru(II) amine, thiol, and thiolate complexes were prepared and characterized by X-ray crystallography. The thiol and amine complexes react slowly with acetonitrile to give free thiol or amine and the acetonitrile complex. With the thiol complex, the reaction is dissociative. The thiolate complex has been oxidized to its Ru(III) radical cation and the solution EPR spectrum of that radical cation recorded. Cobaltocene reduces the thiol complex to the thiolate complex. The 1H and 31P NMR signals of the thiolate complex in acetonitrile become very broad whenever the thiolate and thiol complexes are present simultaneously. The line broadening is primarily due to electron exchange between the thiolate complex and its radical cation; the latter is generated by an unfavorable redox equilibrium between the thiol and thiolate complexes. Pyramidal inversion of sulfur in the thiol complex is fast at room temperature but slow at lower temperatures; major and minor conformers of the thiol complex were observed by 31P NMR at −98 °C in CD2Cl2