6 research outputs found
Light-Driven Hydrogen Production from Aqueous Protons using Molybdenum Catalysts
Homogeneous light-driven systems
employing molecular molybdenum
catalysts for hydrogen production are described. The specific Mo complexes
studied are six-coordinate bis(benzenedithiolate) derivatives having
two additional isocyanide or phosphine ligands to complete the coordination
sphere. Each of the complexes possesses a trigonal prismatic coordination
geometry. The complexes were investigated as proton reduction catalysts
in the presence of [Ru(bpy)<sub>3</sub>]<sup>2+</sup>, ascorbic acid,
and visible light. Over 500 TON are obtained over 24 h. Electrocatalysis
occurs between the Mo<sup>IV</sup>/Mo<sup>III</sup> and Mo<sup>III</sup>/Mo<sup>II</sup> redox couples, around 1.0 V vs SCE. Mechanistic
studies by <sup>1</sup>H NMR spectroscopy show that upon two-electron
reduction the Mo(CNR)<sub>2</sub>(bdt)<sub>2</sub> complex dissociates
the isocyanide ligands, followed by addition of acid to result in
the formation of molecular hydrogen and the Mo(bdt)<sub>2</sub> complex
Light-Driven Hydrogen Production from Aqueous Protons using Molybdenum Catalysts
Homogeneous light-driven systems
employing molecular molybdenum
catalysts for hydrogen production are described. The specific Mo complexes
studied are six-coordinate bis(benzenedithiolate) derivatives having
two additional isocyanide or phosphine ligands to complete the coordination
sphere. Each of the complexes possesses a trigonal prismatic coordination
geometry. The complexes were investigated as proton reduction catalysts
in the presence of [Ru(bpy)<sub>3</sub>]<sup>2+</sup>, ascorbic acid,
and visible light. Over 500 TON are obtained over 24 h. Electrocatalysis
occurs between the Mo<sup>IV</sup>/Mo<sup>III</sup> and Mo<sup>III</sup>/Mo<sup>II</sup> redox couples, around 1.0 V vs SCE. Mechanistic
studies by <sup>1</sup>H NMR spectroscopy show that upon two-electron
reduction the Mo(CNR)<sub>2</sub>(bdt)<sub>2</sub> complex dissociates
the isocyanide ligands, followed by addition of acid to result in
the formation of molecular hydrogen and the Mo(bdt)<sub>2</sub> complex
Crystal Structures of Au<sub>2</sub> Complex and Au<sub>25</sub> Nanocluster and Mechanistic Insight into the Conversion of Polydisperse Nanoparticles into Monodisperse Au<sub>25</sub> Nanoclusters
We previously reported a size-focusing conversion of polydisperse gold nanoparticles capped by phosphine into monodisperse [Au<sub>25</sub>(PPh<sub>3</sub>)<sub>10</sub>(SC<sub>2</sub>H<sub>4</sub>Ph)<sub>5</sub>Cl<sub>2</sub>]<sup>2+</sup> nanoclusters in the presence of phenylethylthiol. Herein, we have determined the crystal structure of [Au<sub>25</sub>(PPh<sub>3</sub>)<sub>10</sub>(SC<sub>2</sub>H<sub>4</sub>Ph)<sub>5</sub>Cl<sub>2</sub>]<sup>2+</sup> nanoclusters and also identified an important side-producta Au(I) complex formed in the size focusing process. The [Au<sub>25</sub>(PPh<sub>3</sub>)<sub>10</sub>(SC<sub>2</sub>H<sub>4</sub>Ph)<sub>5</sub>Cl<sub>2</sub>]<sup>2+</sup> cluster features a vertex-sharing bi-icosahedral core, resembling a rod. The formula of the Au(I) complex is determined to be [Au<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>(SC<sub>2</sub>H<sub>4</sub>Ph)]<sup>+</sup> by electrospray ionization (ESI) mass spectrometry, and its crystal structure (with SbF<sub>6</sub><sup>–</sup> counterion) reveals Au–Au bridged by −SC<sub>2</sub>H<sub>4</sub>Ph and with terminal bonds to two PPh<sub>3</sub> ligands. Unlike previously reported [Au<sub>2</sub>(PR<sub>3</sub>)<sub>2</sub>(SC<sub>2</sub>H<sub>4</sub>Ph)]<sup>+</sup> complexes in the solid state, which exist as tetranuclear complexes (i.e., dimers of [Au<sub>2</sub>(PR<sub>3</sub>)<sub>2</sub>(SC<sub>2</sub>H<sub>4</sub>Ph)]<sup>+</sup> units) through a Au···Au aurophilic interaction, in our case we found that the [Au<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>(SC<sub>2</sub>H<sub>4</sub>Ph)]<sup>+</sup> complex exists as a single entity, rather than being dimerized to form a tetranuclear complex. The observation of this Au(I) complex allows us to gain insight into the intriguing conversion process from polydisperse Au nanoparticles to monodisperse Au<sub>25</sub> nanoclusters
Crystal Structures of Au<sub>2</sub> Complex and Au<sub>25</sub> Nanocluster and Mechanistic Insight into the Conversion of Polydisperse Nanoparticles into Monodisperse Au<sub>25</sub> Nanoclusters
We previously reported a size-focusing conversion of polydisperse gold nanoparticles capped by phosphine into monodisperse [Au<sub>25</sub>(PPh<sub>3</sub>)<sub>10</sub>(SC<sub>2</sub>H<sub>4</sub>Ph)<sub>5</sub>Cl<sub>2</sub>]<sup>2+</sup> nanoclusters in the presence of phenylethylthiol. Herein, we have determined the crystal structure of [Au<sub>25</sub>(PPh<sub>3</sub>)<sub>10</sub>(SC<sub>2</sub>H<sub>4</sub>Ph)<sub>5</sub>Cl<sub>2</sub>]<sup>2+</sup> nanoclusters and also identified an important side-producta Au(I) complex formed in the size focusing process. The [Au<sub>25</sub>(PPh<sub>3</sub>)<sub>10</sub>(SC<sub>2</sub>H<sub>4</sub>Ph)<sub>5</sub>Cl<sub>2</sub>]<sup>2+</sup> cluster features a vertex-sharing bi-icosahedral core, resembling a rod. The formula of the Au(I) complex is determined to be [Au<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>(SC<sub>2</sub>H<sub>4</sub>Ph)]<sup>+</sup> by electrospray ionization (ESI) mass spectrometry, and its crystal structure (with SbF<sub>6</sub><sup>–</sup> counterion) reveals Au–Au bridged by −SC<sub>2</sub>H<sub>4</sub>Ph and with terminal bonds to two PPh<sub>3</sub> ligands. Unlike previously reported [Au<sub>2</sub>(PR<sub>3</sub>)<sub>2</sub>(SC<sub>2</sub>H<sub>4</sub>Ph)]<sup>+</sup> complexes in the solid state, which exist as tetranuclear complexes (i.e., dimers of [Au<sub>2</sub>(PR<sub>3</sub>)<sub>2</sub>(SC<sub>2</sub>H<sub>4</sub>Ph)]<sup>+</sup> units) through a Au···Au aurophilic interaction, in our case we found that the [Au<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>(SC<sub>2</sub>H<sub>4</sub>Ph)]<sup>+</sup> complex exists as a single entity, rather than being dimerized to form a tetranuclear complex. The observation of this Au(I) complex allows us to gain insight into the intriguing conversion process from polydisperse Au nanoparticles to monodisperse Au<sub>25</sub> nanoclusters
Synthesis and Characterization of Heterobimetallic Iridium–Aluminum and Rhodium–Aluminum Complexes
We
demonstrate the synthesis and characterization of a new class of late-transition-metal–aluminum
heterobimetallic complexes via a novel synthetic pathway. Complexes
of this type are exceedingly rare. Joint experimental and theoretical
data sheds light on the electronic effect of ligands containing aluminum
moieties on late-transition-metal complexes
From Seconds to Femtoseconds: Solar Hydrogen Production and Transient Absorption of Chalcogenorhodamine Dyes
A series
of chalcogenorhodamine dyes with oxygen, sulfur, and selenium
atoms in the xanthylium core was synthesized and used as chromophores
for solar hydrogen production with a platinized TiO<sub>2</sub> catalyst.
Solutions containing the selenorhodamine dye generate more hydrogen
[181 turnover numbers (TONs) with respect to chromophore] than its
sulfur (30 TONs) and oxygen (20 TONs) counterparts. This differs from
previous work incorporating these dyes into dye-sensitized solar cells
(DSSCs), where the oxygen- and selenium-containing species perform
similarly. Ultrafast transient absorption spectroscopy revealed an
ultrafast electron transfer under conditions for dye-sensitized solar
cells and a slower electron transfer under conditions for hydrogen
production, making the chromophore’s triplet yield an important
parameter. The selenium-containing species is the only dye for which
triplet state population is significant, which explains its superior
activity in hydrogen evolution. The discrepancy in rates of electron
transfer appears to be caused by the presence or absence of aggregation
in the system, altering the coupling between the dye and TiO<sub>2</sub>. This finding demonstrates the importance of understanding the differences
between, as well as the effects of the conditions for DSSCs and solar
hydrogen production