Diniobium Inverted Sandwich Complexes with μ‑η⁶:η⁶‑Arene Ligands: Synthesis, Kinetics of Formation, and Electronic Structure

Monometallic niobium arene complexes [Nb­(BDI)­(N^<i>t</i>Bu)­(R-C₆H₅)] (<b>2a</b>: R = H and <b>2b</b>: R = Me, BDI = <i>N</i>,<i>N</i>′-diisopropylbenzene-β-diketiminate) were synthesized and found to undergo slow conversion into the diniobium inverted arene sandwich complexes [[(BDI)­Nb­(N^<i>t</i>Bu)]₂(μ-RC₆H₅)] (<b>7a</b>: R = H and <b>7b</b>: R = Me) in solution. The kinetics of this reaction were followed by ¹H NMR spectroscopy and are in agreement with a dissociative mechanism. Compounds <b>7a</b>-<b>b</b> showed a lack of reactivity toward small molecules, even at elevated temperatures, which is unusual in the chemistry of inverted sandwich complexes. However, protonation of the BDI ligands occurred readily on treatment with [H­(OEt₂)]­[B­(C₆F₅)₄], resulting in the monoprotonated cationic inverted sandwich complex <b>8</b> [[(BDI^#)­Nb­(N^<i>t</i>Bu)]­[(BDI)­Nb­(N^<i>t</i>Bu)]­(μ-C₆H₅)]­[B­(C₆F₅)₄] and the dicationic complex <b>9</b> [[(BDI^#)­Nb­(N^<i>t</i>Bu)]₂(μ-RC₆H₅)]­[B­(C₆F₅)₄]₂ (BDI^# = (ArNC­(Me))₂CH₂). NMR, UV–vis, and X-ray absorption near-edge structure (XANES) spectroscopies were used to characterize this unique series of diamagnetic molecules as a means of determining how best to describe the Nb–arene interactions. The X-ray crystal structures, UV–vis spectra, arene ¹H NMR chemical shifts, and large <i>J</i>_CH coupling constants provide evidence for donation of electron density from the Nb d-orbitals into the antibonding π system of the arene ligands. However, Nb L_3,2-edge XANES spectra and the lack of sp³ hybridization of the arene carbons indicate that the Nb → arene donation is not accompanied by an increase in Nb formal oxidation state and suggests that 4d² electronic configurations are appropriate to describe the Nb atoms in all four complexes

Diniobium Inverted Sandwich Complexes with μ‑η⁶:η⁶‑Arene Ligands: Synthesis, Kinetics of Formation, and Electronic Structure

Monometallic niobium arene complexes [Nb­(BDI)­(N^<i>t</i>Bu)­(R-C₆H₅)] (<b>2a</b>: R = H and <b>2b</b>: R = Me, BDI = <i>N</i>,<i>N</i>′-diisopropylbenzene-β-diketiminate) were synthesized and found to undergo slow conversion into the diniobium inverted arene sandwich complexes [[(BDI)­Nb­(N^<i>t</i>Bu)]₂(μ-RC₆H₅)] (<b>7a</b>: R = H and <b>7b</b>: R = Me) in solution. The kinetics of this reaction were followed by ¹H NMR spectroscopy and are in agreement with a dissociative mechanism. Compounds <b>7a</b>-<b>b</b> showed a lack of reactivity toward small molecules, even at elevated temperatures, which is unusual in the chemistry of inverted sandwich complexes. However, protonation of the BDI ligands occurred readily on treatment with [H­(OEt₂)]­[B­(C₆F₅)₄], resulting in the monoprotonated cationic inverted sandwich complex <b>8</b> [[(BDI^#)­Nb­(N^<i>t</i>Bu)]­[(BDI)­Nb­(N^<i>t</i>Bu)]­(μ-C₆H₅)]­[B­(C₆F₅)₄] and the dicationic complex <b>9</b> [[(BDI^#)­Nb­(N^<i>t</i>Bu)]₂(μ-RC₆H₅)]­[B­(C₆F₅)₄]₂ (BDI^# = (ArNC­(Me))₂CH₂). NMR, UV–vis, and X-ray absorption near-edge structure (XANES) spectroscopies were used to characterize this unique series of diamagnetic molecules as a means of determining how best to describe the Nb–arene interactions. The X-ray crystal structures, UV–vis spectra, arene ¹H NMR chemical shifts, and large <i>J</i>_CH coupling constants provide evidence for donation of electron density from the Nb d-orbitals into the antibonding π system of the arene ligands. However, Nb L_3,2-edge XANES spectra and the lack of sp³ hybridization of the arene carbons indicate that the Nb → arene donation is not accompanied by an increase in Nb formal oxidation state and suggests that 4d² electronic configurations are appropriate to describe the Nb atoms in all four complexes

Singlet-Oxygen Generation from Individual Semiconducting and Metallic Nanostructures during Near-Infrared Laser Trapping

Photodynamic therapy has been used for several decades in the treatment of solid tumors through the optical generation of chemically reactive singlet-oxygen molecules (¹O₂). Recently, nanoscale metallic and semiconducting materials have been reported to act as photosensitizing agents with additional diagnostic and therapeutic functionality. To date there have been no reports of observing the generation of singlet-oxygen at the level of single nanostructures, particularly at near-infrared (NIR) wavelengths. Here we demonstrate that NIR laser tweezers can be used to observe the formation of singlet oxygen produced from individual silicon and gold nanowires via use of a commercially available reporting dye. The laser trap also induces two-photon photoexcitation of the dye following a chemical reaction with singlet oxygen. Corresponding two-photon emission spectra confirms the generation of singlet oxygen from individual silicon nanowires at room temperature (30 °C), suggesting a range of applications for investigating semiconducting and metallic nanoscale materials for solid tumor photoablation

Dependence on Crystal Size of the Nanoscale Chemical Phase Distribution and Fracture in Li_<i>x</i>FePO₄

The performance of battery electrode materials is strongly affected by inefficiencies in utilization kinetics and cycle life as well as size effects. Observations of phase transformations in these materials with high chemical and spatial resolution can elucidate the relationship between chemical processes and mechanical degradation. Soft X-ray ptychographic microscopy combined with X-ray absorption spectroscopy and electron microscopy creates a powerful suite of tools that we use to assess the chemical and morphological changes in lithium iron phosphate (LiFePO₄) micro- and nanocrystals that occur upon delithiation. All sizes of partly delithiated crystals were found to contain two phases with a complex correlation between crystallographic orientation and phase distribution. However, the lattice mismatch between LiFePO₄ and FePO₄ led to severe fracturing on microcrystals, whereas no mechanical damage was observed in nanoplates, indicating that mechanics are a principal driver in the outstanding electrode performance of LiFePO₄ nanoparticles. These results demonstrate the importance of engineering the active electrode material in next generation electrical energy storage systems, which will achieve theoretical limits of energy density and extended stability. This work establishes soft X-ray ptychographic chemical imaging as an essential tool to build comprehensive relationships between mechanics and chemistry that guide this engineering design