Water-Soluble Phosphine Capable of Dissolving Elemental Gold: The Missing Link between 1,3,5-Triaza-7-phosphaadamantane (PTA) and Verkade’s Ephemeral Ligand

We herein describe a tricyclic phosphine with previously unreported tris­(homoadamantane) cage architecture. That water-soluble, air- and thermally stable ligand, 1,4,7-triaza-9-phosphatricyclo­[5.3.2.1^4,9]­tridecane (hereinafter referred to as CAP) exhibits unusual chemical behavior toward gold and gold compounds: it readily reduces Au­(III) to Au(0), promotes oxidative dissolution of nanocrystalline gold(0) with the formation of water-soluble trigonal CAP–Au­(I) complexes, and displaces cyanide from [Au­(CN)₂]⁻ affording triangular [Au­(CAP)₃]⁺ cation. From the stereochemical point of view, CAP can be regarded as an intermediate between 1,3,5-triaza-7-phosphaadamantane (PTA) and very unstable aminophosphine synthesized by Verkade’s group: hexahydro-2<i>a</i>,4<i>a</i>,6<i>a</i>-triaza-6<i>b</i>-phosphacyclopenta­[<i>cd</i>]­pentalene. The chemical properties of CAP are likely related to its anomalous stereoelectronic profile: combination of strong electron-donating power (Tolman’s electronic parameter 2056.8 cm^–1) with the low steric demand (cone angle of 109°). CAP can be considered as macrocyclic counterpart of PTA with the electron-donating power approaching that of strongest known phosphine electron donors such as P­(<i>t</i>-Bu)₃ and PCy₃. Therefore, CAP as sterically undemanding and electron-rich ligand populates the empty field on the stereoelectronic map of phosphine ligands: the niche between the classic tertiary phosphines and the sterically undemanding aminophosphines

Expanding the Concept of van der Waals Heterostructures to Interwoven 3D Structures

Several members of a new family of heterostructures [(LaSe)_1.17]₁V_{<i>n</i>(1+<i>y</i>)+1}Se_2<i>n</i>+2 with <i>n</i> = 1, 2, and 3 were prepared using a diffusion constrained, kinetically controlled synthesis approach. Specular diffraction patterns collected as a function of annealing temperature show the evolution of designed precursors into highly ordered heterostructures. Scanning transmission electron microscopy (STEM) images reveal that the structure of <i>n</i> = 3 consists of rock salt structured LaSe bilayers alternating with vanadium selenide layers of varying thickness, which are structurally closely related to V₃Se₄. Interplanar distances obtained from the STEM images were successfully used as the starting point for Rietveld refinements of the specular diffraction patterns of these crystallographically aligned compounds. Utilizing this unorthodox combined approach to extract detailed structural information unambiguously, we demonstrated that these thin film compounds are the first examples of chalcogenide-based heterostructures, where the bulk structures of both building blocks lack a van der Waals gap, yet a nonepitaxial incommensurate interface forms. Moreover, the refinement results of the <i>n</i> = 2 and 3 heterostructures suggest that the structure of the V–Se layers can be varied ranging from VSe₂ to VSe depending on the film composition. The electrical resistivity of the [(LaSe)_1.17]₁V_{<i>n</i>(1+<i>y</i>)+1}Se_2<i>n</i>+2 heterostructures changes systematically from semiconducting toward metallic behavior with increasing <i>n</i>, showcasing the ability to tune physical properties by precisely controlling the layer sequence in these heterostructures

Fiber-Integrated All-Optical Signal Processing Device for Storage and Computing

All-optical signal processing is crucial for high-speed optical fiber communication networks. However, current methods utilizing nonlinear media have limitations such as complex preparation, weak nonlinear effects, and requiring additional energy during operation. To overcome these issues, we demonstrate a fiber-integrated all-optical signal processing device based on Ge2Sb2Te5 (GST). This device can perform a storage function and matrix-vector multiplication (MVM) function. Our device is composed of a single-mode fiber and a step-index multimode fiber with a GST layer deposited on the end face of the multimode fiber. By constructing a special Bessel-like light field, we can achieve the 19-level of storage with low switching energy (90 nJ), large contrast ratio (47%), and fast switching time of a single pulse (200 ns). We also demonstrate MVM operation by connecting two memory units in parallel. These features make our all-optical signal processing unit ideal for data storage/processing applications such as photonic neural networks and neuromorphic computing architectures