Sn2B5O9Cl: A Material with Large Birefringence Enhancement Activated Prepared via Alkaline‐Earth‐Metal Substitution by Tin

The excellent birefringent materials are needed for optical systems. Herein, we reported a new compound, the first tin borate chloride, Sn₂B₅O₉Cl (SBOC) with a large birefringence (0.168 at 546 nm) measured by the polarizing microscope. Its birefringence is 16 times that of the isostructural Ba₂B₅O₉Cl (BBOC) compound (0.010@ at 546 nm). The results show that the birefringence enhancement originates mainly from the Sn²⁺ polyhedra. We propose that the birefringence can be enlarged by substituting the alkaline‐earth metal cation by the Sn²⁺ cation in the isostructural borate with small birefringence. This strategy will guide the discovery of large birefringent materials in the future.     

Rare‐Earth‐ and Uranium‐Mesoionic Carbenes: A New Class of f‐Block Carbene Complex Derived from an N‐Heterocyclic Olefin

Neutral mesoionic carbenes (MICs) have emerged as an important class of carbene, however they are found in the free form or ligated to only a few d‐block ions. Unprecedented f‐block MIC complexes [M(N′′)₃{CN(Me)C(Me)N(Me)CH}] (M=U, Y, La, Nd; N′′=N(SiMe₃)₂) are reported. These complexes were prepared by a formal 1,4‐proton migration reaction when the metal triamides [M(N′′)₃] were treated with the N‐heterocyclic olefin H₂C=C(NMeCH)₂, which constitutes a new, general way to prepare MIC complexes. Quantum chemical calculations on the 5f³ uranium(III) complex suggest the presence of a U=C donor‐acceptor bond, composed of a MIC→U σ‐component and a U(5f)→MIC(2p) π‐back‐bond, but for the d⁰f⁰ Y and La and 4f³ Nd congeners only MIC→M σ‐bonding is found. Considering the generally negligible π‐acidity of MICs, this is surprising and highlights that greater consideration should possibly be given to recognizing MICs as potential π‐acid ligands when coordinated to strongly reducing metals.     

Isopropanol Dehydration on Amorphous Silica–Alumina: Synergy of Brønsted and Lewis Acidities at Pseudo‐Bridging Silanols

The mechanism of isopropanol dehydration on amorphous silica–alumina (ASA) was unraveled by a combination of experimental kinetic measurements and periodic density functional theory (DFT) calculations. We show that pseudo‐bridging silanols (PBS‐Al) are the most likely active sites owing to the synergy between the Brønsted and Lewis acidic properties of these sites, which facilitates the activation of alcohol hydroxy groups as leaving groups. Isopropanol dehydration was used to specifically investigate these PBS‐Al sites, whose density was estimated to be about 10⁻¹ site nm⁻² on the silica‐doped alumina surface under investigation, by combining information from experiments and theoretical calculations.