Unlocking the Electrocatalytic Activity of Antimony for CO2 Reduction by Two‐Dimensional Engineering of the Bulk Material

Two‐dimensional (2D) materials are known to be useful in catalysis. Engineering 3D bulk materials into the 2D form can enhance the exposure of the active edge sites, which are believed to be the origin of the high catalytic activity. Reported herein is the production of 2D “few‐layer” antimony (Sb) nanosheets by cathodic exfoliation. Application of this 2D engineering method turns Sb, an inactive material for CO₂ reduction in its bulk form, into an active 2D electrocatalyst for reduction of CO₂ to formate with high efficiency. The high activity is attributed to the exposure of a large number of catalytically active edge sites. Moreover, this cathodic exfoliation process can be coupled with the anodic exfoliation of graphite in a single‐compartment cell for in situ production of a few‐layer Sb nanosheets and graphene composite. The observed increased activity of this composite is attributed to the strong electronic interaction between graphene and Sb.     

Structure and Bonding in [Sb@In8Sb12]3− and [Sb@In8Sb12]5−

We report the characterization of the compound [K([2.2.2]crypt)]₄[In₈Sb₁₃], which proves to contain a 1:1 mixture of [Sb@In₈Sb₁₂]^3? and [Sb@In₈Sb₁₂]^5?. The tri‐anion displays perfect T_h symmetry, the first completely inorganic molecule to do so, and contains eight equivalent In³⁺ centers in a cube. The gas‐phase potential energy surface of the penta‐anion has eight equivalent minima where the extra pair of electrons is localized on one In⁺ center, and these minima are linked by low‐lying transition states where the electron pair is delocalized over two adjacent centers. The best fit to the electron density is obtained from a model where the structure of the 5? cluster lies close to the gas‐phase transition state.     

Sr6Cd2Sb6O7S10: Strong SHG Response Activated by Highly Polarizable Sb/O/S Groups

A new nonlinear optical (NLO) oxysulfide, Sr₆Cd₂Sb₆O₇S₁₀, which contains the functional groups [SbO_xS_5?x]^7? (x=0, 1) with a 5s² electron configuration, is synthesized by a solid‐state reaction. This compound displays a phase‐matchable second harmonic generation (SHG) response four times stronger than AgGaS₂ (AGS) under laser irradiation at 2.09 μm. Single‐crystal‐based optical measurements reveal a SHG intensity that can be tuned by temperature and novel photoluminescence properties. Theoretical analyses demonstrate that tetragonal [SbOS₄]^7? and [SbS₅]^7? pyramids make the predominant contribution to the enhanced SHG effect. Among those, the [SbOS₄]^7? units with mixed anions make a larger contribution. This work proposes that oxysulfide groups with an ns² electron configuration can serve as new functional building units in NLO materials and opens a new avenue for the design of other optoelectronic materials.     

An Antimony(V) Dication as a Z‐Type Ligand: Turning on Styrene Activation at Gold

With the intent to demonstrate that the charge of Z‐type ligands can be used to modulate the electrophilic character and catalytic properties of coordinated transition metals, we are now targeting complexes bearing polycationic antimony‐based Z‐type ligands. Toward this end, the dangling phosphine arm of ((o‐(Ph₂P)C₆H₄)₃)SbCl₂AuCl ( 1 ) was oxidized with hydrogen peroxide to afford [((o‐(Ph₂P)C₆H₄)₂(o‐Ph₂PO)C₆H₄)SbAuCl₂]⁺ ([ 2 a ]⁺) which was readily converted into the dicationic complex [((o‐(Ph₂P)C₆H₄)₂(o‐Ph₂PO)C₆H₄)SbAuCl]²⁺ ([ 3 ]²⁺) by treatment with 2 equiv AgNTf₂. Both experimental and computational results show that [ 3 ]²⁺ possess a strong Au→Sb interaction reinforced by the dicationic character of the antimony center. The gold‐bound chloride anion of [ 3 ]²⁺ is rather inert and necessitates the addition of excess AgNTf₂ to undergo activation. The activated complex, referred to as [ 4 ]²⁺ [((o‐(Ph₂P)C₆H₄)₂(o‐Ph₂PO)C₆H₄)SbAuNTf₂]²⁺ readily catalyzes both the polymerization and the hydroamination of styrene. This atypical reactivity underscores the strong σ‐accepting properties of the dicationic antimony ligand and its activating impact on the gold center.