Orientational Isomerism and Its Reactivity of a Main Group Sandwich Anion[Ge_(9)-In-Ge_(9)]^(5-)

Two isomers of a sandwich-type anion [Ge_(9)-In-Ge_(9)]^(5–) were synthesized by controlling the chelating agents (2,2,2-crypt/18-C-6). Further reactions with early/late transition metal complexes, Mo(CO)_(6) and Ni(COD)_(2), respectively, yielded two new types of inorganic sandwich derivatives: a half-sandwich cluster [Ge_(9)-In-Mo(CO)_(5)]^(3–) with a low-valence In(I) center and an unsymmetrical sandwich-type cluster {[(Ni@Ge_(9))In(Ni_(0.648)@Ge_(9))]}^(5–) due to the insertion of Ni atoms, respectively. The isolation of these new derivatives demonstrates the reactivity of sandwich-type [Ge_(9)-In-Ge_(9)]^(5–) acting as the precursor, which provides some enlightenment for constructing new inorganic sandwich compounds.

Wear-resistant Ag-MAX phase 3D interpenetrating-phase composites:Processing,structure,and properties

Electrical contact materials are generally Ag-or Cu-based composites and play a critical role in ensuring the reliability and efficiency of electrical equipments and electronic instruments.The MAX(M is an early transition metal,A is an element from III or IV main groups,and X is carbon or/and nitrogen)phase ceramics display a unique combination of properties and may serve as an ideal reinforcement phase for electrical contact materials.The biological materials evolved in nature generally exhibit three-dimensional(3D)interpenetrating-phase architectures,which may offer useful inspiration for the architectural design of electrical contact materials.Here,a series of bi-continuous Ag-Ti_(3)SiC_(2) MAX phase composites with high ceramic contents exceeding 50 vol.%and having micron-and ultrafine-scaled 3D interpenetrating-phase architectures,wherein both constituents were continuous and mutually interspersed,were exploited by pressureless infiltration of Ag melt into partially sintered Ti_(3)SiC_(2) scaffolds.The mechanical and electrical properties as well as the friction and wear performance of the composites were investigated and revealed to be closely dependent on the ceramic contents and characteristic structural dimensions.The composites exhibited a good combination of properties with high hardness over 2.3 GPa,high flexural strength exceeding 530 MPa,decent fracture toughness over 10 MPa·m^(1/2),and good wear resistance with low wear rate at an order of 10^(-5)mm^(3)/(N·m),which were much superior compared to the counterparts made by powder metallurgy methods.In particular,the hardness,electrical conductivity,strength,and fracture toughness of the composites demonstrated a simultaneous improvement as the structure was refined from micron-to ultrafine-scales at equivalent ceramic contents.The good combination of properties along with the facile processing route makes the Ag-Ti_(3)SiC_(2)3D interpenetrating-phase composites appealing for electrical contact applications.

Crystalline Germanium-Dipyrromethene Radicals:from a Delocalized Neutral to a Localized Cation

Both dipyrromethene complexes and radicals of heavier main group elements have been of high interest.However,cationic germanium radicals and dipyrromethene-based radicals of heavier main group elements are still escaped to be isolated.Herein,we report the isolation and full characterization of a neutral Ge(I)-masked dipyrromethene-based radical 3 and the first cationic Ge(III)-centered radical 5^(·+)as stable crystalline solids.3 behaves as a germanium(I)radical in its reaction with diphenyl disulfide to form the Ge-S bond,although X-ray crystallographic,EPR spectroscopic,computational studies revealed that the unpaired electron of 3 is mainly delocalized over the C_(9)N_(2)Ge backbone and the allylic radical character is also significant in 3.In contrast to 3,the spin density of 5^(·+)is mainly localized at the Ge center with minor contribution from the dipyrromethene ligand.Moreover,reduction of 5^(·+)with potassium graphite quantitatively regenerates 5,illustrating a reversible one-electron redox pair.

Carbon-halogen bond activation by a structurally constrained phosphorus(Ⅲ)platform

Theσ-bond activation by main group element has received enormous attention from theoretical and experimental chemists.Here,the reaction of C-X(X=Cl,Br,I)bonds in benzyl and allyl halides with a pincer-type phosphorus(Ⅲ)species was reported.A series of structurally robust phosphorus(Ⅴ)compounds were formed via the formal oxidative addition reactions of C-X bonds to the phosphorus(Ⅲ)center.Density functional theory calculations show that the nucleophilic addition process is more favorable than the direct oxidative addition mechanism.Isomerization of bent structures of phosphorus(Ⅲ)compound to poorly nucleophilic compounds to undergo further C-X bond activation can be rationalized by frontier molecule orbital analysis.This study not only provides a deep understanding of the reactivity of phosphorus(Ⅲ)species but also demonstrates a potential of main group elements for the small-molecule activation.