Metal-Mediated Directional Capping of Rod-Packing Metal–Organic Frameworks

Two new rod-packing metal–organic frameworks (RPMOF) are constructed by regulating the in situ formation of the capping agent. In CPM-s7, carboxylate linkers extend 1D manganese-oxide chains in four additional directions, forming 3D RPMOF. The substitution of Mn²⁺ with a stronger Lewis acidic Co²⁺, leads to an acceleration of the hydrolysis-prone sulfonate linker, resulting in presence of sulfate ions to reduce two out of the four carboxylate-extending directions, and thus forming a new 2D rod-packing CPM-s8. Density functional theory calculations and magnetization measurements reveal ferrimagnetic ordering of CPM-s8, signifying the potential of exploring 2D RPMOF for effective low-dimensional magnetic materials.     

Unexpected Correlation Between Boron Chain Condensation and Hydrogen Evolution Reaction (HER) Activity in Highly Active Vanadium Borides: Enabling Predictions

Transition‐metal borides (TMBs) have recently attracted attention as excellent hydrogen evolution (HER) electrocatalysts in bulk crystalline materials. Herein, we show for the first time that VB and V₃B₄ have high electrocatalytic HER activity. Furthermore, we show that the HER activity (in 0.5 m H₂SO₄) increases with increasing boron chain condensation in vanadium borides: Using a ?23 mV overpotential decrement derived from ?0.296 mV (for VB at ?10 mA cm^?2 current density) and ?0.273 mV (for V₃B₄) we accurately predict the overpotential of VB₂ (?0.204 mV) as well as that of unstudied V₂B₃ (?0.250 mV) and hypothetical “V₅B₈” (?0.227 mV). We then derived an exponential equation that predicts the overpotentials of known and hypothetical V_xB_y phases containing at least a boron chain. These results provide a direct correlation between crystal structure and HER activity, thus paving the way for the design of even better electrocatalytic materials through structure–activity relationships.     

Synthesis,Characterization, and Magnetic Properties of the New Boride Solid Solutions M0.5Ru6.5B3 (M = Cr,Mn, Co,Ni)

Powder samples and single crystals of the borides M_0.5Ru_6.5B₃ (M = Cr, Mn, Co, Ni) were synthesized by arc‐melting the elements in a water‐cooled copper crucible under argon. The new phases were structurally characterized by single‐crystal and powder X‐ray diffraction as well as EDX‐Analyses. They crystallize in the hexagonal Th₇Fe₃ structure type (space group P6₃mc, no. 186, Z = 2) and a pronounced site preferential M/Ru substitution is observed. Magnetic properties of the compounds were investigated and Pauli paramagnetism was observed in all cases. However, a strong temperature dependency is subsequently observed in Mn_0.5Ru_6.5B₃ below 250 K, but no hint of magnetic ordering was found.     

[CrBr2(NH3)4][CrBr4(NH3)2], a new chromium(III) complex

Green single crystals of trans‐tetraamminedibromidochromium(III) trans‐diamminetetrabromidochromate(III), [CrBr₂(NH₃)₄][CrBr₄(NH₃)₂], are found to contain two symmetry‐independent sixfold coordinated Cr^III cations on centres of inversion. The structure is composed of octahedral trans‐[CrBr₂(NH₃)₄]⁺ cations and octahedral trans‐[CrBr₄(NH₃)₂]⁻ anions, and adopts a distorted CsCl‐type lattice. The cations and anions are linked by N—H...Br interactions. This is the first example in which both ions are mixed ammine–bromide Cr^III complexes.     

Singular solutions of the Poisson equation at edges of three‐dimensional domains and their treatment with a predictor–corrector finite element method

Solutions of boundary value problems in three‐dimensional domains with edges may exhibit singularities which are known to influence both the accuracy of the finite element solutions and the rate of convergence in the error estimates. This paper considers boundary value problems for the Poisson equation on typical domains Ω ? ?³ with edge singularities and presents, on the one hand, explicit computational formulas for the flux intensity functions. On the other hand, it proposes and analyzes a nonconforming finite element method on regular meshes for the efficient treatment of the singularities. The novelty of the present method is the use of the explicit formulas for the flux intensity functions in defining a postprocessing procedure in the finite element approximation of the solution. A priori error estimates in H¹(Ω) show that the present algorithm exhibits the same rate of convergence as it is known for problems with regular solutions.     

Synthesis of a missing structural link: the first trigonal planar B4 units in the novel complex boride Ti(1+x)Os(2-x)RuB2 (x = 0.6)

The newly synthesized boride Ti(1+x)Os(2-x)RuB(2) (x = 0.6) has a novel structure featuring one-dimensional chains of titanium atoms, one-dimensional strings of face-sharing empty tetrahedral and square pyramidal clusters and, most importantly, trigonal planar and strongly bonded B4 units with a B-B distance of 1.89 A.     

Synthesis, crystal-structure determination and magnetic properties of two new transition-metal carbodiimides: CoNCN and NiNCN

Synthesis, structure determination, and magnetic properties are reported for the metastable and crystal-chemically isotypic phases cobalt carbodiimide, CoNCN, and nickel carbodiimide, NiNCN, adopting the hexagonal system and space group P63/mmc (NiAs type) with interatomic distances of Co-N = 2.17 Angstrom and Ni-N = 2.12 Angstrom and an octahedral coordination of the transition-metal ions; the NCN(2-) units reveal the carbodiimide shape with two C=N double bonds. The low-susceptibility data go back to strong antiferromagnetic spin-spin coupling, similar to the behavior of the electronically related oxides CoO and NiO.     

On the solution of Maxwell's equations in polygonal domains

This paper is concerned with the structure of the singular and regular parts of the solution of time‐harmonic Maxwell's equations in polygonal plane domains and their effective numerical treatment. The asymptotic behaviour of the solution near corner points of the domain is studied by means of discrete Fourier transformation and it is proved that the solution of the boundary value problem does not belong locally to H² when the boundary of the domain has non‐acute angles. A splitting of the solution into a regular part belonging to the space H², and an explicitly described singular part is presented. For the numerical treatment of the boundary value problem, we propose a finite element discretization which combines local mesh grading and the singular field methods and derive a priori error estimates that show optimal convergence as known for the classical finite element method for problems with regular solutions. Copyright © 2006 John Wiley & Sons, Ltd.