The structure and magnetic properties of chromium(III) molybdate

Magnetic susceptibility measurements have shown that Cr₂(MoO₄)₃ orders magnetically at 42 K. Powder neutron diffraction experiments at 295 and 5 K indicate that Cr₂(MoO₄)₃ is chemically and magnetically isostructural with the L-type ferrimagnet Fe₂(MoO₄)₃, and has a magnetic moment of 2.5 ± 0.2 μ_B per cation at 5 K. The limitations imposed on powder neutron diffraction methods by particle-size effects are discussed.     

A thermally stable nanoporous nickel 5-sulfoisophthalate; crystal structure and adsorption properties

A 3D nanoporous nickel 5-sulfoisophthlate coordination polymer with a high surface area (>700 m(2) g(-1)) has been synthesized hydrothermally and studied using single crystal and variable-temperature powder XRD, TGA, and BET porosimetry.     

Supercritical fluid chromatography tandem-column method development in pharmaceutical sciences for a mixture of four stereoisomers

A tandem-column method using Chiralpak AD-H and Chiralcel OD-H columns was achieved for baseline separation of a mixture of chiral pharmaceutical compounds (i.e., four stereoisomers) via supercritical fluid chromatography (SFC) with a mobile phase consisting of 90% liquid carbon dioxide and 10% ethanol:isopropanol (50:50 v/v). On the contrary, this mixture (mixture A) could not be baseline separated by SFC conditions explored with individual Chiralpak AD-H and Chiralcel OD-H columns. The effects of various mobile phases on elution order, capacity factor, selectivity, and resolution were determined with mixture A on the individual aforementioned columns to develop the tandem-column method.     

Isomorphous substitution of transition-metal ions in the nanoporous nickel phosphate VSB-5

The transition-metal-incorporated nickel phosphate molecular sieves (TMI-VSB-5) have been hydrothermally synthesized at 453 K in weak basic conditions under microwave irradiation. By means of X-ray diffraction, inductively coupled plasma (ICP), ultraviolet-visible (UV-vis) diffuse reflectance, and M?ssbauer spectroscopies, successful isomorphous (at least partial) substitution of transition-metal ions in the VSB-5 framework has been verified. Characterization results show that the framework structure of nanoporous VSB-5 can accommodate a substantial level of isomorphous substitution of transition-metal ions up to about 10, 5, and 3 atom % for Fe, Mn, and V, respectively, in both octahedral nickel sites (Mn and Fe) and tetrahedral phosphorus sites (V). The isomorphous substitution including the replacement mechanism was studied by not only the change of unit cell parameters but also spectroscopic analysis. The unit cell parameters of TMI-VSB-5 including a unit cell volume and a-axis length relied on the ionic radii difference between the incorporated ion and the original framework ions such as Ni or P (RTMI - RNi or RTMI - RP).     

In Situ Observation of Successive Crystallizations and Metastable Intermediates in the Formation of Metal–Organic Frameworks

Understanding the driving forces controlling crystallization is essential for the efficient synthesis and design of new materials, particularly metal–organic frameworks (MOFs), where mild solvothermal synthesis often allows access to various phases from the same reagents. Using high‐energy in situ synchrotron X‐ray powder diffraction, we monitor the crystallization of lithium tartrate MOFs, observing the successive crystallization and dissolution of three competing phases in one reaction. By determining rate constants and activation energies, we fully quantify the reaction energy landscape, gaining important predictive power for the choice of reaction conditions. Different reaction rates are explained by the structural relationships between the products and the reactants; larger changes in conformation result in higher activation energies. The methods we demonstrate can easily be applied to other materials, opening the door to a greater understanding of crystallization in general.     

Polytypism, homochirality, interpenetration, and hydrogen-bonding in transition metal (Mn(II), Ni(II), Cu(II), Zn(II)) 5-hydroxyisophthalate coordination polymers containing 4,4'-bipyridyl

We report the synthesis of five coordination polymers of divalent transition metals combined with 5-hydroxyisophthalic acid (HIP) and 4,4'-bipyridyl (bipy). Mn forms two polytypic two-dimensional coordination polymers, Mn(HIP)(bipy).3H(2)O and Mn(HIP)(bipy).(1/4)bipy.2H(2)O (I and II, with ABAB and ABC stacking sequences, respectively); Ni forms a chiral hexagonal three-dimensional coordination polymer with two interpenetrating trigonal sublattices exhibiting the "dual quartz" topology, Ni(HIP)(bipy)(H(2)O) (III); Cu forms a one-dimensional coordination polymer containing arrays of infinite hydrogen-bonded molecular ribbons, Cu(HIP)(2)(bipy) (IV); and Zn forms a two-dimensional coordination polymer with a stair-stepped layered structure, Zn(2)(HIP)(2)(bipy)(H(2)O)(2).H(2)O (V). The M-HIP-M connections are perpendicular to the M-bipy-M connections in all structures where they are present.     

Formation of unsaturated C3 hydrocarbons by the protolysis of magnesium sesquicarbide with ammonium halides

The protolysis of magnesium sesquicarbide, Mg2C3, with inorganic acids provides an interesting alternative to the more common hydrolysis of ionic carbides for obtaining their respective hydrocarbons. In particular, protolysis reactions with ammonium halides as precursors for hydrogen halides were investigated using in situ methods such as TGA/sDTA/MS and high-temperature XRPD. The protolysis reactions with NH4F and NH4Cl revealed two different reaction mechanisms yielding C3H4 and the respective magnesium halides as expected products. In the case of NH4Cl, intermediate phases that have not been previously observed, specificly (NH4)2MgCl4 (I4/mmm) and two modifications of NH4MgCl3 (P63/mmc), were structurally characterized.     

Manganese Tetraboride,MnB4: High‐Temperature Crystal Structure,p–n Transition, 55Mn NMR Spectroscopy,Solid Solutions,and Mechanical Properties

The structural and electronic properties of MnB₄ were studied by high‐temperature powder X‐ray diffraction and measurements of the conductivity and Seebeck coefficient on spark‐plasma‐sintered samples. A transition from the room‐temperature monoclinic structure (space group P2₁/c) to a high‐temperature orthorhombic structure (space group Pnnm) was observed at about 650 K. The material remained semiconducting after the transition, but its behavior changed from p‐type to n‐type. ⁵⁵Mn NMR measurements revealed an isotropic chemical shift of ?1315 ppm, confirming an oxidation state of Mn close to I. Solid solutions of Cr_1?xMn_xB₄ (two phases in space groups Pnnm and P2₁/c) were synthesized for the first time. In addition, nanoindentation studies yielded values of (496±26) and (25.3±1.7) GPa for the Young’s modulus and hardness, respectively, compared to values of 530 and 37 GPa obtained by DFT calculations.