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.     

Host-guest interactions at self-assembled monolayers of cyclodextrins on gold

We have developed synthesis routes for the introduction of short and long dialkylsulfides onto the primary side of alpha-, beta-, and gamma-cyclodextrins. Monolayers of these cyclodextrin adsorbates were characterized by electrochemistry, wettability studies, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and atomic force microscopy (AFM). The differences in thickness and polarity of the outerface of the monolayers were measured by electro-chemistry and wettability studies. On average about 70% of the sulfide moieties were used for binding to the gold, as measured by XPS. Tof-SIMS measurements showed that the cyclodextrin adsorbates adsorb without any bond breakage. AFM measurements revealed for beta-cyclodextrin monolayers a quasi-hexagonal lattice with a lattice constant of 20.6 A, which matches the geometrical size of the adsorbate. The alpha-cyclodextrin and gamma-cyclodextrin monolayers are less ordered. Interactions of the anionic guests 1-anilinonaphthalene-8-sulfonic acid (1,8-ANS) and 2-(p-toluidinyl)naphthalene-6-sulfonic acid (2,6-TNS) and the highly ordered monolayers of heptapodant beta-cyclodextrin adsorbates were studied by surface plasmon resonance (SPR) and electrochemical impedance spectroscopy. The SPR measurements clearly showed interactions between a beta-cyclodextrin monolayer and 1,8-ANS. Electrochemical impedance spectroscopy measurements gave high responses even at low guest concentrations (< or = 5 microM). The association constant for the binding of 1,8-ANS (K = 289,000 +/- 13,000M-1) is considerably higher than the corresponding value in solution. (Partial) methylation of the secondary side of the beta-cyclodextrin strongly decreases the binding.     

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.