Poster Abstracts - 2010
Silica-based mesoporous materials
Changchang Liu, Yale University
In this study, silica-based mesoporous materials (the M41S family mesoporous molecular sieves) are synthesized using alkyltrimethylammonium bromide with different chain lengths (CnH2n+1N(CH3)3Br, n = 10, 12, 14, 16) as templates. The resulting silica structures are characterized by X-ray diffraction and are found to exhibit the phase transformation from the hexagonal mesophase MCM-41 to the cubic mesophase MCM-48 with the space group of Ia3d. The structural phase transition in our study is proved to be controlled by the alkyl chain length of the surfactant. The amount of ethanol and the autoclaving time are also found to have an influence on the structural integrity, but only to a small extent. With an increased surfactant to silica ratio, the phase transformation can be shifted to the longer chain side.
Tris(hydroxypropyl)phosphine Oxide: A Chiral 3D Material
with Non-linear Optical Properties
Alec C. Durrell, Harry B. Gray, Nilay Hazari,* Christopher D. Incarvito, Jian Liu and Elsa C. Y. Yan, Yale University
The achiral C3v organic phosphine, tris(hydroxypropyl)phosphine oxide, crystallizes in the unusual chiral hexagonal space group P63. The structure is highly ordered because each phosphine oxide moiety forms three hydrogen bonds with adjacent hydroxy groups from three different molecules. The properties of the crystals and the presence of hydrogen bonding interactions were investigated using single crystal Raman spectroscopy. The crystals show non-linear optical properties and are capable of efficient second harmonic generation.
Half-sandwich Complexes of Iridium(III) as Highly Active Catalysts for Water Oxidation and Alcohol Activation.
Nathan D. Schley, James D. Blakemore, Christopher D. Incarvito, and Robert H. Crabtree, Yale University, Department of Chemistry
A series of cyclopentadieneyl and pentamethylcyclopentadieneyl iridium(III) half-sandwich complexes were prepared and studied by single-crystal X-ray diffraction. In recent work, these and related complexes have been shown to catalyze the oxidation of water with cerium(IV)ammonium nitrate, and the alkylation of amines with primary alcohols via a hydrogen transfer pathway. The apparent versatility of half-sandwich iridium complexes as catalysts for these transformations prompted studies of activity and structure in which X-ray crystallography played an important role in elucidating molecular
structure and guiding experimental design.
Vitamin B12 crystallography: new thoughts on an old field.
Nadia Marino, Amy E. Rabideau and Robert P. Doyle, Department of Chemistry, Syracuse University, Syracuse, NY 13244-4100, USA.
In the course of experiments concerning our ongoing project on vitamin B12 (CNCbl) bioconjugates for drug-delivery purposes, we observed the formation of well-shaped red parallelepipeds from a concentrated water solution containing the HPLC-purified vitamin. The X-ray structural investigation (MoKα) at 98 K on these crystals reveals the occurrence of a vitamin B12-TFA adduct, which crystallizes in the standard orthorhombic P212121 space group with formula [CNCbl(H)](TFAc)·14H2O (1, TFAc = trifluoracetate anion). The final full-matrix least squares refinements on F2 converges with R1 = 4.1% for the 18957 significant reflections, one of the lowest crystallographic residuals achieved so far for cobalamins. In this work, the crystal structure of 1 is compared with that of different others CN-cobalamins reported in the literature. Although the cobalt(III) coordination sphere in these structures is similar, differences are found in the upward fold angle of the corrin macrocycle, a parameter that so far has been often related to the steric hindrance of the α-axial base. Here, we attempt to explore the effect of crystal packing forces on the corrin conformation basing upon structural data. Concepts like trans or cis influence as well as the distribution of cobalamins structures in clusters with similar packing are re-investigated and discussed.
Magnetically aligned soft mesophases for applications in templated synthesis and ionic
Pawel Majewski, Yale University
We present a diamagnetic interactions-based approach to impose long range order in self-assembled soft materials. We discuss two chemically different systems which have been successfully aligned with the use of a magnetic field. The orientation and the degree of alignment are quantified by the analysis of two dimensional small-angle X-ray scattering patterns (2D SAXS), polarized optical microscopy (POM) and electrical impedance spectroscopy (EIS). In a lamellar surfactant-water system, the method which we term "rotational annealing," is used to obtain highly ordered structure which can be further utilized as a template for nanomaterials synthesis. Our second system is a Li ion-conducting block copolymer. In this material hexagonally closed-packed PEO domains are embedded in a non-conducting liquid crystalline matrix that is responsive to the field. Our technique allows us to control the orientation of PEO channels across the sample. The electrical conductivity of the samples with PEO domains aligned perpendicular to electrodes is an order of magnitude greater than for samples featuring randomly orientated domains.