Jacqueline M. Nicol

Cooperative Organization of Inorganic-Surfactant and Biomimetic Assemblies

A model that makes use of the cooperative organization of inorganic and organic molecular species into three dimensionally structured arrays is generalized for the synthesis of nanocomposite materials. In this model, the properties and structure of a system are determined by dynamic interplay among ion-pair inorganic and organic species, so that different phases can be readily obtained through small variations of controllable synthesis parameters, including mixture composition and temperature. Nucleation, growth, and phase transitions may be directed by the charge density, coordination, and steric requirements of the inorganic and organic species at the interface and not necessarily by a preformed structure. A specific example is presented in which organic molecules in the presence of multiply charged silicate oligomers self-assemble into silicatropic liquid crystals. The organization of these silicate-surfactant mesophases is investigated with and without interfacial silicate condensation to separate the effects of self-assembly from the kinetics of silicate polymerization.

The crystal structure of a new sodium zinc arsenate phase solved by “simulated annealing”

Abstract The framework structure of a new sodium zinc arsenate, produced by dehydration of the Na 6 (ZnAsO 4 ) 6 ·8 H 2 0 sodalite analog, has been solved by a simulated annealing method. This method utilizes typical tetrahedral-atom bonding schemes with possible space group and unit cell dimensions to randomly generate possible continuous frameworks and their calculated energies. The Rietveld refinement of the Na 6 (ZnAsO 4 ) 6 solution phase was initially performed on room temperature X-ray data and then continued on low-temperature constant wavelength neutron data. This sodium zinc phosphate is a hexagonal polycrystalline material: space group P6 3 (no. 173), with a = b =9.005 (2) A, c = 8.161 (2) A, a = β = 90°, γ = 120°, V = 573.1 A, and Z = 2, with R = 12.35% and R w = 9.76% for 2756 (CW neutron) powder data points. This tridymite structural analog undergoes a room-temperature transformation to the open-framework sodalite structure.

Fourier-transform infrared studies of copper-containing Y zeolites. Dehydration, reduction and the adsorption of ammonia

The reduction of CuII to CuI ions in partially CuII-exchanged zeolite Y by CO plus co-adsorbed NH3 has been studied (298–673 K) using Fouriertransform infrared spectroscopy. While the data are complex the formation of a variety of species including [Cu(NH3)]2+, [CuCO(NH3)n]+, NH+4 and hydrogen-bonded NH3 have been identified. The data indicate that at low temperature reduction by NH3 is dominant while at elevated temperature CO is a more important reducing agent.

Inelastic neutron scattering studies of the interaction of hydrogen with palladium black

Abstract Incoherent inelastic neutron scattering has been used to investigate the interaction of hydrogen with palladium black (a high-surface-area Pd powder). Vibrational spectra of chemisorbed hydrogen have been measured in the energy range 30–230 meV at 80 and 295 K. The dominant surface adsorption site of hydrogen has been identified by comparison of the vibrational frequencies and intensities provided by the scattering data with normal coordinate calculations for model structures of different geometries, force constants and bond lengths. The “best fit” to the data is obtained for surface adsorption sites of threefold symmetry. A vibrational feature observed at 58 meV, which is inconsistent with either surface or bulk PdH species, is assigned to hydrogen occupying subsurface sites of bulk-like octahedral symmetry.

Structural characterization of a dehydrated magnesium/sodium beryllophosphate faujasite phase

Abstract As part of the continuing project to study the ion-exchange capability of this new class of molecular sieves, the synthesis and characterization of a dehydrated magnesium-exchanged sodium beryllophosphate faujasite analog, Mg19Na58(BePO4)96 (MgBePOFAU), is described. The 14 K structure of this dehydrated framework has been determined by Rietveld profile analysis of constant wavelength neutron powder diffraction data. Further characterization includes t.g.a., 31P and 9Be MAS n.m.r., and FTi.r. MgBePOFAU is a face-centered cubic, crystallizing in space group Fd 3 (No. 203), with a = 23.2422 (8) A , V = 12555 (2) A 3 , and Z = 96, with Rp = 6.41% and Rwp = 8.28%. The framework consists of alternating BeO4 and PO4 tetrahedra. The negatively charged framework is charge-balanced by magnesium ions, whose sites have been found in the double six-ring (SI site) and by sodium ions found at the six-ring joining the β-cage and the supercage (SII site), with remaining sites probably in the supercage. X-ray diffraction shows that the framework is stable to dehydration under vacuum at 275°C and can be reversibly hydrated.

Chemisorbed hydrogen and hydrogenous molecules

Abstract Recent incoherent inelastic neutron scattering studies of hydrogen and hydrogenous molecules adsorbed on high-surface-area catalytic materials such as palladium and platinum black, Raney nickel and metal sulphides, are reviewed. Deuterium isotope dilution neutron spectroscopy of adsorbed hydrogen is exemplified as a probe of HH interactions on surfaces. These studies illustrate the utility of inelastic neutron scattering for studying the vibrational spectroscopy and chemical interactions of surface species.

Synthesis, characterization and inelastic neutron scattering spectra of hydrogen insertion compounds of the mixed VMo oxide V9Mo6O40

Abstract Hydrogen insertion compounds of V 9 Mo 6 O 40 have been synthesized and investigated using incoherent inelastic neutron scattering (IINS) vibrational spectroscopy. IINS spectra of H x V 9 Mo 6 O 40 (x=7.8 and 17.5) confirm that in both phases H is present as coordinated hydroxyl groups. There is no evidence for the presence of coordinated water in contrast to the hydrogen insertion compounds of MoO 3 and V 2 O 5 .

The adsorption of ethanal by some type A zeolites : a Fourier-transform infrared study

Infrared studies of the adsorption of ethanal by sodium-A, partially zinc-exchanged sodium-A and fully exchanged silver-A are reported. The complexes formed by the coordination of ethanal to the charge-compensating cations have been characterised by their ν(CO) values (Na+= 1713 cm–1, Zn2+= 1682 cm–1 and Ag+= 1681 cm–1). Interaction with both cation types occurs in the case of the partially Zn-exchanged A. Preliminary studies of the desorption behaviour at room and elevated temperatures are also reported.

Neutron scattering from films of pellicular zirconium phosphate

Neutron-scattering studies have been undertaken in the investigation of crystalline α-zirconium phosphate [Zr(HPO4)2·H2O, α-ZrP] and of films of pellicular zirconium phosphate (p-ZrP). In the inelastic neutron scattering (INS) spectra of p-ZrP films fewer peaks are observed than in the case of α-ZrP and intensities in the region 720–1120 cm–1(associated with acid phosphate groups) are orientation dependent. Quasielastic broadenings are observed in scattering spectra from p-ZrP films at 70 °C.

Inelastic Neutron Scattering Studies of Nonlinear Optical Materials: p-Nitroaniline Adsorbed in Alpo-5

Inelastic neutron scattering has been used to characterize the vibrational spectroscopy below 220 meV of para-nitroaniline adsorbed in the molecular sieve ALPO-5. Samples at loadings of both 3 and 13 weight %, which represent the onset of and the maximum in the nonlinear optical properties respectively, were studied. The torsional vibration of the amino (NH 2 ) group has been identified at ca. 50 meV. The splitting and structure of this mode is sensitive to the loading level. This can be related to differences in the nature of the hydrogen bonding in these materials.