@article {4813,
	title = {Solid-state NMR and X-ray diffraction structural investigations of the p-nitroaniline/ZSM-5 complex},
	journal = {Microporous and Mesoporous Materials},
	volume = {39},
	number = {1-2},
	year = {2000},
	note = {ISI Document Delivery No.: 354ZKTimes Cited: 15Cited Reference Count: 19},
	month = {Sep},
	pages = {291-305},
	type = {Article},
	abstract = {The complex of zeolite ZSM-5 loaded with p-nitroaniline to four molecules per unit cell is of current interest as a potential non-linear optical material. A previous single crystal X-ray diffraction (XRD) investigation has claimed that the p-nitroaniline molecules line up as oriented dipole chains inside the channels of ZSM-5, and it was concluded that this ordering explains how second harmonic generation arises. In another XRD study, it was not possible to distinguish between order and disorder of the p-nitroaniline molecules. The present results from solid-state NMR and single crystal XRD experiments indicate that the p-nitroaniline molecules are disordered in the ZSM-5 channels, i.e., they do not form ordered dipole chains throughout the entire crystal. The quantitative Si-29-MAS spectrum at room temperature shows 48 peaks of equal intensity indicating disorder of the guest molecules, and the N-15-MAS spectrum at 180 K of the N-15-labeled p-nitroaniline in ZSM-5 shows a splitting of the NO2 resonance, which also implies disorder. The single crystal XRD results show that the p-nitroaniline molecules are disordered over four-sites at the channel intersection even when refined in the less symmetric Pn2(l)a space group. The final structure was refined in the orthorhombic Pnma space group to R = 0.0465. The nature of this disorder is discussed. In particular, the possibilities of disorder arising from the average of polar domains or local disorder are examined in the light of the solid-state NMR results. That the p-nitroaniline molecules are disordered in ZSM-5 implies that the mechanism by which second harmonic generation arises may be more complex than is presently assumed. (C) 2000 Elsevier Science B.V. All rights reserved.},
	keywords = {CRYSTAL STRUCTURE-ANALYSIS, DICHLOROBENZENE, harmonic generation, LOCATION, MFI, MOLECULAR-SIEVE, p-nitroaniline, second, SINGLE-CRYSTAL, SOLID-STATE NMR, x-ray diffraction, ZEOLITE H-ZSM-5, ZSM-5},
	isbn = {1387-1811},
	url = {<Go to ISI>://000089361000029},
	author = {Fyfe, C. A. and Brouwer, D. H.}
}
@article {3979,
	title = {F-19/Si-29 distance determinations in fluoride-containing octadecasil from solid-state NMR measurements},
	journal = {Journal of the American Chemical Society},
	volume = {119},
	number = {50},
	year = {1997},
	note = {ISI Document Delivery No.: YN229Times Cited: 48Cited Reference Count: 76},
	month = {Dec},
	pages = {12210-12222},
	type = {Article},
	abstract = {In the present work we report results from CP, REDOR, and TEDOR NMR experiments carried out to locate the fluoride anions within the three-dimensional framework of the silicate octadecasil. Accurate Si-F distances were obtained-through measurements of the F-19/Si-29 dipolar couplings from these experiments. Weighted, nonlinear least-squares fittings of the REDOR and TEDOR data for the silicons in the D4R units gave an average value of D = 1150 +/- 50 Hz from which the Si-F interatomic distance was calculated to be 2.69 +/- 0.04 Angstrom. This distance is in excellent agreement with the value of 2.63 Angstrom reported from the X-ray determined single crystal structure-and confirms that the F- anions are located inside the D4R units. Calculations and fittings of the REDOR and TEDOR data for the silicons not in the D4R gave = 120 +/- 20 Hz when the specific geometrical (tetrahedral) arrangement of the multiple equivalent fluoride anions surrounding the Si nuclei in these T-2 sites was taken into account. This yields a Si-F distance of 5.7 +/- 0.4 Angstrom, compared to the value 5.69 Angstrom obtained from the diffraction measurements. Factors influencing the selection of the optimum experiments to perform in different situations and the dependence of the results on experimental variables are discussed. These studies clearly establish the viability and reliability of F-19/Si-29 REDOR and TEDOR NMR experiments to obtain distance information which can be used to determine the precise location of fluorine-containing species within such framework structures or in suitable cases to assist in the determination of the framework structure itself where it is unknown.},
	keywords = {3-DIMENSIONAL LATTICE CONNECTIVITIES, CROSS-POLARIZATION, CRYSTAL-STRUCTURE, DOUBLE-RESONANCE NMR, INTERATOMIC DISTANCE, MICROPOROUS, MOLECULAR-SIEVE, P-DICHLOROBENZENE, ROTATIONAL-ECHO, SINGLE-CRYSTAL, SOLIDS},
	isbn = {0002-7863},
	url = {<Go to ISI>://000071146000024},
	author = {Fyfe, C. A. and Lewis, A. R. and Chezeau, J. M. and Grondey, H.}
}
