@article {1115,
	title = {Solid state NMR method for the determination of 3D zeolite framework/sorbate structures: H-1/Si-29 CP MAS NMR study of the high-loaded form of p-xylene in ZSM-5 and determination of the unknown structure of the low-loaded form},
	journal = {Journal of the American Chemical Society},
	volume = {127},
	number = {20},
	year = {2005},
	note = {ISI Document Delivery No.: 928AXTimes Cited: 22Cited Reference Count: 57},
	month = {May},
	pages = {7543-7558},
	type = {Article},
	abstract = {A general protocol is described for structure determinations of organic sorbate-zeolite complexes based on the selective, through-space, distance-dependent transfer of magnetization from protons in selectively deuterated organics to framework silicon nuclei. The method was developed using the known structure of the high-loaded ZSM-5/p-xylene complex containing p-xylene-d(6) or p-xylene-d(4). It was then applied to determine the unknown structure of the low-loaded ZSM-5/p-xylene complex using NMR alone. For the high-loaded complex improved data were obtained below 273 K, where slow motions and exchange processes of the p-xylene are eliminated. The general approach was validated by. the exact agreement of the experimental H-1-Si-29 CPMAS spectra obtained at a specific contact time and the complete 24-line spectra simulated using 1/T-CP vs M-2 correlations from only the six clearly resolved resonances. For the low-loaded complex the Si-29 resonances were assigned at 267 K, and variable contact time CP experiments were carried out between 243 and 173 K using the same specifically deuterated p-xylenes. All possible locations and orientations of the p-xylene guests were sampled, and those solutions that gave acceptable linear 1/T-CP vs M-2 correlations were selected. The optimum p-xylene location in this temperature range was determined to be in the channel intersection with the long molecular axis parallel to [0,1,0] (ring center fractional coordinates {-0.009, 0.250, 0.541}) with the ring plane oriented at an angle of 30 +/- 3 degrees about the crystallographic b axis. A subsequent single-crystal X-ray study confirmed this predicted structure.},
	keywords = {3-DIMENSIONAL BONDING CONNECTIVITIES, CROSS-POLARIZATION, CRYSTAL STRUCTURE-ANALYSIS, LATTICE, MAGIC-ANGLE, NATURAL-ABUNDANCE, NUCLEAR-MAGNETIC-RESONANCE, PROTON-ENHANCED NMR, SINGLE-CRYSTAL, SPINNING NMR, structures},
	isbn = {0002-7863},
	url = {<Go to ISI>://000229244600061},
	author = {Fyfe, C. A. and Diaz, A. C. and Grondey, H. and Lewis, A. R. and Forster, H.}
}
@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.}
}
