High-Pressure ¹²⁹Xe NMR Study of Xenon Confined in the Nanochannels of Solid (±)-[Co(en)₃]Cl₃

Abstract

High-pressure 129 Xe NMR measurements were carried out on dehydrated (()-[Co(en) 3 ]Cl 3 to investigate the pore size as well as the local structure about the confined xenon atoms. At xenon gas pressures of 0.3 MPa, the xenon chemical shift was orientation dependent, exhibiting an axially symmetric powder pattern with δ 11 ) 280 ppm and δ 22 ) δ 33 ) 180 ppm. Proton to 129 Xe cross-polarization (CP) experiments selectively enhanced the portion of the powder pattern corresponding to δ 22 ) δ 33 ) δ ⊥ , confirming that the unique component of the chemical shift tensor, δ 11 ) δ | , lies along the pore axis. The isotropic chemical shift δ iso at the zero pressure limit was found to be 212 ppm, and suggested a pore diameter of approximately 0.47 nm. This agrees well with the diameter of 0.44 nm estimated from the crystal structure. On increasing the pressure to 6.5 MPa, δ ⊥ increased from 180 to 220 ppm, whereas δ | was found to be almost independent of pressure. The increase in δ ⊥ with pressure is attributed to Xe-Xe interactions. The paramagnetic shift in the xenon chemical tensor component perpendicular to the nanochannels with increasing pressure is in accord with the recent theoretical predictions of Jameson and de Dios (J.

Xe NMR lineshapes in channels of peptide molecular crystals

“…Such lineshapes have been observed experimentally in 1D channels in various crystalline materials (20)(21)(22)(23), with the observed lineshape varying with changing Xe occupancy within the channel. A theoretical understanding, using the dimer tensor model in grand canonical Monte Carlo (GCMC) simulations (24), permits the prediction of the average Xe chemical shift tensor and the lineshapes that are observed in the Xe NMR spectrum of a polycrystalline sample (24,25) or of a single crystal (26), with no adjustable parameters.…”

Observation of Single‐File Diffusion in Dipeptide Nanotubes by Continuous‐Flow Hyperpolarized Xenon‐129 NMR Spectroscopy

“…[24][25][26][27][28][29][30] Its large chemical shift range allows the adsorbed phase to be distinguished from the free gas, and reveals interactions with the channel interiors and other Xe atoms. l-Alanyl-l-valine (AV) can form hydrophobic crystalline channel structures with interior walls lined with CH 3 groups [31] and an inner diameter of 5.13 , which is just slightly larger than the 4.5 van der Waals diameter of Xe atom.…”

Intermolecular Interactions of Xe Atoms Confined in One-dimensional Nanochannels of Tris(o-phenylenedioxy)cyclotriphosphazene as Studied by High-pressure 129Xe NMR

“…That is, δ ⊥ is mainly attributed to the Xe-Xe collision interactions as described above. In contrast, δ increases by at least 30 ppm, but the increment of δ is much larger than that in AlPO-11 [28] and (±)-[Co(en) 3 ]Cl 3 [15], in which δ changes only slightly after increasing the xenon loading. The pressure dependence of δ implies that the Xe-Xe interaction as well as the Xe-wall interaction should be attributed to δ .…”

“…This technique has been used to characterize the free volumes of synthetic polymers with high equilibrium pressure [11]. It has also been used to investigate the pore size and local structure around the xenon atoms confined in dehydrated (±)-[Co(en) 3 ]Cl 3 [15]. In our previous studies we have clarified that Xe confined in a dehydrated (±)-[Co(en) 3 ]Cl 3 crystal exhibits an axially symmetric chemical shift tensor [15].…”

“…It has also been used to investigate the pore size and local structure around the xenon atoms confined in dehydrated (±)-[Co(en) 3 ]Cl 3 [15]. In our previous studies we have clarified that Xe confined in a dehydrated (±)-[Co(en) 3 ]Cl 3 crystal exhibits an axially symmetric chemical shift tensor [15]. Furthermore, it is found that δ ⊥ increases with increase in pressure of xenon gas, whereas δ is almost independent of pressure, implying that δ ⊥ depends mainly on the xenon density, whereas δ is principally independent of the xenon density.…”