화학공학소재연구정보센터
Journal of Physical Chemistry B, Vol.107, No.1, 180-185, 2003
High-pressure Xe-129 NMR study of xenon confined in the nanochannels of solid (+/-)-[Co(en)(3)]Cl-3
High-pressure Xe-129 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 delta(11) = 280 ppm and delta(22) = delta(33) = 180 ppm. Proton to Xe-129 cross-polarization (CP) experiments selectively enhanced the portion of the powder pattern corresponding to delta(22) = delta(33) = delta(perpendicular to), confirming that the unique component of the chemical shift tensor, delta(11) = delta(parallel to), lies along the pore axis. The isotropic chemical shift delta(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, delta(perpendicular to) increased from 180 to 220 ppm, whereas delta(parallel to) was found to be almost independent of pressure. The increase in delta(perpendicular to) 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.