Abstract
DMOF-1 (Zn-2(bdc)(2)dabco) is a metal-organic framework with tetragonal symmetry. It contains parallel one-dimensional channels with a diameter of about 0.75 nm interconnected by smaller windows.
For carbon dioxide adsorbed in the nanochannels the chemical shift tensor and the diffusion tensor were investigated by C-13 NMR. The spectra acquired under static conditions reveal a powder pattern with a residual chemical shift anisotropy of = -55 ppm.
The collinearity of the axisymmetrical residual chemical shift and the diffusion tensors was utilized to assess the diffusion anisotropy via the diffusion attenuation of the C-13 PFG NMR powder pattern. The results show that carbon dioxide is highly mobile in DMOF-1.
The apparent diffusion coefficient (the trace of diffusion tensor) is (6.2 +/- 1.0) x 10(-9) m(2) s(-1) at 298 K and the corresponding anisotropy expressed as D-parallel to/D-perpendicular to is approximately equal to 3. (C) 2014 Elsevier Inc. All rights reserved.