Long and Local Range Structural Changes in M[(bdc)(ted)0.5] (M = Zn, Ni or Cu) Metal Organic Frameworks Upon Spontaneous Thermal Dispersion of LiCl and Adsorption of Carbon Dioxide.
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Impregnation and thermal dispersion of LiCl were performed onto M(bdc)(ted)0.5 (M = Zn, Ni or Cu) metal-organic frameworks (MOFs). X-ray diffraction (XRD) indicated that LiCl was homogeneously dispersed into the pore channels of the Zn and Ni variants. A displacement of the peaks related to the diffraction planes (110), (002), (200) and (220) suggests that the structures suffer an expansion/contraction process. However, for Cu(bdc)(ted)0.5 the data revealed a remarkable loss in crystallinity. 13C cross-polarization magic angle spinning nuclear magnetic resonance (13C CPMAS NMR) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy suggests a LiCl location near the secondary building unit of the Zn based MOF while Raman spectroscopy shows what appears to be a band corresponding to the formation of a Zn–Cl bond. X-ray photoelectron spectroscopy (XPS) data gathered for the Cu variant exhibited a shift in binding energy in the 2p3 line probably related to a change in the metal node valence from cupric to cuprous. When combined with the 13C CPMAS NMR, DRIFT and Raman data, this observation suggests destruction of the Cu(bdc)(ted)0.5 framework plausibly due to the formation of a CuCN·LiCl complex. Adsorption–desorption of CO2 onto the LiCl and apohost M(bdc)(ted)0.5 (M = Zn or Ni) also resulted in structural changes. A significant hysteresis was observed in the case of (LiCl)[Zn(bdc)(ted)0.5]. In addition, different equilibration time intervals revealed what appears to be a multi-domain or pseudo equilibrium process, involving structural changes characterized by time-scales larger in comparison to those required for adsorption–desorption equilibrium.
