Monitoring adsorption-induced switching by 129Xe NMR spectroscopy in a new metal–organic framework Ni2(2,6-ndc)2(dabco)

Abstract

The synthesis and structure of a new flexible metal-organic framework Ni(2)(2,6-ndc)(2)(dabco) (DUT-8(Ni), DUT = Dresden University of Technology, 2,6-ndc = 2,6-naphthalenedicarboxylate, dabco = 1,4-diazabicyclo[2.2.2]octane) as well as its characterization by gas adsorption and (129)Xe NMR spectroscopy is described. The compound shows reversible structural transformation without loss of crystallinity upon solvent removal and physisorption of several gases. Xenon adsorption studies combined with (129)Xe NMR spectroscopy turn out to be favorable methods for the detection and characterization of the so-called "gate-pressure" effect in this novel MOF material. The linewidth and chemical shift of the (129)Xe NMR signal are shown to be very sensitive parameters for the detection of this structural transition from a narrow pore system with low porosity to a wide pore state. The transition and threshold temperature is clearly detected.

Tolerance of Flexible MOFs toward Repeated Adsorption Stress

“…The syntheses of MIL-53(Al), 18 DUT-8(Ni), 19 pre-ELM-11, 20 and SNU-9 21 were performed according to published procedures. SNU-9 was synthesized in the 120 mL Schott flask, but the synthesis was scaled up 10-fold.…”

Raman spectroscopy studies of the terahertz vibrational modes of a DUT-8 (Ni) metal–organic framework

“…22 The atoms are located in the 8g Wyckoff position. The Raman mode representation in the hexagonal phase at the Brillouin zone center is as follows:…”

“…22,23 The peculiarity of this MOF is that it can be synthesized in ''rigid'' and ''flexible'' forms, depending on the synthetic conditions. 24 The rigid version (DUT-8(Ni)_rigid), consisting of nano sized crystallites, can be desolvated without any phase transition and shows a typical ''Type Ia'' nitrogen physisorption isotherm at 77 K. In contrast, the flexible form (DUT-8(Ni)_flex), crystalized as macro crystals, undergoes a transformation into a closed phase (cp) upon desolvation and can be reversibly transformed into the open phase (op) by adsorption of gases or liquids.…”

Solid-State NMR Spectroscopy of Metal–Organic Framework Compounds (MOFs)

“…In those cases, adsorption of molecules within the resulting pore system is possible. In contrast to the mostly rigid structures of traditional porous materials, some MOFs, e.g., Material Institut Lavoisier-53 (MIL-53, [22]), Dresden University of Technology-8 (DUT-8(Ni), or DUT-8(Co), [23,24]), exhibit a flexible network and show reversible structural transformations during the adsorption/desorption of several gases such as nitrogen, carbon dioxide, or xenon.…”

“…Schematic representation of the metal–organic frameworks (MOF lattice (here: DUT-8(Ni) [23]), consisting of organic linkers and inorganic secondary building units (SBUs). The MOF serves as a host structure for guests such as 129 Xe within the void spaces.…”