Synthesis and Structural Characterization of a 3-D Lithium Based Metal−Organic Framework Showing Dynamic Structural Behavior

A 3-D lithium based metal organic framework Li2(C7H3NO4)·(C3H7NO) [Li2(2,5-PDC)·(DMF), 1; ULMOF-5, UL= ultralight, PDC = pyridinedicarboxylate, space group Pbcn, a = 15.800(3) Å, b = 8.5958(17) Å, c = 18.460(4) Å, V = 2507.1(9) Å3] was synthesized using the solvothermal method and characterized by single crystal and powder X-ray diffraction techniques. Compound 1 contains tetrameric edge and corner sharing lithium polyhedral clusters connected by organic linkers, forming channels along the [001] direction, with coordinated DMF molecules pointing toward each other in these channels. Thermogravimetric analysis shows compound 1 is stable up to 280 °C under N2 atmosphere followed by removal of the coordinated DMF molecules, as evident from the associated weight loss. BET (25.06 m2/g) surface area measurement showed loss of porosity after solvent removal because of a structure change. Solid-state 6Li NMR on the desolvated compound showed the absence of tricoordinated lithium centers, indicating rearrangement of bonds around the lithium center after DMF removal. The desolvated form reverts to the original form upon exposure to DMF, showing dynamic structural behavior.