Fast Interchange of Coordinated and Guest Dimethylformamide Molecules in the Zinc(II) Lactate Terephthalate Metal–Organic Framework

Mobility of <i>N</i>,<i>N</i>-dimethylformamide (dmf) molecules in a homochiral metal–organic framework [Zn₂(bdc)­(<i>S</i>-lac)­(dmf)]·dmf (bdc = 1,4-benzenedicarboxylate; <i>S</i>-lac = <i>L</i>-(−)-lactate) has been studied using ¹³C, ¹H, and ²H solid-state NMR and DSC experiments. The compound exhibits a phase transition in the vicinity of 240 K, associated with disordering of the dmf molecules. In the high-temperature phase, the dmf molecules undergo intense diffusion accompanied by the exchange between the molecules coordinated with Zn and guest molecules in the framework pores. The activation energy of the molecular migration including exchange between coordinated and guest molecules was estimated to be 37 kJ/mol

High Proton Conductivity and Spectroscopic Investigations of Metal–Organic Framework Materials Impregnated by Strong Acids

Strong toluenesulfonic and triflic acids were incorporated into a MIL-101 chromium­(III) terephthalate coordination framework, producing hybrid proton-conducting solid electrolytes. These acid@MIL hybrid materials possess stable crystalline structures that do not deteriorate during multiple measurements or prolonged heating. Particularly, the triflic-containing compound demonstrates the highest 0.08 S cm^–1 proton conductivity at 15% relative humidity and a temperature of 60 °C, exceeding any of today’s commercial materials for proton-exchange membranes. The structure of the proton-conducting media, as well as the long-range proton-transfer mechanics, was unveiled, in a certain respect, by Fourier transform infrared and ¹H NMR spectroscopy investigations. The acidic media presumably constitutes large separated droplets, coexisting in the MIL nanocages. One component of proton transfer appears to be related to the facile relay (Grotthuss) mechanism through extensive hydrogen-bonding interactions within such droplets. The second component occurs during continuous reorganization of the droplets, thus ensuring long-range proton transfer along the porous structure of the material