A Preinstalled Protic Cation as a Switch for Superprotonic Conduction in a Metal–Organic Framework

Metal–organic
frameworks (MOFs), made from various metal
nodes and organic linkers, provide diverse research platforms for
proton conduction. Here, we report on the superprotonic conduction
of a Pt dimer based MOF, [Pt2(MPC)4Cl2Co­(DMA)­(HDMA)·guest] (H2MPC, 6-mercaptopyridine-3-carboxylic
acid; DMA, dimethylamine). In this framework, a protic dimethylammonium
cation (HDMA+) is trapped inside a pore through hydrogen
bonding with an MPC ligand. Proton conductivity and X-ray measurements
revealed that trapped HDMA+ works as a preinstalled switch,
where HDMA+ changes its relative position and forms an
effective proton-conducting pathway upon hydration, resulting in more
than 105 times higher proton conductivity in comparison
to that of the dehydrated form. Moreover, the anisotropy of single-crystal
proton conductivity reveals the proton-conducting direction within
the crystal. The present results offer insights into functional materials
having a strong coupling of molecular dynamic motion and transport
properties.

金属-有机框架（MOFs），由多种金属节点和有机连接体构成，为质子传导研究提供了多元化的平台。本研究报道了一种基于Pt二聚体的超质子传导MOF，[Pt2(MPC)4Cl2Co-(DMA)-(HDMA)·guest]（H2MPC，6-巯基吡啶-3-羧酸；DMA，二甲基胺）。在此框架中，通过质子键与MPC配体的相互作用，质子化的二甲基铵阳离子（HDMA+）被捕获于孔隙之中。质子传导性和X射线测量结果表明，捕获的HDMA+充当预装开关，在水分子的作用下，HDMA+改变其相对位置，形成有效的质子传导途径，与脱水形式相比，其质子传导率提高了超过105倍。此外，单晶质子传导各向异性揭示了晶体内部的质子传导方向。本研究结果为分子动力学运动与传输性能强烈耦合的功能材料提供了新的见解。