Flexible side arms of ditopic linker as effective tools to boost proton conductivity of Ni_(8)-pyrazolate metal-organic framework

摘要

Two primitive metal-organic frameworks(MOFs),Ni L1 and Ni L2,based on Ni_(8)O_(6)-cluster and ditopic pyrazolate linkers,L1(with rigid alkyne arms)and L2(with flexible alkyne chains),were prepared.The proton conductivities of these MOFs in pristine form and imidazole-encapsulated forms,Im@Ni L1 and Im@Ni L2,were measured and compared.Upon introduction of imidazole molecules,the proton conductivity could be increased by 3 to 5 orders of magnitude and reached as high as 1.72×10^(-2)S/cm(at 98%RH and 80℃).Also,whether imidazole molecules were introduced or not,Ni_(8)O_(6)-based MOFs with L2 in general gave better proton conductivity than those with L1 signifying that flexible side arms indeed assist proton conduction probably via establishment of efficient proton-conducting channels along with formation of highly ordered domains of water/imidazole molecules within the network cavities.Beyond the active Ni_(8)O_(6)-cluster,tuning flexibility of linker pendants serves as an alternative approach to regulate/modulate the proton conductivity of MOFs.