Tuning the Electrical Conductivity of Bimetallic Co-Mn-Based MOFs via Precisely Regulating the Atomic Content of Metal Centers and Study on Their Dye Adsorption Properties.

Abstract

Conductive metal organic frameworks (MOFs) are considered as next-generation conducting materials. However, imparting conductivity to this class of materials faces significant challenges owing to their inherently insulating nature. Therefore, herein, a series of isostructural conductive bimetallic MOFs with the structural formula {[(CH3)2NH2][MnxCoy(HCOO)6]} (x = 1, y = 0.2-3.32) were developed. Decomposition of dimethylformamide under solvothermal conditions resulted in a formate ligand and dimethylammonium (DMA) cations, responsible for construction of MOFs and proton conductivity, respectively. The conductivity was also attributed to electron flow through the metal-ligand bonds. MOF1 with a 1:1 Mn/Co ratio showed conductivity as high as 19.73 S cm-1 at 25 °C. Notably, the conductivity may be tuned via regulating the metal content; varying the Mn/Co ratio from 1:0.20 to 1:3.32 resulted in MOFs with conductivities from 0.08 to 19.73 S cm-1 at 25 °C. Even after removal of DMA molecules from pores, the conductivities of the MOFs were impressive owing to the enhanced electron density difference between the metal centers as a result of oxidation of Co2+ to maintain the charge neutrality of the framework. Additionally, the MOFs were found to be effective adsorbents of anionic dyes such as methyl blue owing to the presence of positively charged guests in the pores and free electrons in the frameworks.