Proton-Conducting Cobalt(II) 3D MOFs Incorporating Bis(imidazole) and Polycarboxylate Linkages: Framework Topology and Interpenetration

Metal-organic frameworks are potential proton-conducting electrolytes for proton-exchange membrane fuel cells. Two such new cobalt complexes, namely [Co-2(dip)(2)(obb)(2)]center dot 2H(2)O (1) and [Co-2(dip)(2)(btec)(H2O)]center dot 3H(2)O (2), incorporating an N-donor ligand (dip) and polycarboxylate-based ligands (obb and btec) were prepared from hydrothermal syntheses. As elucidated by X-ray crystallography, their 3D frameworks contain extensive H-bonding networks. Compound 1 possesses a 3-fold interpenetrated cag framework, whereas compound 2 consists of [Co-2(O)(COO)(2)](n) cluster chains, which are connected by 2-connected btec and dip ligands. The proton conduction for both compounds has been appraised by AC impedance with relative humidity (33-98%) and temperature variation (25-80 degrees C). The proton conductivity values of 1 span between 7.01 x 10(-7) and 4.28 x 10(-9) S cm(-1) with 98% RH (relative humidity) at 25-85 degrees C. In contrast, compound 2 displays a significant proton conductivity of 9.56 x 10(-5) S cm(-1) at 65 degrees C under 98% RH.

Automated summary

Metal-organic frameworks incorporating N-donor and polycarboxylate-based ligands were synthesized and shown to exhibit good proton conductivity properties.