Pt Electrodes Enable the Formation of μ4-O Centers in MOF-5 from Multiple Oxygen Sources.

The μ4-O2- ions in the Zn4O(O2C-)6 secondary building units of Zn4O(1,4-benzenedicarboxylate)3 (MOF-5) electrodeposited under cathodic bias can be sourced from nitrate, water, and molecular oxygen when using platinum gauze as working electrodes. The use of Zn(ClO4)2·6H2O, anhydrous Zn(NO3)2, or anhydrous Zn(CF3SO3)2 as Zn2+ sources under rigorous control of other sources of oxygen, including water and O2, confirm that the source of the μ4-O2- ions can be promiscuous. Although this finding reveals a relatively complicated manifold of electrochemical processes responsible for the crystallization of MOF-5 under cathodic bias, it further highlights the importance of hydroxide intermediates in the formation of the Zn4O(O2C-R) secondary building units in this iconic material and is illustrative of the complicated crystallization mechanisms of metal-organic frameworks in general.