Pt electrodes enable the formation of μ₄-O Centers in MOF-5 from multiple oxygen sources

The μ₄-O^2- 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.