Pt Electrodes Enable the Formation of μ[subscript 4]-O Centers in MOF-5 from Multiple Oxygen Sources

Abstract

The μ[subscript 4]-O[superscript 2]– ions in the Zn[subscript 4]O(O[subscript 2]C−)[subscript 6] secondary building units of Zn[subscript 4]O(1,4-benzenedicarboxylate)[subscript 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(ClO[subscript 4])[subscript 2]·6H[subscript 2]O, anhydrous Zn(NO[subscript 3])[subscript 2], or anhydrous Zn(CF[subscript 3]SO[subscript 3])[subscript 2] as Zn2[superscript +] sources under rigorous control of other sources of oxygen, including water and O[subscript 2], 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 Zn[subscript 4]O(O[subscript 2]C–R) secondary building units in this iconic material and is illustrative of the complicated crystallization mechanisms of metal–organic frameworks in general. Keywords: crystals; electrochemistry; electrodeposition; mechanism of reactions; metal−organic frameworks