1 research outputs found
Sequential Hydrolysis of Metal Oxo Clusters Drives Polymorphism in Electrodeposited Zirconium Metal–Organic Frameworks
Over the past few decades, significant developments have been made
in the electrodeposition of
nanomaterials, mainly due to its streamlined process for producing
thin films which are deployed toward various catalysis applications.
Concurrently, advances in the electrodeposition of porous materials
such as metal–organic frameworks (MOFs) in the past decade
have aimed at optimizing their performance for gas storage and catalysis
applications. Despite being a relatively recent fabrication method,
electrodeposition of MOFs has seen success in only a few instances,
which is limited by the formation of unwanted oxide/hydroxide in the
metallic component during the linker attachment step. Some studies
have shown how to prevent these unwanted metal oxides/hydroxides by
controlling solution acidity (or pH) and temperature, resulting in
the successful demonstration of the electrochemical synthesis of a
subset of MOFs (paddlewheel-based Cu and Zn MOFs) on conductive substrates.
However, a comprehensive understanding of the electrochemical synthesis
pathway for these porous frameworks is still lacking. We address this
gap by presenting, for the first time, a detailed deprotonation mechanism
outlining the evolution of Zirconium (Zr) oxo cluster directing the
synthesis of porphyrin-based zirconium MOFs. These MOFs are known
to exhibit diverse polymorphic topologies that are influenced by modulator
type and concentrations. In this work, we show that applied current
can influence the polymorphic topologies of Zr MOF by varying local
cathodic pH. While synthesizing these MOFs electrochemically, the
modulator concentrations are maintained constant to demonstrate the
effect of applied current density and solution pKa leading to phase-pure polymorphs of MOF-525 at a higher
current density and PCN-222 at a lower current density. The density
functional theory calculations reveal that zirconium-oxo clusters
undergo sequential hydrolysis, with the pKa of the cluster dictating the extent of deprotonation. The degree
of deprotonation, in turn, determines the 12- and 8-connections in
MOF-525 and PCN-222, respectively. Finally, the study demonstrates
the robustness of the electrochemical protocol by applying it to pyrene-
and tricarboxylic-linker-based Zirconium MOFs