Electroreduction-Driven Formation and Connectivity of Polyoxometalate Coordination Networks

Area of Science:

• Inorganic Chemistry
• Materials Science
• Electrochemistry

Background:

• Preyssler-type polyoxoanions, such as [NaP5W30O110]14- and [NaP5MoW29O110]14-, are versatile building blocks for coordination networks.
• Metal-aquo complexes ([M(H2O)n]m+, where M = Co2+, Ni2+, Zn2+, Y3+) can serve as bridging ligands in the construction of extended structures.

Purpose of the Study:

• To synthesize novel metal oxide coordination networks using Preyssler-type polyoxoanions and various metal-aquo complexes.
• To investigate the structural characteristics and the role of electrochemical reduction in the formation of these networks.
• To explore the impact of different metal ions (first-row transition metals and Y3+) on the resulting network structures.

Main Methods:

• Electrochemical reduction was employed to induce the formation of coordination networks.
• Synthesis involved bridging Preyssler-type polyoxoanions with metal-aquo complexes.
• X-ray diffraction was used to characterize the structures of the synthesized networks.
• Comparative analysis of networks formed with different metal ions (Co2+, Ni2+, Zn2+, Y3+) and under varying redox conditions (reduction and oxidation).

Main Results:

• Novel metal oxide coordination networks were successfully synthesized based on Preyssler-type polyoxoanions bridged by metal-aquo complexes.
• Networks bridged by first-row transition metals (Co2+, Ni2+, Zn2+) were isostructural with a known cobalt-bridged structure.
• A new Y3+-bridged network structure was identified.
• An uncommon binding motif of metal cations to the oxygen atoms at the cap positions of the polyoxoanions was observed in the reduced networks.
• Oxidation of a Zn2+-bridged network led to the loss of Zn2+-Ocap bonds, confirming the crucial role of electrochemical reduction in establishing this connectivity.

Conclusions:

• Electrochemical reduction is essential for the formation of these specific polyoxometalate-based coordination networks, particularly for establishing the metal-oxygen cap binding motif.
• The choice of bridging metal ion influences the resulting network structure, with transition metals leading to known structures and Y3+ yielding a new structure.
• The observed metal-Ocap bonding is likely a consequence of increased electron density at the cap positions upon reduction, suggesting tunable network formation through redox control.