Structural diversity in multinuclear Pd(II) assemblies that show low-humidity proton conduction

Area of Science:

• Coordination Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Palladium(II) complexes are versatile building blocks in self-assembly.
• Understanding the influence of donor ligand properties on aggregate formation is crucial.
• Exploring novel materials for energy applications like batteries and fuel cells is ongoing.

Purpose of the Study:

• To systematically investigate the synergetic effects of ligand geometry, length, denticity, and asymmetry on palladium(II) aggregate formation.
• To synthesize and characterize unprecedented palladium(II) aggregates using a multicomponent self-assembly approach.
• To evaluate the proton conductivity and water adsorption properties of the newly formed palladium(II) assemblies.

Main Methods:

• Multicomponent self-assembly of a cis-blocked 90° Pd(II) acceptor with a tetratopic donor.
• X-ray crystallography for structural analysis and crystal packing investigation.
• Proton conductivity measurements under varying humidity and temperature conditions.

Main Results:

• Formation of several uncommon Pd(II) aggregates, some representing novel structural types.
• Identification of hydrogen bonds between counteranions (nitrate) and water molecules.
• Observation of 3D water networks within molecular pockets, indicating water-adsorption capabilities.
• Demonstration of proton conductivity (1.87×10⁻⁵–6.52×10⁻⁴ S cm⁻¹) at 296 K and low relative humidity (ca. 46%).
• Proton conductivity increased with enhanced humidity and exhibited activation energies of 0.29–0.46 eV.

Conclusions:

• The synergetic effects of donor ligand properties significantly influence the formation of Pd(II) aggregates beyond simple geometric considerations.
• The synthesized Pd(II) aggregates exhibit unique water-adsorption properties and form intricate 3D water networks.
• These novel palladium(II) assemblies show significant proton conductivity under low-humidity conditions, highlighting their potential as electrolytes for electrochemical devices.