Two 6/10-connected Cu₁₂S₆ cluster-based organic frameworks: crystal structure and proton conduction

Area of Science:

• Materials Science
• Chemistry
• Crystallography

Background:

• Limited research exists on crystalline cluster-based organic framework materials for proton conduction.
• Existing proton conductive materials include sulfonated polymers and novel crystalline solids like MOFs, COFs, and HOFs.

Purpose of the Study:

• To synthesize and investigate a pair of homologous Cu(I)-based organic frameworks containing a Cu12S6 cluster for proton conduction.
• To characterize the structures and analyze the proton conductivity properties of the synthesized materials.

Main Methods:

• Hydrothermal synthesis of two Cu(I)-based organic frameworks ([Cu12(MES)6(H2O)3]n (1) and {[Cu12(MPS)6(H2O)4]·6H2O}n (2)).
• Structural characterization using single-crystal X-ray diffraction, elemental analysis, thermogravimetric analyses, and PXRD measurements.
• Investigation of proton conductivity and water stability, complemented by Hirshfeld surface analysis.

Main Results:

• Two MOFs with distinct topological structures were successfully synthesized.
• Both MOFs exhibit temperature-dependent proton conductive features with conductivities of 3.63 × 10-5 and 2.75 × 10-5 S cm-1 at 333 K and 98% RH.
• The materials demonstrate high water stability, with structural and conductivity differences analyzed in relation to molecular contacts and hydrogen bonding.

Conclusions:

• The synthesized Cu(I)-based MOFs represent a novel class of crystalline cluster-based organic frameworks for proton conduction.
• The study highlights the relationship between structural topology, water stability, and proton conductivity in these materials.
• Further investigation into these materials could lead to advancements in solid-state proton conductor technology.