Order-Disorder Phase Transitions and Topological Isomerization in a Ternary-Ligand Synergistic Coordination Network

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Materials Science

Background:

• Single-crystal-to-single-crystal (SCSC) transformations are crucial for creating novel materials but are rarely reported for supramolecular isomers.
• Investigating dynamic complexes with order-disorder transitions is key to understanding complex material behaviors.

Purpose of the Study:

• To synthesize and characterize a novel iron(II) coordination complex exhibiting cation dynamics and SCSC transformation.
• To explore the impact of topological network isomerization on structural phase transitions and magnetic properties.

Main Methods:

• Single-crystal X-ray diffraction
• Dielectric measurements
• Variable-temperature magnetic susceptibility studies

Main Results:

• Synthesis of a lon topological complex, [H₂DABCO][Fe^II₂(C₂O₄)(HCOO)₂Cl₂]·H₂O (1), with cation dynamics and a 210 K order-disorder transition.
• Observation of an SCSC transformation above 413 K to anhydrous phase 2, featuring a crb zeolite net and retaining coordination geometry.
• Complex 1 shows antiferromagnetism (25 K ordering, 15 K canting), while 2 exhibits disordered organic ammonium ions below 100 K without significant spin canting.

Conclusions:

• The study reports a rare SCSC transformation leading to supramolecular network isomerization in an iron(II) complex.
• Topological network isomerization significantly influences the structural phase transitions and magnetic properties of the complex.
• The findings highlight the potential of SCSC transformations in designing functional coordination materials.