Spin crossover behaviour in one-dimensional Fe(II) compounds based on the [M(CN)4](2-) (M = Pd, Pt) units

Area of Science:

• Inorganic Chemistry
• Materials Science
• Solid-State Chemistry

Background:

• Coordination polymers offer tunable properties for advanced applications.
• Spin Crossover (SCO) materials are of interest for molecular switches and sensors.
• Heterobimetallic systems provide platforms for complex structural and electronic properties.

Purpose of the Study:

• To synthesize and characterize novel one-dimensional heterobimetallic coordination polymers.
• To investigate the structural, magnetic, and thermal properties, focusing on Spin Crossover (SCO) behavior.
• To explore the influence of different metal ions and ligands on SCO characteristics.

Main Methods:

• Synthesis of four heterobimetallic coordination polymers: {Fe(pic)2[M(CN)4]}n and {Fe(pypz)2[M(CN)4]}n (M = Pd(II), Pt(II)).
• Characterization using infrared spectroscopy, X-ray diffraction, magnetic measurements, and differential scanning calorimetry (DSC).
• Single-crystal X-ray diffraction to determine 1D zigzag chain structures and analyze intermolecular interactions (hydrogen bonding, π-π stacking).

Main Results:

• All compounds form 1D neutral zigzag chain structures with [M(CN)4](2-) as a bridging ligand.
• Hydrogen bonding and π-π interactions contribute to the 3D network formation.
• Compounds {Fe(pic)2[Pd(CN)4]}n and {Fe(pic)2[Pt(CN)4]}n exhibit complete SCO near room temperature with narrow hysteresis.
• {Fe(pypz)2[Pd(CN)4]}n and {Fe(pypz)2[Pt(CN)4]}n show abrupt SCO at lower temperatures (186 K and 180 K).
• SCO temperatures are tunable by ligand field strength and influenced by cooperativity between coordination bonds and supramolecular interactions.
• Light-Induced Excited-Spin-State Trapping (LIESST) effect observed in one compound.

Conclusions:

• The synthesized heterobimetallic coordination polymers display diverse SCO behaviors, tunable by metal and ligand choice.
• Structural features, including hydrogen bonding and π-π interactions, play a crucial role in SCO properties.
• These materials demonstrate potential for developing molecular switches and sensors with tailored thermal and light-responsive characteristics.