Dual-supramolecular contacts induce extreme Hofmann framework distortion and multi-stepped spin-crossover

Area of Science:

• Materials Science
• Crystallography
• Coordination Chemistry

Background:

• Hofmann framework materials are known for their diverse structures and properties.
• Supramolecular interactions, such as hydrogen bonding and π-stacking, significantly influence material structures.
• Spin crossover (SCO) materials exhibit temperature- or pressure-induced changes in spin states, impacting their magnetic properties.

Purpose of the Study:

• To investigate the structural and magnetic consequences of using an extended nitro-functionalized 1,2,4-triazole ligand in a 2-D Hofmann framework.
• To understand how competing supramolecular interactions affect lattice distortion and ligand conformations.
• To analyze the spin crossover behavior of iron(II) centers within the distorted framework.

Main Methods:

• Single crystal X-ray diffraction was employed to analyze the crystal structure of [Fe3(N-cintrz)6(Pd(CN)4)3]·6H2O.
• Variable temperature magnetic susceptibility measurements were conducted to study the spin crossover transition.
• Variable temperature structural analyses were performed to correlate structural changes with magnetic transitions.

Main Results:

• The nitro-functionalized ligand induced significant lattice distortion, with hydrogen bonding dominating over π-stacking interactions.
• The 2-D Hofmann layers exhibited varied ligand conformations and local Fe(II) coordination environments.
• A two-step spin crossover transition was observed, involving two distinct crystallographically Fe(II) centers arranged in a 2:1 ratio.

Conclusions:

• The study demonstrates how competing supramolecular interactions can lead to substantial lattice distortion in Hofmann frameworks.
• The observed spin crossover behavior highlights the interplay between crystallographic ordering and spin-state transitions.
• The mismatch in periodicity between crystallographic and spin-state ordering provides insights into elastic interactions and frustration.