Two-Step Spin Crossover in Hofmann-Type Coordination Polymers [Fe(2-phenylpyrazine)2{M(CN)2}2] (M = Ag, Au)

Two 2D Hofmann-type complexes of the composition [Fe(Phpz)2{M(CN)(2)}(2)] (where Phpz = 2-phenylpyrazine; M = Ag, Au) have been synthesized, and their spin-crossover (SCO) behavior has been thoroughly characterized. Single-crystal X-ray analysis reveals that these complexes contain a crystallographically unique Fe(II) center surrounded by two axial Phpz ligands and four equatorial cyanide [M(CN)(2)](-) bridges. It is shown that, using of a ligand with two aromatic rings, an advanced system of weak supramolecular interactions (metal-metal, C-H center dot center dot center dot M, and pi center dot center dot center dot pi stacking contacts) is realized. This ensures additional stabilization of the structures and the absence of solvent-accessible voids due to dense packing. Both complexes are characterized by a highly reproducible two-step SCO behavior, as revealed by different techniques (superconducting quantum interference device magnetometry, optical microscopy, etc.). Research shows the exceptional role of the presence of various supramolecular interactions in the structure and the influence of the bulky substituent in the ligand on SCO behavior. Moreover, the perspective of substituted pyrazines for the design of new switchable materials is supported by this work.

Automated summary

Two 2D Hofmann-type complexes of [Fe(Phpz)2{M(CN)(2)}(2)] (where Phpz = 2-phenylpyrazine; M = Ag, Au) have been synthesized and characterized, showing a highly reproducible two-step spin-crossover behavior influenced by supramolecular interactions and bulky substituents in the ligand. This work supports the potential of substituted pyrazines in designing new switchable materials.