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•••M, and π•••π 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.
We studied the spin-state dependence of the electrical conductivity of two nanocrystalline powder samples of the spin crossover complex [Fe(pyrazine){Au(CN)2}2]. By applying an external pressure (up to 3 kbar), we were able to tune the charge transport properties of the material from a more conductive low spin state to a crossover point toward a more conductive high spin state. We rationalize these results by taking into account the spin-state dependence of the activation parameters of the conductivity.
In the title polymeric complex, {[Fe(CN)2(C10H8N2)2(H2O)2][Au(CN)2]}
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, the FeII ion, which is located on a twofold rotation axis, has a slightly distorted FeN4O2 octahedral geometry. It is coordinated by two phenylpyrazine molecules, two water molecules and two dicyanoaurate anions, the Au atom also being located on a second twofold rotation axis. In the crystal, the coordinated dicyanoaurate anions bridge the FeII ions to form polymeric chains propagating along the b-axis direction. In the crystal, the chains are linked by Owater—H...Ndicyanoaurate anions hydrogen bonds and aurophillic interactions [Au...Au = 3.5661 (3) Å], forming layers parallel to the bc plane. The layers are linked by offset π–π stacking interactions [intercentroid distance = 3.643 (3) Å], forming a supramolecular metal–organic framework.
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