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

Two 2D Hofmann-type complexes of the composition [Fe(Phpz){M(CN)}] (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)] 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.

Crystal structure of -poly[[gold(I)-μ-cyanido-[di-aqua-bis-(2-phenyl-pyrazine)-iron(II)]-μ-cyanido] dicyanidogold(I)].

In the title polymeric complex, {[Fe(CN)(CHN)(HO)][Au(CN)]} , the Fe ion, which is located on a twofold rotation axis, has a slightly distorted FeNO octa-hedral geometry. It is coordinated by two phenyl-pyrazine mol-ecules, two water mol-ecules and two di-cyano-aurate anions, the Au atom also being located on a second twofold rotation axis. In the crystal, the coordinated di-cyano-aurate anions bridge the Fe ions to form polymeric chains propagating along the -axis direction.