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Spin‐crossover complexes with multistep transitions attract much attention due to their potential applications as multi‐switches and for data storage. A four‐step spin crossover is observed in the new iron(II)‐based cyanometallic guest‐free framework compound Fe(2‐ethoxypyrazine)2{Ag(CN)2}2 during the transition from the low‐spin to the high‐spin state. A reverse process occurs in three steps. Crystallographic studies reveal an associated stepwise evolution of the crystal structures. Multiple transitions in the reported complex originate from distinct FeII sites which exist due to the packing of the ligand with a bulky substituent. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In the title polymeric complex, [Au2Fe(CN)4(C4H3IN2)2(C2H6O)]n, the FeII cation is coordinated by two iodo­pyrazine mol­ecules, one ethanol mol­ecule and three di­cyano­aurate anions in a distorted N5O octa­hedral geometry. In the crystal, the di­cyano­aurate anions bridge the FeII cations to form polymeric chains propagating along the b-axis direction. Stabilization of the crystal structure is provided by O—H···N hydrogen bonds and π–π stacking between parallel iodo­pyrazine rings of neighbouring chains, the centroid–centroid distances being 3.654 (10) and 3.658 (9) Å. [ABSTRACT FROM AUTHOR]

Discovery of spin-crossover (SCO) behavior in the family of FeII-based Hofmann clathrates has led to a "new rush" in the field of bistable molecular materials. To date this class of SCO complexes is represented by several dozens of individual compounds, and areas of their potential application steadily increase. Starting from Fe2+, square planar tetracyanometalates MII(CN)42- (MII = Ni, Pd, Pt) and 2-substituted pyrazines Xpz (X = Cl, Me, I) as coligands we obtained a series of nine new Hofmann clathrate-like coordination frameworks. X-ray diffraction reveals that in these complexes FeII ion has a pseudo-octahedral coordination environment supported by four µ4-tetracyanometallates forming its equatorial coordination environment. Depending on the nature of X and M, axial positions are occupied by two 2X-pyrazines (X = Cl and MII = Ni (1), Pd (2), Pt (3); X = Me and MII = Ni (4), Pd (5)) or one 2X-pyrazine and one water molecule (X = I and MII = Ni (7), Pd (8), Pt (9)), or, alternatively, two distinct FeII positions with either two pyrazines or two water molecules (X = Me and MII = Pt (6)) are observed. Temperature behavior of magnetic susceptibility indicates that all compounds bearing FeN6 units (1-6) display cooperative spin transition, while FeII ions in N5O or N4O2 surrounding are high spin (HS). Structural changes in the nearest FeII environment upon low-spin (LS) to HS transition, which include ca. 10% Fe-N distance increase, lead to the cell expansion. Mössbauer spectroscopy is used to characterize the spin state of all HS, LS, and intermediate phases of1-9 (see abstract figure). Effects of a pyrazine substituent and MII nature on the hyperfine parameters in both spin states are established. [ABSTRACT FROM AUTHOR]