Spin crossover behavior in two-dimensional bimetallic coordination polymer FeII(3-bromo-4-picoline)2[AuI(CN)2]2: Synthesis, crystal structures, and magnetic properties

A new novel 2D network bimetallic (FeAuI)-Au-II spin crossover coordination compound based on 3-bromo-4-picoline and bridged cyano ligands, {Fe-II(3-bromo-4-picoline)(2)[Au-I(CN)(2)](2)}(n) (1), has been synthesized and characterized by elemental analyses and IR, using single-crystal X-ray analysis at 293 K and at 90 K and magnetic measurements. The Fe-II ions in 1 have octahedral FeN6 coordination geometries, which are linked by a [Au-I(CN)(2)](-) unit at the equatorial plane to form a polymeric 2D sheet architecture. The two pyridine rings coordinate at the axial positions. The structure of 1 comprises parallel 2D arrays and the layers interact by pairs, defining bilayers with strong binuclear aurophilic Au center dot center dot center dot Au interactions. Furthermore, intermolecular Au center dot center dot center dot Br and B center dot center dot center dot Br distances in 1 are significantly smaller than the sums of the van der Waals radii. Variable-temperature (2-300 K) magnetic susceptibility measurements of 1 have been performed to determine behaviors of spin transition. The susceptibility data of 1 indicates that about 50% of the HS states are changed to LS states at 75 K. The Fe-N bond distances at 90 K show that ratio of high spin states agree with the SQUID data. (c) 2008 Elsevier Ltd. All rights reserved.