Thermal- And Photo-Induced Spin Crossover In The 1d Coordination Polymer [Fe(4-Tbupy)(3)][Au(Cn)(2)](2) (4-Tbupy=4-Tert-Butylpyridine)

Reaction of the unidentate pyridine ligand containing a bulky t-butyl substituent with Fe2+ and [Au(CN)(2)](-) affords a new type of spin crossover (SCO) coordination polymer in the 1D compound [Fe(4-tBupy)(3)][Au(CN)(2)](2).0.5H(2)O (1), which is formed by chains of Fe(II) complexes linked through bridging [Au(CN)(2)](-) with three terminal 4-tBupy and one monodentate [Au(CN)(2)](-) ligands completing the octahedral coordination around Fe(II). Longer reaction times led to the minor products [Fe(4-tBupy)(2)][Au(CN)(2)](2) (2), which presents a 2D structure more similar to that found in the other SCO compounds based on [Au(CN)(2)](-), and the 1D compound [Fe(4-tBupy)(2)(MeOH)][Au(CN)(2)](2) (3), in which one of the three terminal 4-tBupy found in 1 is replaced by a coordinating MeOH molecule. Magnetic measurements of 1 show an abrupt spin transition with the temperature with hysteresis and light-induced excited spin-state trapping effect. Structural analysis of 2 and 3 indicates that Fe(II) remains in the high-spin state in these compounds.