Structural Transformations and Magnetic Effects Induced by Solvent Exchange in the Spin Crossover Complex [Fe(bpp) 2 ][Cr(bpy)(ox) 2 ] 2

Structural, thermal, magnetic and solvent-exchange properties of the spin crossover compound [Fe(bpp)2][Cr(bpy)(ox)2]2 containing paramagnetic anions are given. This complex salt 1 crystallises as a dihydrate with two inequivalent (high-spin and low-spin) FeII sites. The dehydrated compound is a spin-crossover material with T1/2 ↑ = 369 K and T1/2 ↓ = 353 K. Rehydration takes place without loss of crystallinity, yielding a polymorph (2) with 100 % high-spin Fe II sites. The different high-spin fractions in 1 and 2 have been correlated to structural changes in the FeII second coordination sphere. The magnetic response to the presence of different sorbed molecules has also been explored. © Wiley-VCH Verlag GmbH & Co. KGaA, 2005.