Synthetic, structural, magnetic, and Mossbauer spectral study of {Fe[HC(3,5-Me(2)pz)(3)](2)}I-2 and its spin-state crossover behavior

The complex {Fe[HC(3,5-Me(2)pz)(3)](2)}I-2 (1) has been prepared from the reaction of FeI2 and HC(3,5-Me(2)pz)(3) (pz = pyrazolyl ring) in a 1:2 ratio. The complex is high-spin in both the solid state and in solution at ambient temperature, In the solid state, magnetic susceptibility and Mossbauer spectral studies indicate that samples of the complex that have been crystallized and dried change completely from high-spin to low-spin upon cooling below 195 K, with a substantial two-step thermal hysteresis in the transition, The spin-crossover properties of I are sample dependent: powder samples do not change to low-spin at low temperatures. Two crystalline forms of I have been identified by X-ray crystallography, one form containing no solvent of crystallization and the other containing solvent, In both, there is only one iron site, with average Fe-N bond lengths of 2.18 and 2.17 Angstrom, values that confirm that the complex is high-spin. Single crystals of the nonsolvated form shatter at low temperatures whereas single crystals of the solvated form can be cooled to 110 K with no loss of crystallinity and remain fully high spin at this temperature, Crystallographic information: nonsolvated form is triclinic, P (1) over bar, a = 8,8062(2) Angstrom, b = 10.3549(2) Angstrom, c = 11.3549(2) Angstrom, a = 104.0768(10), beta = 110.2473(10)degrees, gamma = 92.6385(11)degrees, Z = 1; solvated form is monoclinic P2(1)/c, a 10.3214(5) Angstrom, b = 12.7753(7) Angstrom, c = 20.1995(11) Angstrom, alpha = 90degrees, beta = 97.5380(10)degrees, gamma = 90degrees, Z = 2.