The role of iron(II) dilution in the magnetic and photomagnetic properties of the series [Fe(x)Zn(1-x)(bpp)₂](NCSe)₂.

The effects of metal dilution on the spin-crossover behavior of iron(II) in the mixed crystal series [FexZn1-x(bpp)(2)](NCSe)(2) (bpp = 2,6-bis(pyrazol-3-yl)pyridine) have been studied using magnetic susceptibility, photomagnetism and diffuse reflectivity measurements. For each mixed-crystal system, the thermal spin transition temperature, T-1/2, and the relaxation temperature of the photo-induced high-spin state, T(LIESST), have been systematically determined. It appears that T-1/2 decreases with the metal dilution while T(LIESST) remains unchanged. Dilution also tends to decrease the hysteresis width and smooth the transition curves. These effects were discussed first qualitatively and then quantitatively on the basis of a kinetic study governing the photo-induced back conversion taking into account the relative sizes of Zn(II) and Fe(II) ions. Interestingly, single crystals were obtained for [Fe0.6Zn0.4(bpp)(2)](NCSe)(2) allowing the X-ray diffraction crystal-structure determination.