Effect of the metal dilution on the thermal and light-induced spin transition in [Fe xMn 1− x(bpp) 2](NCSe) 2: When T(LIESST) reaches T1/2

Abstract

The thermal and light-induced spin transition in [Fe x Mn 1− x (bpp) 2](NCSe) 2 (bpp = 2,6-bis(pyrazol-3-yl)pyridine) has been investigated by magnetic susceptibility, photomagnetism and diffuse reflectivity measurements. These complexes display a thermal spin transition and exhibit the light-induced excited spin state trapping (LIESST) effect at low temperature. 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, suggesting that the two interconversion processes are controlled by different factors; i.e. the photomagnetic properties are governed at the molecular scale and the thermal spin crossover regime is affected by both the ligand field and crystal packing effects. For highly metal-diluted complex with x < 0.2, it is found that when T 1/2 reaches the T(LIESST), the complex remains HS on the whole range of temperature.