An Investigation of Photo- and Pressure-Induced Effects in a Pair of Isostructural Two-Dimensional Spin-Crossover Framework Materials

Two new isostructural iron(II) spin-crossover (SCO) framework (SCOF) materials of the type [Fe(dpms)(2)(NCX)(2)] (dpms=4,4'-dipyridylmethyl sulfide; X=S (SCOF-6(S)), X=Se (SCOF-6(Se))) have been synthesized. The 2D framework materials consist of undulating and interpenetrated rhomboid (4,4) nets. SCOF-6(S) displays an incomplete SCO transition with only approximately 30% conversion of high-spin (HS) to low-spin iron(II) sites over the temperature range 300-4 K (T-1/2 = 75 K). In contrast, the NCSe- analogue, SCOF-6(Se), displays a complete SCO transition (T-1/2 = 135 K). Photomagnetic characterizations reveal quantitative light-induced excited spin-state trapping (LIESST) of metastable HS iron(II) sites at 10 K. The temperature at which the photoinduced stored information is erased is 58 and 50 K for SCOF-6(S) and SCOF-6(Se), respectively. Variable-pressure magnetic measurements were performed on SCOF-6(S), revealing that with increasing pressure both the T-1/2 value and the extent of spin conversion are increased; with pressures exceeding 5.2 kbar a complete thermal transition is achieved. This study confirms that kinetic trapping effects are responsible for hindering a complete thermally induced spin transition in SCOF-6(S) at ambient pressure due to an interplay between close T-1/2 and T(LIESST) values.