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

摘要

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 NCSeü analogue, SCOF- 6(Se), displays a complete SCO transition (T_(1/2)=135 K). Photomagnetic characterizations reveal quantitative lightinduced 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.