Spin-crossover Tuning of the Luminescence in 2D Hofmann-type Compounds in Bulk and Exfoliated Flakes

The synthesis, structure and magnetic and optical characterization of a new, [FeII(furtrz)2(Pt(CN)4)]center dot 4H2O (1), flexible 2D Hofmann-type material is reported together with the optical characterization of the already reported, [Fe3II(saltrz)6(Pt(CN)4)3]center dot 8H2O (2). Both compounds exhibit in the bulk multi-step thermal SCO. The temperature dependence of the luminescence properties of 2, reported for the first time in this work, show a clear interplay between SCO and luminescence, while in the case of 1, resonant emission shows only a subtle change around the SCO temperature. Thanks to their layered structure and weak interlayer interactions, it has been possible to obtain flakes of micrometric lateral sizes and thicknesses of a few nm of the two compounds using the well-known Scotch tape method. The effect of the miniaturization in the SCO properties and luminescence has been studied by Raman spectroscopy and luminescence. In the case of 2, the abrupt SCO is lost in the exfoliated flakes, while in 1 a clear spin transition is still observed in a plethora of flakes with thicknesses ranging from a few nanometers up to hundreds. Two Hofmann-type multifunctional materials are reported, displaying a tuning of the luminescence properties by the spin-crossover, and have exfoliated by in nanometric flakes by the Scotch-tape method.