Bistable Hofmann-Type FeII Spin-Crossover Two-Dimensional Polymers of 4-Alkyldisulfanylpyridine for Prospective Grafting of Monolayers on Metallic Surfaces

Aiming at investigating the suitability of Hofmann-type two-dimensional (2D) coordination polymers {Fe II (L ax ) 2 [M II (CN) 4 ]} to be processed as single monolayers and probed as spin crossover (SCO) junctions in spintronic devices, the synthesis and characterization of the M II derivatives (M II = Pd and Pt) with sulfur-rich axial ligands (L ax = 4-methyl- and 4-ethyl-disulfanylpyridine) have been conducted. The thermal dependence of the magnetic and calorimetric properties confirmed the occurrence of strong cooperative SCO behavior in the temperature interval of 100-225 K, featuring hysteresis loops 44 and 32.5 K/21 K wide for Pt II -methyl and Pt II /Pd II -ethyl derivatives, while the Pd II -methyl derivative undergoes a much less cooperative multistep SCO. Excluding Pt II -methyl, the remaining compounds display light-induced excited spin-state trapping at 10 K with T LIESST temperatures in the range of 50-70 K. Single-crystal studies performed in the temperature interval 100-250 K confirmed the layered structure and the occurrence of complete transformation between the high- and low-spin states of the Fe II center for the four compounds. Strong positional disorder seems to be the source of elastic frustration driving the multistep SCO observed for the Pd II -methyl derivative. It is expected that the peripheral disulfanyl groups will favor anchoring and growing of the monolayer on gold substrates and optimal electron transport in the device.