Spin-State Patterning in an Iron(II) Tripodal Spin-Crossover Complex

A mononuclear
iron­(II) complex that displays a gradual two-step
spin-crossover (SCO) transition is reported. The intermediate plateau
(IP) occurs between HS0.40LS0.60 and HS0.30LS0.70 (HS = high spin; LS = low spin) ratios
over the region of ca. 190–170 K. A phase change occurs at
the IP, breaking the symmetry, resulting in six independent SCO sites
compared to one at the 100% HS and LS plateau regions, respectively.
Variable-temperature X-ray photoelectron spectroscopy shows that the
SCO behavior is completely reversible among the HS, IP, and LS regions.
The results both confirm and extend the related results for the above
system described by Halcrow et al. (Kulmaczewski, R.; Cespedes, O.; Halcrow, M. A. Gradual Thermal Spin-Crossover Mediated By a Reentrant Z′ = 1 → Z′ = 6 → Z′ = 1 Phase Transition, Inorg. Chem. 2017, 56, 3144−3148) in a recent report.