Switchable slow relaxation of magnetization in the native low temperature phase of a cooperative spin-crossover compound† †Electronic supplementary information (ESI) available: CCDC 1493439 and 1493440. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6sc04737h Click here for additional data file. Click here for additional data file.

Table S1. Crystallographic and refinement parameters of 2 p. S4 Table S2. Coordination environment of the Fe sites in 2 p. S5 Table S3. Intermolecular interactions and Fe···Fe separations in 2 p. S6 Figure S1. Views of the structure of 2 showing the inter-layer interactions through C Me –H···A hydrogen bonds p. S7 Figure S2. Magnetization isotherms of 2 plotted vs. H/T p. S8 Figure S3. Temperature dependence of the χT product and magnetization isotherms of 2 p. S9 Figure S4. Applied dc field dependence of the out-of-phase magnetic susceptibility χ'' of 2 at T = 2 K p. S10 Figure S5. Frequency dependence of the ac magnetic susceptibility of 2 at 2000 Oe dc field p. S11 Figure S6. Frequency dependence of the scaled ac magnetic susceptibility at 1500 and 2000 Oe dc field p. S12 Figure S7. Cole-Cole plot of the ac magnetic susceptibility of 2 p. S13 Figure S8. Temperature dependence of the χT product and applied dc field dependence of the ac magnetic susceptibility of 3 at T = 1.9 K p. S14 Figure S9. Diffuse reflectance solid-state absorption spectrum at 77 K for 2.