Regulation of Multistep Spin Crossover Across Multiple Stimuli in a 2-D Framework Material

We investigate the effects of a broad array of external stimuli on the structural, spin-crossover (SCO) properties and nature of the elastic interaction within the two dimensional Hofmann framework material [Fe(cintrz)2Pd(CN)4]·guest (cintrz = N cinnamalidene 4-amino-1,2,4-triazole; A·guest; guest = 3H2O, 2H2O, and Ø). This framework exhibits a delicate balance between ferro- and antiferro-elastic interaction characters; we show that manipulation of the pore contents across guests = 3H2O, 2H2O, and Ø can be exploited to regulate this balance. In A·3H2O, the dominant antiferroelastic interaction character between neighboring FeII sites sees the low-temperature persistence of the mixed spin-state species {HS−LS} for {Fe1−Fe2} (HS = high spin, LS = low spin). Elastic interaction strain is responsible for stabilizing the {HS−LS} state and can be overcome by three mechanisms: (1) partial (2H2O) or complete (Ø) guest removal, (2) irradiation via the reverse light-induced excited spin-state trapping (LIESST) effect (λ = 830 nm), and (3) the application of external hydrostatic pressure. Combining experimental data with elastic models presents a clear interpretation that while guest molecules cause a negative chemical pressure, they also have consequences for the elastic interactions between metals beyond the simple chemical pressure picture typically proposed.Manan Ahmed, Katrina A. Zenere, Natasha F. Sciortino, Kasun S. A. Arachchige, Gemma F. Turner, Jace Cruddas, Carol Hua, Jason R. Price, Jack K. Clegg, Francisco Javier Valverde-Mun, oz, Jose A. Real, Guillaume Chastanet, Stephen A. Moggach, Cameron J. Kepert, Benjamin J. Powell, and Suzanne M. Nevill