Regulation of Multistep Spin Crossover Across Multiple Stimuli in a 2-D Framework Material
Manan Ahmed, Katrina A. Zenere, Natasha F. Sciortino, Kasun S. Athukorala Arachchige, Gemma F. Turner, Jace Cruddas, Carol Hua, Jason R. Price∥, Jack K. Clegg, Francisco Javier Valverde‐Muñoz, José Antonio Real, Guillaume Chastanet, Stephen A. Moggach, Cameron J. Kepert, B. J. Powell, Suzanne M. Neville
Abstract
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.