Regulation of Multistep Spin Crossover Across Multiple Stimuli in a2-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]middotguest (cintrz =N-cinnamalidene 4-amino-1,2,4-triazole;Amiddotguest; guest = 3H2O, 2H2O, and O). This frameworkexhibits a delicate balance between ferro- and antiferro-elastic interaction characters; we showthat manipulation of the pore contents across guests = 3H2O, 2H2O, and O can be exploitedto regulate this balance. InAmiddot3H2O, the dominant antiferroelastic interaction characterbetween neighboring FeIIsites sees the low-temperature persistence of the mixed spin-statespecies {HS-LS} for {Fe1-Fe2} (HS = high spin, LS = low spin). Elastic interaction strain isresponsible for stabilizing the {HS-LS} state and can be overcome by three mechanisms: (1)partial (2H2O) or complete (O) guest removal, (2) irradiation via the reverse light-inducedexcited spin-state trapping (LIESST) effect (lambda= 830 nm), and (3) the application of externalhydrostatic pressure. Combining experimental data with elastic models presents a clearinterpretation that while guest molecules cause a negative chemical pressure, they also haveconsequences for the elastic interactions between metals beyond the simple chemical pressure picture typically proposed.

Automated summary

This study investigates the effects of external stimuli on the Hofmann framework material, showing how manipulation of pore contents can regulate the balance between ferro- and antiferro-elastic interaction characters. The study highlights the complex mechanisms behind elastic interaction and the impact of external pressure and light-induced effects on the material properties.