Cationic Effect on Pressure Driven Spin-State Transition and Cooperativity in Hybrid Perovskites

Hybrid
or metal–organic framework (MOF) perovskites of general
composition, ABX3, are known to show interesting properties
that can lead to a variety of technological applications. Our first-principles
study shows they are also potential candidates for exhibiting cooperative
spin-state transitions upon application of external stimuli. We demonstrate
this by considering two specific Fe-based MOF perovskites, namely
dimethylammonium iron formate, [CH3NH2CH3]­[Fe­(HCOO)3], and hydroxylammonium iron formate,
[NH3OH]­[Fe­(HCOO)3]. Both the compounds are found
to undergo high-spin (S = 2) to low-spin (S = 0) transition at Fe­(II) site upon application of moderate
strength of hydrostatic pressure, along with large hysteresis. This
spin-state transition is signaled by the changes in electronic, magnetic,
and optical properties. We find both the transition pressure and the
width of the hysteresis to be strongly dependent on the choice of
A-site cation, dimethylammonium or hydroxylammonium, implying that
tuning of spin-switching properties is achievable by chemical variation
of the amine cation in the structure. Our findings open up novel functionalities
in this family of materials of recent interest, which can have important
usage in sensors and memory devices.