  Hybrid or metal organic framework (MOF) perovskites of general composition,
ABX$_3$, are known to show interesting properties which can lead to 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,
[CH$_{3}$NH$_{2}$CH$_{3}$][Fe(HCOO)$_3$] and Hydroxylammonium Iron Formate,
[NH$_{3}$OH][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 of the choice of A-site cation,
Dimethylammonium or Hydroxylammonium, implying tuning of spin-switching
properties achievable by chemical variation of the amine cation in the
structure. Our finding opens up novel functionalities in this family of
materials of recent interest, which can have important usage in sensors and
memory devices.
