A Series of Linear {FeIII2FeII} Complexes with Paramagnetic Building‐Block‐Modified Spin Crossover Behaviors

Tuning the spin crossover (SCO) behavior through paramagnetic building blocks with different steric hindrance is of great interest for the synergy between SCO and magnetic interactions. Here we modified the steric effect of specified FeIII building blocks from large steric hindrance Tp* (hydridotris(3,5-dimethylpyrazol-1-yl)borate) analogue to small steric hindrance Tp (hydrotris(pyrazolyl)borate) derivative, the FeII SCO unit and FeIII paramagnetic ions were incorporated into three well-isolated trinuclear complexes featuring thermally- and light-induced SCO properties. Reanalyzing the structures uncovered that π-π-stacking interactions played a key role in the thermal hysteresis and anomalous octahedral distortion parameter Σ around FeII ion; the Tp* ligand showing the largest steric hindrance induced the elongated FeII-N bond lengths and bending of C≡N-FeII angle in 1, as well as its relatively large electron donor effect, leading to the lowest thermal transition temperature among three compounds.