Spin State Chemistry: Modulation of Ligand pKa by Spin State Switching in a [2×2] Iron(II) Grid-Type Complex

The iron­(II) [2×2] grid complex Fe-8H has been synthesized and characterized. It undergoes spin-crossover (SCO) upon deprotonation of the hydrazine-based terpyridine-like ligand. The deprotonation patterns have been determined by X-ray crystallography and 1H NMR spectroscopy and discussed in relation to the spin state of the iron­(II) centers, which influences greatly the pKa of the ligand. The synthesis of the magnetically silent zinc­(II) analogue is also reported, and its (de)­protonation behavior has been characterized to serve as a reference for the study of the FeII grid complexes. DFT computations have also been performed in order to investigate how the successive deprotonation of the bridging ligands affects the SCO behavior within the grid.