Spin State Chemistry: Modulation of Ligand p<i>K</i>_a by Spin State Switching in a [2×2] Iron(II) Grid-Type Complex

The iron­(II) [2×2] grid complex <b>Fe-8H</b> 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 p<i>K</i>_a 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 Fe^II 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