Effect of Ligand\nDeprotonation on the Spin Transition\nin Fe(II) Complexes

The effect of deprotonation of the ligands forming the\nsecond coordination\nsphere of the iron(II) ion on its spin crossover behavior is examined.\nDue to the pronounced changes in the observed magnetic characteristics\nof the iron(II) ion, the proton removal from the ligand in the second\ncoordination sphere is modeled by the appearance of a negative charge\non one of the neutral nitrogens in the nearest surrounding of the\nmetal ion, thus significantly changing the crystal field acting on\nthis ion and, respectively, the conditions for observation of the\nspin transition. Different symmetries of the nearest nitrogen surrounding\nof the iron(II) ion and different locations of the negative charge\nin this surrounding are examined in the frames of the crystal field\nmodel. It is demonstrated that in the model accepted, depending on\nthe location of the negative charge on the nitrogens of the first\ncoordination sphere, the spin conversion can be either suppressed\nor facilitated. Within the framework of the suggested model, a qualitative\nexplanation of the effect of deprotonation on the observed magnetic\nproperties in [Fe<sub>4</sub>(H<i><sub>n</sub></i>L<sub>4</sub>)]<sup>(<i>n</i>)+</sup> (<i>n</i> = 8,\n6, 4) compounds is given.