Structural properties of the valence tautomerism interconversion in Co(diox)2(Py)2 crystals

Abstract

This work reports on the investigation of key chemical environmental factors that modulate valence tautomerism (VT) in Co( diox ) 2 (Py) 2 ( diox = 3,5 -di-tert- butyl semiquinone and Py = pyridine) complexes. Single crystal X - ray diffraction experiments in a wide range of temperatures have been used to charac terize the influence of the crystal packing and solvation in the VT interconversion of Co( diox ) 2 (Py) 2 pyridine solvated crystals crystallized with complex/solvent ratio of 1:0, 2:1 and 1:2. Our results showed that the mobility of the pyridine, and in particular the rotation of Py plane around the Co-Py bond is directly correlated to the possibility of changes in the electronic states that lead to the Co-N and Co-O distances changes upon the High Spin (HS) -CoII ⇔ Low Spin ( LS )-CoIII VT interconversion. A compilation of literature results also shows a correlation between pyridine-like ligands (PyL) angular distribution and the changes in the electronic/magnetic state of the Co( diox ) 2 (PyL) 2. For about 50 Co( diox ) 2 (PyL) 2 structures found in CCDC, the Co -N distances remain constant around 1.95 Å (systems in the LS -CoIII state) with the increasing PyL rotation angle up to a critical value of ~17.5 o above which a second linear regime takes place with Co-N increasing up to ~2.20 Å ( HS -CoII state) when PyL rotation angles range from ~18 o up to almost 30 o . This result highlights the critical role of the so -called innocent ligands in the electronic state of the Co -based VT complexes.