Electronic structure of Schiff-base peroxo{2,2′-[1,2-phenyl­enebis(nitrilo­methanylyl­idene)]bis­(6-meth­oxy­phenolato)}titanium(IV) monohydrate: a possible model structure of the reaction center for the theoretical study of hemoglobin

An extensive characterization of [Ti(C(22)H(18)N(2)O(6))]·H(2)O was performed by topological analysis according to Bader’s quantum theory of atoms in molecules (QTAIM) from the experimentally (multipole model) and theoretically (DFT) determined electron density. To the best of our knowledge, this study is the first example of an experimental electronic structure of a coordination compound in which a peroxo anion is bonded to a 3d central atom. The titanium coordination polyhedron could be described as a deformed tetrahedral pyramid if the midpoint of the peroxide O—O bond (side-on mode) is considered to be in the quasi-apical position. According to the multipole model (MM) results, the titanium atom has a positive QTAIM charge of 2.05 e(−) which does not correspond to the formal Ti (IV) oxidation state. On the other hand, the peroxo oxygen atoms O(1) and O(2) have MM QTAIM charges of −0.27 and −0.12, respectively. This asymmetric charge density distribution on the peroxo oxygens is in agreement with the distorted orientation of the O(2) moiety with respect to the titanium atom. Despite the fact that the overall MM charge of the O(2) moiety is more remote from the formal −2 charge than from neutral O(2), the O—O distance remains close to that in the peroxo O(2) (2−) anion. In the case of DFT results, the titanium atom charge is also found to be close to +2, the O(2) (x−) moiety charge is around −1, the optimized O—O distance is shorter by only ca 0.04 Å than the experimental value of 1.5005 (16) Å, and the DFT d-populations on titanium are found to be lower than the experimental MM value. This study is the first experimental electronic structure of a transition metal peroxo complex.