Synthesis, crystal structure and reactivity of trans-diaquo N,N'-ethylenebis-(3-methoxysalicylideneiminato)chromium(III)

A new chromium(III) Schiff base complex, [Cr(3-methoxysalen)(H2O)(2)]ClO4, where salen = N,N'-ethylenebis- (salicylideneimine), has been synthesized a nd characterized by spectroscopic techniques. Single crystal X-ray data rev eals that the complex assumes a trans-diaquo structure with formulation [Cr (C18H22N2O6)]ClO4 but, unlike in Cr (salen)(H2O)(2)(+), the two trans-water molecules are equidistant from Cr-III. The effect of the substituent on th e phenyl ring in respect of redox reactivity has been investigated. The kin etics of the oxidation of [Cr(Schiff base)- (H2O)(2)]ClO4, where Schiff bas e = salen, (1) and 3-OMe-salen, (2) by PhOI has been studied. The bimolecul ar rate constant for the formation of the O=Cr-v Schiff base in case of (2) was four times faster than that of (1). The introduction of the OMe group substituent on the phenyl ring influences not only the structure and crysta l packing, but also the reactivity of the complex and the electronic enviro nment around the metal ion.