Complexes R2Sn(IV)L with O,N,O'-Donor Schiff Bases: Synthesis, Structures, and Redox Properties

Abstract

New tin(IV) complexes with O,N,O'-donor Schiff bases (L1H2–L4H2) of the (Ln)SnR2 type (R = Ph (I–III), Et (IV–VII)) are synthesized and characterized. The molecular structures of compounds I–III, VI, and VII in the crystalline form are determined by X-ray diffraction (XRD) (CIF files CCDC nos. 2181140 (I), 2181142 (II), 2181143 (III∙CH3CN), 2181141 (VI), and 2181139 (VII)). Tin complexes I–III and VI are mononuclear pentacoordinate compounds. Crystalline complex VII forms dimers via the pairwise bridging coupling between the oxygen and tin atoms of the mononuclear fragments. The redox-active ligand in the synthesized compounds exists as the iminobis(phenolate) dianion. The electrochemical properties of free ligands and complexes I–VII are studied. In the case of compounds I, II, IV, and V with tert-butyl substituents in the redox-active ligand, the formation of relatively stable monocationic and monoanionic species is electrochemically detected for the first time. The presence of the electroactive nitro group results in the destabilization of the oxidized forms of the complexes and induces the appearance of an additional peak in the cathodic range. The energy gaps between the frontier redox orbitals are determined by the electrochemical and spectral methods. The obtained parameters are close and vary in a range of 2.43–2.68 eV.