Structural and conformational analysis of neutral dinuclear diorganotin(IV) complexes derived from hexadentate Schiff base ligands

The synthesis of three hexadentate Schiff base ligands has been carried out, which contain two sets of ONO donor atoms. These were reacted with diorganotin(IV) dichloride derivatives (R = Me, nBu, Ph) to prepare seven dinuclear diorganotin(IV) complexes in moderate yields. Aside from IR and NMR (1H, 13C, 119Sn) spectroscopic studies, mass spectrometry and elemental analysis, four tin complexes were characterized by X-ray diffraction analysis. The spectroscopic analyses showed that in solution the tin atoms have five-coordinate environments with a distorted trigonal bipyramidal geometry. Each tin atom is coordinated to the nitrogen atom and forms covalent bonds with two oxygen atoms and two carbon atoms. Due to the presence of a methylene group as bridge between the two ONO chelates, the overall molecular structures can have cis or trans conformation, having either mirror or C2-symmetry. While in solution a fast equilibrium can be supposed, in the solid state different intermediate conformations have been detected. Furthermore, for the dialkyltin derivatives Sn⋯O intermolecular interactions were found allowing for a dimeric or crinkled polymeric organization, whereas for the diphenyltin derivatives no such interactions were observed.

Graphical abstractThe structural and conformational analysis of seven dinuclear diorganotin (IV) compounds is reported, which have been prepared from hexadentate Schiff base ligands having a twofold ONO donor system. The spectroscopic analyses showed that in solution the compounds have a distorted trigonal bipyramidal coordination geometry for the tin atoms and are apparently involved in a fast equilibrium between two molecular conformations. In the solid state a distorted octahedral geometry can be favored through Sn⋯O intermolecular interactions and a molecular conformation that is intermediate between the cis- and trans-isomer, having mirror and C2-symmetry, respectively.Figure optionsDownload full-size imageDownload as PowerPoint slide