Intriguing binding modes of tetradentate pyridoxal derivatives to molybdenum centre

Abstract

The Schiff base pdxen ligands (H2py2en=N,N′-ethylenebis(pyridoxylideneimine) and H2py2pren=N,N′-prophylenebis(pyridoxylideneimine)) were found to form readily by the mechanochemical synthesis from their corresponding diamine and pyridoxal. Reduction of the Schiff bases with NaBH4 yielded reduced pdxan ligands (H2Rpy2en=N,N′-ethylenebis(pyridoxylamine) and H2Rpy2pren=N,N′-prophylenebis(pyridoxylamine)). A dinuclear molybdenum(VI) complex with the bridging pdxen ligand [{MoO2}2(μ-py2en)(OMe)2(MeOH)2]⋅3MeOH (1⋅3MeOH), and mononuclear complexes with the pdxen ligand [MoO2(py2pren)] (3), as well as with the pdxan ligands: [MoO2(Rpy2en)] (2) and [MoO2(Rpy2pren)] (4) were prepared and characterized. Significant differences in the coordination of the Schiff base ligands were found as a consequence of chain length and ligand flexibility. Complexes 1–4 were obtained either by the reaction of [MoO2(acac)2] or [Mo(CO)6] with the corresponding ligands. Crystal and molecular structures of complexes 1⋅3MeOH, 2 and 3 were determined by the single crystal X-ray diffraction method. All complexes were characterized by microanalysis, FT-IR, NMR, UV, thermogravimetric analysis and powder X-ray diffraction method.