Mono- and dinuclear tin(IV) complexes with Schiff bases: Synthesis, structures, redox and optoelectronic properties

Abstract

A Schiff base (named after Hugo Schiff) is a sub-class of imines, being either secondary ketimines or secondary aldimines depending on their structure. Due to relatively simplicity to synthesize, a Schiff bases allow to tune structural and physico-chemical properties of metal complexes based on them. In the present work Schiff base complexes of tin(IV) are prepared. The interaction was carried out through the microwave-assisted treatment of Et₂SnO with symmetrical and unsymmetrical Schiff base ligands based on salicylaldehyde/naphthaldehyde and a series of hydrazides/thiosemicarbazide. ¹H, ¹³C, ¹¹⁹Sn NMR spectroscopy, high resolution mass spectroscopy, UV–Vis spectroscopy and X-ray analysis were employed to investigate the molecular structure of the produced ligands and its associated metal complexes The use of symmetric derivatives with unconjugated -(CH₂)₄ and conjugated pyridine bridges allows to show that the electrochemical reduction proceeds independently at both “ends” of the molecule in the case of the unconjugated bridge and differs significantly in the case of the bridge participating in the common conjugation. All new mono- and dinuclear Sn(IV) complexes demonstrated rather narrow HOMO-LUMO gap, less than 3 eV.