A solution-processable benzothiazole-substituted formazanate zinc(ii) complex designed for a robust resistive memory device

Abstract

A novel mononuclear bis(formazanate)zinc complex (1) based on a redox-active 1-(benzothiazol-2-yl)-5-(2-benzoyl-4-chlorophenyl)-3-phenyl formazan ligand has been synthesized and characterized. Complex 1 was prepared by reacting one equivalent of Zn(OCOCH₃)·2H₂O with two equivalents of the corresponding formazan derivative. X-ray crystallography was employed to ascertain the solid-state structure of compound 1, and the analysis revealed a distorted octahedral geometry for the complex where the symmetrical ligands exhibit a preference for coordinating with the zinc center in the ‘open’ form, generating five-membered chelate rings. Moreover, cyclic voltammetry analysis reveals that complex 1 exhibits the capacity for electrochemical reduction as well as oxidation, resulting in the formation of radical anionic (L₂Zn⁻) and dianionic (L₂Zn²⁻) states as well as the oxidation state of 1. Additionally, the developed solution-processable complex 1 was employed as the fundamental building material for resistive switching memory applications. The [FTO/Zn^IIL₂(1)]/Ag RRAM device demonstrates exceptional resistive memory switching properties, with a substantial I_ON/I_OFF ratio (10³), low operational V_SET and V_RESET (0.9 V and −0.75 V) voltages, excellent endurance stability (100 cycles), and decent retention time (more than 2000 seconds). The findings presented in this study underscore the importance of redox-active formazanate metal complexes for creating promising memory storage devices.