Singlet Tetra-Radical Nickel(II) Complex Based Versatile Molecular Memristor with Adaptive Learning Capability

Molecular memristors have emerged as pivotal components in next-generation electronics, combining redox-active functionality at the nanoscale with cognitive behaviors. Synthesis, characterization, and redox-induced interconversion of a new binuclear open-shell singlet (S = 0) tetra-radical nickel(II)-complex, [Ni^II₂(L^•–•–)₂] (1) featuring two two-electron reduced dianionic diradical scaffolds 2,9-bis(phenyldiazenyl)-1,10-phenanthroline (L) as a robust resistive switching element is reported. The complex 1 upon one-electron ligand-centered oxidation forms a mono-cationic tri-radical species [Ni^II₂(L^•–•–)(L^•–)]⁺ ([1]⁺), which upon further oxidation transforms to a di-cationic monometallic species [Ni^II(L⁰)₂] [2]²⁺. Controlled ligand-centered reduction in the presence of excess Ni(II)-sources such as NiCl₂ or Ni(ClO₄)₂ transforms the mono-metallic species [2]²⁺ to the binuclear tetra-radical complex 1. Complex 1 demonstrates exceptional performance as a molecular memristor, including high endurance over 750 cycles, 2-h data retention, and ultrafast switching speeds of 55 ns. The consistent On/Off conductivity difference under varying environmental conditions makes it promising for robust data storage and data-processing applications. Moreover, it supports advanced functionalities such as logic gate operations, 4-bit edge computing, and adaptive learning behavior, positioning it as a versatile building block for next-generation all-in-one electronic technologies.