A magnetic and conductive study on a stable defective extended cobalt atom chain

Two pentacobalt(II) EMACs were synthesized. A pyrazine-modulated tripyridyldiamine resulted in an EMAC with fully delocalized Co–Co bonds along molecules. From a pyrazine- and naphthyridine-containing ligand, a defective cobalt linear EMAC with an 8-coordinated cobalt(II) in the center was obtained for the first time. An electrochemistry study on the defective pentacobalt chain compound showed redox peaks at E1/2 = −1.00, +0.76, and +0.98 V (versus EAg/AgCl), indicating that it is quite stable and very resistant to both oxidation and reduction. Research on magnetism revealed that the fully delocalized Co EMAC is a spin mixture, and the defective cobalt EMAC showed a high-spin mononuclear cobalt(II) behaviour with a magnetic moment of 2.63μB per molecule at room temperature. Measurement on molecular electric conductance by STM bj showed a single-molecular resistance of 15.4 (±3.1) MΩ for defective and 12.3 (±2.6) MΩ for delocalized pentacobalt complexes.