Fine‐Tuning of Linear Hexa‐Cobalt and Defective Penta‐Cobalt Metal‐String Complexes

The ligand, 2, 7‐bis(α‐5‐phenylpyrazinamino)‐1, 8‐naphthyridine (H 2 bphpzany), was synthesized by the reaction of 2, 7‐dichloro‐1, 8‐naphthyridine with 2‐amino‐5‐phenylpyrazine in the presence of potassium tert ‐butoxide under palladium(0)‐catalyzed conditions. Linear defective penta‐cobalt metal‐string complex [Co 5 (bphpzany) 4 (NCS) 2 ] ( 1 ) and hexa‐cobalt Co 6 11+ complex [Co 6 (bphpzany) 4 (NCS) 2 ](PF 6 ) ( 2 ) each containing four bphpzany 2– ligands were synthesized, and their structure was determined using single‐crystal X‐ray diffraction. The structure of complex 1 consists of two lantern‐type dinuclear Co 2 fragments at the terminal positions and one rare octacoordinated cobalt at the center forming a linear [Co 2 ··· Co ··· Co 2 ] chain. The magnetic susceptibility measurement of 1 shows a quartet ground state with a significant spin‐orbital contribution of the central Co II ion. Complex 2 consists of a linear Co 6 11+ configuration wrapped by four bphpzany 2– ligands and its magnetic susceptibility measurement reveals a two‐stages magnetic behavior with spin‐states of S = 1/2 at 2 K, and S = 3/2 at 300 K. The cyclic voltammograms display three redox waves at E 1/2 = +0.97, E 1/2 = +0.71 and E 1/2 = –1.02 V for 1 , and four waves at E 1/2 = +1.32, E 1/2 = +0.99, E 1/2 = +0.64, and E 1/2 = –0.14 V for 2 , respectively. The values of single‐molecular resistance for 1 and 2 are 15.5 (±4.84) and 16.1 (±10.4) MΩ, respectively.