Zinc and Cobalt Coordination Polymers Based on the Redox‐Active Linker 4,4′‐(Phenazine‐5,10‐diyl)dibenzoate: Structures and Electrochemical Properties

The novel coordination polymers [Zn(PZDB)(DEF) 2 ] n (Zn‐PZDB) and [Co(HPZDB) 2 (DEF) 2 ] n (Co‐HPZDB) (H 2 PZDB = 4,4′‐(phenazine‐5,10‐diyl)dibenzoic acid, DEF = N,N ‐diethylformamide) are synthesized solvothermally from the metal nitrate salts and the linear H 2 PZDB linker with the redox‐active phenazine‐5,10‐diyl core. Zn–PZDB is composed of zigzag chains with the Zn ion tetrahedrally coordinated by two diethylformamide (DEF) molecules and two carboxyl O‐atoms from the bridging PZDB 2− linker. The crystal structure of Co‐PZDB represents a two‐dimensional (2D) coordination grid. The Co 2+ ion is octahedrally coordinated by two DEF molecules and four carboxyl oxygen atoms of the semi‐deprotonated HPZDB − linker molecules. Yellow Zn‐PZDB and red Co‐PZDB turn green upon air exposure, which is due to linker oxidation, forming the (H)PZDB + radical cation. UV/Vis/NIR spectroelectrochemistry reveals that Me 2 PZDB undergoes two reversible one‐electron oxidations, producing characteristic absorption bands. Similar spectroscopic changes are observed upon oxidation of Zn‐PZDB and Co‐HPZDB. Chemical oxidation with SbCl 5 yields the same color changes together with electron paramagnetic resonance signals typical of ligand‐based radical cations. These findings indicate that the PZDB linker is the primary redox site. Ligand oxidation is followed by disintegration of the coordination polymers.