We report a metal–organic framework (MOF) with rare two-dimensional (2D) secondary building unit (SBU). The SBU comprises mixed-valent Fe2+ and Fe3+ metal ions bridged by oxygen atoms pertaining to the polytopic ligand 3,3′,4,4′,5,5′-hexahydroxybiphenyl, which also define iron-oxide 2D layers. Overall, anionic exhibits topology evidences strong electronic communication between mixed-valence iro...