Mixed‐Valence CuI/CuIII Metal–Organic Frameworks with Non‐innocent Ligand for Multielectron Transfer

We report two novel three‐dimensional copper‐benzoquinoid metal–organic frameworks (MOFs), [Cu4L3]n and [Cu4L3 ⋅ Cu(iq)3]n (LH4=1,4‐dicyano‐2,3,5,6‐tetrahydroxybenzene, iq=isoquinoline). Spectroscopic techniques and computational studies reveal the unprecedented mixed valency in MOFs, formal Cu(I)/Cu(III). This is the first time that formally Cu(III) species are witnessed in metal–organic extended solids. The coordination between the mixed‐valence metal and redox‐non‐innocent ligand L, which promotes through‐bond charge transfer between Cu metal sites, allows better metal‐ligand orbital overlap of the d‐π conjugation, leading to strong long‐range delocalization and semiconducting behavior. Our findings highlight the significance of the unique mixed valency between formal Cu(I) and highly‐covalent Cu(III), non‐innocent ligand, and pore environments of these bench stable Cu(III)‐containing frameworks on multielectron transfer and electrochemical properties. The first metal–organic frameworks with formally Cu(I)/Cu(III) mixed valency are reported. These bench stable Cu(III)‐containing frameworks coordinated by a non‐innocent ligand are characterized and investigated for multielectron redox properties, unveiling the redox‐active sites at both the copper and organic ligand. This is also the first time that formally Cu(III) species are witnessed in metal–organic extended solids.