Confinement Effects of Metal–Organic Framework on the Formation of Charge-Transfer Tetrathiafulvalene Dimers

Three transition metal coordination polymers (CPs) based on the redox-active dimethyl­thio-tetra­thia­fulvalene-bicarbox­ylate (L) and 1,3-bi­(4-pyridyl)­propane (bpp) ligands, formulated as [MnL­(bpp)]_<i>n</i> (<b>1</b>), [CdL­(bpp)]_<i>n</i> (<b>2</b>), and [Cd₂L­(bpp)₂­(H₂O)­(C₂O₄)_0.5]_<i>n</i>·<i>n</i>(ClO₄)·<i>n</i>(H₂O) (<b>3</b>), are crystallographically characterized. Complexes <b>1</b> and <b>2</b> are isostructural 2-D polymers, and <b>3</b> features an unusual 3-D metal–organic framework (MOF). The 3-D MOF is constructed from tetranuclear cluster nodes built through the μ₂-O bridge of the TTF ligand, which is first found for TTF coordination polymers. It is found that the channel generated by the 3-D MOF exerts a confinement effect on the formation of TTF dimers. The TTF dimers show strong intradimer interaction with partial electron transfer or charge transfer, and hence, the Cd compound <b>3</b> has relatively good photocurrent response property in comparison with that of 2-D Cd compound <b>2