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)]n (1), [CdL­(bpp)]n (2), and [Cd2L­(bpp)2­(H2O)­(C2O4)0.5]n·n(ClO4)·n(H2O) (3),
are crystallographically characterized. Complexes 1 and 2 are isostructural 2-D polymers, and 3 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 3 has relatively good photocurrent response property in comparison
with that of 2-D Cd compound 2.