Theoretical and experimental studies on three water-stable, isostructural, paddlewheel based semiconducting metal–organic frameworks

after 4 h). The band structures, density of states and band gaps of MOFs 1-3 were calculated by the GGA-PBE and GGA-PBE+U method implemented in VASP code. The calculations show that all the three compounds can be viewed as bulk intermediate band (IB) materials. The density of states of the IB in MOF 1 is high, which could suppress the non-radiative recombination. The density of states of the IB levels in MOFs 2 and 3 are low, making these levels very effective recombination centres, thus jeopardizing the photocatalytic activities of MOFs 2 and 3. The calculated results are in good agreement with experimental results and explain the photocatalytic activity differences. This study is the first to successfully address the question of how the types of unpaired electron containing electron-rich metal ions (i.e. Cu(ii), Co(ii), Ni(ii)) affect the band gaps and band structures of MOFs and thus their photoelectronic properties.