Two molybdenyl carbonates with different dimensional structures exhibiting huge differences in band gaps

Two novel molybdenyl carbonates named Cs2MoO3(CO3) and Cs3MoO4(HCO3) have been synthesized using a facile solvent evaporation method. Centrosymmetric Cs2MoO3(CO3) features one-dimensional chains composed of MoO6 octahedra and CO3 groups, while noncentrosymmetric Cs3MoO4(HCO3) displays a zero dimensional framework constructed with dispersive MoO4 tetrahedra and HCO3 groups. Remarkably, although these two compounds have the same chemical composition, their band gaps differ as large as 1.04 eV, which is 3.38 eV for Cs2MoO3(CO3) and 4.42 eV for Cs3MoO4(HCO3). The molecular orbital hybridization between MoO6 and CO3 in 1D chains narrows the band gap of Cs2MoO3(CO3), which is further supported by the electron density difference map through theoretical calculations.