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

Abstract

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.