M3MoO4(HCO3) (M = Rb and Cs): cation-tuned synthesis of two noncentrosymmetric molybdate-carbonates with isolated [MoO4] and [HCO3] groups

Abstract

Two molybdate-carbonates, M₃MoO₄(HCO₃) (M = Rb and Cs), were successfully synthesized via cationic tuning. The change in the cation size and coordination resulted in the transformation from the cubic space group P3m of Na₆Li₄(MoO₄)(CO₃)₄ to the orthorhombic space group Pna2₁ of M₃MoO₄(HCO₃) (M = Rb and Cs). The Rb/Cs-based polyhedron as well as isolated [MoO₄] and [HCO₃] anionic groups are connected by sharing oxygen atoms to form an overall three-dimensional structure. Experimental results show that they have excellent stability and wide experimental band gaps of 4.38 and 4.34 eV. In addition, Rb₃MoO₄(HCO₃) exhibits a good crystal growth behavior. Based on this, the crystal of Rb₃MoO₄(HCO₃) with a size of 6 × 2 × 3 mm³ was obtained via the aqueous solution method, and its ultraviolet transmission cutoff edge was about 270 nm, which indicates that it has a potential application value in the ultraviolet region. The relationship between their structure and performance is analyzed using first-principles calculations.