Structural Modulation of Anionic Group Architectures by Cations to Optimize SHG Effects: A Facile Route to New NLO Materials in the ATCO3F (A = K, Rb; T = Zn, Cd) Series

Abstract

A new series of alkali-transition metal fluoride carbonates (KCdCO3F, RbCdCO3F, KZnCO3F, and RbZnCO3F) have been synthesized under subcritical hydrothermal conditions. All crystals are isostructural with the acentric space group P6c2 (188). They were structurally characterized by X-ray single crystal diffraction and exhibited the stacking of alternating [AF]∞(A = K, Rb) and [TCO3]∞(T = Zn, Cd) layers connecting adjacent layers by infinite T–F–T (T = Zn, Cd) chains parallel to c-axis. We found that all [TCO3](T = Zn, Cd) building units aligned perfectly parallel in any given layer, but the rotation from one layer to the next resulted in the nonparallel arrangement of [CO3] groups between two adjacent [TCO3]∞ (T = Zn, Cd) layers. In this work, the relative rotation of [CO3] groups between two successive layers was successfully controlled by introducing cations of different sizes into the structures, which led to different relative rotation angles of [CO3] groups, yielding varying second harmonic generation...