Four new A2CdSn2S6 (A = Cs(1), Rb(2), K(3-β) and K(3-α)) compounds have been synthesized and characterized by X-ray diffraction and spectroscopic methods. The isostructural cesium(1) and rubidium(2) compounds have noncentrosymmetric three-dimensional tetrahedral [CdSn2S6]2- framework structure and show second-harmonic-generation response. The layered potassium compounds, 3-β and 3-α, have centrosymmetric tetrahedral and octahedral [CdSn2S6]2- framework structures respectively and the compound 3-β, on heating, transforms to compound 3-α. The compound 3-α undergoes facile potassium ion-exchange in aqueous medium with various mono-, di- and tri- valent cations at room temperature. © 2019 Elsevier Inc.