Cd(NH2SO3)2·xH2O (x = 0, 2): new sulfamates with a unique coordination environment and reversible phase transitions

Abstract

Two new cadmium sulfamates, namely, centrosymmetric Cd(NH₂SO₃)₂·2H₂O and noncentrosymmetric Cd(NH₂SO₃)₂ have been successfully synthesized. Crystals of Cd(NH₂SO₃)₂·2H₂O grown using an aqua-solution method reveal an infinite chain structure consisting of trans-[CdO₂(H₂O)₂(NH₂)₂] octahedra and [NH₂SO₃] units. Crystals of Cd(NH₂SO₃)₂ obtained during the process of dehydration of Cd(NH₂SO₃)₂·2H₂O exhibit a 3D framework composed of cis-[CdO₄(NH₂)₂] octahedra and [NH₂SO₃] tetrahedra. Temperature- and humidity-induced reversible phase transitions of the title compounds are observed, which is confirmed by TGA and PXRD. Cd(NH₂SO₃)₂ exhibits a phase-matchable SHG response of ca. 0.15 × KDP. Interestingly, nitrogen-containing [CdO₄N₂] octahedra are found in the metal sulfamates for the first time. The unique arrangement is discussed with the hard-and-soft acids and bases theory and further compared with other existing [MO₆] (M = Na, Mg) octahedra in sulfamates. In addition, the discovery would provide a new perspective to design new materials by adjusting the structural arrangement for polar anionic groups.