Syntheses, Structures And Magnetic Properties Of Cadmium Transition-metal Selenites

Transition-metal selenites exhibit various types of crystal structures due to stereochemiclly active lone pairs of Se^?, which results in asymmetric coordination environment. The lone-pair elememts can also be regarded as "structure scissosrs" giving rise to low-dimensional magnetic materials. In this thesis, learning from the development and research of transition-metal selenites, we explore a new experiment idea:selenite radical and magnetic transition-metal ions (Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺) serve as framework, and Cd²⁺ cations with large raidus were introduced inoder to cut or prevente magnetic exchange interaction along three-dimensional direction. We try to devise new transition metal selenite by elemental substitution through hydrothermal reactions. Four new crystalline compounds of Cd-M-Se-O system were synthesized. Those structures were determined by single crystal X-ray diffraction and the purity of those single phases was confirmed by X-ray powder diffraction method. Magnetic properties were investigated and analyzed.1. CdNi?SeO₃?₂·2H₂OBased on the research of CdCu?SeO₃?₂, a new compound, CdNi?SeO₃?₂·2H₂O, was synthesized by a hydrothermal reaction with substituting nickel for copper. The structure of CdNi?SeO₃?₂·2H₂O is different from the dimer-structure prototype CdCu?SeO₃?₂. Ni²⁺ ions are isolate from each other. Each NiO₆ octahedron connect with its neighbouring four SeO₃ polyhedra via corner sharing into a two-dimensional layer. The interaction of the neighbouring layers through Cd²⁺ cationics with large radius results in three-dimensional framework. Magnetic suspectibility suggests that CdNi?SeO₃?₂·2H₂O presents antiferromagnetic long-rang ordering.2. Cd3M?SeO₃?4 (M= Mn²⁺, Co²⁺, Ni²⁺)We explored Cd-M-Se-O system and synthesized series of isostructural compounds Cd3M?SeO₃?4 (M= Mn²⁺, Co²⁺, Ni²⁺). The MO₆ octahedron shares all six oxygen with SeO₃ groups. All the MO₆ octahedrons are further linked by the four SeO₃ groups, which is in the bc-plane, into a two-dimensional layer. The framework of Cd3M?SeO₃?4 is established by the layer that is rich in SeO₃ groups and the charge balance retained by the Cd²⁺ cation. The magnetic measurements show that the the presence of weak antiferromagnetic interactions within these three paramagnetic compounds.