Synthesis And Modulation Of Magnetic Behavior Of Hofmann-type Spin-Crossover Coordination Polymers

Spin crossover materials have attracted great attention in materials science due to their potential applications as molecular switches,molecular sensors and data storage.Great progress have been made over the past three decades,however,we still have many problems unsolved,such as get more spin crossover compounds to achieve the practical application,thoroughly investigate and understand the relationship between structure and properties to precisely control the spin crossover behavior.We focus on construction of Hofmann-type coordination polymers using nitrogen-containing heterocyclic ligands,which favor the formation of supramolecular interactions to enhance the cooperativity of the system.The contents of this dissertation are as follows:1 Four novel bent ligand-pillared three-dimensional Hofmann-type metal-organic frameworks,were synthesized and crystallographically and magnetically characterized,two of which showed incomplete three-step spin-crossover behavior with a reversible three equal-step sequence of HS1.00(?)HS0.75LS0.25(?)HS0.5LS0.5(?)HS0.25LS0.75.2 We have reported the syntheses,crystal structures and magnetic properties of two isostructural Hofmann-type 2D CPs constructed with monodentate Hppy ligand.Both compounds undergo two-step SCO behavior with hysteresis loops The origin of the two-step SCO behavior can be attributed to the occurrence of symmetry-breaking phase transition in the IP region.3 Two Hofmann-like coordination polymers synthesized and crystallographically and magnetically characterized.When left the mother liquor and was exposed in air,the compounds lose crystalline state.Due to different guest molecules,two type of samples display different spin crossover behavior.4 Based on monodentate PyHbim ligand,two two-dimensional(2D)Hofmann-type coordination polymers have been synthesized,which underwent reversible crystal-to-crystal phase transition,which arose from the movements of 2D layers and guest water molecules at room temperature and resulted in distinguishing changes in their spin-crossover behaviors that corresponded to different intermolecule interactions.