Synthesis, Structure And Properties Of Gd^Ⅲ-Based Molecular Coolers And Metal-Azido Compounds

The research of molecular magnetic systems has been of considerable interest for decades. The research of molecular magnetic systems is aiming at elucidating fundamental magnetic phenomena, unveiling magnetostructural correlations, and constructing new magnetic materials with potential applications. In the preparation of molecular refrigeration materials, selecting appropriate ligands and metal ions is particularly important. For the ligand, the formic acid, the smallest organic acid, with rich coordination modes can transfer magnetic couplings effectively and it is also conducive to build a tunnel complex. Sulfate with low molecular weight, multi-negative charge and high coordination number is preferable choice to synthesize molecular based magnetic refrigerants. For metal ions, GdIII ions have large ground state spin S, small magnetic anisotropy, easy spin-flip under weak magnetic field and low energy excited spin state, so it is a good candidate for the synthesis of magnetic refrigeration materials. In the preparation of metal-azido compounds, the azide anion can coordinate to many metal ions and transfer different magnetic couplings effectively.In our work, three new coordination polymers with different structures and good MCE were obtained by modifying the structure of the gadolinium sulfate. Three novel metal-azido complexes were obtained by the assembling of appropriate ligands, azide and different metals in hydrothermal conditions. The details are as follows: 1、 Three new Gd^Ⅲ-based coordination polymers [Gd₂（C₂H₆SO）（SO₄）₃（H₂O）₂]_n(¹),{[Gd₄（HCOO）₂（SO₄）₅（H₂O）₆]·H₂O}_n（2） and [Gd（HCOO）（SO₄）（H₂O）]_n（3） were obtainedby modifying the structure of the gadolinium sulfate. Among them, the structure ofcomplex1 is 2D, and formic acid did not participate in the coordination. The structuresof complex（2） and（3） are 3D, and formic acid participated in the coordination. With theincrease of the volume ratio of HCOOH and DMSO step by step in synthesis, theformate anions begin to take part in coordination, coordination numbers of sulfate anionare increasing and the contents of water and DMSO molecules decrease in thesecomplexes. That enhanced spin densities both per mass and volume which are beneficialfor a large magneto-caloric effect. Magnetic studies reveal that the more formate anionshave, the larger-ΔSmis. Complex 3 exhibits the largest-ΔSm= 49.9J·kg-¹·K-¹ for T = 2Kand ΔH = 7T among these three new complexes. 2、 Three novel metal-azido complexes were obtained by the assembling of appropriateligands, azide and different metals in hydrothermal conditions. Among them,[Fe₃(L¹)₅（N₃）₈]_n（4）(L¹)=1,10-Phenanthroline monohydrate) with zero dimensionalstructure is assembled by Fe ions, L¹, L²(L²=4,5-diazafluoren-9-one) and azide;[Cr₂(L¹)₂(L³)（N₃）2（NO₃）O₂]_n（5）（benzoic acid） with a two nuclear zero dimensionalstructure is assembled by Cr ions, L¹, and azido; [Cd(L¹)（N₃）₂]_n（6） is obtained byassembling Cd ions and L¹, and it possesses one-dimensional chain structure, the coordination mode of azide.