Magnetic metal complexes are a kind of magnetic compounds formed by combining paramagnetic ions and diamagnetic ligands by means of spontaneous assembly and controlled assembly. The paramagnetic ions can be transition metal ions or rare earth metal ions. The magnetism of magnetic metal complexes is related to the paramagnetic center with unpaired electrons, and the paramagnetic center can produce isolation or synergistic action in a coordination chemical environment. By studying the spin state of the isolated paramagnetic ions in the ligand field, the transition between high and low spin states can be realized. Furthermore, by studying the synergistic behavior between spins, the magnetic coupling effect and magnetic ordered temperature can be adjusted, so as to obtain various materials with different magnetic properties. Applications: Magnetic metal complexes are easily modified and can be tailored at the molecular level by chemical methods. Other functional groups can be grafted onto magnetic metal complexes to enable them to have two or more functions, which greatly extends their applications. Multifunctional magnetic metal complexes, such as electric-magnetic materials, optically magnetic materials, chiral and microporous magnetic materials, can be obtained by combining the magnetism with electrical, light or other properties. Magnetic metal complexes have a broad application prospect in energy storage areas, recording materials with high storage density and others. Energy storage areas: In recent years, in order to solve the environmental pollution problem, renewable clean energy is gradually replacing fossil energy, and hydrogen energy is one of the most important renewable clean energy. However, the storage of hydrogen energy has always been a difficult problem. Taking the advantages of light weight and good adsorption performance, magnetic metal complexes can be an ideal candidate.