DFT Studies On Magnetic Coupling For Bridged Transition Metal Dimers And Polymers

The molecular-based fenomagnet is a kind of new ferromagnetic material, which is synthesized with spin carriers and can be magnetized spontaneously under Tc. It has a broad application promising in the material fields for information storage or mobile telephone communication. It also has an important scientific value for the basic research such as the origin of magnetism and the mechanism of exchange coupling. During less than 20 years' development, it has attracted increasing interesting for researchers working in chemistry, physics, and material science.Studies on magnetically coupling systems must be considered lots of atoms, complicated structures and many other influences. And it has been also hindered by serious computational problems: energy splittings of the order of 100 cm"1 or even smaller must be obtained as differences between total energies which are up to seven orders of magnitude larger. Today there are still a lot of fundamental problems pendent as the origin of ferromagnetism, the mechanism of exchange coupling, the exchange coupling ability of ligands, and so on. The theoretical study of magnetic coupling mechanisms is more challenging.In this work, on basis of :he broken symmetry approach and density functional theory (DFT), the magneto-structural characterization of a series of Cu2L2 compounds is systemically studied. It is first found that the change of the orbitals spin densities on the atoms of SOMOs is the leading reason for the influence of the magnetically coupling strength. A new model is induced for analyzing the magnetically coupling properties. A new parameter is proposed to scale the exchange coupling ability of the bridging ligands. By theoretical studies on magnetic coupling for bridging transition metal dimers and polymers, the dependence of the magnetic properties is demonstrated on some structural factor as bond lengths, bridging angles 6 and out-of-plane shift angles T, as well as substituting and structural distortion. It will provide "some theoretical evidences for the designment and synthesis of the molecular-based ferromagnets.In this work, for one thing, after the simple derivation a symmetry-broken equation is given as below,The contact of this equation is opened out with Ruiz's expression and the spin-projection formalism proposed by Noodleman. The two latter are two extremities of the above equation. The applicability of Ruiz's expression is analyzed from the magnetic coupling calculations of H2, Na2, K2 and H-He-H systems.Where L are such μ-O o ligands as oxo, hydroxo, mcthyloxo, the magnetic coupling constants for 33 models are calculated. For hydroxo ligands, it is shown that the coupling constants J are decreased with the increasing bridging angles 0 or bond lengths rCu-O, and increased with increasing out-of-plane angles T. The superexchange coupling mechanism is explored in methyloxo compounds with halogen displacement. The experiential rule proposed by Hatfield is modified in this work.Where L are such μ-N TT ligands as azido, cyanato, thiocyanato, selenocyanato, the J values for 23 models are computed. With increasing 6, the constants J for azido and thiocyanato are also decreased, whereas J for cyanato is ascended first and then descended. The sequence for J is given as N3-