Frustrated Spin Coupling System:Design And Theoretical Study Of Single Molecule Magnet

Hydroximic acid complexes could chelate with metal atoms or cations to form five-membered or six-membered rings according to the existence of O,N and S atoms.Thus,we chose oxime,hydroximic acid as the ligands reacting with the metal ions to obtaining 19 complexes,which the single crystal structures and magnetic properties were characterized.Salicylhydroxamic acid has a hydroxyl group at the adjacent position,so it is selected to react with transition metal and lanthanide ions obtianing 19 metallacrowns,in which nine complexes are called 3d-4f-5d mixed metal metallacrowns possess both transition metals and rare earth metals,the others include nine 3d-4f-4d and one 3d-3d-5d mixed metal metallacrowns.In this thesis,the single crystal structure and magnetic properties of these mixed metal metallacrowns were characterized and the magnetostructural correlation was investigated in details.The main contents are listed as follows:1.Salicylhydroxamic acid reacting with manganese,rare earth and octacyanotungstate ions,9 complexes were obtained as 3d-4f-5d mixed metal metallacrowns:(Et4N)5[MnⅢ4LnⅢ(shi)4(OAc)4WⅤ(CN)8](WO4(0.5(LnⅢ=YⅢ(1),,GdⅢ(2),TbⅢ(3),DyⅢ(4),HoⅢ(5),EnⅢ(6),TmⅢ(7),YbⅢ(8),LuⅢ(9)),which were characterized by single-crystal X-ray diffraction,elemental analysis and FT-IR spectra.The 12-MC-4 metallacrown comprise four manganese ions and four deprotoned salicylhydroxamic acid ligands together with a rare earth metal ion in the center of the ring.All manganese ions are bridged to the rare earth metal ion by an acetate,while the octacyanotungstate coordinates to the four MnⅢ ions on the MC ring by cyanide.Studies of the magnetic properties indicate the presence of dominant antiferromagnetic in these complexes,however,all the magnetic data show the ferromagnetic polarization resulting from the spin frustration effect.2.When octacyanomolybdate replaces octacyanostangstate ions,9 complexes as 3d-4f-4d mixed metal metallacrowns were obtained:(Et4N)5[MnⅢ4LnⅢ(shi)4(OAc)4MoⅤ(CN)8](MoO4)0.5(LnⅢ=YⅢ(10),GdⅢ(11),TbⅢ(12),DyⅢ(13),HoⅢ(14),ErⅢ(15),TmⅢ(16),YbⅢ(17),LuⅢ(18)),which were also characterized by single-crystal X-ray diffraction,elemental analysis and FT-IR spectra.The structure are very similar to octacyanotungstate-bridged 3d-4f-5d complexes.Studies of the magnetic properties indicate the coupling between metal ions is still antiferromagnetic in these complexes,but all the measured magnetic results showed the dominantly antiferromagnetic fashion different from those of octacyanotungstate-bridged 3d-4f-5d metallacrowns.This phenomenon is also ascribed to the spin frustration effect and the difference of octacyano-molybdate and-tangastate system is because that the coupling between 5d and 3d spins is stronger than between 4d and 3d spins.3.Salicylhydroxamic acid reacting with manganese and octacyanotungstate ions,one 3d-3d-5d mixed metal metallacrown complex was obtained as(Et4N)3[MnⅢ4MnⅡ(shi)4(OOCH)2(OMe)2WⅤ(CN)8](19),which is different from the 3d-4f-5d mixed metal metallacrowns.The characterization in magnetic properties showed the antiferromagnetic fashion between the 5d and 3d metal ions.The ground state was remarkably deduced by antiferromagnetic interactions.However,complex 19 showed much more obvious single-molecule magnetism than other complexes due to spin frustration effect.