Síntese e caracterização de compostos magnéticos moleculares contendo ligantes nitróxido, nitronil-nitróxido e oxamato

Abstract

properties; from compounds with cooperative magnetic properties to the ones which the properties has molecular origin. Within molecular magnetism, compounds with single-chain magnets (SCMs) behavior is an important class, as their properties comes from the individual molecular chains and have potential applications in hard density memory devices. This work aims to synthesize and to study the structural and magnetic properties of molecular magnetic compounds using post-synthetic modifications when direct synthesis is not possible. The ligands 2-(3-phenylazide)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (m- N3PhNN), 1-Piperidinyloxy,4-(2-ethoxy-2-oxoethyl)-2,2,6,6-tetramethyl (DCC) and 4,4′- sulfonylbis(phenylene)bis(oxamate)(H2Et2L) were used to synthesize six new compounds. The structure of four of them were solved by using single crystal X-ray diffraction data (SCXRD). The small crystals of Cu(L)A complex were quickly obtained directly from the reaction. The results obtained by using infrared spectroscopy, CHN and TGA analyses suggest the oxamate ligand is coordinated to Cu2+ ions leading to complex with molecular formula C16H8CuN2Na2O12.68S. Powder X-ray diffraction analysis showed that Cu(L)A is different than the Cu2+ compounds synthesized using ligand (L) previously described in the literature. It was found out that when crystals of Cu(L)A are in contact with coordinating solvents, they undergo presumably to a post-synthetic modification changing their color from blue to green. Cu(L)A was used as reagent to synthesize the Co(L)T and Mg(L)T compounds. For the former, the structure is described as chains along the 111 direction. The magnetic measurements were performed and Co(L)T presents typical highly anisotropic Co2+ ion behavior. The crystal structure of Mg(L)T was solved and it presents three Mg2+ ions hexacoordinated being two of them crystallographically independent. The structure is a 3-dimensional network with pores filled with chloride and water molecules, which are connected through hydrogen bonds. New metal-radical coordination compounds have been synthesized. The crystal structure of [Co(hfac)2(H2O)2].2DCC was determined and show intermolecular hydrogen bonds between water molecules coordinated to the Co2+ ion and DCC molecules. The complexes [Co(hfac)2(m-N3PhNN)]n(ComN3NN) e [Mn(hfac)2(m-N3PhNN)]n (MnmN3NN) were synthesized and they crystallize in P31 space group, with helical three-fold chains running parallel to the crystallographic axis c. Both behave as ferrimagnetic chain, therefore ComN3NN showed single chain magnet behavior with blocking temperature of 9.0 K and coercivity field of approximately 32 kOe at 2.0 K. The AC magnetic susceptibility measurements were performed and two maxima in in-phase and out-of-phase magnetic susceptibilities attributed to two different relaxation processes presumably due to two different family of magnetic chains.