Síntese, caracterização e estudo das propriedades magnéticas de complexos mononucleares de cobalto(ii) contendo ligantes β-dicetonatos

Abstract

The synthesis and investigation of the magnetic properties of mononuclear first raw transition metal complexes that exhibit the magnetic behavior of Single Molecule Magnets –SMMs are one of the main aims of Molecular Magnetism area. SMMs can exhibit magnetic hysteresis at low temperatures and exhibit slow magnetization relaxation due to magnetic bistability caused by the presence of the energy barrier for the reversal of magnetization. Due to these characteristics, SMMs are sought for their potential application in the construction of high-density information storage devices and their potential use as spin qubits in quantum computing. In this work, four mononuclear cobalt(II) compounds were synthesized and characterized: [Co(PhCF3)2(H2O)2] (1), [Co(tfac)2(H2O)2] (2), [Co(PhCF3)2(NCCH3)2] (3) and [Co(tfac)2(MeOH)2] (4), where tfac = 1,1,1-trifluoromethylacetylacetonate, MeOH=methanol, NCCH3 = acetonitrile and PhCF3 = 4,4,4-trifluoro-1-phenyl-1,3-butanedione. The structure of the three of them was resolved by using single crystal X-ray diffraction data. In all cases, the coordination environment of metal ion is distorted octahedral, being coordinated by two bidentate β-diketone and two monodentate solvent molecules. 1 and 2 have trans geometry while 3 presents cis geometry. SQUID magnetometry and AC susceptometry measurements have been performed for 1, where the anisotropy parameters of cobalt(II) was determined by fitting the DC data, as well as the study of the slow relaxation mechanism of magnetization. A high anisotropy value was obtained |D| ~ 80 cm-1 and a significant rhombic anisotropy parameter. The slow relaxation process presented the Raman and QTM mechanisms, where n = 3.5, C = 62 K-3.5 s-1 and 1/QTM = 12563 s-1. The compound 1 presents an SMM behavior induced by a static magnetic field