Synthesis, Structures And Properties Of Novel Nitronyl Nitroxide Radicals And Its Multi-spin Metal Complexes

Two novel nitronyl nitroxide radicals NITPhOCF3(2-(4-trifluoromethoxy-phenyl)-4,4,5,5-teramethylimidazoline-1-oxyl-3-oxide) and NITPhSCF3(2-(4-trifluoro-methyl-thiophenyl)-4,4,5,5-teramethylimidazoline-1-oxyl-3-oxide) were prepared successfully. Theywere characterized by IR, UV-vis, XRD and ESR. Nine mononuclear lanthanide complexesLn(hfac)3(NITPhOCF3)2[LnIII=SmIII(1), EuIII(2), GdIII(3), TbIII(4), DyIII(5)] andLn(hfac)3(NITPhSCF3)2[LnIII=SmIII(6), GdIII(7), TbIII(8), DyIII(9)] were prepared withLn(hfac)3·2H2O (hfac=hexafluoroacetylacetonate) and the two novel radical ligands.Additionally, one dinuclear complex [Mn(hfac)2(IMHPhOCF3)]2(NITPhOCF3)(10) wassynthesized with the transition metal ion MnIIand NITPhOCF3radical ligand.In the mononuclear radical-lanthanide complexes Ln(hfac)3(NITPhOCF3)2[LnIII=SmIII(1), EuIII(2), GdIII(3), TbIII(4), DyIII(5)] and Ln(hfac)3(NITPhSCF3)2[LnIII=SmIII(6),GdIII(7), TbIII(8), DyIII(9)], central lanthanide ion LnIIIis eight-coordinated with six oxygenatoms from three didentate hfac ligands and two nitroxide groups. The coordinationpolyhedron may be represented as a distorted dodecahedron with triangular faces. In thedinuclear MnIIcomplex [Mn(hfac)2(IMHPhOCF3)]2(NITPhOCF3)(10), two IMHPhOCF3function as bridging ligands connecting two MnIIions, in which IMHPhOCF3is a reducedform of NITPhOCF3. Each central MnIIion is six-coordinated with four oxygen atoms fromtwo didentate hfac ligands and two bridging IMHPhOCF3. The noticeable characteristic isthat there is an uncoordinated NITPhOCF3radical ligand in the simplified asymmetric unit ofthe dinuclear MnIIcomplex.The molar heat capacities of the two series of lanthanide-radical complexesLn(hfac)3(NITPhOCF3)2and Ln(hfac)3(NITPhSCF3)2were measured with differentialscanning calorimetry(DSC). The experimental molar heat capacities were fitted to apolynomial equation with the least-squares method. Besides, the smoothed molar heatcapacities and the thermodynamic functions (HT-H298.15K),(ST-S298.15K) and (GT-G298.15K) werecalculated by the relevant equations.Additionally, the magnetic properties of the complexes Gd(hfac)3(NITPhOCF3)2(3), Tb(hfac)3(NITPhOCF3)2(4), Dy(hfac)3(NITPhOCF3)2(5), Sm(hfac)3(NITPhSCF3)2(6),Gd(hfac)3(NITPhSCF3)2(7), Tb(hfac)3(NITPhSCF3)2(8), Dy(hfac)3(NITPhSCF3)2(9) and[Mn(hfac)2(IMHPhOCF3)]2(NITPhOCF3)(10) were measured and studied. Weakferromagnetic interactions were found between Gd(III) and radical ligand in complexes (3)and (7). Due to the strong spin-obrit coupling effects, it’s difficult to analysis the interactionsbetween TbIII(or DyIII) and radical ligands theoretically. The Sm(III) of complex (6), inaddition to the ground state6H5/2, the first (6H7/2) and even higher excited states can beconsiderably populated at room temperature. Therefore, the decrease of χMT value for6onlowering the temperature can be explained due to the thermal depopulation of the excitedlevels. For complex (10), the magnetic between the two central Mn(II) ions bridged by thereduced amidino-oxide oxygen atoms is weak antiferromagnetic interaction.