Three hetero-tri-spin Ln₂CuNIT complexes based on a 1-methyl-3-pyrazole nitronyl nitroxide radical: Syntheses, structures and magnetic properties

Three hetero-tri-spin complexes, namely [Ln(2)Cu(hfac)(8)(1-Me-3-NIT-Pyz)(2)]center dot CH2Cl2 (Ln = Gd (1), Tb (2), Dy (3); hfac = hexafluoroacetylacetone; 1-Me-3-NIT-Pyz = 2-{3-(1-methyl)-pyrazolyl]}-4,4,5,5-tetramethylimidazoline1-oxyl-3-oxide), have been successfully obtained through the reaction of Cu(hfac)(2) and the pre-synthesized compounds [Ln(hfac)(3)(1-Me-3-NIT-Pyz)]. These 2p-3d-4f complexes are isomorphic three-nuclear clusters with the structure sequence of [Ln-Rad-Cu-Rad-Ln], in which each 1-Me-3-NIT-Pyz ligand exists as a tridentate bridging ligand by chelating to one Ln(hfac)(3) unit through one NO group and one pyrazole nitrogen atom, the other NO group is coordinated to the Cu(hfac)(2) unit. The static magnetic properties of all the three complexes were measured. For complex 1, with the help of a spin Hamiltonian calculation and the MAGPACK program, it was concluded that there exist ferromagnetic couplings not only between the Gd-III ion and the NIT radical but also between the Cu-II ion and the NIT radical, with J(1) = 4.2(1) and J(2) = 23.6(1) cm(-1), respectively. The fitted antiferromagnetic constant (J(3)) between radical and radical is -6.7(1) cm(-1). The dynamic magnetic results indicate that the Tb and Dy complexes show no distinct out-of-phase signals.