Synthesis,Magnetic Properties And DFT-BS Theoretical Study Of Functional Nitronyl Nitroxide Radical Complexes

Five Ln（III）-nitronyl nitroxide radical complexes:[Ln（hfac）₃（NITPh-2-OCH₂Ph）（IMHPh-2-OCH₂Ph）]（Ln=Tb（1）,Dy（2））and[Ln（hfac）₃（NITPh-2-OCH₂Ph）₂]（Ln=Ho（3）,Er（4）,Yb（5））（hfac=hexafluoroacetylacetonate,NITPh-2-OCH₂Ph=2-（2-benzyloxyphenyl）-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide,IMHPh-2-O-CH₂Ph=the reduced derivative of NITPh-2-OCH₂Ph）,have been synthesized successfully.They were characterized by IR and single-crystal X-ray diffraction.The paramagnetic nitroxide radical（NITR）is partially reduced and converted to the diamagnetic IMHR in complexes 1 and 2,respectively.All complexes show weak antiferromagnetic coupling between Ln（III）ion and NITR radical.Complexes 1 and 2exhibit frequency-dependent ac magnetic susceptibilities at low temperature,the behaviors of single molecule magnets（SMMs）.With the density functional theory combined with broken-symmetry approach（DFT-BS）scheme,the magnetic coupling constants of six complexes（as three series）:Ni（II）-nitroxide radicals,diamagetic Zn（II）or Cd（II）-nitroxide radicals and dimer Mn（II）molecules have been calculated based on the single crystal structure data.Meanwhile,the magnetic coupling mechanisms were discussed with the computed spin density plot and the molecular magnetic orbitals.The antiferromagnetic interaction of Ni（II）…NIT4py in complex[Ni（NIT4-py）₂（ip）（H₂O）]_n（7）is mainly caused by the spin polarization（SP）mechanism.In complex[Ni（IM2-py）₂Au₂（CN）₄]_n（8）,the strong Ni（II）…IM2py ferromagnetic interaction results from the orbital orthogonality of dσ（Ni（II））andπ^*（IM2py）.In complexes[Zn（NIT4-py）₂（ia）]（9）and[Cd（NIT4-py）₂（ia）（H₂O）]（10）,the intermolecular antiferromagnetic interaction（caused by NO…ON close contact）is the main factor,which is significantly larger than the intramolecular superexchange interaction.In the dinuclear Mn（II）complexes Mn₂（hfac）₄（IMHPh-2,4-（OCH₃）₂）₂（11）and[Mn₂（hfac）₄（IMHPh-2-F-5-Br）₂]（NITPh-2-F-5-Br）（12）,two Mn（II）ions are bridged by diamagnetic IMHR.The weak anti-ferromagnetic superexchange is observed between two Mn（II）ions in the molecule,which is closely related to the Mn-O bond lengths.This paper attemptted to explore the magnetic coupling mechanism and the magneto-structural correlations through the quantum chemical calculation method,but the deep research needs to be further developed.