Regulating Spin Dynamics of Nitronyl Nitroxide Biradical Lanthanide Complexes through Introducing Different Transition Metals

Abstract

Four biradical-Ln complexes with different transition metal ions, namely [LnM(hfac) 5 (NITPh-PyPzbis)] (M II = Mn II and Ln III = Gd 1, Dy 2; M II = Ni II and Ln III = Tb 3, Dy 4), were prepared by the reaction of Ln(hfac) 3 • 2H 2 O, Mn(hfac) 2 • 2H 2 O or Ni(hfac) 2 • 2H 2 O with NITPh-PyPzbis biradical (hfac = hexafluoroacetylacetonate, NITPh-PyPzbis = 5-(3-(2-pyridinyl)-1Hpyrazol-1-yl)-1,3-bis(1'-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5hydro-1H-imidazol-2-yl)benzene). In complexes 1-4, the NITPh-PyPzbis biradical chelates one Ln III ion by means of its aminoxyl moieties and the transition metal ion is introduced through the two N donors from the pyridyl pyrazolyl moiety. Magnetic investigations indicate that complex 4 displays visible maxima in frequency/temperature-dependent χ'' signals with two-step relaxation processes, but complex 2 exhibits no slow magnetization relaxation. The comparison of structure parameters of both Dy complexes indicates that the symmetries of coordination spheres of two Dy ions are D 2d for 2 and C 2v for 4, which thus probably results in different magnetic relaxation behaviors. This work provides new insight for improving properties of Ln-biradical based SMMs.

Supramolecular heptanuclear Ln–Cu complexes involving nitronyl nitroxide biradicals: structure and magnetic behavior

“…It is appealing to compare complex 3 with related biradicalbased Dy complexes. By reviewing complexes with related isolated [NIT-Dy-NIT] tri-spin fragment (Table S6 †), 46,[59][60][61] those nitronyl nitroxide biradical Dy complexes exhibit magnetic relaxation behavior except for a MnDy complex 59 in which the local symmetry of the Dy ion belongs to D 2d . This means that the symmetry of the local crystal-field of Dy ion play crucial role on the magnetic relaxation.…”

Tuning spin dynamics of binuclear Dy complexes using different nitroxide biradical derivatives

“…The fitting parameters were determined as follows: C = 3.73(2) s −1 K −1.6 , n = 2.32(6), U eff = 50.9(3) K, and τ 0 = 2.69(1) × 10 −6 s. As for complex 3 with two crystallographically equivalent Dy III ions, the dual relaxation process may be related to the phonon effects, weak intermolecular magnetic coupling, or field induction. 31,57–59 We notice a change in the exponent of the Raman process from 2 ( n = 4.17) to 3 ( n = 2.32). As is known, Raman relaxation, which mainly dominates at low temperature, arises from low-energy phonons, and molecular vibrations beyond the metal ion's first coordination sphere play an important role in the spin–phonon coupling via the electrostatic polarization effect.…”

Heterometallic Molecular Architectures Based on Fluorinated β-Diketone Ligands

“…The coordination of 3d β-diketonate with the nitroxyl radical was accompanied by the Ln(III) tris-β-diketonate transformation into the corresponding Ln(III) tetrakis-β-diketonate anion (Figure 36) [110][111][112]. In most cases, the co-crystallization of 3d and 4f β-diketonates proceeded in the presence of the aza-heteroaryl-substituted nitronyl nitroxyls to provide the additional coordination centers with metal ions (Figure 37) [113][114][115][116][117][118][119]. The Ln(III) center predominantly formed an [LnO8] environment due to both the β-diketonate anions and nitroxyl oxygen atoms.…”

“…In turn, 3d metal bis-diketonates were coordinated by either two nitrogen atoms of the heterocyclic substituents in a ligand or a nitroxyl oxygen atom and aza-heterocycle. In most cases, the co-crystallization of 3d and 4f β-diketonates proceeded in the presence of the aza-heteroaryl-substituted nitronyl nitroxyls to provide the additional coordination centers with metal ions (Figure 37) [113][114][115][116][117][118][119]. The Ln(III) center predominantly formed an [LnO 8 ] environment due to both the β-diketonate anions and nitroxyl oxygen atoms.…”