Family of Isomeric Cu^II–Ln^III (Ln = Gd, Tb, and Dy) Complexes Presenting Field-Induced Slow Relaxation of Magnetization Only for the Members Containing Gd^III

Abstract

The strategic design and synthesis of two isomeric Cu II complexes, [CuL A ] and [CuL B ], of asymmetrically dicondensed N 2 O 3 -donor Schiff-base ligands (where H 2 L A and H 2 L B are N-salicylidene-N′-3-methoxysalicylidenepropane-1,2-diamine and N-3-methoxysalicylidene-N′-salicylidenepropane-1,2-diamine, respectively) have been accomplished via a convenient Cu II template method. These two complexes have been used as metalloligands for the synthesis of three pairs of Cu−Ln isomeric complexes [CuL(μ-NO 3 )Ln(NO 3 ) 2 (H 2 O)]• CH 3 CN (for complexes 1A−3A, L = L A , and for complexes 1B−3B, L = L B and Ln = Gd, Tb, and Dy, respectively), all of which have been characterized structurally. In all six isomorphous and isostructural complexes, the decacoordinated Ln III centers and pentacoordinated Cu II centers possess sphenocorona and square-pyramidal geometries, respectively. The isomeric pair of Cu−Gd compounds shows field-induced slow relaxation of magnetization, although they present the typical isotropic behavior of Gd III complexes, indicating that slow relaxation is not due to the usual energy barrier originating from the magnetic anisotropy. The isostructural derivatives with the ion-anisotropic lanthanides Tb III and Dy III do not show slow magnetic relaxation with or without a direct-current bias field, demonstrating that the magnetic response of the isotropic system Cu II −Gd III occurs through different mechanisms than the rest of the Ln cations.

Quasi-isotropic SMMs: slow relaxation of the magnetization in polynuclear CuII/MnIIcomplexes

“…4h,i,p The only Gd III derivative that can be assumed as an SMM corresponds to one Cu II Gd III coupled dimer with a defined S = 3 ground state. 5 The high spin Mn II cation, having a half-filled shell ( 6 A 1g in an O h environment), also has provided some examples of slow relaxation of the magnetization for an octahedral cis-complex 6a that was earlier reported in 2014 and very recently, a similar response has been found for two mononuclear Mn II complexes in trans-octahedral 6b,c or pentagonal bipyramidal coordination environments. 6d Due to the zero contribution of ligand field stabilization energy, the coordination sphere around the Mn II ion is very plastic and thus, strongly distorted O h , penta-or heptacoordinated environments are easily accessible employing adequate ligands.…”

Modulation of Slow Magnetic Relaxation in Gd(III)‐Tetrahalosemiquinonate Complexes

“…Where A represents direct relaxation coefficient, τ QTM −1 is the rate of QTM, τ 0 −1 is the Orbach coefficient, U eff the effective energy barrier to Orbach relaxation, C the Raman coefficient and n the Raman exponent. It should be noted that the relaxation behavior of Gd‐SMMs previously reported has been fit using both Raman and Orbach relaxation processes [50–57] . The EPR measurements for 1 clearly indicate that | D Gd | 0.10 cm −1 , implying an extension of the ground S =3 multiplet of ca.…”

“…It should be noted that the relaxation behavior of Gd-SMMs previously reported has been fit using both Raman and Orbach relaxation processes. [50][51][52][53][54][55][56][57] The EPR measurements for 1 clearly indicate that j D Gd j �0.10 cm À 1 , implying an extension of the ground S = 3 multiplet of ca. 1.5 cm À 1 .…”

One-Dimensional Gadolinium (III) Complexes Based on Alpha- and Beta-Amino Acids Exhibiting Field-Induced Slow Relaxation of Magnetization

“…Heterometallic 3d-4f mixed systems, radical bridged compounds, mono-and polynuclear lanthanide (III) complexes containing highly anisotropic 4f ions, mainly Dy (III) and to a lesser extent Tb (III), Ho (III) and Er (III), were investigated during the last two decades in the field of molecular magnetism [9][10][11][12][13][14][15][16][17]. More recently, mononuclear SMMs, also known as single-ion magnets (SIMs), based on dysprosium metallocenes were reported displaying energy barriers of magnetization reversal exceeding the 1500 cm -1 value and blocking temperatures as high as that of the liquid nitrogen (>77 K), which exemplify the current progress in this research area [18,19].…”