A Chiral Bipyrimidine-Bridged Dy2 SMM: A Comparative Experimental and Theoretical Study of the Correlation Between the Distortion of the DyO6N2 Coordination Sphere and the Anisotropy Barrier

Abstract

Chiral bipyrimidine-bridged dinuclear LnIII complexes of general formula [(μ-bipym){((+)-tfacam)3Ln}2] and [(μ-bipym){((-)-tfacam)3Ln}2], have been prepared from the assembly of Ln(AcO)3·nH2O (LnIII = Dy, Gd), (+)/(−)-3-(trifluoroacetyl)camphor enantiopure ligands ((+)/(-)-Htfacam) and bipyrimidine (bipym). The structure and chirality of these complexes have been supported by single-crystal X-Ray diffraction and circular dichroism. The study of the magnetic properties of the GdIII complexes revealed a very weak antiferromagnetic interaction between the GdIII ions through the bipyrimidine bridging ligand. Ab initio CASSCF calculations indicated that the ground Kramers doublet (KD) of both DyIII centers is almost purely axial with the anisotropy axis located close to the two tfacam−ligands at opposite sides of each DyIIIatom, which create an axial crystal field. In keeping with this, ac dynamic measurements indicated slow relaxation of the magnetization at zero field with Ueff = 55.1 K, a pre-exponential factor of τo = 2.17·10−6 s and τQTM = 8 μs. When an optimal dc field of 0.1 T is applied, QTM is quenched and Ueff increases to 75.9 K with τo = 6.16 × 10−7 s. The DyN2O8 coordination spheres and SMM properties of [(μ-bipym){((+)-tfacam)3Ln}2] and their achiral [(Dy(β-diketonate)3)2(μ-bpym)]analogous have been compared and a magneto-structural correlation has been established, which has been supported by theoretical calculations. In contrast to the GdIII compounds, the magnetic exchange interaction between the DyIII ions has been calculated to be very weak and, generally, ferromagnetic in nature. Relaxation mechanisms for [(μ-bipym){((+)-tfacam)3Ln}2] and previously reported analogous have been proposed from ab initio calculations. As the magnetic exchange interaction found to be very weak, the observed magnetization blockade in these systems are primarily dictated by the single ion anisotropy of DyIII ions.

Chiral or Luminescent Lanthanide Single-Molecule Magnets Involving Bridging Redox Active Triad Ligand

“…The best fit was obtained for τ 0 = 3.2(7) × 10 −6 s and ∆ = 53(2) K parameters which are used to simultaneously fit the log(τ) vs. T plots at 0 Oe and 1200 Oe with shared Raman parameters and additional QTM process in zero fields. It is worth noticing that this effective energy barrier is close to the value of 55.1 K found in a similar dinuclear complex involving the simple 2,2 bipyrimidine bridging ligand instead of L [78]. The best simultaneous fit was obtained for τ 0 = 3.2 × 10 −6 s (fixed) and ∆ = 53 K (fixed), C = 0.10(2) s −1 K −n with n = 3.94 (15) and τ TI = 1.30(8) × 10 −4 s (Figure S24).…”

Homochiral Ferromagnetic Coupling Dy2 Single-Molecule Magnets with Strong Magneto-Optical Faraday Effects at Room Temperature

“…Recent research has shown that 6-chloro-2-hydroxypyridine can be used as the bridging ligand or as the terminal ligand for assembling 3d–4f SMMs. , We chose 6-chloro-2-hydroxypyridine as the coligand to evaluate its ability for bridging lanthanide (III) ions, while the chiral β-diketone ligand (−)/(+)-3-trifluoroacetyl camphor was responsible for the introduction of chirality. − When 6-chloro-2-hydroxypyridine and (−)/(+)-3-trifluoroacetyl camphor were treated with Dy­(Ac) 3 ·4H 2 O in MeOH–MeCN–H 2 O solution at room temperature in the presence of potassium tert -butoxide, the homochiral Dy­(III) dinuclear complexes [Dy 2 ( l -tfc) 4 (chp) 2 (MeOH) 2 ] ( l - 1 ) and [Dy 2 ( d -tfc) 4 (chp) 2 (MeOH) 2 ] ( d - 1 ) could be obtained. Their purity could be confirmed by comparing their XRD spectra with the simulated diffraction patterns according to their single crystal structures (Figures S1 and S2), and the corresponding peaks coincide with each other well for both l - 1 and d - 1 .…”

“…Comparably, the bridging ligand used in another pair of enantiomerically pure Dy 2 complexes of (+)/(−)-3-trifluoroacetyl camphor, [(μ-bipym)­{((+)/(−)-tfc) 3 Dy} 2 ], is the electrically neutral [N 4 ] tetradentate ligand, bipyrimidine (bipym), and their coordination configuration is the DyN 2 O 6 square antiprism.…”

Role of the Templating Heteroatom on Both Structural and Magnetic Properties of POM‐Based SIM Lanthanoid Complexes

“…For mononuclear heteroleptic (LPOM + auxiliary ligand) Ln III [3,52,53] The dynamic properties of the first Dy III compound were studied under an applied dc field of 2000 kG, with the best fit parameters of U eff = 36.4 cm À 1 , τ 0 = 5.3 × 10 À 9 s, τ QTM = 0.021 s, A = 8.61 s À 1 K À 1 , n = 3.65 and C = 0.997 K À n s À 1 (Figure 7). [52] The Ln III ion have SAPR geometry like its inorganic analogue [Dy III (PW 11 O 39 ) 2 ] 11À .…”

“…This means that the ligand defines the coordination and symmetry of the complex, so the combination of different types of ligands should have an effect on the geometry that the Ln III ion will adopt. [2,3] Ln III complexes usually formed compounds with high coordination number with weak metal-ligand bonds. In the literature it is possible to find systems in which the coordination number varying from 6 to 12.…”