Das Sourav, Dey Atanu, Biswas Sourav, Colacio Enrique, Chandrasekhar Vadapalli
Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur-208016, India.
Inorg Chem. 2014 Apr 7;53(7):3417-26. doi: 10.1021/ic402827b. Epub 2014 Mar 27.
The reaction of the lanthanide(III) chloride salts [Gd(III), Tb(III), and Dy(III)] with a new chelating, flexible, and sterically unencumbered multisite coordinating compartmental Schiff-base ligand (E)-2-((6-(hydroxymethyl)pyridin-2-yl)methyleneamino)phenol (LH2) and pivalic acid (PivH) in the presence of triethylamine (Et3N) affords a series of tetranuclear Ln(III) coordination compounds, [Ln4(L)4(μ2-η(1)η(1)Piv)4]·xH2O·yCH3OH (1, Ln = Gd(III), x = 3, y = 6; 2, Ln = Tb(III), x = 6, y = 2; 3, Ln = Dy(III), x = 4, y = 6). X-ray diffraction studies reveal that the molecular structure contains a distorted cubane-like Ln4(μ3-OR)4 core, which is formed by the concerted coordination action of four dianionic L(2-) Schiff-base ligands. Each lanthanide ion is eight-coordinated (2N, 6O) to form a distorted-triangular dodecahedral geometry. Alternating current susceptibility measurements of complex 3 reveal frequency- and temperature-dependent two-step out-of-phase signals under zero direct current (dc) field, which is characteristic of single-molecule magnet behavior. Analysis of the dynamic magnetic data under an applied dc field of 1000 Oe to fully or partly suppress the quantum tunneling of magnetization relaxation process affords the anisotropic barriers and pre-exponential factors: Δ/kB = 73(2) K, τ0 = 4.4 × 10(-8) s; Δ/kB = 47.2(9) K, τ0 = 5.0 × 10(-7) s for the slow and fast relaxations, respectively.
镧系（III）氯化物盐[钆（III）、铽（III）和镝（III）]与一种新型螯合、柔性且空间位阻较小的多位点配位间隔席夫碱配体（E）-2-（（6-（羟甲基）吡啶-2-基）亚甲基氨基）苯酚（LH₂）以及新戊酸（PivH）在三乙胺（Et₃N）存在下反应，得到一系列四核镧系（III）配位化合物，[Ln₄（L）₄（μ₂-η（1）η（1）Piv）₄]·xH₂O·yCH₃OH（1，Ln = 钆（III），x = 3，y = 6；2，Ln = 铽（III），x = 6，y = 2；3，Ln = 镝（III），x = 4，y = 6）。X射线衍射研究表明，分子结构包含一个扭曲的类立方烷Ln₄（μ₃-OR）₄核，它由四个二价阴离子L²⁻席夫碱配体的协同配位作用形成。每个镧系离子通过八配位（2N，6O）形成扭曲的三角十二面体几何构型。配合物3的交流磁化率测量表明，在零直流（dc）场下存在频率和温度依赖的两步异相信号，这是单分子磁体行为的特征。在1kOe的外加直流场下对动态磁数据进行分析，以完全或部分抑制磁化弛豫过程的量子隧穿，得到各向异性势垒和预指数因子：对于慢弛豫和快弛豫，Δ/kB分别为73(2)K，τ₀ = 4.4×10⁻⁸ s；Δ/kB = 47.2(9)K，τ₀ = 5.0×10⁻⁷ s。
