A series of three isostructural tetranuclear complexes with the general molecular formula [Ln₄(μ₃-OH)₄(L)₄(μ₂-piv)₄(MeOH)₄] (Ln = Gd 1, Dy 2 and Ho 3; LH = [1,3-bis(o-methoxyphenyl)-propane-1,3-dione]) were isolated and unambiguously characterized by single crystal XRD. Under similar reaction conditions, simply changing the co-ligand from pivalate to 2,6-bis(hydroxymethyl)-p-cresol (LH′₃) led to the isolation of dinuclear Ln(III) complexes with the general molecular formula [Ln₂(L)₄(μ₂-LH′₂)₂]·4DMF (Ln = Gd 4, Dy 5 and Ho 6). Direct current magnetic susceptibility data studies on the polycrystalline sample of 1–6 and the results reveal the existence of weak antiferromagnetic exchange interactions between the lanthanide ions in 1 which is evident from the spin Hamiltonian (SH) parameters (J₁ = −0.055 cm⁻¹ and g = 2.01) extracted by fitting χ_MT(T). On the other hand, though complex 4 exhibits weak antiferromagnetic coupling (J₁ = −0.048 cm⁻¹ and g = 1.99) between the Gd(III) ions, the χ_MT(T) data of complexes 5 and 6 unambiguously disclose the presence of ferromagnetic interactions between Dy(III) and Tb(III) ions at lower temperature. Magnetization relaxation dynamics studies performed on 2 show frequency dependent out-of-phase susceptibility signals in the presence of an optimum external magnetic field of 0.5 kOe. In contrast, complex 5 shows slow magnetization relaxation with an effective energy barrier (U_eff) of 38.17 cm⁻¹ with a pre-exponential factor (τ₀) of 1.85 × 10⁻⁶ s. The magnetocaloric effect (MCE) of complexes 1 and 4 was extracted from the detailed magnetization measurement and the change in the magnetic entropy (−ΔS_m) of 1 and 4 was found to be 25.57 J kg⁻¹ K⁻¹ and 12.93 J kg⁻¹ K⁻¹, respectively, at 3.0 K for ΔH = 70 kOe.

中文翻译：

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配位几何形状对一系列Ln ₂和Ln ₄羟基簇的磁性的影响†

一系列三种同构的四核配合物与一般分子式[LN ₄（μ ₃ -OH）₄（L）₄（μ ₂ -piv）₄（甲醇）₄ ]（Ln为钆1，DY 2和Ho 3 ;分离出LH ＝ [1，3-双（邻甲氧基苯基）丙烷-1，3-二酮]，并通过单晶XRD明确表征。在类似的反应条件下，简单地改变从新戊酸酯的共配位体2,6-双（羟甲基） - p甲酚（LH' ₃）导致的双核LN（的隔离III与一般分子式）配合物[LN₂（L） ₄（μ ₂ -LH' ₂） ₂ ]·4DMF（Ln为钆4，镝5和Ho 6）。上的多晶样品直流磁化率数据研究1-6和结果揭示了镧系元素的离子之间的弱反铁磁交换相互作用在存在1从自旋哈密顿（SH）的参数（明显Ĵ ₁ = -0.055厘米^{- 1}和克= 2.01）通过拟合提取χ_中号Ť（ Ť）。另一方面，尽管复杂4展品弱反铁磁耦合（Ĵ ₁ = -0.048厘米^-1和克钆（之间= 1.99）III）离子时，χ_中号Ť（Ť）络合物的数据5和6清楚地公开了Dy的铁磁相互作用的存在（III）和Tb（III）离子。对2进行的磁化弛豫动力学研究显示，在存在0.5 kOe的最佳外部磁场的情况下，频率相关的异相磁化率信号。相比之下，复杂5示出慢磁化弛豫与有效能垒（Ú _EFF）的38.17厘米^-1具有预指数因子（τ ₀为1.85×10）^-6秒。复合物的磁热效应（MCE）1和4被从详细的磁化测量，并在磁熵（-Δ变化提取小号_米的）1和4被认为是25.57Ĵ千克^-1 ķ ^-1和12.93Ĵ对于ΔH = 70 kOe ，在3.0 K时分别为kg ^-1 K ^-1。