Exchange Coupling and Its Chemical Trend Studied by High-Frequency EPR on Heterometallic [Ln2Ni] Complexes

We applied high-frequency electron paramagnetic resonance to trinuclear 4f–3d heterometallic complexes, [{Ln­(hfac)3}2{Ni­(dpk)2(py)2}] (Ln = Y, Gd, Tb, and Ho; hfac = hexafluoroacetylacetonate, dpk = di-2-pyridyl ketoximate, and py = pyridine), and determined the exchange parameter JLn–Ni as well as nickel­(II) zero-field splitting parameters. In contrast to the antiferromagnetic Dy analogue, ferromagnetic couplings were precisely characterized as JGd–Ni/kB = +0.301(4) K, JTb–Ni/kB = +0.216(12) K, and JHo–Ni/kB = +0.110(3) K (defined as −JLn–Ni∑JLnzSNi).

我们将高频电子顺磁共振（high-frequency electron paramagnetic resonance）技术应用于三核4f-3d异金属配合物[{Ln(hfac)₃}₂{Ni(dpk)₂(py)₂}]（其中Ln=Y、Gd、Tb和Ho；hfac=六氟乙酰丙酮根（hexafluoroacetylacetonate），dpk=二(2-吡啶基)酮肟基（di-2-pyridyl ketoximate），py=吡啶（pyridine）），并测定了Ln与Ni间的交换耦合常数$J_{Ln-Ni}$以及镍(II)的零场分裂参数。与反铁磁性的镝（Dy）类似物不同，我们精准表征了铁磁性耦合参数：$J_{Gd-Ni}/k_B = +0.301(4)$ K、$J_{Tb-Ni}/k_B = +0.216(12)$ K以及$J_{Ho-Ni}/k_B = +0.110(3)$ K，该参数定义为 $-J_{Ln-Ni}·∑J_{Lnz}·S_{Ni}$。