A small but growing number of molecular compounds have been isolated featuring divalent lanthanides with 4fn5dz21 electron configurations. While the majority of these possess trigonal coordination geometries, we previously reported the first examples of linear divalent metallocenes Ln(CpiPr5)2 (Ln = Tb, Dy; CpiPr5 = pentaisopropylcyclopentadienyl). Here, we report the synthesis and characterization of the remainder of the Ln(CpiPr5)2 (1-Ln) series (including Y and excluding Pm). The compounds can be synthesized through salt metathesis of LnI3 and NaCpiPr5 followed by potassium graphite reduction for Ln = Y, La, Ce, Pr, Nd, Gd, Ho, and Er, by in situ reduction during salt metathesis of LnI3 and NaCpiPr5 for Ln = Tm and Lu, or through salt metathesis from LnI2 and NaCpiPr5 for Ln = Sm, Eu, and Yb. Single crystal X-ray diffraction analyses of 1-Ln confirm a linear coordination geometry with pseudo-D5d symmetry for the entire series. Structural and ultraviolet–visible spectroscopy data support a 4fn+1 electron configuration for Ln2+ = Sm, Eu, Tm, and Yb and a 4fn5dz21 configuration for the other lanthanides ([Kr]4dz21 for Y2+). Characterization of 1-Ln (Ln = Y, La) using electron paramagnetic resonance spectroscopy reveals significant s–d orbital mixing in the highest occupied molecular orbital and hyperfine coupling constants that are the largest reported to date for divalent compounds of yttrium and lanthanum. Evaluation of the room temperature magnetic susceptibilities of 1-Ln and comparison with values previously reported for trigonal Ln2+ compounds suggests that the more pronounced 6s–5d mixing may be associated with weaker 4f–5d spin coupling.

中文翻译：

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具有线性配位几何结构和显着 6s–5d 轨道混合的二价镧系茂金属配合物

已经分离出少量但数量不断增加的分子化合物，这些化合物具有 4f n 5d z 2 1电子构型的二价镧系元素。虽然其中大多数具有三角配位几何结构，但我们之前报道了线性二价茂金属 Ln(Cp iPr5 ) 2（Ln = Tb、Dy；Cp iPr5 = 五异丙基环戊二烯基）的第一个例子。在这里，我们报告了 Ln(Cp iPr5 ) 2 ( 1-Ln ) 系列（包括 Y，不包括 Pm）的其余部分的合成和表征。该化合物可通过LnI 3和NaCp iPr5的盐复分解合成随后对 Ln = Y、La、Ce、Pr、Nd、Gd、Ho 和 Er 进行钾石墨还原，对Ln = Tm 和 Lu在 LnI 3和 NaCp iPr5的盐复分解过程中进行原位还原，或通过盐复分解从对于 Ln = Sm、Eu 和 Yb，LnI 2和 NaCp iPr5 。1-Ln的单晶 X 射线衍射分析证实了整个系列具有伪D 5 d对称性的线性配位几何。结构和紫外-可见光谱数据支持 Ln 2+ = Sm、Eu、Tm 和 Yb 的4f n +1电子构型和 4f n 5d z 2其他镧系元素的1配置（[Kr]4d z 2 1用于 Y 2+）。使用电子顺磁共振波谱表征 1-Ln（Ln = Y，La）揭示了最高占据分子轨道和超精细耦合常数中显着的 s-d 轨道混合，这是迄今为止报道的钇和镧二价化合物中最大的。对1-Ln的室温磁化率的评估以及与先前报道的三角 Ln 2+化合物的值的比较表明，更明显的 6s-5d 混合可能与较弱的 4f-5d 自旋耦合有关。