Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM, USA.
Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM, USA.
Nature. 2021 Nov;599(7885):421-424. doi: 10.1038/s41586-021-04027-8. Epub 2021 Nov 17.
Californium (Cf) is currently the heaviest element accessible above microgram quantities. Cf isotopes impose severe experimental challenges due to their scarcity and radiological hazards. Consequently, chemical secrets ranging from the accessibility of 5f/6d valence orbitals to engage in bonding, the role of spin-orbit coupling in electronic structure, and reactivity patterns compared to other f elements, remain locked. Organometallic molecules were foundational in elucidating periodicity and bonding trends across the periodic table, with a twenty-first-century renaissance of organometallic thorium (Th) through plutonium (Pu) chemistry, and to a smaller extent americium (Am), transforming chemical understanding. Yet, analogous curium (Cm) to Cf chemistry has lain dormant since the 1970s. Here, we revive air-/moisture-sensitive Cf chemistry through the synthesis and characterization of [Cf(CMeH)ClK(OEt)] from two milligrams of Cf. This bent metallocene motif, not previously structurally authenticated beyond uranium (U), contains the first crystallographically characterized Cf-C bond. Analysis suggests the Cf-C bond is largely ionic with a small covalent contribution. Lowered Cf 5f orbital energy versus dysprosium (Dy) 4f in the colourless, isoelectronic and isostructural [Dy(CMeH)ClK(OEt)] results in an orange Cf compound, contrasting with the light-green colour typically associated with Cf compounds.
锎（Cf）是目前可获得的微克级以上最重的元素。Cf 同位素由于其稀缺性和放射性危害，给实验带来了极大的挑战。因此，从 5f/6d 价轨道的可及性来参与成键，到电子结构中自旋轨道耦合的作用，以及与其他 f 元素相比的反应性模式等化学奥秘仍然难以捉摸。金属有机分子在阐明元素周期表中周期性和键合趋势方面发挥了重要作用，21 世纪钍（Th）通过钚（Pu）化学，以及在较小程度上通过镅（Am）化学的复兴，改变了人们对化学的理解。然而，类似的锔（Cm）到 Cf 化学自 20 世纪 70 年代以来一直处于休眠状态。在这里，我们通过从两毫克 Cf 中合成和表征[Cf（CMeH）ClK（OEt）]，重新激活 Cf 的空气/水分敏感化学。这种弯曲的金属茂基元，以前除铀（U）之外，尚未在结构上得到证实，包含了第一个结晶学上表征的 Cf-C 键。分析表明，Cf-C 键主要是离子键，具有较小的共价贡献。在无色、等电子和等结构的[Dy（CMeH）ClK（OEt）]中，Cf 5f 轨道能量低于镝（Dy）4f，导致 Cf 化合物呈橙色，与通常与 Cf 化合物相关的淡绿色形成对比。
