δ-Bonding and Electron Localisation in Crystalline Divalent Rare Earth Arene Complexes
crossref(2024)
摘要
Landmark advances in rare earth (RE) chemistry have shown that formally divalent complexes can be isolated with non-Aufbau 4fn5d(dz2)1 or 4fn{5d/6s}1 electron configurations, which facilitate novel bonding motifs and phenomenal magnetic properties. We report an unprecedented series of divalent bis-tethered arene complexes, [RE(NHAriPr6)2] (2RE; RE = Sc, Y, La, Sm, Eu, Tm, Yb; NHAriPr6 = {N(H)C6H3-2,6-(C6H2-2,4,6-iPr3)2}), where 2Sc, 2Y, and 2La show metal-arene δ-bonding via nd(x2-y2)- and π* orbital mixing, while 2Sm, 2Eu, 2Tm, and 2Yb contain 4fn+1 ions without δ-bonds. Fluid solution EPR spectroscopy gives giso = 1.9995, 1.998, 1.989 for 2Sc, 2Y, and 2La, respectively, consistent with formal nd1 configurations, while metal hyperfine interactions suggest extensive delocalisation. Solution and crystalline phase EPR and UV-Vis-NIR spectroscopy for 2Y show incongruities due to minor structural changes between these phases that markedly alter the metal 4d(x2-y2) character to the SOMO (22% vs 12%, respectively). In contrast to existing 4fn5d(dz2)1 or 4fn{5d/6s}1 complexes where the valence d-based electron resides in a non-bonding orbital, the sensitivity of 2Y to its local environment suggests RE(II) arene δ-bonding represents a hitherto unexplored opportunity to tune the electronic structure properties of nd1 rare earth ions.
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