Structural, Spectroscopic, and Theoretical Comparison of Traditional vs Recently Discovered Ln²⁺ Ions in the [K(2.2.2-cryptand)][(C₅H₄SiMe₃)₃Ln] Complexes: The Variable Nature of Dy²⁺ and Nd²⁺

Abstract

The Ln(3+) and Ln(2+) complexes, Cp'3Ln, 1, (Cp' = C5H4SiMe3) and [K(2.2.2-cryptand)][Cp'3Ln], 2, respectively, have been synthesized for the six lanthanides traditionally known in +2 oxidation states, i.e., Ln = Eu, Yb, Sm, Tm, Dy, and Nd, to allow direct structural and spectroscopic comparison with the recently discovered Ln(2+) ions of Ln = Pr, Gd, Tb, Ho, Y, Er, and Lu in 2. 2-La and 2-Ce were also prepared to allow the first comparison of all the lanthanides in the same coordination environment in both +2 and +3 oxidation states. 2-La and 2-Ce show the same unusual structural feature of the recently discovered +2 complexes, that the Ln-(Cp' ring centroid) distances are only about 0.03 Å longer than in the +3 analogs, 1. The Eu, Yb, Sm, Tm, Dy, and Nd complexes were expected to show much larger differences, but this was observed for only four of these traditional six lanthanides. 2-Dy and 2-Nd are like the new nine ions in this tris(cyclopentadienyl) coordination geometry. A DFT-based model explains the results and shows that a 4f (n)5d(1) electron configuration is appropriate not only for the nine recently discovered Ln(2+) ions in 2 but also for Dy(2+) and Nd(2+), which traditionally have 4f (n+1) electron configurations like Eu(2+), Yb(2+), Sm(2+), and Tm(2+). These results indicate that the ground state of a lanthanide ion in a molecule can be changed by the ligand set, a previously unknown option with these metals due to the limited radial extension of the 4f orbitals.

Reactivity and Properties of Metal Complexes Enabled by Flexible and Redox-Active Ligands with a Ferrocene Backbone

“…106 However, chemists never stopped pushing synthetic limits and, recently, low valent lanthanide chemistry has emerged as a fast developing field. [107][108][109] Recent advancements feature the synthesis and characterization of divalent lanthanide complexes for the complete lanthanide series, [110][111][112][113][114][115][116] reduced dinitrogen complexes, [117][118][119][120][121] reduced arene complexes, 26-29, 57, 122-126 and bimetallic reductive cleavage of aromatic C-H bonds. 40,44 Our group focused on the reduction chemistry of rare-earth metal complexes with non-innocent  ligands, followed by a small molecule activation study.…”

A Macrocyclic Chelator That Selectively Binds Ln4+ over Ln3+ by a Factor of 1029

“…Moreover, recent work has shown that ligand fields can be used to tune lanthanide redox chemistry 65,[104][105][106][107][108][109] and ground state electronic configurations. [110][111][112][113][114][115] Clearly, efforts to advance understanding of the roles that covalency and electronic structure play in governing chemical and physical properties would benefit from broader integration of synthetic, spectroscopic, and theoretical research efforts.…”

Reactivity of the Ln2+ Complexes [K(2.2.2-cryptand)][(C5H4SiMe3)3Ln]: Reduction of Naphthalene and Biphenyl

“…Yttrium was the initial metal of choice due to its favorable NMR characteristics associated with a 100% naturally abundant I = 1/2 89 Y nucleus. To contrast the chemistry of this smaller rare earth ion with that of larger metal ions, the analogous reactions with the largest lanthanides, lanthanum and cerium, 19 were examined. The dysprosium analogue 19 was also studied as a typical openshell lanthanide and a member of the set of traditional six Ln 2+ ions described above.…”

“…To contrast the chemistry of this smaller rare earth ion with that of larger metal ions, the analogous reactions with the largest lanthanides, lanthanum and cerium, 19 were examined. The dysprosium analogue 19 was also studied as a typical openshell lanthanide and a member of the set of traditional six Ln 2+ ions described above. Not only was reduction of aromatic substrates observed, but these reactions also led to the isolation of the tetrakis(trimethylsilylcyclopentadienyl) complexes, (Cp′ 4 Ln) − .…”

“…Ce, 23 Dy 19 ), [K(2.2.2-cryptand)]-[Cp′ 3 Ln]·THF, 1-Ln (Ln = Y, La, Ce, Dy), 4,19 and [Cp′ 2 Y(THF) 2 ]-[BPh4 ],2 were prepared according to the literature, and the La, Ce, and Dy complexes were prepared analogously 19. 2.2.2-Cryptand,(4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane), (Aldrich) was placed under vacuum (10 −3 Torr) for 12 h before use 1.…”