A Trinuclear Gadolinium Cluster with a Three-Center One-Electron Bond and an S = 11 Ground State

The recent discovery of metal−metal bonding and valence
delocalization in the dilanthanide complexes (Cp^iPr5)₂Ln₂I₃ (Cp^iPr5 = pentaisopro-
pylcyclopentadienyl; Ln = Y, Gd, Tb, Dy) opened up the prospect of harnessing the
4fⁿ5d_z2¹ electron configurations of non-traditional divalent lanthanide ions to access
molecules with novel bonding motifs and magnetism. Here, we report the trinuclear
mixed-valence clusters (Cp^iPr5)₃Ln₃H₃I₂ (1-Ln, Ln = Y, Gd), which were synthesized
via potassium graphite reduction of the trivalent clusters (Cp^iPr5)₃Ln₃H₃I₃.
Structural, computational, and spectroscopic analyses support valence delocalization
in 1-Ln resulting from a three-center, one-electron σ bond formed from the 4d_z2 and
5d_z2 orbitals on Y and Gd, respectively. Dc magnetic susceptibility data obtained for
1-Gd reveal that valence delocalization engenders strong parallel alignment of the σ-
bonding electron and the 4f electrons of each gadolinium center to afford a high-spin
ground state of S = 11. Notably, this represents the first clear instance of metal−
metal bonding in a molecular trilanthanide complex, and the large spin−spin exchange constant of J = 168(1) cm⁻¹ determined for
1-Gd is only the second largest coupling constant characterized to date for a molecular lanthanide compound.