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 (CpiPr5)2Ln2I3(CpiPr5= pentaisopropylcyclopentadienyl; Ln = Y, Gd, Tb, Dy) opened up the prospect of harnessing the 4fn5dz21electron configurations of non-traditional divalent lanthanide ions to access molecules with novel bonding motifs and magnetism. Here, we report the trinuclear mixed-valence clusters (CpiPr5)3Ln3H3I2(1-Ln, Ln = Y, Gd), which were synthesized via potassium graphite reduction of the trivalent clusters (CpiPr5)3Ln3H3I3. Structural, computational, and spectroscopic analyses support valence delocalization in 1-Lnresulting from a three-center, one-electron σ bond formed from the 4dz2and 5dz2orbitals on Y and Gd, respectively. Dc magnetic susceptibility data obtained for 1-Gdreveal 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–1determined for 1-Gdis only the second largest coupling constant characterized to date for a molecular lanthanide compound.