Unexpected Assembly of a Novel Triply Bridged Diiron(II) Core by a Bidentate Schiff Base Ligand.

The unusual dinucleating properties of a simple bidentate Schiff base (LH, 1) in the presence of weakly coordinating methanol solvent lead to the self-assembly of [Fe(II) (2)(L(b))(2)(L(t))(2)(μ-MeOH)] (2) (b and t refer to bridging and terminally bound ligands, respectively). Complex 2 is the first diiron(II) species in which the two metal centers are triply bridged by single atoms in an asymmetric fashion, involving both μ-O(Ph) and μ-OH(Me) bridges. This binding mode produces an Fe···Fe distance of 3.139(1) Å. Dinucleation appears to be driven by a combination of ligand deficiency and solvent-mediated chemistry reminiscent of host-guest interactions. The presence of a μ-MeOH ligand is unprecedented in iron chemistry. Parallel-mode EPR spectra of complex 2 recorded at 4 K show an intense negative signal at g(||) ≈ 16, suggesting the dimeric form exists in solution.