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 [Fe2II(Lb)2(Lt)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-OPh and μ-OHMe 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∥≈16g∥≈16, suggesting the dimeric form exists in solution.

Graphical abstractA novel sal-type bidentate Schiff base (LH, 1) and ferrous ion assemble in the presence of weakly coordinating methanol to form [Fe2II(L)4(μ-MeOH)] (2), the first diiron(II) species, in which the two metal centers are triply bridged by single-atom donors in an asymmetric fashion involving a weakly bound methanol molecule. EPR spectra of complex 2 suggest a dimeric unit also exists in solution.Figure optionsDownload full-size imageDownload as PowerPoint slide