Strong Electronic Communication by Direct Metal−Metal Interaction in Molecules with Halide-Bridged Dimolybdenum Pairs

Reactions of [cis-Mo2(DAniF)2(NCCH3)4](BF4)2, DAniF = N,N‘-di-p-anisylformamidinate, with an excess of anhydrous
Bun4NX (X = Cl, Br, I), produced the halide-bridged tetranuclear clusters, [cis-Mo2(DAniF)2]2(μ-X)4, X = Cl (1), Br
(2), and I (3). All three compounds show two reversible one-electron oxidation processes with potential separations
(ΔE1/2) between the two oxidation processes of 540, 499, and 440 mV, respectively. These ΔE1/2 values show that
the strength of the electronic coupling between the dimetal units decreases as the Mo2···Mo2 distance increases
from 1 to 2, and then to 3. The structures, EPR spectra, and near-IR (NIR) spectra of the corresponding mixed-valence species (1-PF6, 2-PF6, and 3-PF6) indicate that the clusters are electronically delocalized. Calculations at
the DFT level indicate that the strong electronic communication is principally due to a direct overlap between the
δ orbitals from the adjacent dimetal units.