An Isomeric Pair of Fluoride-Bridged Cyclic Dimolybdenum Triads

A pair of isomeric cyclic triads containing three quadruply bonded [Mo2] units, [Mo2(cis-DAniF)2]2+ (DAniF = N,N‘-di-p-anisylformamidinate), bridged by six fluoride anions, has been synthesized and crystallographically characterized. For the α isomer, the three [Mo2] units are oriented in two orthogonal directions. Two of them are structurally equivalent and parallel to each other, but oriented perpendicular to the third one. The β isomer is a triangle with three geometrically identical [Mo2] units, parallel to each other, as the vertices. Thus, the β isomer possesses idealized D3h symmetry while the α isomer only has C2v symmetry. These two isomers do not interconvert in boiling THF or toluene or under irradiation with ultraviolet light, but oxidation of the α isomer first generates an α+ species that changes to β+. The two isomers have very similar electrochemical behavior, both showing three reversible one-electron redox processes for the [Mo2] centers and similar potential separations (ΔE1/2). The first and second redox couples are well separated (ca. 390−410 mV), while the second and third ones are separated by only about 150 mV.