Large Ligand Folding Distortion in an Oxomolybdenum Donor–Acceptor Complex

Interligand charge transfer is examined in the novel metallo-dithiolene complex MoO­(SPh)2(iPr2Dt0) (where iPr2Dt0 = N,N′-isopropyl-piperazine-2,3-dithione). The title complex displays a remarkable 70° “envelope”-type fold of the five-membered dithiolene ring, which is bent upward toward the terminal oxo ligand. A combination of electronic absorption and resonance Raman spectroscopies have been used to probe the basic electronic structure responsible for the large fold-angle distortion. The intense charge transfer transition observed at ∼18 000 cm–1 is assigned as a thiolate → dithione ligand-to-ligand charge transfer (LL′CT) transition that also possesses Mo­(IV) → dithione charge transfer character. Strong orbital mixing between occupied and virtual orbitals with Mo­(x2–y2) orbital character is derived from a strong pseudo Jahn–Teller effect, which drives the large fold-angle distortion to yield a double-well potential in the electronic ground state.