A crystal-to-crystal transformation of (DAniF)(3)Mo-2(mu-OH)(2)Mo-2(DAniF)(3) (1) to (DAniF)(3)Mo-2(mu-O)(2)Mo-2(DAniF)(3) (2), where DAniF is the anion (p-anisyl)NC(H)N(p-anisyl), by dioxygen provides rare insight into the deprotonation process effected by dioxygen. In this dimolybdenum system, the conversion occurs without significant loss of crystallinity. Although no intermediates have been directly observed, a compound containing the [(DAniF)(3)Mo-2(mu-OH)(mu-O)Mo-2(DAniF)(3)](+) cation, a proposed intermediate, has been obtained independently. Possible pathways for the overall conversion of 1 to 2 are discussed.