The reaction of formohydroxamic acid [NH(OH)CHO, FHA] with Pu-III should result in stabilization of the trivalent oxidation state. However, slow oxidation to Pu-IV occurs, which leads to formation of the dimeric plutonium(IV) formohydroxamate complex Pu-2(FHA)(8). In addition to being reductants, hydroxamates are also strong pi-donor ligands. Here we show that formation of the Pu2(FHA)8 dimer occurs via covalency between the 5f orbitals on plutonium and the pi* orbitals of FHA-anions, which gives rise to a broad and intense ligand-to-metal charge-transfer feature. Time-dependent density functional theory calculations corroborate this assignment.