Rationale: These experiments were conducted to measure the diversity of organo-U(IV) and U(III) ions created using multidimensional tandem MS and collision-induced dissociation of halogen-substituted U VIO 2-phenide complexes [UO 2(C 6H 3FX)] +, X = Cl, Br, or I. Methods: Samples of UO 2(O 2C-C 6H 3FX) 2 were prepared by digesting UO 3 with appropriate halogen-substituted carboxylic acids in deionized water. Solutions for ESI were created by diluting the digested sample in 50:50 H 2O/CH 3OH. Precursor ions for multiple-stage tandem MS were generated by electrospray ionization (ESI). Multiple-stage collision-induced dissociation (He collision gas) in a linear quadrupole ion trap mass spectrometer was used to prepare species such as [U IVFX(C≡CH)] + and U IIIF(C≡CH)] + for subsequent study of ion-molecule reactions with adventitious neutrals in the ion trap. Results: Multiple-stage CID of the [UO 2(C 6H 3FX)] +, X= Cl, Br, or I, complexes caused removal of both “yl” oxo ligands from of the UO 2 2+ moiety to create ions such as [U IVFX(C≡CH)] + and [U IIIFX] +. For [U IVFXC≡CH] + and [U IIIFC≡CH] + products, hydrolysis to generate [U IVFX(OH)] + and [U IIIF(OH)] +, with concomitant loss of HC≡CH, was observed. When X = Cl and Br, elimination of HX was competitive with loss of HC≡CH. CID of [UO 2(C 6H 3FBr)] + and [UO 2(C 6H 3FI)] + caused reductive elimination of the respective halogen radicals to generate interesting organo-U(III) species such as [U IIIF(C≡CH)] + and [U IIIC 2] +. Conclusions: The use of “preparative” tandem mass spectrometry and a suite of halogen substituted benzoic acid ligands can be used to remove both oxo ligands of UO 2 2+ and generate a group of homologous organo-U(IV) and organo-U(III) ions for studies of intrinsic reactivity.