Both title compounds, bis(triphenylphosphine)iminium tetrabromooxomolybdate(V), (C₃₆H₃₀NP₂)[MoOBr₄], and tetraphenylphosphonium aquatetraiodooxomolybdate(V), (C₂₄H₂₀P)[MoOI₄(H₂O)], form by air-oxidation of solutions containing the [Mo₃X₁₂]^3- anion, i.e. the bis(triphenylphosphine)iminium salt for X = Br and the tetraphenylphosphonium salt for X = I. Both anions have been reported previously in different salts. The geometry of the tetrabromooxomolybdate(V) anion is square pyramidal with the oxo ligand occupying the apical position, whereas the aquatetraiodooxomolybddate(V) anion can be described as a pseudo-octahedron with the aqua and oxo ligands occupying trans positions.