The unusual linear trinuclear complex [Mo3O4(TPP)(3)](+) is Formed in solution upon the reaction of [MoO(TPP)-(OClO3)] with {[MoO(TPP)](2)O}, and an equilibrium between [Mo3O4(TPP)(3)](+) and its constituent species is rapidly established. Spectrophotometric experiments suggest that [Mo3O4(TPP)(3)](+) is the predominant species found in solutions resulting from the mixture of [MoO(TPP)(OClO3)] and {[MoO(TPP)](2)O}, and its formation is strongly favored (log K = 5.5 +/- 0.5 M-1). No evidence of higher oligomers has been observed. A mechanism for the formation of [Mo3O4(TPP)(3)](+) by the controlled hydrolysis of [MoO(TPP)(OClO3)] is proposed.