Transformation of tetranuclear [{MoO<sub>3</sub>(L<sup>cat</sup>)Cu}<sub>2</sub>]<sup>2-</sup> into trinuclear [MoO<sub>2</sub>(L<sup>cat</sup>)<sub>2</sub>Cu<sub>2</sub>] and possible implications for the formation of Bis(MPT)Mo by MobA.