Equilibrium studies based on pH-potentiometric and spectrophotometric measurements as well as some theoretical simulations are reported for the complexes of Mo(VI) with a dihydroxamate type siderophore analogue, the piperazine-1,4-bis-(N-methyl-acetohydroxamic acid) (PIPDMAHA). It has been found that the complexation process starts below pH 2 and that PIPDMAHA forms more stable O,O-hydroxamate bis-chelated complexes with Mo(VI) than any of the formerly studied dihydroxamic acids. The experimental data were fitted with two complexation models based either on dinuclear or on mononuclear species. However, ESI-MS showed that the dimmer is much more abundant than the monomer. This feature was further suggested by theoretical simulation studies, which indicated the dimeric species is more stable than the monomeric one.