The reaction of mercury(II) acetate with diethylene triamine (dien) in the presence of NaX (X −=ClO 4 − and PF 6 − ) afforded two completely different products. When the anion is smaller (ClO 4 − ), the product is a dien bridged mercury(II) dimer of the formulation [Hg 2(dien) 3](ClO 4) 4 ( 1), which is a first example of dien-bridged dimeric metal complex of mercury. However, with a larger anion as PF 6 − , the product is only a monomeric mercury(II) complex [Hg(dien)(H 2O)](PF 6) 2 ( 2). The complexes 1 and 2 have been characterized by elemental analysis, NMR, IR and FAB mass spectroscopy, as well as by X-ray diffraction analysis. Cyclic voltammetry of 1 and 2 in DMF shows irreversible oxidative voltammograms at a glassy carbon electrode, with E 1/2=0.030 and 0.026 V versus SCE, respectively, at scan rate 50 mV s −1