The development of 68Ge/68Ga generators has made the positron emitting 68Ga isotope widely accessible, raising interest in new chelate complexes of Ga3+. The hexadentate DATAm ligand and its bifunctional analogue, DATA5m, rapidly form complexes with 68Ga in high radiochemical yield. The stability constants of DATAm and DATA5m complexes formed with Ga3+, Zn2+, Cu2+, Mn2+ and Ca2+ have been determined by pH-potentiometry, spectrophotometry (Cu2+) and 1H- and 71Ga-NMR spectroscopy (Ga3+). The stability constants of Ga(DATAm) and Ga(DATA5m) complexes are slightly higher than those of the Ga(AAZTA). The species distribution calculations indicate the predominance of Ga(L)OH mixed hydroxo complexes at physiological pH. The 1H- and 71Ga-NMR studies provided information about the coordinated functional groups of ligands and on the kinetics of exchange between the Ga(L) and Ga(L)OH complexes. The transmetallation reactions between the Ga(L) complexes and Cu2+-citrate (68.5) occur through both spontaneous and OH- assisted dissociation of the Ga(L)OH species. At pH=7.4 and 25 °C, the half lives of the dissociation of Ga(DATAm), Ga(DATA5m) and Ga(AAZTA) are 11 h, 44 h and 24 h, respectively. Similar half-lifes have been obtained for the ligand exchange reactions between the Ga(L)OH complexes and transferrin. The equilibrium and kinetic data indicate that the Ga(DATA5m) complex is a good candidate as a 68Ga-based radiodiagnostic.