Two Co III -cyclam-acac complexes have been synthesized and isolated (acac −0 = acetylacetonate ion): [Co III (cyclam)(acac)](acac) 2 and [Co III (cyclam)(acac)](BF 4 ) 2 . Fast atom bombardment mass spectrometry has been used to characterize [Co III (cyclam)(acac)](BF 4 ) 2 Electrochemistry, spectrophotometry and IR spectroscopy helped to clear-up the role of acac − . The acetylacetonato ligand is in the Co III coordination sphere of [Co III (cyclam)(acac)](BF 4 ) 2 . In [Co III (cyclam)(acac)](acac) 2 , acac − is a ligand for the metal ion and also a counter-ion for the cationic complex, identical in both compounds. The various protons [Co III (cyclam)(acac)](BF 4 ) 2 have been identified using 1 H NMR (1D, 2D, COSY-DQF). 13 C NMR reveals that a symmetry element exists in the complex; the α carbons of cyclam have been identified using an inverse 1 H- 13 C correlation (HMQC). An X-ray crystallographic study ascertained the probable structure deduced from these methods. Co III is six coordinated, the octahedron being slightly distorted: two of the four N atoms of the tetraazamacrocycle occupy adjacent positions of the equatorial plane, the O atom of acacetylacetonate the two others.