Pure samples2of Re(hfac)3and Re(acac)3have been prepared and their physical properties studied by ultraviolet–visible and infrared spectroscopy, mass spectrometry, magnetic susceptibility measurements, and X-ray diffraction. The compounds are monomeric and the physical properties may be explained if the rhenium atom sits in an essentially octahedral ligand field. Re(hfac)3has a hexagonal unit cell and the acetyl-acetone complex adopts the monoclinic cell of the α-form of the three typical crystal structure types which Astbury (1) observed for trispentane-2,4-dionatometal(III) compounds. The properties observed for trispentane-2,4-dionatorhenium(III) differ from those reported previously (2, 3). The difficulties experienced in obtaining pure Re(C5H7O2)3were caused by the ease with which the material is oxidized.