One of the compounds obtained by reacting acetylacetone with oxoethoxodichlorobis(triphenylphosphine)rhenium(V) has been shown by single crystal X-ray diffraction to be trans-dichlorobis(pentane-2,4-dionato)rhenium(IV). The crystals are triclinic, a = 8.032(4), b = 8.344(6), c = 7.429(6) Å, α = 118.1(2), β = 92.3(2), γ = 55.5(2)°, [Formula: see text], Z = 1. Intensities were measured with a microdensitometer from photographs recorded on an integrating precession camera. Of the 991 measured reflections all were observed and 984 were used in the refinement. The structure was refined by full matrix least squares to an R2 value of 0.0685. The compound was found to be a trans-monomer, in contrast to the dimeric structure claimed to exist in solution. The ligand atoms bonded to rhenium lie almost exactly at the apices of an octahedron and the bond lengths (Re—Cl, 2.326(8); Re—O1, 1.97(1); Re—O2, 2.01(1) Å) are in the range expected.