Abstract The crystal structure of trans-bis(acetato)(1,1-cyclobutanedicarboxylato)ethylenediamineplatinum(IV) trihydrate, trans-Pt IV(en)(CBDCA)(OCOCH 3) 2·3H 2O, was determined by X-ray crystallographic analysis. The title compound crystallized in the monoclinic space group P2 1/ c with four formula units in a cell of dimensions a=10.320(4), b=18.764(6), c=9.926(4) Å and β=90.89(3)°. The structure was refined using 2903 observed Mo Kα reflections to R=0.036. The coordination about Pt is a slightly distorted octahedron with the Pt atom only 0.03 Å out of the equatorial plane formed by the two bidentate ligands 1,1-cyclobutanedicarboxylate and ethylenediamine. As might be anticipated, both δ and λ forms of the bound ethylenediamine ligand occurred with equal frequency in the crystal. A comparison of bond distances between the CO double bond and the CO single bond for each COO group suggested that there is no significant delocalization of any of the four CO bonds. A strong network of hydrogen bonding involving the three water molecules of solvation was observed, and the two axial acetate ligands appeared to be locked into position by intramolecular hydrogen bonds to the ethylenediamine.