Preparation and crystal structure of trans- S,S-[ N,N′-bis(2-hydroxyethyl)ethylenediamine(oxalato)platinum(II)]: a spontaneous resolution of individual crystals of pure optical isomers upon recrystallization

Abstract

The crystal structure of the antitumor compound trans- S,S-[ N,N′]-bis(2-hydroxyethyl)- ethylenediamine(oxalato)platinum(II)] has been determined by X-ray diffraction. This pure optical compound is tetragonal and has the following parameters: space group P4 12 12, a=6.816(5), c=26.139(15) Å, Z=4. The structure was refined on 1042 non-zero Mo Kα reflections to R=0.035. The slightly distorted square planar environment of the platinum atom includes two nitrogens of the diamine in cis positions and two oxygens from the bidentate oxalate. The PtN and PtO distances average 2.025 and 2.037 Å, respectively. The binding of the diamine ligand gives a NPtN angle of 84.7°, whereas the smaller OPtO angle of 82.5° probably results from a slight torsional twist of the oxalate. The molecular chirality facilitates the formation of two OH···O and two NH···O hydrogen bonds per molecule. This favorable pattern of hydrogen bonding is a possible driving force for resolution of the trans- S,tS- pure optical isomer in a mixture upon crystallization into individual crystals.