Aust. J. Chem., 1982, 35, 1829-40 Cycloserine Derivatives as Ligands. The Coordinating Ability of 4,4'-[P,4-Phenylenebis(methy1- idynenitrilo)]bis(isoxazo~idin-3-one) towards Chromium(111), Ruthenium(111) and Rhodium(111) Halides Carlo Preti, Lorenzo Tassi, Giuseppe Tosi, Paolo Zannini and Aline Franca Zanoli Istituto di Chimica Generale ed Inorganica, University of Modena, 41100 Modena, Italy. Abstract The complexes of the cycloserine derivative, 4,4'-[1,4-phenylenebis(methylidynenitrilo)]bis(isoxa- zolidin-3-one) or terizidone, with chromium(~rr), rutheniurn(111)and rhodium(111) have been synthetized ; their structures have been suggested on the basis of analytical, conductivity, spectral (visible, infrared and far-infrared) and magnetic data, and the thermal analyses have revealed the extent of coordi- nated water among the chromium and ruthenium complexes. The various ligand field parameters have been evaluated; the B' values suggest a strong covalency in the metal-ligand n bond and the Dq values show a medium-strong ligand field. The position and multiplicity of the metal-halogen stretching modes in the far-infrared region have been extensively investigated and discussed; the results are particularly useful in distinguishing between the mer- and fac-isomers in the octahedral compounds of the ML,X, type. The ligand is monodentate 0-bonded or N-bonded through the oxygen of the keto group or through the nitrogen of the imino group of the isoxazole ring. We have never observed a metal-induced cycloserine ring opening under the present experimental conditions. Introduction Our interest in the coordination properties of 4,4'-[1,4-phenylenebis(methy1idyne- nitrilo)]bis(isoxazolidin-3-one), commercially known as terizidone (hereafter abbre- viated trz), derives from the fact that this molecule has wide application as a drug commonly used in clinical therapeutics, being a typical example of a sustained-release pharmaceutical preparation, whose action is attributed to a slow production of cycloserine in vivo. The transition metal complexes of cycloserine, 4-aminoisoxazolid-3-one, have been investigated in considerable and derivatives in different metallligand stoichiometric ratios, with the ligand acting always as monodentate through the different donor sites, have been obtained. The cycloserine shows in aqueous solution the equilibria given in Scheme 1, where pK, and pK, are 4.4 and 7.4 respectively. Taking into account that in the terizidone molecule (1) the above equilibria are absent, the study of its derivatives represents a valid aid in the interpretation of the results of the cycloserine derivatives too. Preti, C., and Tosi, G., J. Coord. Chem., 1979, 9, 125. Preti, C., Tosi, G., and Zannini, P., Z. Anorg. Allg. Chem., 1979, 453, 173. Preti, C., and Tosi, G., Aust. J. Chem., 1980, 33, 57.