Redox Properties of Platinum Uracil "Blues": A New Type of Paramagnetic Species

Platinum pyrimidine "blues," a class of potent antitumor drugs [1] derived from cw-dichlorodiammineplatinum(II) (a's-PDD) or the corresponding hydrolysis product as-diaquodiammineplatinum(II) (cis-PDDa), have lately been the subject of considerable research effort in order to elucidate their structure and mode of action. The structure of platinum a-pyridone "blue," a Pt pyridine complex in some respects acting like the Pt pyrimidine "blues," has been determined by X-ray analysis since it can be obtained in the crystalline form [2]. As yet, all attempts to crystallize the Pt pyrimidine "blues" have been unsuccessful. The Pt pyrimidine "blues" are obtained in the course of the reaction of a square-planar Pt(II) complex with certain pyrimidine ligands. The Pt uracil "blues" under study here exhibit paramagnetism and blue or green colours. These phenomena are considered to be the result of an axial Pt-Pt stacking and an overlap of atomic wave functions of mainly 5dz2-character. The "blues" may be classified as Mixed Valence Compounds. We employed ESR spectroscopy and optical absorption spectroscopy to study the compounds' redox properties.