Relationship of cis-diammineplatinum α-pyridone blue to other platinum blues. An x-ray photoelectron study

The x-ray photoelectron spectrum (XPS) of crystalline cis-diammineplatinum a-pyridone blue, [Pt_2(NH_3)_4(C_5H_4ON)_2]_2(NO_3)_5, has been investigated and the Pt 4f binding energies of this complex found to be similar to those exhibited by Pt(II) complexes such as cis-(H_3N)_2PtCl_2. This result is in accord with the previous assignment of a formal platinum oxidation state of 2.25 in the blue a-pyridone complex. The widths of the Pt 4f peaks (fwhm ~ 1.3) indicate that the binding energies associated with the two geometrically different types of Pt environments in the α-pyridone oligomer are very similar, the implication being that within the Pt4 unit there must be a considerable delocalization of charge. A comparison of the XPS data for the α-pyridone blue with that found for the platinum uracil and acetamide blues shows that these species have similar electronic structures, there being no evidence that they are pure derivatives of Pt(IV). The XPS of some samples of the acetamide blue ("Platinblau") show the presence of small amounts of higher oxidation state contaminants, consistent with the difficulty in preparing this species in a reproducibly pure form. The Pt(III) dimer K_2Pt_2(SO_4)_4·3H_2O possesses Pt 4f binding energies which are much closer to those of coordination complexes of Pt(IV) than Pt(II)