Diammineplatinum a-Pyridone Blue

Submitted by PRADIP K. MASCHARAK and STEPHEN J. LIPPARDt Checked by F. ALBERT COTTON and DANIEL P. BANCROFT  

Although the isolation of the first blue platinum compound was reported as early as 1908, the nature of the bonding in the platinum blues re- 

DIAMMINEPLATINUM(2.25-I-))1 PENTANITRATE HYDRATE (cis-DIAMMINEPLATINUM o-PYRIDONE BLUE OR PPB) 

2 g (4 mmol) of cis-[(NH3)2Ptl2] (ref. 8) is allowed to react with 1.35 g (8 nunol) of silver nitrate in 35 mL of water at 60° for 1 hr and the mixture is filtered through Celite to remove silver iodide. A 400 mg (4.2 mmol) 

The product obtained from these procedures is pure. However, PPB can be recrystallized from 0.1 Af nitric acid solution to produce dark platelike crystals. 

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The first direct evidence for the structure of platinum-blues was provided by the single-crystal X-ray studies of cis-diammineplatinum a-pyridonate-blue, [Pt(2.25+)4(NH3)8(/x-a-pyridonato-N,0)4] (N03)5 H20 (48, 49). In the study, Barton and Lippard selected a-pyridone as a simplified model of pyrimidine bases (see Fig. 3), which must be the primary reason of their success in obtaining the first crystalline-blue material. 

Crystals of PPB are stable in air and dissolve in water to give a deep blue solution, which slowly bleaches with time. The blue color is enhanced and stabilized in the presence of nitric or perchloric acid (pH 1) and/or 0.1 Af sodium nitrate or perchlorate. In 0.1 M nitric acid PPB exhibits three optical spectroscopic bands at 680, 480, and 405 nm. The blue color is rapidly discharged in the presence of chloride ion and can be restored by removing chloride with silver nitrate. cu-Diammineplatinum a-pyridone blue is paramagnetic and exhibits strong ESR signals at room temperature, with g values of 2.37 and 1.99. 

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