Platinum blue

A rich family of intensely blue-coloured, linear platinum complexes, called platinum blues , has received a great body of attention in the years from 1970 to 1990, not only for their unusual physico-chemical properties, but also for their antitumor properties.14 

Our interest towards such derivatives is dictated by the fact that they are mixed-valent complexes, which means that electrons may easily flow along their metal frame. 

As a consequence of the P -P -Pt11- 11 assignment, the formal oxidation state of each platinum atom in the pentacation is + 2.25. 

Interestingly, the one-electron reduced, yellow-green, species [Pt4(NH3)8(C5H4N0)4](N03)4 was also structurally characterized. The tetracation has a geometry essentially identical to that of the pentacation, the main structural variation being a significant increase of the Pt-Pt distances (Ptl-Pt2 = 2.88 A Pt2-Pt3 = 3.13 A), which agrees with the electronic structure Ptn-Ptn—Ptn—Ptn (or, formal oxidation state of each platinum atom +2.00).16 

A similar behaviour holds for the strictly related redox couple [Pt4(en)4(C5H4NO)4]5 + /[Pt4(en)4(C5H4NO)4]4+. On passing from the blue PtII-PtIII-PtII-Ptn to the yellow PtII-PtII-PtII-Pt11, the Pt-Pt distances vary from (Pt 1—Pt2 = 2.83 A, Pt2-Pt3 = 2.92 A to (Ptl-Pt2 = 2.99 A, Pt2-Pt3 = 3.24 A. 18 

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Platinum blue formation, 2,265 Platinum complexes, S, 351-500 acetylacetone reactions, 2,380 acetylides reactions, 5,402 alcohols, 5,465 alkene-1,2-dithiolates optica] recording systems, 6,126 alkenes, 5,403 bonding, 5,403... 

Platinum blue. Berichte der Deutschen Chemischen GesellschaJi, 41, 312-314. 

Stein and co-workers have reported the structure of an unusual tetranuclear platinum(II) complex possessing both ammine and carbonato ligands.325 During a study of the reaction of cisplatin with Ag+, followed by the addition of 2 -deoxyuridine to afford platinum blue -like products from aqueous solution (pH < 2), a colorless minor product was isolated from the reaction mixture. X-ray crystallography confirmed that the product was a cyclo tetra-cation... 

Platinum-Blues and the Related Amidate-Bridged Platinum111 Compounds... 

Structures and Reactivities of Platinum-Blues and the Related Amidate-Bridged Platinum111 Compounds Kazuko Matsumoto and Ken Sakai... 

STRUCTURES AND REACTIVITIES OF PLATINUM-BLUES AND THE RELATED AMIDATE-BRIDGED PLATINUM111 COMPOUNDS... 

III. Basic Spectroscopic Properties of Platinum-Blues and Related Platinum(III) Complexes... 

VII. Antitumor Active Platinum-Blue Complexes References... 

In contrast to the usual yellow, orange, red, or colorless platinum complexes, platinum-blues are unusual for their intense blue or purple colors. The first blue platinum compound was prepared by German chemists at the beginning of this century (19). This unusual material was prepared by the reaction of Ag2S04 with yellow cis-... 

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. 

Followed by the X-ray studies on cc-pyridonate-blue, various platinum-blues and the related complexes of exocyclic amidate and imidate ligands (see Fig. 3) have been prepared and structurally ana-... 

Pt(2.5 + ), and Pt(3.0+). These oxidation states correspond to their formal oxidation states of Pt(II)2, Pt(II)3Pt(III), Pt(II)2Pt(III)2 and Pt(III)2, respectively. To date the Pt(2.75+) state corresponding to Pt(II)Pt(III)3 has never been found. In addition to this classification, the structures can also be grouped according to the orientation of the two bridging amidate ligands within a dimeric unit head-to-head (HH) and head-to-tail (HT) are known to Pt(II)2 and Pt(III)2 compounds (52, 53, 94, 95) (see A-l, A-2, D-l, and D-3 in Fig. 5). However, only the HH isomers afford a dimer of dimers, leading to the tetrapla-tinum chain structure of platinum-blues. On the other hand, the HT... 

As mentioned above, the Pt(2.25+)4 species (B1 and B2) possesses one unpaired electron of Pt(III) (S = 1/2) and is the only species which exhibits paramagnetism among the four oxidation states. The ESR spectrum of the ce-pyridonate-blue species shown in Fig. 7 exhibits an axial signal characteristic of the platinum-blues (g = —2.4 and g = —2.0) (48, 49, 70, 96). Similar signal patterns are also observed for several other blue compounds (34, 47, 57, 86, 88, 89), and these common features show that the unpaired electron resides on the dz2 orbital located along the Pt chain. The g values observed for the para-... 

A solution of the isolated platinum blue compound usually contains several chemical species described in the previous section. Such complicated behaviors had long been unexplored, but were gradually unveiled as a result of the detailed equilibrium and kinetic studies in recent years. The basic reactions can be classified into four categories (l)HH-HT isomerization (2) redox disproportionation reactions (3) ligand substitution reactions, especially at the axial coordination sites of both Pt(3.0+)2 and Pt(2.5+)4 and (4) redox reactions with coexisting solvents and atmosphere, such as water and 02. In this chapter, reactions 1-4 are summarized. 

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