Platinum mixed-valence compounds

Platinum is unusual in the extraordinary variety of mixed-valence compounds that it forms. Many of these have novel spectroscopic, electronic, and structural properties. 

The localized-valence halogen-bridged platinum(II)/platinum(IV) complexes (175) are of interest because of their highly anisotropic electrical and optical properties. The complexes are characterized by broad and intense intervalence bands in their electronic spectra.542 Partial oxidation of [PtCl(dien)]Cl with iodine yields the mixed valence species [PtI(dien)][PtI3(dien)]I2,543 but when 4Me-dien is used, the mixed valence compound is only obtained if it is trapped quickly, before isomerization of the meridional platinum(IV) complex to a facial form.544 Although these species nominally have localized valences, the extent of delocalization increases as the bridging halide... 

The salt may be best described as a mixed-valence compound containing platinum in the 2.3+ oxidation state. The combination of the mixed-valence state, the very short Pt— Pt separation of 2.89 A (only approximately 0.1 A longer than in platinum metal), and the formation of linear Pt—Pt chains along the c axis gives rise to the high, anisotropic metallic conductivity in this material.1... 

Miscellaneous. Reduction of a palladium salt by CO is the basis of a visual test for ambient carbon monoxide (227). Palladium compounds are used as photographic sensitizers (228). The low dimensional mixed valence compound Csq 3[Pd(S2C2(CN)2)] 0.5H2O behaves as a semimetal at room temperature (229). Palladium compounds isostructural with potent platinum antitumor compounds have poor antitumor activity (230). 

Pt complexes have been reviewed. These are often mixed Pt VPt complexes many have a chain structure with M M interactions or even M M bonds. Others have Pt -Hal-Pt -Hal-Pt chains. An example of the latter has Pt L4Cl2 " units alternating with Pt L2Cl2 units. Many analogs are now known. The related platinum blues are oligomeric mixed valence compounds with Pt- Pt interactions and formed from [PtCl2(NH3)2] and pyrimidines, of which examples have now been crystallized. ... 

Nickel(II), palladium(II) and platinum(II) form planar complexes with 1,2-diondioximato ligands. The compounds crystallize in columnar stacks with different angles of inclination between the molecular planes and the stacking direction. The metal-metal distances depend strongly on the electronic and steric properties of the ligands. Upon oxidation with molecular iodine mixed valence compounds can be obtained. The stacking direction becomes perpendicular to the molecular planes, in these solids and the metal-metal distances decrease considerably. I -anions are incorporated into the lattice to form linear arrays parallel to the metal chains (1). 

We bave previously prepared and described binuclear orthometallated complexes of palladium(II) which could be used as precursors to prepare potoitially mixed-valence compounds. Hie presence of unusual Pd-N amido bonds in these complexes adds further interest based cm the reactivity shown by amides of the platinum group metals. ... 

As with the trihalides , some formally platinum(III) compounds are in fact mixed-valence species [161]. Thus ... 

The squarate ion is also assmned to have the potential for providing a pathway for electron conduction when it bridges metal atoms in polymeric complexes (61). Some workers have used partial oxidation to enhance the possibility that compounds will exhibit conductivity. For example, Toftlund (110) showed that the partially oxidized platinum salt K2[Pt(C404)2l 2H2O has the properties of a one-dimensional conductor, while Wrobleski and Brown (18) reported that some mixed-valence iron squarate complexes display semiconductivity. 

Treatment of aqueous solutions of t -[PtCl2(NH.i)2] with a variety of pyrimidines yields blue, oligomeric (Pu) compounds of the type known since the early 20th century as platinum blues. They are mostly, mixed valence, paramagnetic compounds and although some have been characterized others are less well-defined and include green and violet materials. 

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