Platinum complexes partially oxidized

In the early stage of the development of molecular conductors based on metal complexes, partially oxidized tetracyanoplatinate salts (for example, KCP K2 [Pt(CN)4]Br0.30-3H2O) and related materials were intensively studied [6], In this system, the square-planar platinum complexes are stacked to form a linear Pt-atom chain. The conduction band originates from the overlap of 5dz2 orbitals of the central platinum atom and exhibits the one-dimensional character. 

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... 

From the neutral 1 2 complexes introduced before, two kinds of materials were obtained by electrocrystallization fully oxidized salts where both TTF CH= CH—py moieties are oxidized, and mixed valence salts in which the two ligands are partially oxidized. All oxidized complexes were obtained by oxidation at constant current of a neutral 1 2 complex in an electrolyte containing the anions, and using electrocrystallization technique with platinum wires (0 = 1mm) electrodes. 

Electrochemical Syntheses of Partially Oxidized Platinum Complexes 13... 

ELECTROCHEMICAL SYNTHESES OF PARTIALLY OXIDIZED PLATINUM COMPLEXES... 

In addition to the partially oxidized tetracyanoplatinates, bis(oxalato)platinate-(II) can be nonstoichiometrically oxidized by chemical oxidants13 to form highly lustrous needlelike crystals containing platinum in the 2.36 oxidation state. These complexes have not been characterized to the extent of the tetracyano-platinate complexes however, the oxalato complexes are reported to be highly conducting.13 The starting material is bis(oxalato)platinate(II), which can be prepared in 30% yields from hexachloroplatinate(lV) and potassium oxalate.9... 

Partially oxidized and mixed-valence platinum amine complexes 427... 

Cyanide complexes of platinum occur most commonly in the divalent state, although there has been increasing interest in the complexes formed with platinum in a higher oxidation state. Among the complexes most recently studied have been the mixed valent complexes where platinum cyanides in the divalent state are partially oxidized. These complexes form one-dimensional stacks with Pt-Pt interactions. In the solid state these materials show interesting electrical conductivity properties, and these compounds are discussed by Underhill in Chapter 60. In this section the preparative procedures and spectroscopy of the complexes will be covered, but for solid state properties the reader is referred to Chapter 60. 

The distances found between platinum centers in these molecules have been correlated with the resonating valence bond theory of metals introduced by Pauling. The experimentally characterized partially oxidized one-dimensional platinum complexes fit a correlation of bond number vs. metal-metal distances, and evidence is presented that Pt—Pt bond formation in the one-dimensional chains is resonance stabilized to produce equivalent Pt—Pt distances.297 The band structure of the Pt(CN)2- chain has also been studied by the extended Huckel method. From the band structure and the density of states it is possible to derive an expression for the total energy per unit cell as a function of partial oxidation of the polymer. The equilibrium Pt-Pt separation estimated from this calculation decreases to less than 3 A for a loss of 0.3 electrons per platinum.298... 

The macrocyclic phthalocyanine ligand will form a complex Pt(phthalocyanine).1106 The crystal structure shows two polymorphs present because of molecular packing.1107 The platinum is in a square planar coordination geometry with a mean Pt—N distance of 1.98 A. The complex can be partially oxidized with iodine to give conducting mixed valence solids.1108 Eighteen fundamental and overtone combination bands are observed in the resonance Raman spectrum of platinum phthalocyanine, and from this data the symmetry of the excited singlets are found to be Dy.. Qlv or D2.1109... 

Binuclear platinum complexes with the o -pyridinato ligand can be formed with the metals in a divalent oxidation state. Two such complexes are the head-to-tail dimer [Pt(QH4NO)(NH3)2]2+ and the head-to-head tetramer [Pt2(CsH4NO)2(NH3)4]2+. This tetrame-ric platinum(II)-(II) compound is prepared under experimental conditions where the pH is kept around neutrality to avoid the formation of the partially oxidized complex.1120 Platinum-195 NMR spectroscopy can be used to show that the head-to-head to head-to-tail isomerization of these complexes involves dissociation of one ligand arm followed by an intramolecular linkage isomerization. Finally bond formation occurs between the divalent platinum with the vacant coordination site and the uncoordinated end of the ligand.1121... 

The rubidium salt Rbii67[Pt(C204)2]1.5H20 (RbOP) is a compound exhibiting a commensurate 2kF structure and, therefore, the distortion of the Pt chain has been determined precisely.66 The unit cell contains a distorted nonlinear sixfold Pt atom chain and involves six fPt(C204)2]1-67" units in one repeating unit of 17.11 A. There are three independent Pt—Pt distances of 2.716, 2.830 and 3.015 A. The Pt—Pt distance of 2.717 A is the shortest spacing so far observed in partially oxidized platinum complexes and it is shorter than the 2.77 A interatomic distance in Pt metal. 

The partially oxidized complex K2Pt(CN)4Bro.3-3H20 behaves as a onedimensional conductor, owing to overlap of the platinum 5d 2 orbitals atoms along a chain composed of stacking of square-planar [Pt(CN)4]L7 units (Fig. 4.1.2). 

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. 

Spectroscopic evidence obtained recently indicates that the electrosorption of methanol on platinum is probably a very complex process, in which several different partially oxidized species may be formed, in ratios that depend both on the potential and on the bulk concentration of methanol. 

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