Platinum sulfur inversion

Figure 17.6 Sulfur inversion process in methionine-platinum complexes.

Gurnmin, D. D., Ratilla, E. M. A. and Kostic, N. M. (1986) Variable-temperature platinum-195 NMR spectroscopy, a new technique for the study of stereodynamics, sulfur inversion in a platinum(II) complex with methionine. Inorg. Chem., 25, 2429-2433. 

When 2 forms a complex with Pt(PF6>2, the Pt2+ lies at an inversion center surrounded by a distorted square planar array of four atoms. The two oxygen atoms lie trans to each other and oriented away from the Pt center, precluding any Pt-O interactions. In the complex, the S-O-S unit adopts a meridional rather than facial coordination mode. The Pt-O distances in 2-Pt(PF6)2 complex is 3.730(5) A and the Pt-S bond lengths average 2.317(2) A. In this structure, the platinum(n) ion lies 0.018 A above the mean plane of the four sulfur atoms. 

The fuel cell effect was first discovered in 1838 (published in 1989) by C.F. Schoenbein who found the inverse electrolysis principle in his experiment using platinum electrodes immersed in dilute sulfuric acid solution.However, the invention of the fuel cell is credited to W.R. Grove who demonstrated Schoenbein s discovery on a practical scale by inventing the gas battery during 1839-1845. Fig. 1 shows an early experiment in which hydrogen and oxygen gases... 

The fuel cell concept has been known for more than 150 years. It was Christian Friedrich Schonbein who recognized and described the appearance of inverse electrolysis [4] shortly before Sir William Grove, the inventor of the platinum/ zinc battery, constructed his first gas voltaic battery [5]. Grove used platinum electrodes and dilute sulfuric acid as a proton conducting electrolyte. Sulfuric acid is still used today for the impregnation of porous separators serving as the electrolyte in direct methanol laboratory fuel cells [6], but the most commonly used fuel cell electrolytes today are hydrated acidic ionomers. As opposed to aqueous sulfuric acid, where the dissociated protons and the diverse sulfate anions (conjugated... 

In this compound and several other structurally analogous organic and inorganic compounds, the conductivity is inversely dependent on temperature over a limited temperature region, and other characteristically metal-like properties are observed. Included in this group are polymeric sulfur nitride, (SN)a , and a group of partially oxidized, square planar platinum and iridium complexes that are collectively referred to as KCP in Figure 1 both are discussed elsewhere in this volume. 

Figure 5.2. Importance of solvation effects on the barriers for inversion at sulfur in platinum...

Kinetics of intramolecular processes of tungsten(O) complexes of thio-ligands are mentioned in Section 8.11.2 in connection with inversion at sulfur coordinated to platinum(IV). 

At lower temperatures, these cis and trans complexes exhibit inversion at the coordinated sulfur atoms, as do the complexes [MX2 MeS(CH2) CH=CH2 ] where M = Pt or Pd, and n = 2 or Inversion at sulfur in thioether complexes of platinum(II) has been documented, and an example of such inversion at rhodium(III) was mentioned in Section The whole area of fluxional... 

Urea hydrolyzes about 3 x 10 times faster coordinated to [Rh(NH3)5] than in the uncoordinated state. This is a marked acceleration, but still very much less than the promotion of base hydrolysis of acetonitrile by [Ru(NH3)5] (cf. Section 8.3.2). Formation and aquation reactions of carbonato complexes are often coordinated ligand reactions, involving C-0 rather than Rh-0 bond formation and breaking. "" " Inversion at coordinated sulfur has an activation barrier (AG ) of 87.3 and 85.5 kJ moP in d(,-DMSO (at 383 and 378 K, respectively) in the dithiahexane complexes [Rh(dth)Cl4] and [Rh(dth)Br4) . As one might well expect, these barriers, though high, are less than that for the platinum(IV) analogue [Pt(dth)Cl4] " (cf. Section 8.7.2, and see Sections 8.3.1 and 8.6). 

The barrier to inversion at coordinated sulfur in the dithiahexane complex [Ir(dth)Cl4] is 63kJmor at 283 K in CDCI3/DMSO solution. Surprisingly, this is much lower than for the rhodium(III) analogue (Section 8.5.10) expectedly, the barrier is much lower than for the platinum(IV) analogue [Pt(dth)Cl4]. ... 

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