Palladium(II) cyanide

Palladium(II) cyanide

Palladium(II) cyanide describes any chemical species with the empirical formula Pd(CN)n(2-"n")-. The dicyanide ("n" = 2, CAS: [2035-66-7] ) is a coordination polymer of minor significance. It likely has a structure consisting of square planar Pd(II) centers linked by cyanide ligands, which are bonded through both the carbon and nitrogen atoms.

The slightly more topical palladium(II) cyanide is the dianion [Pd(CN)4] 2-. This compound is renowned for its extraordinary stability, with a predicted stability constant of 1065 to 1075 as defined by the following process::: [Pd(H2O)4] 2+ + 4 CN- → [Pd(CN)4] 2- + 4 H2OThe affinity of Pd for cyanide is so great that palladium metal is attacked by cyanide solutions:::Pd(s) + 2 H+ + 4 CN- → [Pd(CN)4] 2- + H2This reaction is reminiscent of the “cyanide process” for the extraction of gold, although in the latter reaction O2 is proposed to be involved, to give H2O.

Exchange of between free cyanide ion and [Pd(CN)4] 2- has been evaluated by 13C NMR spectroscopy. That exchange occurs at all illustrates the ability of some compounds to be labile (fast reactions) but also stable (high formation constants). The reaction rate is described as follows:::rate = "k"2 [M(CN)42-] [CN-] , where "k"2 120 M-1-s-1The bimolecular kinetics implicate a so-called associative pathway. The associative mechanism of exchange entails rate-limiting attack of cyanide on [Pd(CN)4] 2-, possibly with the intermediacy of a highly reactive pentacoordinate species [Pd(CN)5] 3-. By comparison, the rate constant for [Ni(CN)4] 2- is > 500,000 M-1-s-1, whereas [Pt(CN)4] 2-exchanges more slowly at 26 M-1s-1. Such associative reactions are characterized by large negative entropies of activation, in this case: -178 and -143 kJ/(mol·K) for Pd and Pt, respectively.

References

*R. D. Hancock, A. Evers “Formation Constant of Pd(CN)42-” Inorganic Chemistry, Volume 15, 995-6 (1976).
*J. J. Pesek, W. R. Mason “Cyanide Exchange Kinetics for Planar Tetracyanometalate Complexes by Carbon-13 NMR” Inorganic Chemistry 1983, 22, 2958-2959.


Wikimedia Foundation. 2010.

Игры ⚽ Поможем решить контрольную работу

Look at other dictionaries:

  • Palladium — (pronounced pəˈleɪdiəm) is a rare and lustrous silvery white metal that was discovered in 1803 by William Hyde Wollaston, who named it palladium after the asteroid Pallas, which in turn, was named after the epithet of the Greek goddess Athena,… …   Wikipedia

  • Copper(I) cyanide — IUPAC name Copper(I) cyanide …   Wikipedia

  • Determination of equilibrium constants — Equilibrium constants are determined in order to quantify chemical equilibria. When an equilibrium constant is expressed as a concentration quotient, it is implied that the activity quotient is constant. In order for this assumption to be valid… …   Wikipedia

  • Gold — This article is about the metal. For the color, see Gold (color). For other uses, see Gold (disambiguation). platinum ← gold → mercury …   Wikipedia

  • Silver — This article is about the chemical element. For the color, see Silver (color). For other uses, see Silver (disambiguation). palladium ← silver → cadmium …   Wikipedia

  • coordination compound — Chem. complex (def. 10). Also called coordination complex. * * * ▪ chemistry Introduction  any of a class of substances with chemical structures in which a central metal atom is surrounded by nonmetal atoms or groups of atoms, called ligands… …   Universalium

  • Chemikalienliste — Die Chemikalienliste stellt eine alphabetisch sortierte Liste von Chemikalien dar, ohne Anspruch auf Vollständigkeit. Elemente sind fett gekennzeichnet, Stoffgruppen kursiv. Der Haupteintrag zu einer Chemikalie ist gleichzeitig der Name des… …   Deutsch Wikipedia

  • Liste chemischer Verbindungen — Die Chemikalienliste stellt eine alphabetisch sortierte Liste von Chemikalien dar, ohne Anspruch auf Vollständigkeit. Elemente sind fett gekennzeichnet, Stoffgruppen kursiv. Der Haupteintrag zu einer Chemikalie ist gleichzeitig der Name des… …   Deutsch Wikipedia

  • Liste von chemischen Verbindungen — Die Chemikalienliste stellt eine alphabetisch sortierte Liste von Chemikalien dar, ohne Anspruch auf Vollständigkeit. Elemente sind fett gekennzeichnet, Stoffgruppen kursiv. Der Haupteintrag zu einer Chemikalie ist gleichzeitig der Name des… …   Deutsch Wikipedia

  • Rhodium — Rh redirects here. For other uses, see rh (disambiguation) Rhodium (pronEng|ˈroʊdiəm) is a chemical element with the symbol Rh and atomic number 45. A rare, silvery white hard transition metal and a member of the platinum group, rhodium is found… …   Wikipedia

Share the article and excerpts

Direct link
… Do a right-click on the link above
and select “Copy Link”