Palladium: Inorganic & Coordination Chemistry
Published Online: 15 DEC 2011
Copyright © 2011 John Wiley & Sons, Ltd. All rights reserved.
Encyclopedia of Inorganic and Bioinorganic Chemistry
How to Cite
Albéniz, A. C. and Espinet, P. 2011. Palladium: Inorganic & Coordination Chemistry. Encyclopedia of Inorganic and Bioinorganic Chemistry. .
- Published Online: 15 DEC 2011
Palladium is a group 10 metal used in the manufacture of exhaust autocatalysts in the automobile industry, in dental palladium alloys, in the electronics industry, in jewelry alloys, and in the manufacture of industrial catalysts. Although the latter represents only about 5% of Pd use, it is extremely important. A remarkable property of metallic palladium is its ability to absorb considerable amounts of hydrogen. The inorganic and coordination chemistry of palladium is mostly that of their oxidation states 0 and +2, but the oxidation states +1 and +4 are also well represented. Only in a few examples Pd can be guaranteed as Pd +3, while in others the ligands of Pd are noninnocent and the apparent oxidation state assigned to Pd can be deceptive. Only one Pd(V) and one Pd(VI) compound have been reported but not confirmed by independent research groups. The Pd(0) complexes reported include compounds with many possible ligands, which are known in [PdL4], [PdL3], and [PdL2] stoichiometries. The former are formed with conventional ligands and have the tendency to dissociate at least one ligand in solution, while the latter are formed with bulky ligands and are more reactive toward oxidative addition. In addition to Pd on carbon, colloids and polymer-stabilized forms of Pd are catalytically important. All Pd(I) compounds reported feature PdPd or PdM bonds, with or without supporting bridges, displaying quite a large range of distances. Pd(II) compounds are commonly four-coordinated square planar, but there are a considerable number of five-coordinated compounds. Three-coordinated Pd(II) compounds are not known. One doubtless case of a four-coordinated tetrahedral (and accordingly paramagnetic) complex has been reported. Pdf2 is a rare example of six-coordinated Pd(II). Square-planar Pd(II) fragments are building blocks in the construction of extended self-assembled structures. Coordination to cis-‘PdL2’ fragments can be used to define corners, while trans-‘PdL2’ moieties can help build linear edges. Mononuclear complexes of Pd(III) can be stabilized by some tridentate macrocyclic ligands containing S and N as donors. A binuclear Pd(III) compound, displaying the shortest PdPd bond is also known. In both cases, the coordination number for Pd is six. Pd(IV) is not an uncommon oxidation state, although it is quite oxidant. Complexes with many different ligands, which show octahedral coordination are known.
- square planar;