Editing Metallocene (section)

==Derivatives==
{{Main|Sandwich compound}}
After the discovery of ferrocene, the synthesis and characterization of derivatives of metallocene and other sandwich compounds attracted researchers’ interests.

===Metallocenophanes===
[[Metallocenophanes]] feature linking of the cyclopentadienyl or polyarenyl rings by the introduction of one or more heteroannular bridges. Some of these compounds undergo thermal [[ring-opening polymerization]]s to give soluble high molecular weight polymers with transition metals in the polymer backbone. [[Ansa-metallocene]]s are derivatives of metallocenes with an intramolecular [[bridge (chemical)|bridge]] between the two cyclopentadienyl rings.

===Polynuclear and heterobimetallic metallocenes===
*Ferrocene derivatives: biferrocenophanes have been studied for their mixed [[valence (chemistry)|valence]] properties. Upon one-electron oxidation of a compound with two or more equivalent ferrocene moieties, the electron vacancy could be localized on one ferrocene unit or completely [[delocalized]].
*[[Ruthenocene]] derivatives: in the solid state biruthenocene is disordered and adopts the transoid conformation with the mutual orientation of Cp rings depending on the intermolecular interactions.
*[[Vanadocene]] and [[rhodocene]] derivatives: vanadocene complexes have been used as starting materials for the synthesis of heterobimetallic complexes. The 18 [[valence electron]] ions [Cp<sub>2</sub>Rh]<sup>+</sup> are very stable, unlike the neutral monomers Cp<sub>2</sub>Rh which [[dimer (chemistry)|dimerize]] immediately at room temperature and they have been observed in [[matrix isolation]].

===Multi-decker sandwich compounds===
[[File:Ni-triple-sandwich.png|thumb|150px|Nickel triple-decker sandwich complex]]
Triple-decker complexes are composed of three Cp anions and two metal cations in alternating order. The first triple-decker sandwich complex, {{chem2|[Ni2Cp3](+)}}, was reported in 1972.<ref>{{cite journal|last1=Werner|first1=Helmut|last2=Salzer|first2=Albrecht|date=1972-01-01|title=Die Synthese Eines Ersten Doppel-Sandwich-Komplexes: Das Dinickeltricyclopentadienyl-Kation|journal=Synthesis and Reactivity in Inorganic and Metal-Organic Chemistry|volume=2|issue=3|pages=239–248|doi=10.1080/00945717208069606|issn=0094-5714}}</ref> Many examples have been reported subsequently, often with [[carborane|boron-containing rings]].<ref>{{cite journal|first= R. N.|last= Grimes|title= Boron clusters come of age|journal= [[J. Chem. Educ.]]|year= 2004|volume= 81|pages= 657–672|doi=10.1021/ed081p657|issue= 5|bibcode= 2004JChEd..81..657G|doi-access= free}}</ref>

===Metallocenium ions===
The most famous example is [[ferrocenium]], {{chem2|[Fe(C5H5)2](+)}}, the blue iron(III) complex derived from oxidation of orange iron(II) ferrocene. The lithocene anion, [Li(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>]<sup>–</sup>,<ref> {{cite journal|last1=Harder|first1=Sjoerd
|last2=Prosenc|first2=Marc Heinrich|title=The Simplest Metallocene Sandwich: the Lithocene Anion|journal=Angewandte Chemie International Edition in English|volume=33|issue=17|date=16 September 1994|page=1744-1746|doi=10.1002/anie.199417441}}</ref> is the best-documented example of a metallocene anion; otherwise such ions are little known.