C5H5 ligand

Fig. 1. Crystal structure of //-methylene-bisldicarbonylttf-cyclopentadienyllmanga-nesel(Mn—Mn) (3a) determined by X-ray diffraction techniques at - I45°C (127). Identical sets of ligands (C5H5/C5H5 and (COhACOy dispose positions trans to each other.

Delavaux-Nicot, B. Bigeard, A. Bousseksou, A. Com-nienges. G. Reactivity of the acyclic diazadioxa redox active ligand [(C5H5)Fe(C5H4CH2N(CH3)(CH2)20CH2-)]2 NMR. electrochemical, and Mossbauer studies. Crystal structure of its copper complex. Inorg. Chem. 1997, 36. 4789-4797. 

In their extended Hiickel calculations, Thorn and Hoffmann treat the carbon portion of the metallacycle as a monoanionic ligand (C5H5 ). It serves as a 4e donor to the metal, and these electrons form the two M—C a-bonds. In the Thorn/Hoffmann analysis, the metallacycle possesses six -electrons and therefore obeys the Hiickel 4n + 2 rule. Four electrons reside in relatively low-lying carbon fragment. Tr-orbitals In and 2ti, Chart 2). ° The remaining two jr-electrons are contributed by the filled metal Axz orbital (or hybrid of appropriate symmetiy), which interacts in a back-bonding fashion with the empty Zti carbon fragment orbital (Chart 2). 

Ln stands for Y, La and Ce-Lu. LniC H ij is an organometallic compound of the metal and cyclopentadienyl ligands C5H5. Values taken from ref [17.12]. 

Investigating several different lanthanide metals it was shown that the rate of polymerization increased with an increase of ionic radius of the metals (Sm > Y > Yb > Lu) and decreased with an increase of steric bulk of the auxiliary ligands (C5H5 > CsMes). 

In organometaUic chemistry in particular, but also in coordination chemistry, use of the Greek prefix p (eta) is encountered the letter is accompanied by a superscript number (e.g. p ). This prefix describes the number of atoms in a ligand which directly interact with the metal centre, the hapticity of the ligand. For example, the cyclopentadienyl ligand, [C5H5] or... 

Symbol t], stands for hapto (from the Greek word haptein, meaning fasten) thus, ligand C5H5 carries also the name pentahaptocyclopentadienyl group. The use of r) is recommended by lUPAC. 

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