The following coordination compound was given in the book Concise Inorganic Chemistry by J.D. Lee (Adapted by Sudarsan Guha) under the topic 'Effective Atomic Number (EAN)':
$\ce{[Ti(\sigma -C5H5)2 (\pi -C5H5)2]^0}$
What is meant by the quantifiers $\sigma$ and $\pi$ in front of the ligand? I have not seen this format with other ligands? If this is to signify $\sigma$ and $\pi$ bonds, why is it not used in the formulas of metal carbonyls which have synergic bonds (a combination of both $\sigma$ and $\pi$ bonds)?
In all the 67 occurrences of 'cyclopentadienyl' in the IUPAC Red Book, I was unable to see $\ce{C5H5-}$ having a $\sigma$ or $\pi$ in front of it. Instead I only saw $\eta$ being used in the name. I came to know that it is meant to denote 'hapticity'. Is this related to the presence of $\sigma$, $\pi$?