What is difference between sigma- cyclopentadienyl ligand and pie -cyclopentadienyl ligand..... how sigma- cyclopentadienyl ligand acts as Π acid ligand?

it can be differentiated by hapticity represen5ed by n if hapticity is one it means it forms only one bond i.e., sigma. if it's value is greater than one that means it forms pi bon...

will sigma cyclopentadienyl ligand become Pi acceptor ligand...? bcse in booklet they say it is pi acceptor?? If yes then How?

in sigma cylcopentadienyl donation happens through sigma bond while in pi donation goes through pi bond electronic density.