What are pi-donors ligands give the examples?

Ligands such as OR−, F−, and Cl− are π donors as a result of the lone pairs that are left after one lone pair has formed the M−L σ bond. Instead of stabilizing the dπ electrons of a d6 ion as does a π acceptor, these electrons are now destabilized by what is effectively a repulsion between two filled orbitals. 

Examples of pi-donor ligands given as;

Related Questions;

(1) What type of ligands are known ?

(2) What is the common formula of “Prussian blue is” and “Turn bull's blue”?  

(3) What is denticity of NO and NO+ ligands ?

(4) Although both [Mn(H2O)6]2+ and [FeF6]3- have a d5 configuration and high-spin complexes. But the dilute solutions of Mn2+ and Fe +3 complexes are therefore colorless. Why?

(5)Which of the Complex of the following pairs has the highest value of CFSE?

(6) Colour of Complexes due to charge transfer: 

(7) Why violet colour of [Ti(H2O)6]Cl3 disapear (colourless) on heating heating ? 

(8) Why [Ni(CN)4]-2 is colourless while [Ni(H2O)4]-2 although both have +2 oxidation state and 3d*8 configuration ?

(9) Why [FeF6]3– is colourless whereas [CoF6]3– is coloured ? 

(10) Why Fe(CO)5 is colourless while Fe(bipy)(CO)3 is intensely purple in colour ?
Why all the tetrahedral Complexes are high spin Complexes ?