2671
The cycloheptatrienyl ring in these systems usually acts as an " innocent spectator ligand " , but reactivity can arise from the second ligand Y or the Lewis acidity of the , formally , Zr ( + iv ) center , which was probed in selected examples and put in perspective to related studies .
 Chemical: cycloheptatrienyl; Chemical: Zr ( + iv )
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: cycloheptatrienyl; Chemical: Zr ( + iv )