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A comparative study of the rotational dynamics of PF6 ( - ) anions in the crystals and liquid states of 1 - butyl - 3 - methylimidazolium hexafluorophosphate : results from 31P NMR spectroscopy .
 Chemical: PF6 ( - ); Chemical: 1 - butyl - 3 - methylimidazolium hexafluorophosphate; Chemical: 31P
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: PF6 ( - ); Chemical: 1 - butyl - 3 - methylimidazolium hexafluorophosphate; Chemical: 31P