316398
These complexes may be homoleptic , that is containing only CO ligand s , such as nickel carbonyl ( Ni ( CO ) 4 ) , but more commonly metal carbonyls are heteroleptic and contain a mixture of ligands .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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