18869
The periodic trend in methane binding energies in the [ M ( pyridine ) 2 ( CH4 ) ] ( 2 + ) complexes follows the trend in electron affinity until the Mn complex but then exhibits decreasing energies from Fe to Zn .
 Chemical: methane; Chemical: [ M ( pyridine ) 2 ( CH4 ) ] ( 2 + ); Chemical: Mn; Chemical: Fe; Chemical: Zn
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: methane; Chemical: [ M ( pyridine ) 2 ( CH4 ) ] ( 2 + ); Chemical: Mn; Chemical: Fe; Chemical: Zn