7094
However , interactions between nuclei and unpaired electrons in paramagnetic systems ( e . g . , Cu ( II ) - based MOFs ) pose a considerable challenge , not only for spectral acquisition , but also in the assignment and interpretation of the spectral resonances .
 Chemical: Cu ( II )
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: Cu ( II )