Some prefer Richard to be containing iron (6)
I believe the answer is:
ferric
'containing iron' is the definition.
(I've seen this before)
'some prefer richard to' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'FERRIC' is hidden in the letters of 'prefer richard to'.
'be' is the link.
(Other definitions for ferric that I've seen before include "Of trivalent iron" , "made of iron" , "Containing iron" , "Relating to one form of iron" , "Of iron with a valency of three" .)