Metallic derivative of platinum (3)
I believe the answer is:
tin
'metallic' is the definition.
'of platinum' is the wordplay.
'of' indicates a hidden word.
'TIN' is hidden in the letters of 'platinum'.
'derivative' is the link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for tin that I've seen before include "With copper, makes bronze" , "1 down, symbol Sn" , "A silvery-white metal, symbol Sn" , "Element, symbol Sn" , "Silver-white metal, used to make cans" .)