Criminals purchasing island? They're minted! (5)
I believe the answer is:
coins
'they're minted' is the definition.
(coins are manufactured in a mint)
'criminals purchasing island?' is the wordplay.
'criminals' becomes 'cons' (short for convicts).
'purchasing' means one lot of letters goes inside another (some letters take possession of others).
'island?' becomes 'i'.
'cons' going around 'i' is 'COINS'.
(Other definitions for coins that I've seen before include "Metal money" , "change" .)