Carbon that is about to freeze (3)
I believe the answer is:
ice
'freeze' is the definition.
(as in water turning into ice)
'carbon that is about' is the wordplay.
'carbon' becomes 'C' (chemical symbol).
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'about' indicates putting letters inside.
'c' put within 'ie' is 'ICE'.
'to' is the link.
(Other definitions for ice that I've seen before include "Decorate a cake" , "Frozen liquid" , "Rocks on which drink is served?" , "such an age" , "Diamonds (informal)" .)