The Collaborative International Dictionary of English v.0.48:

Platinic \Pla*tin"ic\, a. (Chem.)
   Of, pertaining to, or containing, platinum; -- used
   specifically to designate those compounds in which the
   element has a higher valence, as contrasted with the
   platinous compounds; as, platinic chloride (PtCl4).
   [1913 Webster]