A series of trans-platinum(IV) complexes with functionalized aromatic carboxylate ligands, cis,cis,trans-Pt(NH₃)₂Cl₂(CO₂C₆H₄R)₂ (R = H (3), p-vinyl (4), p-methoxy (5), p-iodo (6), p-cyano (7), or o-carboxyl (8)) was synthesized and characterized by spectroscopic methods. Crystal structures of 3, 4, 7, and 8 were obtained, which revealed that their structural conformations were influenced by intramolecular H-bonding interactions. The complexes were evaluated for cellular uptake and inhibition of cell proliferation against a panel of lung, colon, and breast carcinoma cell lines. The functionalization of the aromatic carboxylate ligand was found to have a profound influence on the uptake, and hence, efficacy, of this class of complex.