High-performance liquid chromatography was used to isolate two new trimetallic nitride endohedral fullerenes, Gd3N@C-2n (n = 42 and 44), and they were characterized by MALDI-TOF mass spectrometry, UV-vis-NIR, and cyclic voltammetry. It was found that their electronic HOMO-LUMO gaps depend pronouncedly on the size of the cage, from a large band gap for Gd3N@C-80 (2.02 V) to a small band gap for Gd3N@C-88 (1.49 V). The electrochemical properties also change dramatically with the size of the cage, going from irreversible for the C-80 cage to reversible for Gd3N@C-88. The latter is the largest trimetallic cluster inside C-88 isolated and characterized to date. Gd3N@C-88 has one of the lowest electrochemical energy gaps for a nonderivatized metallofullerene.