Ni(mnt)(2) salts of 1',1"'-diisopropyl-1,1"-biferrocene (1) and 1',1"'-dibenzyl-1,1"-biferrocene (2) have been prepared. Both complexes show segregated-stack crystal structure, consisting of a mixed-valent biferrocenium monocation and a Ni(mnt)(2) monoanion. The D-A ratio is 1:1 in both compounds. The trapped-valence state is demonstrated for 2 at room temperature.