The reactions of nitriles (RCN) with arachno-4,6-C2B7H12- provide a general route to functionalized tricarbaclecaboranyl anions, 6-R-nido-5,6,9-C3B7H9-, R = C6H5 (2-), NC(CH2)(4) (4-), (p-BrC6H4)(Me3SiO)CH (6-), C14H11 (8-), and H3BNMe2(CH2)(2) (10-). Further reaction of these anions with (eta(5)-C5H5)Fe(CO)(2)I yields the functionalized ferratricarbadecaboranyl complexes 1-(eta(5)-C5H5)-2-C6H5-closo-1,2,314-FeC3B7H9 (3), 1-(eta(5)-C5H5)-2-NC(CH2)(4)-closo-1,2,3,4-FeC3B7H9 (5), 1 -(eta(5) -C5H5)-2-[(p-BrC6H4)(Me3SiO)CH]-closo-1,2,3,4-FeC3B7H9 (7), 1-(eta(5)-C5H5)-2-C14H11-closo-1,2,3,4-FeC3B7H9 (9), and 1-(eta(5)-C5H5)-2-H3BNMe2(CH2)(2)-closo-1,2,3,4-FeC3B7H9 (11). Reaction of 11 with DABCO (triethylenediamine) resulted in removal of the BH3 group coordinated to the nitrogen of the side chain, giving 1-(eta(5) -C5H5)-2-NMe2(CH2)(2)-closo-1,2,3,4-FeC3B7H9 (12). Crystallographic studies of complexes 3, 5, 7, 9, and 11 confirmed that these complexes are ferrocene analogues in which a formal Fe2+ ion is sandwiched between the cyclopentadienyl and tricarbaclecaboranyl monoanionic ligands. The metals are eta(6)-coordinated to the puckered six-membered face of the tricarbadecaboranyl cage, with the exopolyhedral substituents bonded to the low-coordinate carbon adjacent to the iron.