The nitrido-encapsulated heterometallic cluster anions [Co10Rh(N)(2)(CO)(21)](3-) ( 1), [Co10Rh2(N)(2)(CO)(24)](2-) ( 2), and [Co11Rh(N)(2)(CO)(24)](2-) ( 3) have been obtained by tailored redox-condensation reactions. These three anions are rare high-nuclearity mixed-metal clusters containing two interstitial nitrogen atoms. Their structures have been determined by single-crystal X-ray diffraction on their [NR4](+) salts (R = Me for 1 and 3, R = Et for 2), and their electrochemical and ESR properties have been studied in detail. It is noteworthy that 1 has an unprecedented stereochemistry that does not exhibit a close geometrical resemblance with the isoelectronic homometallic anion [Co11N2(CO)(11)(mu(2)-CO)(10)](3-), and 2, despite its even number of electrons, is a paramagnetic species.