Synthesis, structural and electrochemical characterization of the nitrido-carbonyl cluster anion [Co 13N 2(CO) 24] 3-. The different redox propensity of the two isostructural families [Co 13N 2(CO) 24] n- and [Co 13C 2(CO) 24] m

The anion [Co 13N 2(CO) 24] 3- (1) has been obtained by pyrolisis at 100°C of [Co 14N 3(CO) 26] 3- (K + salt) in buffered water solution (pH 11). The X-ray crystal structure ([NMe 4] + salt) revealed that the metal cage of the anion is composed by a three-layered polyhedron with the two nitrides in trigonal prismatic environments. Anion 1, with 178 cluster valence electrons (CVE), is isostructural with the carbido species [Co 13C 2(CO) 24] 3- (2, 176 CVE) and [Co 13C 2(CO) 24] 4- (3, 177 CVE). In acetonitrile solution 1 undergoes two reversible one-electron additions. Comparison with the dicarbido tetraanion 3 evidences that the two clusters do not display isoelectronic redox paths. Actually, [Co 13N 2(CO) 24] n- undergoes the three-membered redox sequence (n=3-5) from 178 to 180 CVE, whereas [Co 13C 2(CO) 24] m- undergoes the four-membered series (m=3-6), from 176 to 179 CVE. The different redox behaviour and the minor differences in the Co-Co bond distances point out that carbide and nitride have different role in stabilizing the two compounds. © 2003 Elsevier Science B.V. All rights reserved.