Metal Segregation in Bimetallic CoPd Carbide Carbonyl Clusters: Synthesis, Structure, Reactivity and Electrochemistry of [H6−nCo20Pd16C4(CO)48]n−(n=3-6)

Nanometric CoPd bimetallic [H6-nCo 20Pd16C4(CO)48]n- (n=3-6) tetracarbide carbonyl clusters have been prepared by redox condensation of [Co6C(CO)15]2- with [PdCl2(Et 2S)2]. The crystal structures of both the dihydride tetra-anion and monohydride penta-anion have been determined as their [NEt 4]4[H2Co20Pd16C 4(CO)48]×4 CH3COCH3 and [NMe3(CH2Ph)][NMe4]4[HCo 20Pd16C4(CO)48]×5 CH 3COCH3 salts, respectively. The two species are isostructural and their structures display a perfect segregation of the two metals. They are composed of a cubic close-packed (ccp) Pd16 core stabilised on its surface by four {Co5C(CO)12} organometallic fragments. Their polyhydride nature has been corroborated by the study of their reactions with acids and bases, and confirmed by electrochemical studies. In addition, the reactions of [H2Co20Pd 16C4(CO)48]4- with Na/naphthalene and PPh3/CO allowed the isolation of other lower nuclearity homoleptic and heteroleptic clusters, that is, [H6-nCo 16Pd2C3(CO)28]n- (n=5, 6), [Co4Pd2C(CO)11(PPh3) 2], [Co2Pd5C(CO)8(PPh 3)5], and [Co4Pd4C 2(PPh3)4(CO)10Cl]-. [H6-nCo16Pd2C3(CO) 28]n- (n=5, 6) represent the first homoleptic metal-carbonyl clusters containing three interstitial carbide atoms. Kept apart: Bimetallic nanometric CoPd tetracarbide carbonyl clusters have been prepared by redox condensation. Their crystal structures, in which a cubic close-packed (ccp) Pd16 core is stabilised by four Co 5C(CO)12 organometallic fragments, display a perfect segregation of the two metals (see figure)