Metal Segregation in Bimetallic CoPd Carbide Carbonyl Clusters: Synthesis, Structure, Reactivity and Electrochemistry of [H6-n Co20 Pd16 C4 (CO)48 ]n- (n=3-6).

Nanometric CoPd bimetallic [H6-n Co20 Pd16 C4 (CO)48 ]n- (n=3-6) tetracarbide carbonyl clusters have been prepared by redox condensation of [Co6 C(CO)15 ]2- with [PdCl2 (Et2 S)2 ]. The crystal structures of both the dihydride tetra-anion and monohydride penta-anion have been determined as their [NEt4 ]4 [H2 Co20 Pd16 C4 (CO)48 ]⋅4 CH3 COCH3 and [NMe3 (CH2 Ph)][NMe4 ]4 [HCo20 Pd16 C4 (CO)48 ]⋅5 CH3 COCH3 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 {Co5 C(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 [H2 Co20 Pd16 C4 (CO)48 ]4- with Na/naphthalene and PPh3 /CO allowed the isolation of other lower nuclearity homoleptic and heteroleptic clusters, that is, [H6-n Co16 Pd2 C3 (CO)28 ]n- (n=5, 6), [Co4 Pd2 C(CO)11 (PPh3 )2 ], [Co2 Pd5 C(CO)8 (PPh3 )5 ], and [Co4 Pd4 C2 (PPh3 )4 (CO)10 Cl]- . [H6-n Co16 Pd2 C3 (CO)28 ]n- (n=5, 6) represent the first homoleptic metal-carbonyl clusters containing three interstitial carbide atoms.