Metal Segregation in Bimetallic CoPd Carbide Carbonyl Clusters: Synthesis, Structure, Reactivity and Electrochemistry of [H_6−nCo₂₀Pd₁₆C₄(CO)₄₈]ⁿ⁻ (n=3–6)

Abstract

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

Cobalt-platinum heterometallic clusters containing N-heterocyclic carbene ligands

“…The Co 4 Pt 2 ( 6 -C) core is a distorted octahedron, in accord with PSEPT for a cluster valence electron count of 86, and the puckered basal plane is made up of the four cobalt atoms. This molecular geometry closely resembles that of the only known [Pd(PPh 3 )] analogue, [Co 4 Pd 2 (µ 6 -C)(PPh 3 ) 2 (µ 2 -CO) 5 (CO) 6 ] (5')[10] (Figure 4).…”

Cluster Core Isomerism Induced by Crystal Packing Effects in the [HCo15Pd9C3(CO)38]2– Molecular Nanocluster

“…Thus, [NMe 3 (CH 2 Ph)] 4 [H 2 Co 20 Pd 16 C 4 (CO) 48 ] was synthesized by reacting [NMe 3 (CH 2 Ph)] 2 [Co 6 C(CO) 15 ] and Pd(Et 2 S)Cl 2 in thf according to the literature procedure. 31 After workup, [NMe 3 (CH 2 Ph)] 4 [H 2 Co 20 Pd 16 C 4 (CO) 48 ] was extracted in dmf and the cation exchanged by adding a saturated solution of [CAT]X (CAT = NMe 3 (CH 2 Ph), NBu 4 , NEt 3 (CH 2 Ph), and MePPh 3 ; X = Cl, Br) in H 2 O. The resulting [CAT] 4 [H 2 Co 20 Pd 16 C 4 (CO) 48 ] was dissolved in acetone and treated with an excess of HBF 4 ·Et 2 O.…”

“…An inner triangular Pd 3 unit is present also in the [Os 18 Pd 3 C 2 (CO) 48 ] 2– cluster, where the Pd 3 core is bonded to two Os 9 C(CO) 24 fragments. 33 These [Os 18 Pd 3 C 2 (CO) 48 ] 2– and [Co 13 Pd 3 C 3 (CO) 29 ] − clusters, as well as the parent [H 3– n Co 15 Pd 9 C 3 (CO) 38 ] n − ( n = 0–3) 30 and [H 6– n Co 20 Pd 16 C 4 (CO) 48 ] n − ( n = 3–6), 31 may be viewed as Pd n clusters stabilized by Co and Os organometallic fragments.…”

Structural rearrangements induced by acid–base reactions in metal carbonyl clusters: the case of [H3−nCo15Pd9C3(CO)38]n−(n = 0–3)

“…In this paper, we have reported the synthesis, spectroscopic, structural and electrochemical characterization of the new bimetallic [H 3−n Co 15 Pd 9 C 3 (CO) 38 ] n− (n = 0-3) tri-carbide polyhydride carbonyl clusters, obtained from the acid-induced degradation of the previously reported [H 6−n Co 20 Pd 16 C 4 -(CO) 48 ] n− (n = 3-6) tetra-carbide poly-hydride MCCs. 20 All these clusters are composed of an inner Pd 9 (μ 3 -CO) 2 or Pd 16 kernel stabilised by three or four Co 5 C(CO) 12 fragments, respectively. They may be viewed as ultra-small metal nanoparticles stabilised by organometallic fragments 37 As previously found for other large MCCs, [15][16][17][18] [H 3−n Co 15 Pd 9 C 3 (CO) 38 ] n− (n = 0-3) as well as the parent [H 6−n Co 20 Pd 16 C 4 (CO) 48 ] n− (n = 3-6) 20 possess poly-hydride nature and display reversible redox processes.…”

“…) in thf results in the formation of [H 3 Co 20 Pd 16 C 4 (CO) 48 ] 3− (ν(CO) at 2026(s) and 1854(m) cm −1 ), as previously described. 20 After removing the solvent in vacuo and dissolving the residue in CH 2 Cl 2 , without removing the excess of acid, the ν(CO) bands are sensibly shifted to 2035(s) and 1865(m) cm Formation of [HCo 15 Pd 9 C 3 (CO) 38 ] 2− requires an excess of acid and the use of CH 2 Cl 2 as a solvent, whereas the same product is not obtained in thf (see Scheme 1). It is likely that the lower ability of CH 2 Cl 2 to interact with H + compared to thf makes the acid more reactive and induces the reaction.…”