Cooperative Effects of Electron Donors and Acceptors for the Stabilization of Elusive Metal Cluster Frameworks: Synthesis and Solid-State Structures of [Pt19(CO)24(μ4-AuPPh3)3]− and [Pt19(CO)24{μ4-Au2(PPh3)2}2]

Looking at platinum carbonyl nanoclusters as superatoms

Although the chemistry of carbonyl-protected platinum nanoclusters is well established, their bonding mode remains poorly understood. In most of them, the average Pt oxidation state is zero or slightly negative, leading to the apparent average configuration 5d¹⁰ 6s^ε (ε = 0 or very small) and the apparent conclusion that metal-metal bonding cannot arise from the completely filled 5d shell nor from the empty (or almost empty) 6s orbitals. However, DFT calculations show in fact that in these species the actual average configuration is 5d^10-x 6s^x, which provides to the whole cluster a significant total number of 6s electrons that ensures metal-metal bonding. This ("excited") average configuration is to be related to that of coinage metals in ligated group 11 nanoclusters (nd¹⁰ (n + 1)s^x). Calculations show that metal-metal bonding in most of these platinum nanoclusters can be rationalized within the concepts of superatoms and supermolecules, in a similar way as for group 11 nanoclusters. The "excited" 5d^10-x 6s^x configuration results from a level crossing between 5d combinations and 6s combinations, the former transferring their electrons to the latter. This level crossing, which does not exist in the bare Pt_n clusters, is induced by the ligand shell, the role of which being thus not innocent with respect to metal-metal bonding.

Heterometallic rhodium clusters as electron reservoirs: Chemical, electrochemical, and theoretical studies of the centered-icosahedral [Rh12E(CO)27]n- atomically precise carbonyl compounds

In this paper, we present a comparative study of the redox properties of the icosahedral [Rh₁₂E(CO)₂₇]^n- (n = 4 when E = Ge or Sn and n = 3 when E = Sb or Bi) family of clusters through in situ infrared spectroelectrochemistry experiments and density functional theory computational studies. These clusters show shared characteristics in terms of molecular structure, being all E-centered icosahedral species, and electron counting, possessing 170 valence electrons as predicted by the electron-counting rules, based on the cluster-borane analogy, for compounds with such metal geometry. However, in some cases, clusters of similar nuclearity, and beyond, may show multivalence behavior and may be stable with a different electron counting, at least on the time scale of the electrochemical analyses. The experimental results, confirmed by theoretical calculations, showed a remarkable electron-sponge behavior for [Rh₁₂Ge(CO)₂₇]^4- (1), [Rh₁₂Sb(CO)₂₇]^3- (3), and [Rh₁₂Bi(CO)₂₇]^3- (4), with a cluster charge going from -2 to -6 for 1 and 3 and from -2 to -7 for cluster 4, making them examples of molecular electron reservoirs. The [Rh₁₂Sn(CO)₂₇]^4- (2) derivative, conversely, presents a limited ability to exist in separable reduced cluster species, at least within the experimental conditions, while in the gas phase it appears to be stable both as a penta- and hexa-anion, therefore showing a similar redox activity as its congeners. As a fallout of those studies, during the preparation of [Rh₁₂Sb(CO)₂₇]^3-, we were able to isolate a new species, namely, [Rh₁₁Sb(CO)₂₆]^2-, which presents a Sb-centered nido-icosahedral metal structure possessing 158 cluster valence electrons, in perfect agreement with the polyhedral skeletal electron pair theory.

Monomeric Chini-Type Triplatinum Clusters Featuring Dianionic and Radical-Anionic π*-Systems

Owing to their unique topologies and abilities to self-assemble into a variety of extended and aggregated structures, the binary platinum carbonyl clusters [Pt3 (CO)6 ]n (2-) ("Chini clusters") continue to draw significant interest. Herein, we report the isolation and structural characterization of the trinuclear electron-transfer series [Pt3 (μ-CO)3 (CNAr(Dipp2) )3 ](n-) (n=0, 1, 2), which represents a unique set of monomeric Pt3 clusters supported by π-acidic ligands. Spectroscopic, computational, and synthetic investigations demonstrate that the highest-occupied molecular orbitals of the mono- and dianionic clusters consist of a combined π*-framework of the CO and CNAr(Dipp2) ligands, with negligible Pt character. Accordingly, this study provides precedent for an ensemble of carbonyl and isocyanide ligands to function in a redox non-innocent manner.