Effects of ligand coverage on properties of palladium clusters. A density functional theory study

Abstract

International audienceLigand stabilized clusters of palladium are treated at density functional theory level to investigate effects of ligand coverage on properties, such as preferred coordination sites, metal–ligand binding energies, and structure. Systems investigated include cores of Pdn, for n = 1,2,13,16,19,23,35,39, stabilized by CO, PH3, and P(CH3)3, which are either known experimentally or have been proposed as intermediates in syntheses. Some of these systems, e.g. Pd13(CO)i, served as models to study aspects of ligand metal binding. The main results are the following. CO binds preferably as μ3 such that coordination sites share at most one vertex atom. The ligand coverage weakens Pd–Pd bonding and quenches the high spin of pure metal clusters. Ligands tend to stabilize Pd cores showing icosahedral Pd13 structural units such as biicosahedra in Pd19 and Pd23, whereas the corresponding bare metal clusters are most stable as octahedron and decahedron, respectively. The BP86 density functional yields reliable structure parameters and ligand metal binding energies in cases where comparison with experiment or accurate calculations is possible, only Pd(CO)i, i = 1–4, appears to be an exception

DFT Study of Small Palladium Clusters Pdn and Their Interaction with a CO Ligand (n = 1–9)

“…This can be proven experimentally [3] and theoretically. [15] Regarding the CO ligand, its physicochemical characteristics, bond length (d Pd-CO ) and stretching vibration (ν CO ), are consistent with the coordination mode and are generally independent of the number of palladium atoms in the clusters. This CO stretching frequency may thus be considered as a good probe of the structural binding of the ligand to the cluster.…”

“…This result is consistent with the structural study conducted by the group of V. Bertin [14] and the group of P. Nava. [15] Comparing to PdCO, there is greater charge transfer from 4d orbitals to the π* orbitals of the CO for the Pd 2 CO complex. Consequently, the CO bond is weaker in the case of the dimer complex (decrease in bond length and increase in stretching frequency).…”

“…[8][9][10][11][12] Recently, palladium clusters with larger nuclearity were also studied by molecular dynamics. [13] Interactions of ligands with the metal core have also been the subject of a series of works which include, among others, interactions with CO, [14,15] NO, [16] S and Cl, [17] O 2 [18] or H and CH x . [19] In this work, we intend to push further the investigation of these species by addressing in greater detail their electronic structure.…”

Quantum chemical treatments of metal clusters

“…This was done in two papers (Nava et al 2003(Nava et al , 2004, which addressed the following questions: What is the preferred packing and shape of Pd n ? How does the total spin change with cluster size?…”

Infrared Photodissociation Spectra of Mass‐Selected Homoleptic Dinuclear Palladium Carbonyl Cluster Cations in the Gas Phase

“…[23][24][25] In addition, bond dissociation energies of palladium trimer anion carbonyls, 3 Pd (CO) n -(n＝1-6) were measured in the gas phase by the energy resolved collision-induced dissociation method. [26] Although palladium clusters stabilized by multiple CO ligands were calculated at density functional theory level to investigate effects of ligand coverage on properties such as preferred coordination sites, metal-ligand binding energies and structure, [27] and some dinuclear and trinuclear palladium carbonyl cluster anions including 2 Pd (CO) n -(n＝0-4) and 3 Pd (CO) m -(m＝0-6) were studied by anion photoelectron spectroscopy, [25] the electronic and geometric structures of gaseous palladium carbonyl clusters with multiple CO ligands are relatively unknown.…”