Silver clusters bonding energy

A comparison of the bonding energy per atom (BE/n) for silver clusters of one- and three-dimensional structure is made in Fig. 3. The stability increases in the order 3d < 2d < Id in this size range. The geometries treated were straight-chain linear, square planar, and symmetric three-dimensional structures. 

Palladium and silver, which have very low metal-metal bond energy values, form considerably fewer clusters than their homologs, and their stable polynuclear carbonyls are not known. 

Lower stability of palladium clusters compared to nickel and platinum ones is explained by lower energy of the Pd —Pd bond. It is assumed that the energy of a M — M bond can be measured by the energy of sublimation, which for Ni, Pd, and Pt is 427, 354, and 565 kJ mol respectively. For Cu, Ag, and Au, the energy of sublimation is 339, 285, and 364 kJ mol respectively. It turns out that in the case of group 11 metals, according to predictions, the number of silver clusters is smaller than that of copper and gold clusters. 

Li and Be aggregates [140] C particles [141], Fe chains [142], Ni [143] Ag [144] [14S] and Na aggregates [146]. In all cases the electronic properties of the small particles are different from bulk properties. It was found with silver that the LP. decreases from its single atom value towards the bulk work function as cluster size increases. In the case of Na particles [146] it was found that smaller particles exhibit the higher ionisation potential and excitation energy but lower bond energy. 

The nature of bonding of the adsorbed species to the model cluster of metal surfaces can be analyzed in terms of the so-called constrained space orbital variation (CSOV) method. For halogen anions adsorbed on various silver surfaces, it has been found that Pauli repulsion, metal polarization, and charge transfer to the metal surface mainly contribute to the binding energy of the ions [104, 301]. 

An adsorption of silver dimer on a rutile (110) surface has been studied using a DFT model within both cluster and periodic approaches. The calculations show that the interaction of silver dimers can occur both with bridging chain of oxygen atoms or with atoms located in the hollows between chains. The bonding of Ag2 in the hollow is characterized by the positive adsorption energy according to the periodic model. On the other hand, the geometry optimization of similar structures within the cluster model leads to desorption or dissociation of silver dimer. The periodic model is shown more appropriate for this system. 

Table 1. Binding energies ( o ), bond distances between the nearrat atoms of silver and oxygesi t

Figure 6. A structural comparison of hydrogen bonded and metallic clusters.The lowest-energy conformations of neutral and anionic clusters of water, gold, and silver (H20)2-6,8, (Au2-6,8), (Ag2-6,8) - Note that in both the cases, the presence of an extra electron either geometrically or energetically stabilizes the corresponding neutral structure.

The assignment that the emissions arise from a LMCT [E M4] excited state with mixing of a metal-centered d sjd p) state has been substantiated by ab initio and Fenske-Hall molecular orbital calculations performed for the silver(I) clusters. These results revealed that the HOMOs of the clusters are principally Ag—E bonding orbitals, while the LUMOs are metal-localized orbitals with predominantly 55 and 5p character. Furthermore, the calculated HOMO-LUMO energy gaps decrease in the order (13a) > (13b) > (13c), consistent with the observed trend for the emission energies of the complexes. 

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