Doping effect on the structure and properties of eight-electron silver nanoclusters

Abstract

The bimetallic M20 and M21 compounds, {[Cu3Ag17{S2P(O i Pr)2}12]0.5 [Cu4Ag16{S2P(O i Pr)2}12]0.5} ({[1a]0.5[1b]0.5}) and [Cu4Ag17{S2P(O i Pr)2}12](PF6) (2) have been structurally characterized, in which the Cu(I) ions are randomly distributed on the eight outer positions capping the 8-electron [Ag13] 5+ core. DFT calculations show that his statistical disorder results from the nearly neutral preference of copper to occupy any of the eight outer positions. Surprisingly, the UV-Vis absorption spectra of the M20 and M21 bimetallic nanoclusters display an almost identical absorption profile as that of their homometallic [Ag20{S2P(O i Pr)2}12] and [Ag21{S2P(O i Pr)2}12] + relatives. This is rationalized by TD-DFT calculations which show that the frontier orbitals of such 8-electron alloys are largely independent from the nature of the capping metal ions. A blue-shifted absorption is observed upon replacing by Au the central Ag atom in 2, forming the trimetallic compound [Cu4AuAg16{S2P(O i Pr)2}12](PF6) (3).

Alloying dichalcogenolate-protected Ag21 eight-electron nanoclusters: a DFT investigation

“…65. Not only they all possess a formally 8-electron centered icosahedral M 13 core, but in all of them the 12 dichalcogenolate ligands are arranged in such a way that the 12 metal atoms occupying icosahedral vertices are coordinated to one sulfur/selenium atom in a radial orientation and the 8 peripheral outer d 10 centers are coordinated in a trigonal planar mode, making thus locally stable 16electron complexes. These d 10 metals are capping icosahedral faces, but their interaction with the icosahedral core is weak [41][42][43][44][45][46][47][48]52 (mainly of metallophilic nature). Assuming a homometallic [Ag 21 {E 2 P(OR) 2 } 12 ] + cluster in any of the three structures defined above, the substitution of any of the Ag atoms by one hetero-metal generates several positional isomers to calculate, the number of which becoming very large in the case of the structure of C 1 symmetry.…”

“…For example, in the case of M = Au, the unique central site (type I) will be first occupied, then additional Au atoms will occupy icosahedron vertices (type II), as exemplified by the X-ray structure of [{Au@Au 2 Ag 18 }{Se 2 P(O i Pr) 2 } 12 ] + . 47 The preference for outer capping positions for Cu (Type III) let to consider the theoretical limit number of 8 atoms in such positions. So far, up to 4 capping positions have been shown to be occupied by Cu in [{Ag@Ag 16 Cu 4 }{S 2 P(O i Pr) 2 } 12 ] + and [{Au@Ag 17 Cu 3 }{S 2 P(O i Pr) 2 } 12 ].…”

“…On the other hand, its validity has been proven in many occasions. [41][42][43][44][45][46][47][48]52 The BP86 functional 53,54 was used together with the general triple-ζ polarized Def2-TZVP basis set from EMSL Basis Set Exchange Library, 55,56 in conjunction with effective core potentials (ECP's) for the eight heavier elements, thus permitting to somewhat account for scalar relativistic effects. All the optimized geometries were ascertained as true minima on the potential energy surface by carrying out vibrational frequency calculations.…”

“…From these data it is also possible to reasonably predict the structure of polysubstituted species. For example, in the case of M = Au, the unique central site (type I) will be first occupied, then additional Au atoms will occupy icosahedron vertices (type II), as exemplified by the X-ray structure of [{Au@Au 2 Ag 18 }{Se 2 P(O i Pr) 2 } 12 ] + 47. The preference for outer capping positions for Cu (Type III) let to consider the theoretical limit number of 8 atoms in such positions.…”

“…2 } 12 ] + ,46 [Au@Ag 20 }{Se 2 P(O i Pr) 2 } 12 ] + ,47 [{Au@Au 2 Ag 18 }{Se 2 P(O i Pr) 2 } 12 ] + ,47 [{Ag@Ag 16 Cu 4 }{S 2 P(O i Pr) 2 } 12 ] + 48 and [{Au@Ag 16 Cu 4 }{S 2 P(O i Pr) 2 } 12 ].…”