Isostructural [Au6Pd6(Pd6-xNix)Ni20(CO)44]6- and [Au6Ni32
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- 作者：Nguyet T. Tran ; Masaki Kawano ; Douglas R. Powell ; Randy K. Hayashi ; Charles F. Campana ; and Lawrence F. Dahl
- 刊名：Journal of the American Chemical Society
- 出版年：1999
- 出版时间：June 30, 1999
- 年：1999
- 卷：121
- 期：25
- 页码：5945 - 5952
- 全文大小：148K
- 年卷期：v.121,no.25(June 30, 1999)
- ISSN：1520-5126
文摘
Efforts to obtain large trimetallic Au-Pd-Ni carbonyl clusters have given rise to the first reportedhigh-nuclearity trimetallic carbonyl cluster [Au6Pd6(Pd6-xNix)Ni20(CO)44]6- (1). The centrosymmetric architectureof its 38-atom core ideally consists of the hcp stacking of two inner Au3M3Ni6 and two outer Pd3 layers alongwith two Pd3-capped and six AuNi2-capped Ni atoms. The resulting octahedral-like Au6 kernel is antiprismaticallycapped on opposite triangular faces by the two Pd3 triangles. The microscopic nature of its nonstoichiometriccomposition was unequivocally established from complete X-ray diffraction analyses via a SMART CCDsystem of seven crystals of its [PPh4]+ salt from different samples. A substitutional Pd/Ni crystal disorder wasfound at only six specific nonadjacent atomic M sites (three crystallographically independent); for the compositesix-site crystal disorder of the (6 - x) Pd/x Ni atoms, x was determined for the seven crystals to range from2.1 (65% Pd, 35% Ni) to 5.5 (8% Pd, 92% Ni). The overall geometry of 1 including the 44 CO ligands (in thecrystal-averaged unit cell) ideally has trigonal D3d(
f">2/m) symmetry. A structure/bonding analysis as to whythis particular Pd/Ni substitutional crystal disorder is found in 1 provides a striking illustration that the occurrenceof a bimetallic substitutional crystal disorder at only certain crystallographic sites (coloring problem) in aheterometallic carbonyl cluster is critically dependent upon the extent of dissimilarity in the composite relativebond-energy effects of metal-metal/metal-CO interactions. 1 was obtained as a major product (35-40%yields) from reactions of [Ni6(CO)12]2- with Pd(OAc)2/Au(PPh3)Cl mixtures in DMSO. Our desire to obtainthe hypothetical isostructrual [Au6Ni32(CO)44]6- (2), in which all Pd atoms are replaced with Ni ones, led tothe designed synthesis and structural determination of 2, which in turn provided an "operational test" of our"coloring-problem" analysis of 1. The maximum metal-core diameters in 1 and 2 are ca. 1.1 nm parallel and0.8 nm perpendicular to the principal 3-fold axis.
f">2/m) symmetry. A structure/bonding analysis as to whythis particular Pd/Ni substitutional crystal disorder is found in 1 provides a striking illustration that the occurrenceof a bimetallic substitutional crystal disorder at only certain crystallographic sites (coloring problem) in aheterometallic carbonyl cluster is critically dependent upon the extent of dissimilarity in the composite relativebond-energy effects of metal-metal/metal-CO interactions. 1 was obtained as a major product (35-40%yields) from reactions of [Ni6(CO)12]2- with Pd(OAc)2/Au(PPh3)Cl mixtures in DMSO. Our desire to obtainthe hypothetical isostructrual [Au6Ni32(CO)44]6- (2), in which all Pd atoms are replaced with Ni ones, led tothe designed synthesis and structural determination of 2, which in turn provided an "operational test" of our"coloring-problem" analysis of 1. The maximum metal-core diameters in 1 and 2 are ca. 1.1 nm parallel and0.8 nm perpendicular to the principal 3-fold axis.