Isostructural [Au<sub>6</sub>Pd<sub>6</sub>(Pd<sub>6</sub><sub>-<i>x</i></sub>Ni<i><sub>x</sub></i>)Ni<sub>20</sub>(CO)<sub>44</sub>]<sup>6</sup><sup>-</sup> and [Au<sub>6</sub>Ni<sub>32</sub>(CO)<sub>44</sub>]<sup>6</sup><sup>-</sup> Clusters Containing Corresponding Nonstoichiometric Au<sub>6</sub>Pd<sub>6</sub>(Pd<sub>6</sub><sub>-<i>x</i></sub>Ni<i><sub>x</sub></i>)Ni<sub>20</sub> and Stoichiometric Au<sub>6</sub>Ni<sub>32</sub> Nanosized Cores: Substitutional Pd/Ni Crystal Disorder (Coloring Problem) at Only Six Specific Nonadjacent Pseudoequivalent Metal Sites in the 38-Atom Trimetallic Close-Packed Framework
作者:Nguyet T. Tran、Masaki Kawano、Douglas R. Powell、Randy K. Hayashi、Charles F. Campana、Lawrence F. Dahl
DOI:10.1021/ja982637c
日期:1999.6.1
Efforts to obtain large trimetallic Au-Pd-Ni carbonyl clusters have given rise to the first reported high-nuclearity trimetallic carbonyl cluster [Au6Pd6(Pd6-xNix)Ni-20(CO)(44)](6-) (1). The centrosymmetric architecture of its 38-atom core ideally consists of the hcp stacking of two inner Au3M3Ni6 and two outer Pd-3 layers along with two Pds-capped and six AuNi2-capped Ni atoms. The resulting octahedral-like Aug kernel is antiprismatically capped on opposite triangular faces by the two Pd3 triangles. The microscopic nature of its nonstoichiometric composition was unequivocally established from complete X-ray diffraction analyses via a SMART CCD system of seven crystals of its [PPh4](+) Salt from different samples. A substitutional Pd/Ni crystal disorder was found at only six specific nonadjacent atomic M sites (three crystallographically independent); for the composite six-site crystal disorder of the (6-x) Pd/x Ni atoms, x was determined for the seven crystals to range from 2.1 (65% Pd, 35% Ni) to 5.5 (8% Pd, 92% Ni). The overall geometry of 1 including the 44 CO ligands (in the crystal-averaged unit cell) ideally has trigonal D-3d((3) over bar 2/m) symmetry. A structure/bonding analysis as to why this particular Pd/Ni substitutional crystal disorder is found in 1 provides a striking illustration that the occurrence of a bimetallic substitutional crystal disorder at only certain crystallographic sites (coloring problem) in a heterometallic carbonyl cluster is critically dependent upon the extent of dissimilarity in the composite relative bond-energy effects of metal-metal/metal-CO interactions. 1 was obtained as a major product (35-40% yields) from reactions of [Ni-6(CO)(12)](2-) With Pd(OAc)(2)/Au(PPh3)Cl mixtures in DMSO. Our desire to obtain the hypothetical isostructural [Au6Ni32(CO)(44)](6-) (2), in which all Pd atoms are replaced with Ni ones, led to the 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 and 0.8 nm perpendicular to the principal 3-fold axis.
作者:Michail N. Vargaftik、Victor P. Zagorodnikov、Igor P. Stolyarov、Ilya I. Moiseev、Vladimir A. Likholobov、Dmitry I. Kochubey、Andrew L. Chuvilin、Valdimir I. Zaikovsky、Kirill I. Zamaraev、Galina I. Timofeeva
DOI:10.1039/c39850000937
日期:——
and ultracentrifuging data show that a new catalytically active cluster prepared by reduction of Pd(OAc)2 by H2 in the presence of L = 1,10-phenanthroline, or 2,2′-bipyridine, followed by O2 treatment, contains a close-packed metal nucleus (570 ± 30 Pd atoms) bearing 60 ± 3 co-ordinated L and 180 ± 10 OAc– in the outer sphere of the cluster.