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de Silva N, Nichiporuk RV, Dahl LF: Syntheses and structural analyses of variable-stoichiometric Au-Pt-Ni carbonyl/phosphine clusters, Pt3 (Pt (1-x) Ni (x))(AuPPh3) 2 (mu2-CO) 4 (CO)(PPh3) 3 and Pt2 (Pt (2-y) Ni (y))(AuPPh3) 2 (mu2-CO) 4 (CO) 2 (PPh3) 2, with ligation-induced site-specific Pt/Ni substitutional disorder within butterfly-based Pt3 (Pt (1-x) Ni (x)) Au2 and Pt2 (Pt (2-y) Ni (y)) Au2 core-geometries. Dalton Trans. 2006 May 21;(19):2291-300. Epub 2006 Feb 14.
In ongoing attempts of directed synthesis of high-nuclearity Au-Pt carbonyl/phosphine clusters with [Ni6 (CO) 12] 2- used as reducing agent and CO source, we have isolated and characterized two new closely related variable-stoichiometric trimetallic clusters, Pt3 (Pt (1-x) Ni (x))(AuPPh3) 2 (mu2-CO) 4 (CO)(PPh3) 3 (1) and Pt2 (Pt (2-y) Ni (y))(AuPPh3) 2 (mu2-CO) 4 (CO) 2 (PPh3) 2 (2). Their M4Au2 cores may be envisioned as substitutional disordered butterfly-based M4Au2 frameworks (M = Pt/Ni) formed by connections of the two basal M (B) atoms with both (Au-Au)-linked Au (PPh3) moieties. Based upon low-temperature CCD X-ray diffraction studies of eight crystals obtained from different samples, ligation-induced site-specific Pt/Ni substitutional disorder (involving formal insertion of Ni in place of Pt) in a given crystal was found to occur only at the one OC-attached basal M (B) site in 1 or at both OC-attached basal M (B) sites in 2 corresponding to a crystal composite of the Pt3 (Pt (1-x) Ni (x)) Au2 core in 1 or of the Pt2 (Pt (2-y) Ni (y)) Au2 core in 2; the Ph3P-attached M (B) site (M (B) = Pt) in 1 and two wingtip M (w) sites (M (w) = Pt) in 1 and 2 were not substitutionally disordered. The resulting variable stoichiometry of the M4Au2 core in 1 may be viewed as a crystal composite of two superimposed individual stereoisomers, Pt4 (AuPPh3) 2 (mu2-CO) 4 (CO)(PPh3) 3 (1a) and Pt3Ni (AuPPh3) 2 (mu2-CO) 4 (CO)(PPh3) 3 (1b), in the averaged unit cell of a given crystal. Likewise, 2 represents the crystal-averaged composite of three individual stereoisomers, Pt4 (AuPPh3) 2 (mu2-CO) 4 (CO) 2 (PPh3) 2 (2a), Pt3Ni (AuPPh3) 2 (mu2-CO) 4 (CO) 2 (PPh3) 2 (2b), and Pt2Ni2 (AuPPh3) 2 (mu2-CO) 4 (CO) 2 (PPh3) 2 (2c). Formal Ni substitution for Pt at only the basal M (B) site (s) in the four crystal composites each of 1 and 2 was found to vary widely from 17% to 79% Ni in 1 and from 21% to 95% Ni in 2. Nevertheless, reasonably close Pt/Ni occupancy factors were found within each of the four pairs of composite crystals selected from samples obtained from duplicate syntheses. Both 1 and 2 may be formally derived from the electronically equivalent classic butterfly Pt4 (mu2-CO) 5 (PPh3) 4 cluster by replacement of its bridging mu2-CO ligand spanning the basal M (B)-M (B) edge with two one-electron donating (Au-Au)-linked AuPPh3 moieties along with the substitution of a terminal CO in place of one or both M (B)-attached PPh3 ligands in 1 and 2, respectively; site-specific Pt/Ni substitutional disorder occurs only at the CO-attached M (B) sites. The variable-stoichiometric 1 and 2 re also electronically equivalent and geometrically related to the crystal-ordered butterfly-based Pt4 (mu2-CO) 4 (PR3) 4 (mu3-HgX) 2 clusters (R3 = Ph3, MePh2; X = CF3, Br, I). |
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