Syntheses and structural analyses of variable-stoichiometric Au-Pt-Ni carbonyl/phosphine clusters, Pt3(Pt1-xNix)(AuPPh3)2(μ2-CO)4(CO)(PPh3)3 and Pt2(Pt2-yNiy)(AuPPh3)2(μ2-CO)4(CO)2(PPh3)2, with ligation-induced site-specific Pt/Ni substitutional disorder within butterfly-based Pt3(Pt1-xNix)Au2 and Pt2(Pt2-yNiy)Au2 core-geometries

In ongoing attempts of directed synthesis of high-nuclearity Au - Pt carbonyl/phosphine clusters with [Ni-6(CO)(12)](2-) used as reducing agent and CO source, we have isolated and characterized two new closely related variable-stoichiometric trimetallic clusters, Pt-3(Pt1-xNix)(AuPPh3)(2)(mu(2)-CO)(4)(CO)(PPh3)(3) ( 1) and Pt-2(Pt2-yNiy)(AuPPh3)(2)(mu(2)-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 Pt-3( Pt1-xNix) Au-2 core in 1 or of the Pt-2(Pt2-yNiy) Au-2 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, Pt-4(AuPPh3)(2)(mu(2)-CO)(4)(CO)(PPh3)(3) (1a) and Pt3Ni(AuPPh3)(2)(mu(2)-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, Pt-4(AuPPh3)(2)(mu(2)-CO) (4)(CO)(2)(PPh3)(2) ( 2a), Pt3Ni(AuPPh3)(2)(mu(2)-CO)(4)(CO)(2)(PPh3)(2) ( 2b), and Pt2Ni2(AuPPh3)(2)(mu(2)-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 Pt-4(mu(2)-CO)(5)(PPh3)(4) cluster by replacement of its bridging mu(2)-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 are also electronially equivalent and geometrically related to the crystal-ordered butterfly-based Pt-4(mu(2)-CO)(4)(PR3)(4)(mu(3)-HgX)(2) clusters (R-3 = Ph-3, MePh2; X = CF3, Br, I).