Acid/Base-Controlled Au1/Au0 Reductive Transformations of the Monogold [(μ14-Au)Pd22(CO)20(PEt3)8]+ Monocation into Three Different Neutral Digo Id Nanoclusters: Au2Pd21(CO)20(PEt3)10, Au2Pd28(CO)26(PEt3)10, and New Five-Layer Hexagonal Close-Packed (μ12-Au)2Pd42(CO)30(PEt3)12 with a Trigonal-Bipyramidal AuPd3Au Kernel

The monogold [(mu(14)-Au)Pd-22(CO)(20)(PEt3)(8)](+) nanocation (2, with a [(CF3CO2)(2)H](-) counterion) is shown to be a versatile precursor for the generation of three different neutral Au-Pd nanoclusters with double gold content in their distinctly dissimilar bimetallic architectures. These carbon monoxide (CO)-induced conversions are based on the reduction of AuI to Au-0 that is controlled by the reaction medium. Under basic and acidic conditions, the known Au2Pd21(CO)(20)(PEt3)(10) (3; >90% yield) and Au2Pd28(CO)(26)(PEt3)(10) (4; similar to 40% yield), respectively, were obtained, whereas neutral conditions gave rise to the new (mu(12)-Au)(2)Pd-42(CO)(30)(PEt3)(12) (1; similar to 10-20% yield; all yields based on gold). The molecular structure of 1, established from a 100 K CCD X-ray diffraction study, consists of a five-layer hexoganol close-packed (hcp) Au2Pd42 framework of pseudo-D-3h symmetry (crystallographic D-3 site symmetry) of the Pd-6/AuPd9/Pd-12/AuPd9/Pd-6 layer sequence, with the Au atoms centering two identical hcp (mu(12)-Au)Pd-12 face-fused anti-cuboctahedral fragments. The 12 Et-3-attached P atoms are coordinated to the triangular vertex Pd atoms in the four outer layers (except the middle Pd-12); all five layers are stapled by interlayer bridging COs. The radial Au-cent-Pd mean distance of 2.79 angstrom within the two symmetry-equivalent (mu(12)-Au)Pd-12 anti-cuboctahedral fragments of 1 is identical with the radial Pd-cent-Pd mean distances within hcp (mu(12)-Pd)Pd-12 anti-cuboctahedral fragments of the two geometrically related nondistorted layered structures of Pd-52(CO)(36)(PEt3)(14) and [Ni9Pd33(CO)(41)(PPh3)(6)](4-) ([PPh4](+) counterion), indicating a strain-free structural effect upon the substitution of Au for Pd in their analogous hcp layer-stacked arrangements. It provides prime evidence for an extension to 1 of our previous self-consistent experimental/theoretical-based hypothesis for delocalization of the 6s valence Au electrons in Au2Pd21 (3) and Au2Pd28 (4) toward a formal closed-shell Au+ configuration that is electronically equivalent to that of zerovalent Pd.