Nanosized Au2Pd41(CO)(27)(PEt3)(15) containing two geometrically unprecedented 13-coordinated Au-centered (mu(13)-Au)Pd-13 polyhedra connected by triangular face-sharing and three interpenetrating 12-coordinated Pd-centered (mu(12)-Pd)Au2Pd10 icosahedra: geometrical change in centered polyhedra induced by Au/Pd electronegativity-mismatch

The synthesis, isolation, and stereochemical characterization of Au2Pd41(CO)(27)(PEt3)(15) (1) are described. This nanosized Au2Pd41 cluster (maximum metal-core diameter, 1.04 nm) was originally obtained with Au2Pd21(CO)(20)(PEt3)(10) as low-yield by-products together with Pd-145(CO)(x)(PEt3)(30) (xsimilar to60) from the reaction of Pd(PEt3)(2)Cl-2 and Au(PPh3)Cl in DMF with NaOH under CO atmosphere. The subsequent preparation of Au2Pd21(CO)(20)(PEt3)(10) in greatly improved yields (preceding article) thereby provided the starting material that led to the isolation of 1 in reasonable yields (54%) from an overnight refluxing of the preformed Au2Pd21 cluster in THF under N-2. Both the composition (subsequently ascertained from elemental analysis) and molecular geometry of 1 were unequivocally established from a low-temperature CCD X-ray diffraction study, which revealed a cubic unit cell of P2(1)3 symmetry with four molecules of 1 and four co-crystallized triphenylphosphine oxide molecules each lying on a crystallographic three-fold axis. The entire Au2Pd41 core of pseudo-C-3h symmetry may be viewed as a central Au2Pd29 fragment of pseudo-D-3h symmetry composed of two heretofore geometrically unknown 13-coordinated Au-centered (mu(13)-Au)Pd-13 polyhedra that share a common internal Pd(i)(3) triangular face perpendicular to the C-3 principal axis and of three three-fold-related interpenetrating 12-coordinated Pd-centered (mu(12)-Pd)Au2Pd10 icosahedra. A comparative analysis of this central Au2Pd29 fragment in 1 with an internal Au(i)(2)Pd(i)(3) trigonal bipyramid vs. the corresponding central Pd-29 fragment in the known homopalladium Pd-35(CO)(23)(PMe3)(15) (2) with an internal Pd(i)(5) trigonal bipyramid resulting from five interpenetrating 12-coordinated Pd-centered [(mu(12)-Pd)Pd-12] icosahedra is particularly illuminating; it provides a striking illustration of the remarkable observed difference between Pd-vs. Au-centered polyhedra which is attributed to a large electronegativity-mismatch in radial bonding interactions that occurs upon replacement of the Pd-centered atom with a highly electronegative Au-centered atom. The entire Au2Pd41 core-geometry is obtained by additional face-condensations of 12 tetracapping Pd(cap) atoms. This cluster is stabilized by 15 PEt3 ligands and 27 doubly- and triply-bridging CO ligands. A close geometrical resemblance between the three three-fold-related Au2Pd14 moities within the Au2Pd41 core in 1 and the entire Au2Pd14 core in the known [Au2Pd14(CO)(9)(PMe3)(11)](2+) dication (3) is observed; resulting stereochemical implications are given.