High-nuclearity [Pd13Ni13(CO)34]4− containing a 26-atom Pd13Ni13 core with an unprecedented five-layer close-packed triangular stacking geometry: possible substitutional Pd/Ni crystal disorder at specific intralayer nickel sites
[Pd13Ni10(Ni3 − xPdx)(CO)34]4−1 has been prepared in essentially quantitative yields (>90%) from room-temperature reactions of [Ni6(CO)12]2− with either Pd(OAc)2 in DMF or Pd(MeCN)4(BF4)2 in DMSO. The crystal structure of 1 as the [PPh4]+ salt was determined from low-temperature CCD X-ray crystallographic analyses of three crystals. 1 was also characterized by elemental analysis, IR, 1H NMR, and electrochemical (CV) measurements. Its structurally unprecedented 26-atom metal polyhedron consists of a 5-layer close-packed triangular stacking arrangement of pseudo-C3v symmetry with an [a(Ni)b(Ni3)c(Pd6)a(Pd7Ni3)c(Ni3M3)] sequence. The overall geometry of the 20-atom ν3 tetrahedral Pd13Ni7 framework in the top four ccp layers is analogous to the pseudo-Td cubic geometry of the metal-core previously found in [Pd16Ni4(CO)22(PPh3)4]2− and [Os20(CO)40]2−. Each M in the bottom fifth Ni3M3 layer denotes an inner triangular atomic site where a substitutional Pd/Ni crystal disorder may occur; the composite composition of the three M sites corresponds to Ni3 − xPdx with x = 0.45 for crystal A and 0 for B and C. We thereby formulate 1 to possess a stoichiometric Pd13Ni13 core even though crystallographic evidence from crystal A indicates the existence of a crystal disorder involving a small substitution of Pd for Ni at two of the three inner atomic M sites within the Ni3M3 layer. The entire geometry of 1 (including the 34 carbonylligands) ideally conforms to C3v trigonal symmetry. A qualitative structure/bonding analysis was performed in order to correlate the geometry of 1 with its electron count. The maximum metal-core diameter is ca. 0.87 nm parallel and 0.56 nm perpendicular to the principal 3-fold axis.
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