High-Nuclearity Close-Packed Palladium-Nickel Carbonyl Phosphine Clusters: Heteropalladium [Pd_16Ni_4(CO)_22(PPh_3)_4]~(2-) and [Pd_33Ni_9(CO)_41(PPh_3)_6]~(4-) Containing Pseudo-T_d ccp Pd_16Ni_4 and Pseudo-D_3h hcp Pd_33Ni_9 Cores

摘要

[Pd_16N_4(CO)_22(PPh3)_4r- (I) and [Pd_33Ni_9(CO)_41(PPh_3)_6]~(4-) (2) were obtained as the two major products from the reduction of PdCh(PPh_3)_2 with [Ni_6(CO)_12r-. Their crystal structures as [PPh4]+ salts were unambiguously determined from CCD X-ray crystallographic analyses; the resulting stoichiometries were ascertained from elemental analyses. Infrared, multinuclear IH, JP{IH} NMR, UV-vis, CV, variable-temperature magnetic susceptibility, and ESI Ff/ICR mass spectrometric measurements were performed. The Pdl~i4 core of I ideally conforms to a ccp V3 tetrahedron of pseudo-Td (43m) symmetry. Its geometry normal to each tetrahedral Pd_7Ni_3 face (i.e., along each of the four 3-fold axes) may be viewed as a four-layer stacking of 20 metal atoms in a ccp [a(Nil) b(Pd_3) c(P~) a(Pd_7Ni_3)] sequence. A comparative analysis of the different ligand connectivities about the analogous metal-core geometries in I and the previously reported [OS_20(CO)_40r- has stereochemical implications pertaining to the different possible modes of carbon monoxide attachment to ccp metal( 1 1 I ) surfaces. The unique geometry of the Pd_33Ni_9 core of 2, which has pseudo-D3h (62m) symmetry, consists offive equilateral triangular layers that are stacked in a hcp [a(Pd_7Ni_3) b(P~) a(Pd_7Ni_3) b(P~) a(Pd_7Ni_3)] sequence. Variable-temperature magnetic susceptibility measurements indicated both land 2 to be diamagnetic over the entire temperature range from 5.0 to 300 K. Neutral Pd1iCO)_12(PPh_3)_6 (3) and [Pd_29(CO)_28(PPh_3)7r- (4) as the [PPh4]+ salt were obtained as minor decomposition products from protonation reactions of I and 2, respectively, with acetic acid. Compound 3 of pseudo-D3d (32/m) symmetry represents the second highly deformed hexacapped octahedral member of the previously established homopalladium family of clusters containing uncapped, monocapped, bicapped, and tetracapped Pd6 octahedra. The unprecedented centered 28-atom polyhedron for the Pd_29 core of 4 of pseudo-C3v .(3m) symmetry may be described as a four-layer stacking of 29 metal atoms in a mixed hcp/ccp [a(Pdu b(Pd_3) a(Pd1o) C(Pd_15)] sequence.