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Presented herein are the geometrical features of a stoichiometric capped three-shell palladium carbonyl phosphane cluster 1. Its pseudo I h metal core (see Figure 1) consists of a central Pd atom surrounded by 12 Pd atoms (shell 1), which in turn are encapsulated by 42 Pd atoms (shell 2), which in turn are encapsulated by 60 Pd atoms (shell 3). Thirty additional Pd atoms cap the 30 square polygons of the third-shell polyhedron with a triethylphosphane ligand attached to each capping Pd atom. It is currently presumed that 60 CO groups (crystal-disordered) edge-bridge the 30 capping Pd atoms with one-half of the square basal Pd atoms (in accordance with an IR carbonyl spectrum). The diameter of the entire Pd 145 core of 1 between two centrosymmetrically opposite capping Pd atoms is 1.65 nm; the spherical-like geometry of the centered three-shell Pd 115 kernel (that is, without the 30 capping Pd atoms) is evidenced by the similarity of the corresponding distances for the centrosymmetrically opposite pentagonal faces (1.22 nm), square faces (1.27 nm), and triangular faces (1.27 nm) of the third shell.This remarkable Pd 145 nanocluster, whose metal-core geometry was unambiguously characterized from complete crystallographic analyses of X-ray data for two crystals (from different preparations, crystals A and B), [1, 2] was isolated from the reduction of a monomeric square-planar palladium precursor, [Pd(PEt 3 ) 2 Cl 2 ]. [3, 4] The geometrical conformity of the 55 interior metal atoms within the third shell of 1 to the well-known two-shell icosahedral Mackay hard-sphere model [5] had not been previously observed in single-crystal X-ray crystallographic determinations. [6,7] The third-shell polyhedron in this unprecedented close-packed multi-shell metal carbonyl cluster possesses 60 equivalent vertices along with 12 pentagonal, 20 equilateral triangular, and 30 square faces; [8] this semi-regular (Archimedean) polyhedron, named rhombicosidodecahedron (with Schläfli symbol 3.4.5.4), [9] is a heretofore crystallographically unknown stereoisomer of the universally familiar C 60 buckyball, an icosahedrally truncated semi-regular polyhedron of I h symmetry with 60 equivalent vertices and 12 pentagonal and 20 hexagonal faces.Because the formation of 1 is extremely sensitive to reaction boundary conditions, extensive systematic preparative efforts have been made during the last 24 months to provide a reproducible but (as yet) low-yield synthesis. The Goddess Fortuna recently revisited our laboratory in that crystals of 1 were again isolated and its crystal structure redetermined. The fact that 1 has 55 interior Pd atoms makes it an ideal model for experimental operational tests of previous interpretations of size-dependent physical properties (attributed to quantum-size effects) reported [10] for several giant noncrystalline, (N,O)-ligated, full-shell palladium clusters (ideally formulated from other measurements as fiveshell Pd 561 species by the Moiseev and Schmid groups [11, 12] and as seven-/eight-shell Pd 1415 /Pd 205...

Dedicated to Professor Boon Teo on the occasion of his 55th birthday Palladium possesses exceptional versatility as a unique transition metal in forming an unparalleled assembly of highly condensed carbonyl-phosphane clusters containing either ccp-, mixed ccp/hcp-, or icosahedral-based metal-core architectures. Examples of high-nuclearity homopalladium clusters (that is, clusters arbitrarily designated by us to possess at least ten metal-core atoms with direct metal-metal bonding) with ccp or mixed ccp/hcp layer-stacking geometries include [Pd 10 (CO) 14 ] with interpenetrating ("twinned-core") cuboctahedral Pd 20 kernels.[9] High-nuclearity homopalladium clusters built on centered icosahedral frameworks are illustrated by [Pd 16 (CO) 13 (PR 3 ) 9 ] (R = Me, [10] Et [11] ) with a single Pd 13 -centered icosahedron, and [Pd 34 (CO) 24 (PEt 3 ) 12 ] with four interpenetrating Pd 26 -centered icosahedra. [6,12] [Pd 35 (CO) [10] each contain a face-fused Pd 23 -centered biicosahedron with linear (D 3h ) and bent (C 2v ) geometries, respectively; the D 3h central Pd 29 polyhedron of the Pd 35 core ideally conforms to five interpenetrating centered icosahedra. [10] [Pd 59 (CO) 32 (PMe 3 ) 21 ] [10,13] has two Pd 13 -centered icosahedra that are indirectly connected through trans double-face sharing with an inner face-fused Pd 9 bioctahedron. The unique nanosized [Pd 145 (CO) x (PEt 3 ) 30 ] cluster (with x % 60) contains a capped three-shell 145-atom metal core that closely conforms to I h icosahedral symmetry. [14] Herein we report the preparation, isolation, and structural determination of another type of nanosized icosahedral-based cluster, [Pd 69 (CO) 36 (PEt 3 ) 18 ] (1), which has two new important stereochemical features: 1) a linear face-condensation of three centered icosahedra that gives rise to a linear facesharing Pd 33 -centered triicosahedron, and 2) a hexagonalshaped Pd 30 tube formed by cyclic trans edge-sharing of six Pd 7 -centered hexagons (host), inside of which resides the linear triicosahedron (guest).It is particularly noteworthy that this face-condensed icosahedral growth pattern in 1 is completely different from the general vertex-sharing growth sequence of the extraordinary centered polyicosahedral Au/Ag and Au/Ag/M halide phosphane supraclusters (where M = Ni, Pd, Pt are centered M atoms) proposed by Teo, Zhang, and co-workers [15] (see below). In addition, the well-defined stoichiometries and widely diversified but precise geometries of 1 and other homopalladium carbonyl phosphane clusters have especially important stereochemical implications concerning multitwinned structures and growth patterns of much larger ligated and nonligated palladium nanoparticles, and hence are of relevance in nanotechnology.Compound 1 was obtained in moderate yields (% 50 %) from a reproducible (optimized) synthesis involving the use of the preformed tetracapped octahedral [Pd 10 (CO) 12 (PEt 3 ) 6 ]. [16] Its composition as well as its atomic arrangement were unequivocally established from low-temperature...