Evgueni G. Mednikov

Syntheses, structures and properties of primarily nanosized homo/heterometallic palladium CO/PR3-ligated clusters.

Syntheses, properties and structures of nanosized palladium CO/PR3-ligated homo- and heterometallic clusters containing up to 165 metal atoms are the focus of this review. The work discussed is primarily that of the authors and their coworkers. We propose that the unparalleled variety of structural types and the distinctive reactivities of neutral Pdn(CO)x(PR3)y clusters composed of zerovalent Pd atoms are a consequence of relatively weak Pd–L(ligand) and Pd(0)–Pd(0) interactions that result from the stable 5s04d10 closed-shell electron configuration of atomic Pd in its ground state.

Crystallographically Proven Nanometer‐Sized Gold Thiolate Cluster Au102(SR)44: Its Unexpected Molecular Anatomy and Resulting Stereochemical and Bonding Consequences

C rystallographic determinations of giant close-packed metal clusters, especially monodisperse ligated Mn nanoparticles with n> 40 atoms, are of great importance and high interest in light of at least two factors. First, single-crystal X-ray diffraction is still the most powerful analytical method that normally provides unambiguous information concerning the nanoparticle metal core and its ligand environment. Second, even though theoretical calculations are usually wellgrounded for naked nanoparticles, they are generally not sufficiently reliable for predictions of real ligated nanostructures. Furthermore, it is normally difficult to deduce ligated nanoparticle structures on the basis of related crystallographically characterized, relatively small metal clusters. A particularly striking illustration of this difficulty is given by the recent landmark achievement of Kornberg and co-workers in performing the first crystal-structure determination at atomic resolution (1.1 Å) of a thiolate-ligated gold nanocluster, Au102(p-SR)44 (1) where HSR denotes p-mercaptobenzoic acid. Although 1 was obtained by a generally well-known synthetic approach involving reaction of an arylthiol with borohydride–reduced HAuCl4, [6] their finding of the ‘‘right’’ arylthiolate SR ligand and their use of protein-based methodology for purification and crystallization of the nanometer-sized gold thiolate cluster (1) in strictly

Isolation and Structural Characterization of a Mackay 55-Metal-Atom Two-Shell Icosahedron of Pseudo-Ih Symmetry, Pd55L12(μ3-CO)20 (L = PR3, R = Isopropyl): Comparative Analysis with Interior Two-Shell Icosahedral Geometries in Capped Three-Shell Pd145, Pt-Centered Four-Shell Pd–Pt M165, and Four-Shell Au133 Nanoclusters

We present the first successful isolation and crystallographic characterization of a Mackay 55-metal-atom two-shell icosahedron, Pd55L12(μ3-CO)20 (L = PPr(i)3) (1). Its two-shell icosahedron of pseudo-Ih symmetry (without isopropyl substituents) enables a structural/bonding comparison with interior 55-metal-atom two-shell icosahedral geometries observed within the multi-shell capped 145-metal-atom three-shell Pd145(CO)72(PEt3)30 and 165-metal-atom four-shell Pt-centered (μ12-Pt)Pd164-xPtx(CO)72(PPh3)20 (x ≈ 7) nanoclusters, and within the recently reported four-shell Au133(SC6H4-p-Bu(t))52 nanocluster. DFT calculations carried out on a Pd55(CO)20(PH3)12 model analogue, with triisopropyl phosphine substituents replaced by H atoms, revealed a positive +0.84 e charge for the entire Pd55 core, with a highly positive second-shell Pd42 surface of +1.93 e.

Formation of thallium(I) sandwich M3TlM3 clusters, [(μ6-Tl)M6(μ2-CO)6(PEt3)6]+(M = Pt, Pd), with two unconnected triangular M3(μ2-CO)3(PEt3)3 units: implications of comparative analysis of isostructural 5d106s2 Tl(I)–(M3)2 sandwiches (M = Pt, Pd) with known 5d10 Au(I)–(Pt3)2 sandwich

The preparation, isolation, and structural/spectroscopic IR, 31P{1H} NMR characterization of two new isostructural 5d106s2 Tl(I) sandwich clusters, [(μ6-Tl)Pt6(μ2-CO)6(PEt3)6]+ (1) and [(μ6-Tl)Pd6(μ2-CO)6(PEt3)6]+ (2) as [PF6]− salts are presented. Each of these closed-subshell M3TlM3 sandwiches (M = d10 Pt (1), Pd (2)) containing two unconnected triangular M3(μ2-CO)3(PR3)3 units is held together solely by delocalized/electrostatic M3–Tl–M3 bonding. 1 and 2 were synthesized in ca. 90% yields by reactions (under markedly different boundary conditions) of M4(μ2-CO)5(PEt3)4 (M = Pt (3), Pd (4)) with TlPF6. Their isostructural geometries and stoichiometries were unequivocally established from low-temperature CCD X-ray crystallographic determinations. Both 1 and 2 (without their P-attached ethyl substituents) closely conform to a centrosymmetric trigonal-antiprismatic architecture of trigonal D3d symmetry. A comparison of their well-refined isomorphous crystal structures reveals that the Tl–Pd mean of 2.91 A in 2 is 0.05 A smaller than the Tl–Pt mean of 2.96 A in 1. In solution, 2 is much more kinetically labile than 1 and (unlike 1) readily converts under N2 into the recently reported [Tl2Pd12(μ2-CO)6(μ3-CO)3(PEt3)9]2+ (5) as the [PF6]− salt, which was isolated in ca. 90% yield from the same reactants (viz., Pd4(μ2-CO)5(PEt3)4 and TlPF6). In fact, obtaining crystalline material of 2 from recrystallization procedures was greatly hampered by its facile transformation into large quantities of co-crystallized 5. A comparative analysis of the molecular parameters and relative stabilities of the closed-subshell 5d106s2 Tl(I)–(M3)2 sandwiches (M = d10 Pt (1), Pd (2)) with the corresponding known closed-subshell 5d10 Au(I)–(Pt3)2 sandwich together with an examination of relative shifts of corresponding bridging carbonyl IR frequencies for selected pairs of related clusters provide compelling evidence that the so-called “inert” 6s2 electron-pair on the Tl(I) exerts an overall destabilizing influence: namely, that the highly electrophilic 5d10 Au(I) forms considerably stronger delocalized sandwich Pt3–Au–Pt3 bonding (due to its empty, relativistically stabilized 6s acceptor AO) which is presumed to have considerable covalent character. The Tl(I)–Pt(0) distances in 1 are similar to the Tl(I)–Au(I) distances found for another recently reported class of two electronically equivalent closed-subshell Au3TlAu3 sandwich units (i.e., 5d10 Au(I) vs. 5d10 Pt(0)) formed by intercalation of Tl+ between two electron-rich intramolecular, weakly bonded (aurophilic) Au3 triangles in trinuclear cyclic gold(I) benzylimidazolate and carbeniate molecules; the Au3TlAu3 sandwich units stack into linear chains with intermolecular aurophilic Au(I)–Au(I) interactions between four of the six Au(I) atoms in adjacent units. Of particular interest is that the Tl(I)–Au(I) distances (means, 3.02 and 3.09 A) in the distorted trigonal-prismatic (μ6-Tl)Au6 sandwich units of the geometrically related Tl+-intercalated TR(bzim) and TR(carb) complexes are 0.2–0.3 A longer than the Ag(I)–Au(I) distances (mean, 2.81 A) in the initially known Au3AgAu3 sandwich unit of the Ag+-intercalated TR(bzim) analogue; it is similarly proposed that this parallel (M′–Au) bond-length difference may likewise be attributed to the considerably smaller electrophilic character of the central 5d106s2 Tl(I) vs. that of the 4d10 Ag(I) due to the overall destabilizing effect of the thallium(I) 6s2 electron-pair.

Ion Exchange of Protons by Coinage Metals to Give Gold and Silver Encapsulation within a Pseudo‐D2d Distorted Face‐Capped Pd14 Cubic Kernel: [(μ14‐M)Pd22(CO)20(PEt3)8]+ (M=Au, Ag)

Heart of gold (or silver): The pseudo-D2d distorted MPd14 cubic kernel of [(μ14-M)Pd22(CO)20(PEt3)8](+) cations, with M = Au (1), Ag (2), has an encapsulated M atom (see picture; yellow) coordinated to eight cubic corner (black) and six face-capping Pd atoms (gray). Compounds 1 and 2 were obtained (28-60 % yields) from two-step/one-pot reactions of a Pd10 precursor with CF3CO2 H followed by coinage-metal ion exchange of protons.

How innocent is thallium(I)? Corrected formulations of [Tl2Pd14(CO)9(PMe3)11][PF6]2 and [TlPd9(CO)9(PPh3)6][PF6] clusters previously reported as corresponding Au2Pd14 and AuPd9 clusters

Two previously reported cationic clusters, Au(2)Pd(14) (1-Me) and AuPd(9) (2-Ph), obtained by similar reactions of CO/PR(3)-ligated Pd(0) clusters with in the presence of TlPF(6) are shown to be [Tl(2)Pd(14)(CO)(9)(PMe(3))(11)](2+) (1a-Me) and [TlPd(9)(CO)(9)(PPh(3))(6)](+) (2a-Ph), respectively. These clusters ([PF(6)](-) counterion) were prepared without the presence of gold by reactions of either Pd(10)(CO)(12)(PMe(3))(6) or Pd(10)(CO)(12)(PPh(3))(6) with TlPF(6) and characterized crystallographically and spectroscopically.

Acid/base-controlled AuI/Au0 reductive transformations of the monogold [(μ14-Au)Pd22(CO)20(PEt3)8]+ monocation into three different neutral digold 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 [(μ(14)-Au)Pd(22)(CO)(20)(PEt(3))(8)](+) nanocation (2, with a [(CF(3)CO(2))(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 Au(I) to Au(0) that is controlled by the reaction medium. Under basic and acidic conditions, the known Au(2)Pd(21)(CO)(20)(PEt(3))(10) (3; >90% yield) and Au(2)Pd(28)(CO)(26)(PEt(3))(10) (4; ∼40% yield), respectively, were obtained, whereas neutral conditions gave rise to the new (μ(12)-Au)(2)Pd(42)(CO)(30)(PEt(3))(12) (1; ∼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) Au(2)Pd(42) framework of pseudo-D(3)h symmetry (crystallographic D(3) site symmetry) of the Pd(6)/AuPd(9)/Pd(12)/AuPd(9)/Pd(6) layer sequence, with the Au atoms centering two identical hcp (μ(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 Å within the two symmetry-equivalent (μ(12)-Au)Pd(12) anti-cuboctahedral fragments of 1 is identical with the radial Pd(cent)-Pd mean distances within hcp (μ(12)-Pd)Pd(12) anti-cuboctahedral fragments of the two geometrically related nondistorted layered structures of Pd(52)(CO)(36)(PEt(3))(14) and [Ni(9)Pd(33)(CO)(41)(PPh(3))(6)](4-) ([PPh(4)](+) 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 Au(2)Pd(21) (3) and Au(2)Pd(28) (4) toward a formal closed-shell Au(+) configuration that is electronically equivalent to that of zerovalent Pd.