How structural and vibrational features affect optoelectronic properties of non-stoichiometric quantum dots: computational insights.

While stoichiometric quantum dots (QDs) have been well studied, a significant knowledge gap remains in the atomistic understanding of the non-stoichiometric ones, which are predominantly present during the experimental synthesis. Here, we investigate the effect of thermal fluctuations on structural and vibrational properties of non-stoichiometric cadmium selenide (CdSe) nanoclusters: anion-rich (Se-rich) and cation-rich (Cd-rich) using ab initio molecular dynamics (AIMD) simulations. While the excess atoms on the surface fluctuate more for a given QD type, the optical phonon modes are mostly composed of Se atoms dynamics, irrespective of the composition. Moreover, Se-rich QDs have higher bandgap fluctuations compared to Cd-rich QDs, suggesting poor optical properties of Se-rich QDs. Additionally, non-adiabatic molecular dynamics (NAMD) suggests faster non-radiative recombination for Cd-rich QDs. Altogether, this work provides insights into the dynamic electronic properties of non-stoichiometric QDs and proposes a rationale for the observed optical stability and superiority of cation-rich candidates for light emission applications.

Octahedral Hexapalladium Pseudo-Td Pd6(µ3-CO)4(PEt3)6 with 80 Electron-Deficient Cluster Valence Electrons (CVEs) and a Comparison with Octahedral Hexapalladium Pseudo-C2v Pd6(µ3-CO)4(PMe3)7 with 82 CVEs: Computational Analysis and Resulting Implications.

The elusive octahedral hexapalladium Pd6(µ3-CO)4(PEt3)6 (1) was obtained by the reaction of Pd10(CO)12(PEt3)6 with TlCo(CO)4 in tetrahydrofuran under N2 at 55 °C. Its pseudo-Td octahedral structure, established from a CCD X-ray diffractometry study at 100 K, has the highest ideal symmetry of any of the characterized octahedral-based CO/PR3-ligated homopalladium Pdn clusters (n = 6, 7, 8, 10). Each Pd atom in 1 is coordinated to a PEt3 ligand, and each nonadjacent triangular Pd3 face is capped by a triply bridging µ3-CO ligand. The 31P{1H} NMR and IR spectra of 1 are in accordance with its solid-state molecular structure. Cluster 1 has a total of 80 cluster valence electrons (CVEs), the lowest reported for octahedral-based metal polyhedra that normally conform to the Wade-Mingos bonding rule with an 86 CVE count. Comparative density functional theory calculations involving natural population analysis are presented for trimethylphosphine analogues of the triethylphosphine (1-Me) and the previously reported octahedral hexapalladium trimethylphosphine Pd6(µ3-CO)4(PMe3)7 (2), which has pseudo-C2v symmetry with 82 total CVEs.

Adverse events, side effects and complications in mesenchymal stromal cell-based therapies.

Numerous clinical studies have shown a wide clinical potential of mesenchymal stromal cells (MSCs) application. However, recent experience has accumulated numerous reports of adverse events and side effects associated with MSCs therapy. Furthermore, the strategies and methods of MSCs therapy did not change significantly in recent decades despite the clinical impact and awareness of potential complications. An extended understanding of limitations could lead to a wider clinical implementation of safe cell therapies and avoid harmful approaches. Therefore, our objective was to summarize the possible negative effects observed during MSCs-based therapies. We were also aimed to discuss the risks caused by weaknesses in cell processing, including isolation, culturing, and storage. Cell processing and cell culture could dramatically influence cell population profile, change protein expression and cell differentiation paving the way for future negative effects. Long-term cell culture led to accumulation of chromosomal abnormalities. Overdosed antibiotics in culture media enhanced the risk of mycoplasma contamination. Clinical trials reported thromboembolism and fibrosis as the most common adverse events of MSCs therapy. Their delayed manifestation generally depends on the patient's individual phenotype and requires specific awareness during the clinical trials with obligatory inclusion in the patient' informed consents. Finally we prepared the safety checklist, recommended for clinical specialists before administration or planning of MSCs therapy.

Manufacturing of Complex Silicon-Carbon Structures: Exploring SixCy Materials.

This paper reports on the manufacturing of complex three-dimensional Si/C structures via a chemical vapor deposition method. The structure and properties of the grown materials were characterized using various techniques including scanning electron microscopy, aberration-corrected transmission electron microscopy, confocal Raman spectroscopy, and X-ray photoelectron spectroscopy. The spectroscopy results revealed that the grown materials were composed of micro/nanostructures with various compositions and dimensions. These included two-dimensional silicon carbide (SiC), cubic silicon, and various SiC polytypes. The coexistence of these phases at the nano-level and their interfaces can benefit several Si/C-based applications ranging from ceramics and structural applications to power electronics, aerospace, and high-temperature applications. With an average density of 7 mg/cm3, the grown materials can be considered ultralightweight, as they are three orders of magnitude lighter than bulk Si/C materials. This study aims to impact how ceramic materials are manufactured, which may lead to the design of new carbide materials or Si/C-based lightweight structures with additional functionalities and desired properties.

Complex pH-Dependent Interactions between Weak Polyelectrolyte Block Copolymer Micelles and Molecular Fluorophores.

Amphiphilic block copolymers with weak polyelectrolyte blocks can assemble stimulus-responsive nanostructures and interfaces. Applications of these materials in drug delivery, biomimetics, and sensing largely rely on the well-understood swelling of polyelectrolyte chains upon deprotonation, often induced by changes in pH or ionic strength. This deprotonation can also tune interfacial interactions between the polyelectrolyte blocks and surrounding solution, an effect which is less studied than morphological swelling of polyelectrolytes but can be just as critical for intended function. Here, we investigate whether the pH-driven morphological response of polyelectrolyte-bearing nanostructures also affects the interactions of these nanostructures with molecules in solution, using micelles of a short-chain polybutadiene-block-poly(acrylic acid) (pBd-pAA) as a model system. We introduce a Förster resonance energy transfer (FRET) approach to probe interactions between micelles and fluorescent molecular solutes as a function of solution pH. As expected, the pAA corona of these pBd-pAA micelles increases in thickness monotonically as a function of pH. However, FRET efficiency, which provides a metric of the spatial proximity of fluorescently labeled micelles and freely diffusing fluorophores, exhibits complex nonmonotonic behavior as a function of pH, indicating that the average separation of micelles and acceptor fluorophores is not strictly correlated with micelle swelling. Dialysis experiments quantify the affinity of fluorophores for micelles as a function of pH, confirming that changes in FRET are driven almost entirely by the pH-dependent affinity of the pAA block for the investigated molecular fluorophores, not simply by a shape change of the pAA corona. This study provides key insights into the interfacial interactions between weak-polyelectrolyte-bearing nanostructures and molecular solutes, of importance for the development of their stimulus-responsive applications.

The intrinsic electrochemical behavior of layered Cu2WSe4nanoparticles.

Nanoplates of Cu2WSe4(∼50 nm) were synthesized via a hot-injection method by one-pot selenation of WCl6and Cu(acac)2. This synthetic route provided another perspective towards the intrinsic electrochemical properties of Cu2MSe4(M = Mo or W), where their nanoparticles were previously synthesized via a metathesis route. Cations-dependent cathodic events and surface activation anodic events were identified by cyclic voltammetry in acetonitrile.

MnSn2and MnSn2-TiO2nanostructured anode materials for lithium-ion batteries.

The high theoretical lithium storage capacity of Sn makes it an enticing anode material for Li-ion batteries (LIBs); however, its large volumetric expansion during Li-Sn alloying must be addressed. Combining Sn with metals that are electrochemically inactive to lithium leads to intermetallics that can alleviate volumetric expansion issues and still enable high capacity. Here, we present the cycling behavior of a nanostructured MnSn2intermetallic used in LIBs. Nanostructured MnSn2is synthesized by reducing Sn and Mn salts using a hot injection method. The resulting MnSn2is characterized by x-ray diffraction and transmission electron microscopy and then is investigated as an anode for LIBs. The MnSn2electrode delivers a stable capacity of 514 mAh g-1after 100 cycles at a C/10 current rate with a Coulombic efficiency >99%. Unlike other Sn-intermetallic anodes, an activation overpotential peak near 0.9 V versus Li is present from the second lithiation and in subsequent cycles. We hypothesize that this effect is likely due to electrolyte reactions with segregated Mn from MnSn2. To prevent these undesirable Mn reactions with the electrolyte, a 5 nm TiO2protection layer is applied onto the MnSn2electrode surface via atomic layer deposition. The TiO2-coated MnSn2electrodes do not exhibit the activation overpotential peak. The protection layer also increases the capacity to 612 mAh g-1after 100 cycles at a C/10 current rate with a Coulombic efficiency >99%. This higher capacity is achieved by suppressing the parasitic reaction of Mn with the electrolyte, as is supported by x-ray photoelectron spectroscopy analysis.

Unravelling Magnetic Nanochain Formation in Dispersion for In Vivo Applications.

Self-assembly of iron oxide nanoparticles (IONPs) into 1D chains is appealing, because of their biocompatibility and higher mobility compared to 2D/3D assemblies while traversing the circulatory passages and blood vessels for in vivo biomedical applications. In this work, parameters such as size, concentration, composition, and magnetic field, responsible for chain formation of IONPs in a dispersion as opposed to spatially confining substrates, are examined. In particular, the monodisperse 27 nm IONPs synthesized by an extended LaMer mechanism are shown to form chains at 4 mT, which are lengthened with applied field reaching 270 nm at 2.2 T. The chain lengths are completely reversible in field. Using a combination of scattering methods and reverse Monte Carlo simulations the formation of chains is directly visualized. The visualization of real-space IONPs assemblies formed in dispersions presents a novel tool for biomedical researchers. This allows for rapid exploration of the behavior of IONPs in solution in a broad parameter space and unambiguous extraction of ​the parameters of the equilibrium structures. Additionally, it can be extended to study novel assemblies formed by more complex geometries of IONPs.

Peptidoglycan-Free Bacterial Ghosts Confer Enhanced Protection against Yersinia pestis Infection.

To develop a modern plague vaccine, we used hypo-endotoxic Yersinia pestis bacterial ghosts (BGs) with combinations of genes encoding the bacteriophage ɸX174 lysis-mediating protein E and/or holin-endolysin systems from λ or L-413C phages. Expression of the protein E gene resulted in the BGs that retained the shape of the original bacterium. Co-expression of this gene with genes coding for holin-endolysin system of the phage L-413C caused formation of structures resembling collapsed sacs. Such structures, which have lost their rigidity, were also formed as a result of the expression of only the L-413C holin-endolysin genes. A similar holin-endolysin system from phage λ containing mutated holin gene S and intact genes R-Rz coding for the endolysins caused generation of mixtures of BGs that had (i) practically preserved and (ii) completely lost their original rigidity. The addition of protein E to the work of this system shifted the equilibrium in the mixture towards the collapsed sacs. The collapse of the structure of BGs can be explained by endolysis of peptidoglycan sacculi. Immunizations of laboratory animals with the variants of BGs followed by infection with a wild-type Y. pestis strain showed that bacterial envelopes protected only cavies. BGs with maximally hydrolyzed peptidoglycan had a greater protectivity compared to BGs with a preserved peptidoglycan skeleton.

Charge-Separated and Lewis Paired Metal-Organic Framework for Anion Exchange and CO2 Chemical Fixation.

Charge-separated metal-organic frameworks (MOFs) are a unique class of MOFs that can possess added properties originating from the exposed ionic species. A new charge-separated MOF, namely, UNM-6 synthesized from a tetrahedral borate ligand and Co2+ cation is reported herein. UNM-6 crystalizes into the highly symmetric P43n space group with fourfold interpenetration, despite the stoichiometric imbalance between the B and Co atoms, which also leads to loosely bound NO3 - anions within the crystal structure. These NO3 - ions can be quantitatively exchanged with various other anions, leading to Lewis acid (Co2+ ) and Lewis base (anions) pairs within the pores and potentially cooperative catalytic activities. For example, UNM-6-Br, the MOF after anion exchange with Br- anions, displays high catalytic activity and stability in reactions of CO2 chemical fixation into cyclic carbonates.

2D nanocrystalline ternary selenides Cu2MSe4 (M = Mo/W).

A high-temperature metathesis reaction between CuBr and [Ph4P]2MSe4 (M = Mo or W) gave rise to nanocrystalline Cu2MSe4 with a phase-pure M = Mo compound that was obtained for the first time. After exploring the formation mechanism, we found that the sub-stoichiometric ratios of CuBr to MSe42- resulted in the formation of a linear byproduct impurity, [Ph4P]CuMSe4 (M = Mo or W). However, excess CuBr selectively steered the reaction to the desired Cu2MSe4. As a consequence of the newfound similarity in the reaction conditions for both metals, we have demonstrated the applicability of this method towards a mixed Mo/W quaternary composition.

Structure elucidation and gene cluster characterization of the O-antigen of Yersinia kristensenii С-134.

Mild acid degradation of the lipopolysaccharide of Yersinia kristensenii C-134 afforded a glycerol teichoic acid-like O-polysaccharide, which was studied by sugar analysis, O-deacetylation and dephosphorylation along with 1D and 2D NMR spectroscopy. The following structure of the O-polysaccharide was established: This structure is related to those of other Y. kristensenii O-polysaccharides studied earlier. The O-antigen gene cluster of Y. kristensenii С-134 was analyzed and found to be consistent with the O-polysaccharide structure established.

Cubic SnGe nanoalloys: beyond thermodynamic composition limit.

Tin-germanium alloys are increasingly of interest as optoelectronic and thermoelectric materials as well as materials for Li/Na ion battery electrodes. However, the lattice incompatibility of bulk Sn and Ge makes creating such alloys challenging. By exploiting the unique strain tolerance of nanosized crystals, we have developed a facile synthetic method for homogeneous SnxGe1-x alloy nanocrystals with composition varying from essentially pure Ge to 95% Sn while still maintaining the cubic structure.

Molecular chains of coordinated dimolybdenum isonicotinate paddlewheel clusters.

A growing focus on the use of coordination polymers for active device applications motivates the search for candidate materials with integrated and optimized charge transport modes. We show herein the synthesis of a linear coordination polymer comprised of Mo2(INA)4 (INA = isonicotinate) metal-organic clusters. Single-crystal X-ray structure determination shows that this cluster crystallizes into one-dimensional molecular chains, whose INA-linked Mo2 cores engage in alternate axial and equatorial binding motifs along the chain axis. Electron paramagnetic resonance spectra, absorption spectra, and density functional theory calculations show that the aforementioned linear coordination environment significantly modifies the electronic structure of the clusters. This work expands the synthetic foundation for assembly of coordination polymers with tailorable dimensionalities and charge transport properties.

Full structure and insight into the gene cluster of the O-specific polysaccharide of Yersinia intermedia H9-36/83 (O:17).

Lipopolysaccharide was isolated from bacteria Yersinia intermedia H9-36/83 (O:17) and degraded with mild acid to give an O-specific polysaccharide, which was isolated by GPC on Sephadex G-50 and studied by sugar analysis and 1D and 2D NMR spectroscopy. The polysaccharide was found to contain 3-deoxy-3-[(R)-3-hydroxybutanoylamino]-d-fucose (d-Fuc3NR3Hb) and the following structure of the heptasaccharide repeating unit was established: The structure established is consistent with the gene content of the O-antigen gene cluster. The O-polysaccharide structure and gene cluster of Y. intermedia are related to those of Hafnia alvei 1211 and Escherichia coli O:103.

Non-volatile iron carbonyls as versatile precursors for the synthesis of iron-containing nanoparticles.

The most commonly used method for the formation of well-defined iron and iron-containing heterometallic nanoparticles is the thermal decomposition of iron pentacarbonyl (Fe(CO)5). However, iron pentacarbonyl is highly toxic and volatile, which introduces safety concerns and drastically diminishes control over the reaction stoichiometry. Here we alleviate these issues by beginning with an easy-to-handle solid, triiron dodecacarbonyl (Fe3(CO)12). The issue of poor solubility of this cluster is addressed by its reaction with amine, which renders the cluster fully soluble in common high boiling point solvents. This reaction generates non-volatile anionic iron carbonyl species in solution which are subsequently used as the nanoparticle precursor. We demonstrate that the thermolysis of this novel precursor solution yields well-defined Fe, Fe1-xCox, and Fe1-xPtx nanoparticles. In addition, the same approach overcomes the solubility issue of another poorly soluble iron carbonyl compound, diiron nonacarbonyl (Fe2(CO)9). By using these precursors in an array of nanoparticle-forming reactions, we demonstrate a convenient replacement for the commonly used Fe(CO)5, producing particles of similar quality, but without the drawbacks of the precursor volatility and high toxicity.

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.

Nanosized {Pd4(µ4-C)}Pd32(CO)28(PMe3)14 Containing Tetrahedrally Deformed Pd4 Cage with Encapsulated Carbide Atom: Formal Substitution of Geometrically Analogous Interior Au4 Entity in Isostructural Au4Pd32(CO)28(PMe3)14 by Electronically Equivalent Pd4(µ4-C) and Computational/Catalytic Implications.

This first homopalladium carbido cluster, {Pd4(µ4-C)}Pd32(CO)28(PMe3)14 (1), was isolated (3-7% yields) from an ultimately simplified procedure-the reaction of CHCl3 under N2 with either Pd8(CO)8(PMe3)7 or Pd10(CO)12(PMe3)6 at room temperature. Charge-coupled device (CCD) X-ray diffraction data at 100 K for 1·2.5 C6H14 (1a) and 1·3 CHCl3 (1b) produced closely related molecular parameters for 1. This {Pd4C}Pd32 cluster (1) possesses a highly unusual tetracoordinated carbide atom that causes a major distortion of a central regular Pd4 tetrahedron into a new symmetry type of encapsulated Pd4 cage of pseudo-D2 (222) symmetry. Mean Pd-Pd distances for the three pairs of opposite twofold-equivalent Pd-Pd tetrahedral-like edges for 1a are 2.71, 2.96, and 3.59 Å; the mean of the four Pd-C distances [range, 1.87(2)-1.94(2) Å] is 1.91 Å. An astonishing molecular feature is that this {Pd4C}Pd32 cluster (1) is an isostructural and electronically equivalent analogue of the nanosized Au4Pd32(CO)28(PMe3)14 (2). Cluster 2, likewise a pseudo-D2 molecule, contains a geometrically analogous tetrahedrally deformed interior Au4 entity encapsulated within an identical Pd32(CO)28(PMe3)14 shell; mean distances for the three corresponding symmetry-equivalent pairs of slightly smaller opposite tetrahedral-distorted Au-Au edges are 2.64, 2.90, and 3.51 Å. A computational study by both a natural population analysis (NPA) and an atoms-in-molecules (AIM) method performed on model analogues {Pd4C}Pd32(CO)28(PH3)14 (1-mod) and Au4Pd32(CO)28(PH3)14 (2-mod) suggested that the negatively charged Au4 entity in 2-mod may be described as two weakly interacting electron-pair Au2 intradimers. In contrast, an NPA of the {Pd4C} entity in 1-mod revealed that two similarly oriented identical Pd2 intradimers of 2.71 Å are primarily stabilized by Pd-C bonding with a negatively charged carbide atom. The isostructural stabilizations of 1 and 2 are then attributed to the similar sizes, shapes, and overall negative charge distributions of the electronically equivalent interior {Pd4C} and Au4 entities. This resulting remarkable structural/electronic equivalency between 1 and 2 is consistent with the greatly improved performances of commercial palladium catalysts for vinyl acetate synthesis by gold-atom incorporation to suppress carbonization of the Pd atoms, namely, that the extra Au 6s(1) valence electron of each added Au atom provides an effective "negative charge protection" against electron-donating carbon atoms forming Pd carbido species such as {Pd4C}.

Passivating ligand and solvent contributions to the electronic properties of semiconductor nanocrystals.

We examine in detail the impact of passivating ligands (i.e., amines, phosphines, phosphine oxides and pyridines) on the electronic and optical spectra of Cd(33)Se(33) quantum dots (QDs) using density functional theory (DFT) and time-dependent DFT (TDDFT) quantum-chemical methodologies. Most ligand orbitals are found deep inside in the valence and conduction bands of the QD, with pyridine being an exception by introducing new states close to the conduction band edge. Importantly, all ligands contribute states which are highly delocalized over both the QD surface and ligands, forming hybridized orbitals rather than ligand-localized trap states. In contrast, the states close to the band gap are delocalized over the QD atoms only and define the lower energy absorption spectra. The random detachment of one of ligands from the QD surface results in the appearance of a highly localized unoccupied state inside the energy gap of the QD. Such changes in the electronic structure are correlated with the respective QD-ligand binding energy and steric ligand-ligand interactions. Polar solvent significantly reduces both effects leading to delocalization and stabilization of the surface states. Thus, trap and surface states are substantially eliminated by the solvent. Polar solvent also blue-shifts (e.g., 0.3-0.4 eV in acetonitrile) the calculated absorption spectra. This shift increases with an increase of the dielectric constant of the solvent. We also found that the approximate single-particle Kohn-Sham (KS) approach is adequate for calculating the absorption spectra of the ligated QDs. Besides a systematic blue-shift, the KS spectra are in very good agreement with their respective counterparts calculated with the more accurate TDDFT method.

CO-induced formation of an interpenetrating bicuboctahedral Au2Pd18 kernel in nanosized Au2Pd28(CO)26(PEt3)10: formal replacement of an interior (µ12-Pd)2 fragment in the corresponding known isostructural homopalladium Pd30(CO)26(PEt3)10 with nonisovalent (µ12-Au)2 and resulting experimental/theoretical implications.

Initially isolated from Pd(10)(CO)(12)(PEt(3))(6) (5) and Au(SMe(2))Cl precursors in a two-step carbon monoxide (CO)-involved procedure, the nanosized interpenetrating bicuboctahedral gold (Au)-palladium (Pd) Au(2)Pd(28)(CO)(26)(PEt(3))(10) (1) was then directly obtained in 25-30% yield from the CO-induced reaction of the CO-stable Au-centered cuboctahedral Au(2)Pd(21)(CO)(20)(PEt(3))(10) (3) with the structurally analogous CO-unstable Pd(23)(CO)(20)(PEt(3))(10) (4). Our hypothesis that this latter synthesis is initiated by the reaction of 3 with coordinatively unsaturated homopalladium species resulting from CO-induced fragmentation of 4 was subsequently substantiated by the alternatively designed synthesis of 1 (∼25% yield) from the CO-induced reaction of 3 with the structurally dissimilar CO-unstable Pd(38)(CO)(28)(PEt(3))(12) (6). The composition of 1, unambiguously established from a 100 K CCD X-ray diffractometry study, is in accordance with single-crystal X-ray Au-Pd field-emission microanalysis. The pseudo-C(2h) 30-atom Au(2)Pd(28) geometry of 1 may be formally derived via substitution of the interior (µ(12)-Pd)(2) moiety in the interpenetrating bicuboctahedral Pd(20) kernel of the known isostructural Pd(30)(CO)(26)(PEt(3))(10) (2) with the corresponding interior (µ(12)-Au)(2) moiety, in which the otherwise entire metal-core geometry and CO/PR(3)-ligated environment are essentially not altered. Of major significance is that this interior nonisovalent Pd-by-Au replacement in 2 produces CO-stable 1, whereas nanosized CO/PR(3)-ligated homopalladium Pd(n) clusters with n > 10 are generally unstable under CO. Because the two adjacent encapsulated Au atoms of 2.811(1) Å separation are not present on the metal surface, isolation of 1 under CO is ascribed to an electronic property. The virtually ideal geometrical site-occupancy fit between 1 and 2 provides definite crystallographic evidence for extensive delocalization in 1 of the two valence Au 6s electrons over the entire cluster (instead of a "localized" covalent Au-Au electron-pair interaction). Gradient-corrected (pseudo-scalar-relativistic) density functional theory (DFT) calculations were performed on the isostructural Au(2)Pd(28)(CO)(26)(PH(3))(10) (1-H) and Pd(30)(CO)(26)(PH(3))(10) (2-H) model clusters along with hypothetical [Au(2)Pd(28)(1-H)](2+) and [Pd(30)(2-H)](2-) analogues (with phosphine ethyl substituents replaced by hydrogen ones). Natural population analysis of these four model clusters revealed similar highly positively charged metal surfaces of 28 Pd atoms relative to the two negatively charged interior metal atoms, which reflect a partially oxidized metal surface due to dominant CO back-bonding. The surprising observation that each less electronegative interior Pd atom in 2-H is more negatively charged by 0.30e than each interior Au atom in 1-H points to a more cationic Au in 1 than interior Pd in 2; this unexpected (opposite) charge difference is consistent with delocalization of each Au 6s valence electron toward a Au(+) configuration. This premise is in agreement with the calculated Wiberg bond index (WBI) value of 0.055 for the Au-Au bond order in 1-H versus the WBI single-bond value of 1.01 obtained from analogous DFT calculations for the bare, neutral Au(2) dimer, which has a much shorter spectroscopically determined gas-phase distance of 2.472 Å (that corresponds to a "localized" electron-pair interaction). Isolation of 1 under CO is of prime importance in nanoscience/nanotechnology in establishing relative stabilizations toward CO in well-defined CO/PEt(3)-ligated nonisovalent Pd(2)-by-Au(2)-substituted Au(2)Pd(n-2) clusters [namely, n = 30 (1) and 23 (3)]. These important stereochemical implications have a direct relevance to the recent report of the higher tolerance to CO poisoning of highly active Au-Pd nanoparticle catalysts used for the complete conversion of formic acid into high-purity hydrogen (and CO(2)) for chemical hydrogen storage.