Computational investigation of structural, electronic, and spectroscopic properties of Ni and Zn metalloporphyrins with varying anchoring groups.

Porphyrins are prime candidates for a host of molecular electronics applications. Understanding the electronic structure and the role of anchoring groups on porphyrins is a prerequisite for researchers to comprehend their role in molecular devices at the molecular junction interface. Here, we use the density functional theory approach to investigate the influence of anchoring groups on Ni and Zn diphenylporphyrin molecules. The changes in geometry, electronic structure, and electronic descriptors were evaluated. There are minimal changes observed in geometry when changing the metal from Ni to Zn and the anchoring group. However, we find that the distribution of electron density changes when changing the anchoring group in the highest occupied and lowest unoccupied molecular orbitals. This has a direct effect on electronic descriptors such as global hardness, softness, and electrophilicity. Additionally, the optical spectra of both Ni and Zn diphenylporphyrin molecules exhibit either blue or red shifts when changing the anchoring group. These results indicate the importance of the anchoring group on the electronic structure and optical properties of porphyrin molecules.

Atomically precise nanoclusters predominantly seed gold nanoparticle syntheses.

Seed-mediated synthesis strategies, in which small gold nanoparticle precursors are added to a growth solution to initiate heterogeneous nucleation, are among the most prevalent, simple, and productive methodologies for generating well-defined colloidal anisotropic nanostructures. However, the size, structure, and chemical properties of the seeds remain poorly understood, which partially explains the lack of mechanistic understanding of many particle growth reactions. Here, we identify the majority component in the seed solution as an atomically precise gold nanocluster, consisting of a 32-atom Au core with 8 halide ligands and 12 neutral ligands constituting a bound ion pair between a halide and the cationic surfactant: Au32X8[AQA+•X-]12 (X = Cl, Br; AQA = alkyl quaternary ammonium). Ligand exchange is dynamic and versatile, occurring on the order of minutes and allowing for the formation of 48 distinct Au32 clusters with AQAX (alkyl quaternary ammonium halide) ligands. Anisotropic nanoparticle syntheses seeded with solutions enriched in Au32X8[AQA+•X-]12 show narrower size distributions and fewer impurity particle shapes, indicating the importance of this cluster as a precursor to the growth of well-defined nanostructures.

Halogenated Carboxylates as Organic Anodes for Stable and Sustainable Sodium-Ion Batteries.

Organic materials are competitive as anodes for Na-ion batteries (NIBs) due to the low cost, abundance, environmental benignity, and high sustainability. Herein, we synthesized three halogenated carboxylate-based organic anode materials to exploit the impact of halogen atoms (F, Cl, and Br) on the electrochemical performance of carboxylate anodes in NIBs. The fluorinated carboxylate anode, disodium 2, 5-difluoroterephthalate (DFTP-Na), outperforms the other carboxylate anodes with H, Cl, and Br, in terms of high specific capacity (212 mA h g-1), long cycle life (300 cycles), and high rate capability (up to 5 A g-1). As evidenced by the experimental and computational results, the two F atoms in DFTP reduce the solubility, enhance the cyclic stability, and interact with Na+ during the redox reaction, resulting in a high-capacity and stable organic anode material in NIBs. Therefore, this work proves that fluorinating carboxylate compounds is an effective approach to developing high-performance organic anodes for stable and sustainable NIBs.

Au20 (t Bu3 P)8 : A Highly Symmetric Metalloid Gold Cluster in Oxidation State 0.

Metalloid gold clusters have unique properties with respect to size and structure and are key intermediates in studying transitions between molecular compounds and the bulk phase of the respective metal. In the following, the synthesis of the all-phosphine protected metalloid cluster Au20 (t Bu3 P)8 , solely built from gold atoms in the oxidation state of 0 is reported. Single-crystal X-ray analysis revealed a highly symmetric hollow cube-octahedral arrangement of the gold atoms, resembling gold bulk structure. Quantum-chemical calculations illustrated the cluster can be described as a 20-electron superatom. Optical properties of the compound have shown molecular-like behavior.

A new reductant in gold cluster chemistry gives a superatomic gold gallium cluster.

The low valent gallium(i) compound GaCp was primarily used in gold cluster chemistry to synthesize the superatomic cluster [(PPh3)8Au9GaCl2]2+, complementing the borane-dominated set of reducing agents in gold chemistry, opening a whole new field for further research. Using density functional theory calculations, the cluster can be described by the jellium model as an 8-electron superatom cluster.

Computational Comparative Analysis of Small Atomically Precise Copper Clusters.

Atomically precise copper clusters (APC) have attracted attention for their promise in sensing, water remediation, and electrochemical technologies. However, smaller-sized APCs and the evolution of their properties as a function of size and composition are not clearly understood. Here, we have performed an investigation into the electronic structure, geometry, and optical properties of small atomically precise copper clusters using density functional theory (DFT) and time-dependent DFT. Through comparative analysis, we show that the electronic structures of the experimentally characterized clusters, Cu4(PN(C6H5)2CH)4 and Cu4(SN2C7H11)4, are similar with the closed-shell superatom character 1S21P2. By changing the ligand on Cu4(PN(C6H5)2CH)4 and Cu4(SN2C7H11)4, there were no major changes observed in the tetrahedral Cu4 core geometry, electronic structure, or optical spectra. However, a change in the anchor atom causes an increase in the electronic gap and induces a hypochromic shift in the onset peak in the optical spectrum of the small clusters. Increasing the copper core size showed small changes Cu-Cu bond lengths, lower electronic gap values, and a bathochromic shift in the optical spectra. Computational results not only provide detailed physical insight into APCs but also aid in identifying compound compositions of small atomically precise nanoclusters from data collected in the experiment.

ReaxFF MD Simulations of Peptide-Grafted Gold Nanoparticles.

Functionalized gold nanoparticles have critical applications in biodetection with surface-enhanced Raman spectrum and drug delivery. In this study, reactive force field molecular dynamics simulations were performed to study gold nanoparticles, which are modified with different short-chain peptides consisting of amino acid residues of cysteine and glycine in different grafting densities in the aqueous environment. Our study showed slight facet-dependent peptide adsorption on a gold nanoparticle with the 3 nm core diameter. Peptide chains prefer to adsorb on the Au(111) facet compared to those on other facets of Au(100) and Au(110). In addition to the stable thiol interaction with gold nanoparticle surfaces, polarizable oxygen and nitrogen atoms show strong interactions with the gold surface and polarize the gold nanoparticle surfaces with an overall positive charge. Charges of gold atoms vary according to their contacts with peptide atoms and lattice positions. However, at the outmost peptide layer, the whole functionalized Au nanoparticles exhibit overall negative electrostatic potential due to the grafted peptides. Moreover, simulations show that thiol groups can be deprotonated and subsequently protons can be transferred to water molecules and carboxyl groups.

Synthesis and Characterization of Three Multi-Shell Metalloid Gold Clusters Au32 (R3 P)12 Cl8.

Three multi-shell metalloid gold clusters of the composition Au32 (R3 P)12 Cl8 (R=Et, n Pr, n Bu) were synthesized in a straightforward fashion by reducing R3 PAuCl with NaBH4 in ethanol. The Au32 core comprises two shells, with the inner one constituting a tilted icosahedron and the outer one showing a distorted dodecahedral arrangement. The outer shell is completed by eight chloride atoms and twelve R3 P groups. The inner icosahedron shows bond lengths typical for elemental gold while the distances of the gold atoms in the dodecahedral arrangement are in the region of aurophilic interactions. Quantum-chemical calculations illustrate that the Jahn-Teller effect observed within the cluster core can be attributed to the electronic shell filling. The easily reproducible synthesis, good solubility, and high yields of these clusters render them perfect starting points for further research.

Balancing the Micro-Mesoporosity for Activity Maximization of N-Doped Carbonaceous Electrocatalysts for the Oxygen Reduction Reaction.

Carbonaceous porous structures have instigated global research interest as promising low-cost electrocatalysts for numerous energy technologies. However, the rational design principle of pore structures for activity maximization is still unclear. In this work, a series of N-doped carbon (N-C) catalysts with exclusively different micro-mesoporosity are investigated for the oxygen reduction reaction (ORR). By combining the experiment results and a pioneering mathematical model, it was observed that the best catalytic activity can only be attained by balancing the micro-mesoporosity. These findings offer a definite criterion for pore structure optimization in carbon-based ORR catalysts, which is of great importance for various energy technologies.

[PtZn2Ge18(Hyp)8] (Hyp = Si(SiMe3)3): A Neutral Polynuclear Chain Compound with Ge9(Hyp)3 Units.

The reaction of [ZnGe18(Hyp)6] (Hyp = Si(SiMe3)3) with Pt(PPh3)4 gives the neutral polynuclear complex of Ge9(Hyp)3 units [HypZn-Ge9(Hyp)3-Pt-Ge9(Hyp)3-ZnHyp], 1. Within 1, the central Pt atom is bound η3 to both Ge9(Hyp)3 units to which further ZnHyp units are bound again, symmetric η3, to the other side of the Ge9(Hyp)3 units, leading to the longest chain compound exhibiting Ge9(Hyp)3 units that is known to date. Dissolved crystals of 1 give a violet solution, showing an absorption maximum around 543 nm. Further UV-vis investigations on different M xGe9(Hyp)3 compounds show that the absorption maximum depends on the number of transition metal atoms bound to the Ge9(Hyp)3 unit, which is supported by TD-DFT calculations.

Au70S20(PPh3)12: an intermediate sized metalloid gold cluster stabilized by the Au4S4 ring motif and Au-PPh3 groups.

Reducing (Ph3P)AuSC(SiMe3)3 with l-Selectride® gives the medium-sized metalloid gold cluster Au70S20(PPh3)12. Computational studies show that the phosphine bound Au-atoms not only stabilize the electronic structure of Au70S20(PPh3)12, but also behave as electron acceptors leading to auride-like gold atoms on the exterior.