Experimental and Theoretical Study of the Features of Zinc(II) and Cadmium(II) Complexation with the Substituted closo-Hydridoborate Anion [2-B10H9(OH)]2−

Herein, we studied the experimental and theoretical foundations of the process of zinc(II) and cadmium(II) complexation with 2-hydroxido-nonahydrido-closo-decaborate(2−) anion [2-B₁₀H₉(OH)]²⁻ in the presence of azaheterocyclic ligands L (L=2,2′-bipyridyl (bipy), 1,10-phenanthroline (phen), and 2,2′-bipyridylamine (bpa)), which can be used as model system for obtaining complexes with the required composition and structure. The first examples of mixed-ligand Zn(II) and Cd(II) complexes with [2-B₁₀H₉(OH)]²⁻ coordinated by the metal atom were isolated selectively. The structures of zinc(II) complexes [Zn(bipy)₂(2-B₁₀H₉(OH)-κ²H¹,O)] ⋅ 2CH₃CN ( 1 ⋅ 2CH₃CN) and [Zn(phen)₂(2-B₁₀H₉(OH)-κ²H⁹,O)] ⋅ 2CH₃CN ( 2 ⋅ 2CH₃CN), as well as two cadmium(II) bond isomers [Cd(bipy)₂(2-B₁₀H₉(OH)-κ²H¹,O)] ( 4 a ) and [Cd(bipy)₂(2-B₁₀H₉(OH)-κ²H⁹,H¹⁰)] ( 4 b ) bound into a dimeric pair in the complex [Cd(bipy)₂(2-B₁₀H₉(OH))] ( 4 ), and cadmium(II) complex [Cd(bpa)₂(2-B₁₀H₉(OH)-κ²H⁷,H¹⁰)] ( 7 ) were solved by single-crystal X-ray diffraction (XRD). Density functional theory (DFT) calculations show that for cadmium(II) the formation of both multicenter BH−Cd−HB and BO(H)−Cd−HB bonds is equally probable. The affinity of zinc(II) for oxygen leads to preferential formation of complexes via BO(H)−Zn−HB bonds than BH−Zn−HB bonds. The M−B(H) bonding was found to be presumably electrostatic in nature, which could be the reason of topological isomerism of zinc(II) and cadmium(II) decaborates.     

Isolation and Structural Determination of a Hexacoordinated Antimony(V) Dication

The hexacoordinated antimony(V) dication [(ppy)₃Sb]²⁺ ([ 1 ]²⁺; ppy=2-(2-pyridyl)phenyl), stabilized by three intramolecular donor–acceptor interactions, has been isolated as its hexachloroantimonate salt [ 1 ][SbCl₆]₂, prepared by the oxidative addition of chlorine to the neutral stibine [(ppy)₃Sb] ( 1 ), followed by the abstraction of chloride. Air-stable [ 1 ][SbCl₆]₂ exhibits remarkable thermal stability and the three ppy ligands on the antimony atom are shown to be magnetically inequivalent in the ¹H and ¹³C NMR spectra. A hexacoordinated, meridional octahedral bonding geometry has been determined for [ 1 ][SbCl₆]₂ by X-ray crystallographic analysis. Theoretical calculations were performed to investigate why the meridional form was generated preferentially over the facial form. In addition, the dynamics of the ppy ligands were investigated by variable-temperature ¹H NMR spectroscopy. The potential to generate dications by using a single-electron-transfer reagent has also been investigated. The dication [ 1 ]²⁺ is the first [12–Sb–6]²⁺ chemical species to have been structurally determined.     

Re‐examination of the C6Li6 Structure: To Be,or not To Be Symmetric

The potential energy surface of C₆Li₆ was re‐examined and a new non‐symmetric global minimum was found. The new structure can be described as three C₂^2? fragments strongly aggregated through lithium bridges. At high temperatures, fluxionality is perceived instead of dissociation. At 600 and 900 K, the BOMD simulations show that the lithium mobility is high, indicating that the cluster behaves in a liquid‐like manner (BOMD=Born–Oppenheimer molecular dynamics).     

A Triphenylamine with Two Phenoxy Radicals Having Unusual Bonding Patterns and a Closed‐Shell Electronic State

Reported herein is the structure and the electronic properties of a novel triphenylamine derivative having two phenoxy radicals appended to the amino nitrogen atom. X‐ray single crystal analysis and the magnetic resonance measurements demonstrates the unexpected closed‐shell electronic structure, even at room temperature, of the molecule and two unusual C? N bonds with multiple‐bond character. The theoretical calculations support the experimentally determined molecular geometry with the closed‐shell electronic structure, and predicted a small HOMO–LUMO gap originating from the nonbonding character of the HOMO. The optical and electrochemical measurements show that the molecule has a remarkably small HOMO–LUMO gap compared with its triphenylamine precursor.     

Isolation and Crystallographic Characterization of the Labile Isomer of Y@C82 Cocrystallized with Ni(OEP): Unprecedented Dimerization of Pristine Metallofullerenes

Although the major isomers of M@C₈₂ (namely M@C_2v(9)‐C₈₂, where M is a trivalent rare‐earth metal) have been intensively investigated, the lability of the minor isomers has meant that they have been little studied. Herein, the first isolation and crystallographic characterization of the minor Y@C₈₂ isomer, unambiguously assigned as Y@C_s(6)‐C₈₂ by cocrystallization with Ni(octaethylporphyrin), is reported. Unexpectedly, a regioselective dimerization is observed in the crystalline state of Y@C_s(6)‐C₈₂. In sharp contrast, no dimerization occurs for the major isomer Y@C_2v(9)‐C₈₂ under the same conditions, indicating a cage‐symmetry‐induced dimerization process. Further experimental and theoretical results disclose that the regioselective dimer formation is a consequence of the localization of high spin density on a special cage‐carbon atom of Y@C_s(6)‐C₈₂ which is caused by the steady displacement of the Y atom inside the C_s(6)‐C₈₂ cage.     

Donor-Stabilized Silylene/Phosphine-Supported Carbon(0) Center with High Electron Density

An isolable donor-stabilized silavinylidene phosphorane was synthesized. This molecule, which can also be regarded as a new carbon(0) complex featuring a phosphine and a donor-stabilized silylene ligand, presents a central carbon atom with a remarkably high electron density (−1.82). Furthermore, the experimental electron-density study of this compound demonstrates the delocalization of the σ-lone pair at the central carbon atom toward the silicon center, a feature which is remarkably different from electronic situation of other bent-allene-type molecules. This result clearly demonstrates the powerful electron-donating ability of donor-stabilized silylene ligands, as well as their excellent electron-acceptor properties.     

Face-Centered-Cubic Ag Nanoclusters: Origins and Consequences of the High Structural Regularity Elucidated by Density Functional Theory Calculations

Face-centered-cubic (FCC) silver nanoclusters (NCs) adopting either cubic or half-cubic growth modes have been recently reported, but the origin of these atomic assembly patterns and how they are achieved, which would inform our understanding of larger FCC silver nanomaterials, are both unknown. In this study, the cubic and half-cubic growth modes have been unified based on common structural characteristics, and differentiated depending on the starting blocks (cubic vs. half cubic). In both categories, the silver atoms adopt octahedral Ag₆, linear AgS₂ (in projection drawing), or tetrahedral AgS₃P binding modes, and the sulfur atoms adopt T-shaped SAg₃ and orthogonal SAg₄ modes. An additional T-shaped AgS₃ mode is oriented on the surface edge in cubic NCs to complete the cubic framework. Density functional theory calculations indicated that the high structural regularity originates from the strong diffusing capacity of the Ag(5d) and S(3p) orbitals, and the angular momentum distribution of the formed superatomic orbitals. The equatorial orientation of μ⁴-S or μ⁴-Ag determines whether growth stops or continues. In particular, a density-of-states analysis indicated that the octahedral silver atoms are chemically more reactive than the silver atoms in the AgS₃P motif, regardless of whether the parent NC functions as an electron donor or acceptor.     

Synthesis and Analysis of Substituted Bullvalenes

Herein we detail a practical synthesis of bullvalene and a variety of mono‐ and disubstituted analogues through cobalt‐catalysed [6+2] cycloaddition of cyclooctatetraene to alkynes, followed by photochemical di‐π‐methane rearrangement. The application of isomer‐network analysis, coupled with quantum‐chemical calculations, provides a powerful automated tool for predicting the properties of bullvalene isomer networks.     

Directing Foldamer Self-Assembly with a Cyclopropanoyl Cap

The rational design of self-assembling organic materials is extremely challenging due to the difficulty in precisely predicting solid-state architectures from first principles, especially if synthons are conformationally flexible. A tractable model system to study self-assembly was constructed by appending cyclopropanoyl caps to the N termini of helical α/β-peptide foldamers, designed to form both N−H⋅⋅⋅O and C^α−H⋅⋅⋅O hydrogen bonds, which then rapidly self-assembled to form foldectures (foldamer architectures). Through a combined analytical and computational investigation, cyclopropanoyl capping was observed to markedly enhance self-assembly in recalcitrant substrates and direct the formation of a single intermolecular N−H⋅⋅⋅O/C^α−H⋅⋅⋅O bonding motif in single crystals, regardless of peptide sequence or foldamer conformation. In contrast to previous studies, foldamer constituents of single crystals and foldectures assumed different secondary structures and different molecular packing modes, despite a conserved N−H⋅⋅⋅O/C^α−H⋅⋅⋅O bonding motif. DFT calculations validated the experimental results by showing that the N−H⋅⋅⋅O/C^α−H⋅⋅⋅O interaction created by the cap was sufficiently attractive to influence self-assembly. This versatile strategy to harness secondary noncovalent interactions in the rational design of self-assembling organic materials will allow for the exploration of new substrates and speed up the development of novel applications within this increasingly important class of materials.     

Adding a Structural Context to the Deprotometalation and Trans‐Metal Trapping Chemistry of Phenyl‐Substituted Benzotriazole

Organometallic bases are becoming increasingly complex, because mixing components can lead to bases superior to single‐component bases. To better understand this superiority, it is useful to study metalated intermediate structures prior to quenching. This study is on 1‐phenyl‐1H‐benzotriazole, which was previously deprotonated by an in situ ZnCl₂ ? TMEDA/LiTMP (TMEDA=N,N,N′,N′‐tetramethylethylenediamine; TMP=2,2,6,6‐tetramethylpiperidide) mixture and then iodinated. Herein, reaction with LiTMP exposes the deficiency of the single‐component base as the crystalline product obtained was [{4‐R‐1‐(2‐lithiophenyl)‐1H‐benzotriazole ? 3THF}₂], [R=2‐C₆H₄(Ph)NLi], in which ring opening of benzotriazole and N₂ extrusion had occurred. Supporting lithiation by adding iBu₂Al(TMP) induces trans‐metal trapping, in which C?Li bonds transform into C?Al bonds to stabilise the metalated intermediate. X‐ray diffraction studies revealed homodimeric [(4‐R′‐1‐phenyl‐1H‐benzotriazole)₂], [R′=(iBu)₂Al(μ‐TMP)Li], and its heterodimeric isomer [(4‐R′‐1‐phenyl‐1H‐benzotriazole){2‐R′‐1‐phenyl‐1H‐benzotriazole}], whose structure and slow conformational dynamics were probed by solution NMR spectroscopy.