Boron Nanowheels with Axles Containing Noble Gas Atoms: Viable Noble Gas Bound M©B10- Clusters (M=Nb, Ta)

Dispersion, Rehybridization, and Pentacoordination: Keys to Understand Clustering of Boron and Aluminum Hydrides and Halides

The structure, stability, and bonding characteristics of dimers and trimers involving BX₃ and AlX₃ (X = H, F, Cl) in the gas phase, many of them explored for the first time, were investigated using different DFT (B3LYP, B3LYP/D3BJ, and M06-2X) and ab initio (MP2 and G4) methods together with different energy decomposition formalisms, namely, many-body interaction-energy and localized molecular orbital energy decomposition analysis. The electron density of the clusters investigated was analyzed with QTAIM, electron localization function, NCIPLOT, and adaptive natural density partitioning approaches. Our results for triel hydride dimers and Al₂X₆ (X = F, Cl) clusters are in good agreement with previous studies in the literature, but in contrast with the general accepted idea that B₂F₆ and B₂Cl₆ do not exist, we have found that they are predicted to be weakly bound systems if dispersion interactions are conveniently accounted for in the theoretical schemes used. Dispersion interactions are also dominant in both homo- and heterotrimers involving boron halide monomers. Surprisingly, B₃F₉ and B₃Cl₉ C_3v cyclic trimers, in spite of exhibiting rather strong B-X (X = F, Cl) interactions, were found to be unstable with respect to the isolated monomers due to the high energetic cost of the rehybridization of the B atom, which is larger than the two- and three-body stabilization contributions when the cyclic is formed. Another important feature is the enhanced stability of both homo- and heterotrimers in which Al is the central atom because Al is systematically pentacoordinated, whereas this is not the case when the central atom is B, which is only tri- or tetra-coordinated.

In silico capture of noble gas atoms with a light atom molecule

Noble gas atoms (Ng = He, Ne, Ar, and Kr) can be captured in silico with a light atom molecule containing only C, H, Si, O, and B atoms. Extensive density functional theory (DFT) calculations on series of peri-substituted scaffolds indicate that confined spaces (voids) capable to energy efficiently encapsulate and bind Ng atoms are accessible by design of a tripodal peri-substituted ligand, namely, [(5-Ph₂B-xan-4-)₃Si]H (xan = xanthene) comprising (after hydride abstraction) four Lewis acidic sites within the cationic structure [(5-Ph₂B-xan-4-)₃Si]⁺. The host (ligand system) thereby provides an adoptive environment for the guest (Ng atom) to accommodate for its particular size. Whereas considerable chemical interactions are detectable between the ligand system and the heavier Ng atoms Kr and Ar in the host guest complex [(5-Ph₂B-xan-4-)₃Si·Ng]⁺, the lighter Ng atoms Ne and He are rather tolerated by the ligand system instead of being chemically bound to it, nicely highlighting the gradual onset of (weak) chemical bonding along the series He to Kr. A variety of real-space bonding indicators (RSBIs) derived from the calculated electron and pair densities provides valuable insight to the situation of an "isolated atom in a molecule" in case of He, uncovering its size and shape, whereas minute charge rearrangements caused by polarization of the outer electron shell of the larger Ng atoms results in formation of polarized interactions for Ar and Kr with non-negligible covalent bond contributions for Kr. The present study shows that noble gas atoms can be trapped by small light-atom molecules without the forceful conditions necessary using cage structures such as fullerenes, boranes and related compounds or by using super-electrophilic sites like [B₁₂(CN)₁₁]^- if the chelating effect of several Lewis acidic sites within one molecule is employed.

Structural transformations in boron clusters induced by metal doping

In the last decades, experimental techniques in conjunction with theoretical analyses have revealed the surprising structural diversity of boron clusters. Although the 2D to 3D transition thresholds are well-established, there is no certainty about the factors that determine the geometry adopted by these systems. The structural transformation induced by doping usually yields a minimum energy structure with a boron skeleton entirely different from that of the bare cluster. This review summarizes those clusters no larger than 40 boron atoms where one or two dopants show a radical transformation of the structure. Although the structures of these systems are not easy to predict, they often adopt familiar shapes such as umbrella-like, wheel, tubular, and cages in various cases.

OsB9 -: An Aromatic Osmium-Centered Monocyclic Boron Ring

Transition-metal-centered monocyclic boron wheels are important candidates in the family of planar hypercoordinate species that show intriguing structure, stability and bonding situation. Through the detailed potential energy surface explorations of MB₉⁻ (M = Fe, Ru, Os) clusters, we introduce herein OsB₉⁻ to be a new member in the transition-metal-centered borometallic molecular wheel gallery. Previously, FeB₉⁻ and RuB₉⁻ clusters were detected by photoelectron spectroscopy and the structures were reported to have singlet D_9h symmetry. Our present results show that the global minimum for FeB₉⁻ has a molecular wheel-like structure in triplet spin state with C_s symmetry, whereas its heavier homologues are singlet molecular wheels with D_9h symmetry. Chemical bonding analyses show that RuB₉⁻ and OsB₉⁻ display a similar type of electronic structure, where the dual σ + π aromaticity, originated from three delocalized σ bonds and three delocalized π bonds, accounts for highly stable borometallic molecular wheels.

Noble Gas Binding Ability of an Au(I) Cation Stabilized by a Frustrated Lewis Pair: A DFT Study

The noble gas (Ng) binding ability of a monocationic [(FLP)Au]⁺ species has been investigated by a computational study. Here, the monocationic [(FLP)Au]⁺ species is formed by coordination of Au(I) cation with the phosphorous (Lewis base) and the boron (Lewis acid) centers of a frustrated Lewis pair (FLP). The bonds involving Au and P, and Au and B atoms in [(FLP)Au]⁺ are partially covalent in nature as revealed by Wiberg bond index (WBI) values, electron density analysis and energy decomposition analysis (EDA). The zero point energy corrected bond dissociation energy (D₀), enthalpy and free energy changes are computed for the dissociation of Au-Ng bonds to assess the Ng binding ability of [(FLP)Au]⁺ species. The D₀ ranges from 6.0 to 13.3 kcal/mol, which increases from Ar to Rn. Moreover, the dissociation of Au-Ng bonds is endothermic as well as endergonic for Ng = Kr-Rn, whereas the same for Ng = Ar is endothermic but exergonic at room temperature. The partial covalent character of the bonds between Au and Ng atoms is demonstrated by their WBI values and electron density analysis. The Ng atoms get slight positive charges of 0.11–0.23 |e|, which indicates some amount of charge transfer takes place from it. EDA demonstrates that electrostatic and orbital interactions have equal contributions to stabilize the Ng-Au bonds in the [(FLP)AuNg]⁺ complex.

LiB13: A New Member of Tetrahedral-Typed B13 Ligand Half-Surround Cluster

It will get entirely unusual derivatives with gratifying chemical bonding schemes for boron clusters by doping with lithium, the lightest alkalis. The geometric structures and electronic properties of the LiBn0/- (n = 10-20) clusters have been studied through Crystal structure AnaLYsis by Particle Swarm Optimization (CALYPSO) structural search approach along with the density functional theory (DFT) calculations. The low-lying candidates of LiBn0/- (n = 10-20) are reoptimized at the B3LYP functional in conjunction with 6-311 + G(d) basis set. Three forms of geometric configurations are identified for the ground-state structures of LiBn0/- clusters: half-sandwich-type, quasi-planar and drum-type structures. The photoelectron spectra (PES) of the LiBn- clusters have been calculated through time-dependent density functional theory (TD-DFT). A promising LiB13 with tetrahedral-typed B13 ligand half-surround cluster and robust stability is uncovered. The molecular orbital and adaptive natural density partitioning (AdNDP) analysis show that B-B bonds in the B13 moiety combined with the interaction between the B13 shell and Li atom stabilize the C2v LiB13 cluster. Our results advance the fundamental understanding about the alkali metal doped boron clusters.

A quasi-plane IrB18− cluster with high stability

A quasi-plane anionic IrB₁₈⁻ cluster with high stability is uncovered by a CALYPSO structural search method.

Re©B8- and Re©B9-: New Members of the Transition-Metal-Centered Borometallic Molecular Wheel Family

Transition-metal-centered monocyclic boron wheel clusters (M©B _n ^q) represent a family of interesting borometallic compounds with double aromaticity. A variety of early and late transition metal atoms have been found to form such structures with high symmetries and various B _n ring sizes. Here we report a combined photoelectron spectroscopy and quantum-chemistry theoretical study of two M©B _n^- clusters from the middle of the transition metal series: Re©B₈^- and Re©B₉^-. Global minimum structure searches revealed that ReB₈^- adopts a pseudo- C_{8 v} structure while ReB₉^- is a perfectly planar D_{9 h} molecular wheel. Chemical bonding analyses showed that both clusters exhibit σ and π double aromaticity and obey the electronic design principle for metal-centered borometallic molecular wheels. The central Re atoms are found to possess unusually low oxidation states of +I in Re©B₈^- and +II in Re©B₉^-, i.e., the Re atom behaves similarly to late transition metal elements (Ru, Fe, Co, Rh, Ir) in the M©B _n^- molecular wheels. These two clusters become new members of the family of transition-metal-centered monocyclic borometallic molecular wheels, which may be viable for chemical syntheses with appropriate ligands.

Noble-Noble Strong Union: Gold at Its Best to Make a Bond with a Noble Gas Atom

This Review presents the current status of the noble gas (Ng)‐noble metal chemistry, which began in 1977 with the detection of AuNe⁺ through mass spectroscopy and then grew from 2000 onwards; currently, the field is in a somewhat matured state. On one side, modern quantum chemistry is very effective in providing important insights into the structure, stability, and barrier for the decomposition of Ng compounds and, as a result, a plethora of viable Ng compounds have been predicted. On the other hand. experimental achievement also goes beyond microscopic detection and characterization through spectroscopic techniques and crystal structures at ambient temperature; for example, (AuXe₄)²⁺(Sb₂F₁₁⁻)₂ have also been obtained. The bonding between two noble elements of the periodic table can even reach the covalent limit. The relativistic effect makes gold a very special candidate to form a strong bond with Ng in comparison to copper and silver. Insertion compounds, which are metastable in nature, depending on their kinetic stability, display an even more fascinating bonding situation. The degree of covalency in Ng–M (M=noble metal) bonds of insertion compounds is far larger than that in non‐insertion compounds. In fact, in MNgCN (M=Cu, Ag, Au) molecules, the M−Ng and Ng−C bonds might be represented as classical 2c–2e σ bonds. Therefore, noble metals, particularly gold, provide the opportunity for experimental chemists to obtain sufficiently stable complexes with Ng at room temperature in order to characterize them by using experimental techniques and, with the intriguing bonding situation, to explore them with various computational tools from a theoretical perspective. This field is relatively young and, in the coming years, a lot of advancement is expected experimentally as well as theoretically.

NbB12−: a new member of half-sandwich type doped boron clusters with high stability

The global minimum structure of a NbB₁₂⁻ cluster of half-sandwich type.

Exhaustive exploration of MgBn (n = 10–20) clusters and their anions

An unexpected tubular-shaped MgB₁₈ cluster is identified for the first time in alkaline-earth metal-doped boron clusters.