Recent advances in atomic cluster synthesis: a perspective from chemical elements

Despite its potential significance, "cluster chemistry" remains a somewhat marginalized topic within the chemistry field. However, atomic clusters with their unusual and unique structures and properties represent a novel material group situated between molecules and nanoparticles or solid matter, judging from both scientific standpoints and historical backgrounds. Surveying an entire material group, including all substances that can be regarded as a cluster, is essential for establishing cluster chemistry as a more prominent chemistry field. This review aims to provide a comprehensive understanding by categorizing, summarizing, and reviewing clusters, focusing on their constituent elements in the periodic table. However, because numerous disparate synthetic processes have been individually developed to date, their straightforward and uniform classification is a challenging task. As such, comprehensively reviewing this field from a chemical composition viewpoint presents significant obstacles. It should be therefore noted that despite adopting a synthetic method-based classification in this review, the discussions presented herein could entail inaccuracies. Nevertheless, this unorthodox viewpoint unfolds a new scientific perspective which accentuates the common ground between different development processes by emphasizing the lack of a definitive border between their synthetic methods and material groups, thus opening new avenues for cementing cluster chemistry as an attractive chemistry field.

Consistent Analytical Second Derivatives of the Kohn-Sham DFT Energy in the Framework of the Conductor-Like Screening Model through Gaussian Charge Distributions

The use of implicit solvation models such as the conductor-like screening model (COSMO) in quantum chemical calculations is very common, as both a rough estimate of solvation effects as well as a general tool for stabilizing ionic molecular structures. In order to generate a smooth potential energy surface as well as consistent gradients, it is necessary to apply the Gaussian charge model (GCM) for the COSMO charges. This work introduces an efficient implementation for consistent analytical second derivatives of the electronic energy with COSMO-GCM in the framework of the Kohn-Sham density functional theory. This is used to investigate the infrared spectroscopy of amino acids in aqueous solution, where the impact of pH on the molecular structure and vibrational spectra is examined. Furthermore, the structure and stability of selected all-metal aromatic cluster ions are assessed.

Two-dimensional correlation infrared spectroscopy study on vanadoborate anionic skeleton regulated by countercations

Two novel vanadoborate compounds, [Cu(en)2]3[Li(H2O)]4[Li(H2O)3]2[V12B18O50(OH)10(H2O)]2·33.5H2O (1) and (H2en)4[Li(H2O)]4[V12B18O55(OH)5(H2O)]·14H2O (2), were synthesized via hydrothermal synthesis under identical conditions except for temperature. Structural analysis revealed that although both contain [V12B18O60]n- cluster anion, the different countercations potentially lead to variations in the [V12B18O60]n- cluster anion skeletons. In compound 1, the V4+/V5+ ratio was 10:2; while in compound 2 the ratio was 11:1. It is speculated that different countercations may influence the valence states of cluster anions. In this study, quantum chemical calculations revealed that the aromaticity and activity of the two compounds were different, and two-dimensional correlation infrared spectroscopy (2D-COS-IR) under magnetic perturbation confirmed that distinct response peaks of functional group vibrations to the magnetic field due to the different V4+/V5+ ratios and aromaticity of the two compounds. An electrochemical analysis revealed that compound 2 exhibits higher electrocatalytic activity. The results of quantum chemical calculations are aligned not only with the changes in the 2D-COS-IR spectra but also with the conclusions obtained from experiments on electrochemical properties. Overall, this work proposes a novel strategy for interpreting the alteration of vanadoborate anionic skeleton due to the introduction of different countercations by combining 2D-COS-IR with quantum chemical calculations.

Reactive Solubilization of Heterometallic Clusters by Treatment of (TrBi3 )2- Anions (Tr=Ga, In, Tl) with [Mn{N(SiMe3 )2 }2 ]

Lowering the charge of Zintl anions by (element-)organic substituents allows their use as sources of (semi)metal nanostructures in common organic solvents, as realized for group 15 anions or Ge₉ ^4- and Sn₉ ^4- . We developed a new strategy for other anions, using low-coordinate 3d metal complexes as electrophiles. [K(crypt-222)]⁺ salts of (TrBi₃ )^2- anions dissolved in situ in Et₂ O and/or THF when reacted with [Mn(hmds)₂ ]. Work-up afforded soluble [K(crypt-222)]⁺ salts of [{(hmds)₂ Mn}₂ (TlBi₃ )]^2- (in 1), [{(hmds)₂ Mn}₂ (Bi₂ )]^2- (in 2), and [{(hmds)Mn}₄ (Bi₂ )₂ ]^2- (in 3) (crypt-222=4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane; Tr=Ga, In, Tl; hmds=N(SiMe₃ )₂ ), representing rare cases of Zintl clusters with open-shell metal atoms. 1 comprises the first coordination compound of the (TlBi₃ )^2- anion, 2 features a diamond-shaped {Pn₂ M₂ } unit, and 3 is a mixed-valent Mn^I /Mn^II compound. The uncommon electronic structures in 1-3 and magnetic coupling were studied by comprehensive DFT calculations.

Superalkali Coated Rydberg Molecules

A series of complexes of Na, K, NH₄, and H₃O with [bpy.bpy.bpy]cryptand, [2.2.2]cryptand, and spherical cryptand were investigated via DFT and ab initio methods. We found that by coating Rydberg molecules with the “organic skin” one could further decrease their ionization potential energy, reaching the values of ∼1.5 eV and a new low record of 1.3 eV. The neutral cryptand complexes in this sense possess a weakly bounded electron and may be considered as very strong reducing agents. Moreover, the presence of an organic cage increases the thermodynamic stability of Rydberg molecules making them stable toward the proton detachment.

Sn368‒: A 2.7 nm Naked Aromatic Tin Rod

In this work, we synthesize naked tin cluster anion Sn368‒, representing the first example of pure Sn nanowire assembled through oxidative coupling reactions of a super atomic cluster Sn94-. Theoretical...

Occurrence of Double Bond in π-Aromatic Rings: An Easy Way to Design Doubly Aromatic Carbon-Metal Structures

A chemical bonding of several metallabenzenes and metallabenzynes was studied via an adaptive natural density partitioning (AdNDP) algorithm and the induced magnetic field analysis. A unique chemical bonding pattern was discovered where the M=C (M: Os, Re) double bond coexists with the delocalized 6c-2e π-bonding elements responsible for aromatic properties of the investigated complexes. In opposition to the previous description where 8 delocalized π-electrons were reported in metallabenzenes and metallabenzynes, we showed that only six delocalized π-electrons are present in those molecules. Thus, there is no deviation from Hückel's aromaticity rule for metallabenzynes/metallabenzenes complexes. Based on the discovered bonding pattern, we propose two thermodynamically stable novel molecules that possess not only π-delocalization but also retain six σ-delocalized electrons, rendering them as doubly aromatic species. As a result, our investigation gives a new direction for the search for carbon-metal doubly aromatic molecules.

Ternary aromatic and anti-aromatic clusters derived from the hypho species [Sn2Sb5]3

Heterometallic clusters have attracted broad interests in the synthetic chemistry due to their various coordination modes and potential applications in heterogeneous catalysis. Here we report the synthesis, experimental, and theoretical characterizations of four ternary clusters ([M₂(CO)₆Sn₂Sb₅]^3- (M = Cr, Mo), and [(MSn₂Sb₅)₂]^4-, (M = Cu, Ag)) in the process of capturing the hypho- [Sn₂Sb₅]^3- in ethylenediamine (en) solution. We show that the coordination of the binary anion to transition-metal ions or fragments provides additional stabilization due to the formation of locally σ-aromatic units, producing a spherical aromatic shielding region in the cages. While in the case of [Mo₂(CO)₆Sn₂Sb₅]^3- stabilization arises from locally σ-aromatic three-centre and five-centre two-electron bonds, aromatic islands in [(AgSn₂Sb₅)₂]^4- and [(CuSn₂Sb₅)₂]^4- render them globally antiaromatic. This work describes the coordination chemistry of the versatile building block [Sn₂Sb₅]^3-, thus providing conceptual advances in the field of metal-metal bonding in clusters.

Aromaticity in Phenyl Decorated closo-Monocarboranes. Planar-Spherical Aggregates Involving 7-12-Vertex Cages

The characterized phenyl decorated closo-monocarboranes with variable sizes from 7- to 12-vertex cages, [Ph-closo-CB_nH_n]^-, n = 6-11, allow us to address the role of the varying size and shape of the carborane cage in dual planar-spherical aromatic species. Our results show the formation of adjacent shielding cone characteristics enabled from both planar and spherical aromatic fragments, despite the different structures of the closo-monocarboranes. Under a field perpendicular to the phenyl ring, both shielding cones are enabled, which overlap at long-range regions, in contrast to other orientations leading to a short-range response from the planar aromatic fragment. Thus, a two- or one-aromatic circuit is enabled selectively within the same molecular unit, by controlling the orientation of the external field. Along with the series, a variable extension of the shielding cone from the carborane cage is observed, which is larger for the -CB₁₁H₁₁ case, decreasing toward -CB₆H₆, denoting a similar extension from both the planar and spherical aromatic regions at the [4-Ph-closo-4-CB₈H₈]^- (4) counterpart. The analysis of such multiple aromatic structures shows that, despite the different sizes and shapes of the closo cages, a similar aromatic behavior remains. In addition, the anisotropy of the induced magnetic field is given graphically, denoting a larger anisotropy for the planar aromatic moiety owing to its two-dimensional structure, which is suggested to discriminate between planar and spherical aromatic fragments within the same molecule.

Insights into Formation and Relationship of Multimetallic Clusters: On the Way toward Bi-Rich Nanostructures

Bismuth-rich polyanions show a unique potential in constructing nanostructured bismuth-based materials, but they are still poorly investigated. We use a ternary precursor of the nominal composition "K₅Ga₂Bi₄" for the formation of [K(crypt-222)]⁺ salts of novel Bi-rich polyanions [Bi@Ga₈(Bi₂)₆]^q- (q = 3, 5; in 1), (Ga₂Bi₁₆)^4- (in 2), and [{Ru(cod)}₄Bi₁₈]^4- (in 3). Their bismuth contents exceed that of the largest homoatomic polyanion, Bi₁₁^3-. The numbers of bismuth atoms in the anions in 2 and 3 furthermore surmount that of the Bi-richest binary main-group anion, (Ge₄Bi₁₄)^4-, and they equal (2) or surmount (3) that reported for the anion and the cations with the largest number of Bi atoms so far, [K₂Zn₂₀Bi₁₆]^6-, [(Bi₈)Ru(Bi₈)]⁶⁺, and [(Bi₈)Au(Bi₈)]⁵⁺. Compounds 1 and 2 were obtained from reaction mixtures that contain [La(C₅Me₄H)₃], apparently assisting in the network formation without being included in the products. In the presence of [Ru(cod)(H₂CC(Me)CH₂)₂], yet another reaction pathway leads to the formation of the anions in 3 (conformers 3a and 3b), which are Bi-Bi linked dimers of two "[{Ru(cod)}₂Bi₉]^2-" subunits. They comprise the largest connected assemblies of Bi atoms within one molecule and may be viewed as snapshots on the way toward even larger polybismuthide units and, ultimately, new bismuth modifications. Mass spectrometry allowed insight into the processes in solution that precede the cluster formation. In-depth quantum chemical studies were applied to explain structural peculiarities, stabilities of the observed isomers, and bonding characteristics of these bismuth-rich nanoarchitectures. The work demonstrates the high potential of the method for the access of new Bi-based materials.

[Bi6Mo3(CO)9]4-: a multiple local σ-aromatic cluster containing a distorted Bi6 triangular prism

The first Zintl cluster containing a distorted Bi₆ triangular prism, [Bi₆Mo₃(CO)₉]^4-, has been synthesized and structurally characterized. Quantum chemical calculations indicated that the distorted cage cluster features multiple local σ-aromaticity.

All-metal σ-antiaromaticity in dimeric cluster anion {[CuGe9Mes]2}4

In this work, we report a dimeric cluster anion, {[CuGe9Mes]2}4-, which was isolated as the [K(2,2,2-crypt)]+ salt and characterized by using single-crystal X-ray diffraction and ESI mass spectroscopy. The title cluster represents the first locally σ-antiaromatic compound in the solid state, as well as the first heteroatomic antiaromatic compound.

Frontiers in the solution-phase chemistry of homoatomic group 15 Zintl clusters

Recent developments in the solution-phase chemistry of polypnictogen Zintl cluster are discussed, including the preparation of new clusters, wet synthetic methods, and their subsequent small molecule activations.

Th@C86, Th@C82, Th@C80, and Th@C76: role of thorium encapsulation in determining spherical aromatic and bonding properties on medium-sized endohedral metallofullerenes

Thorium encapsulated metallofullerenes (Th-EMFs) with external C76, C80, C82, and C86 cages have been synthesized, with the 13C-NMR spectrum recorded for Th@C82. Here, we explore computationally the chemical bonding, NMR and spherical aromaticity of Th@C82 and related thorium-encapsulated metallofullerenes. Our results show that these Th-EMFs are new examples of spherical aromatic structures, representing interesting low-symmetry exceptions to the Hirsch 2(N + 1)2 rule of spherical aromaticity. Their electronic structures are based on π-electron counts of 80, 84, 86, and 90, respectively, with a shell structure ranging from S2P6D10F14G18H22I8 to S2P6D10F14G18H22I18, where the partially filled I-shell remains as a frontier orbital. Their behavior is comparable to that of the spherical aromatic alkali-C606- phases, which in addition to the favorable endohedral Th-fullerene bonding account for their particular abundance exhibiting the ability to sustain a long-range shielding cone as a result of the favorable metal-cage bonding. This rationalization of such species as neutral spherical aromatic EMFs suggests the possibility of an extensive series of aromatic fullerenes with nuclearity larger than C60 buckminsterfullerene as stable building blocks towards nanostructured metal-organic materials.