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Aromatic Inorganic and Metallic Compounds
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Aromatic Inorganic and Metallic Compounds

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Inorganic Chemistry".

Deadline for manuscript submissions: closed (31 December 2023) | Viewed by 7914

Special Issue Editors

Prof. Dr. Jinchang Guo

E-Mail Website
Guest Editor
Nanocluster Laboratory, Institute of Molecular Science, Shanxi University, Taiyuan 030006, China
Interests: computational chemistry; materials chemistry; theoretical design; photoelectron spectroscopy; structural chemistry
Dr. Venkatesan S. Thimmakondu

E-Mail Website
Guest Editor
Department of Chemistry and Biochemistry, San Diego State University, San Diego, CA 92182, USA
Interests: planar tetracoordinate carbon; astrochemistry; quantum chemistry; molecular spectroscopy
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

As one of the most important concepts in chemistry, aromaticity was originally used to help understand the relationship between the structure and properties of cyclic π-conjugated molecules. In 1931, Hückel proposed a simple and effective 4n+2 electronic rule to judge the aromaticity of the ground states of ring-like π-conjugated molecules, in which n was the number of delocalized π electrons. Later, 4n electronic antiaromaticity was added to the Hückel rule by Breslow. The connotations and extensions of aromaticity have been evolving in recent years. Aromatic systems are no longer confined to organic hydrocarbons but extend to inorganic and metallic compounds. As supplements to π aromaticity, σ, δ, and φ aromaticity have been found. Aromaticity is responsible not only for the regular shape, extra stability, and low reactivity of compounds but also for their exotic dynamical properties. In addition, the concept of aromaticity extends from planar molecules to three-dimensional species, such as spherical aromaticity and cubic aromaticity.

There are many ways to evaluate the aromaticity of systems, including: the molecular orbital (MO) method combined with Huckel's rule; adaptive natural density partitioning (AdNDP); nucleus-independent chemical shifts (NICSs); the anisotropy of the induced current density (AICD); aromatic ring chemical shieldings (ARCS); magnetic susceptibility exaltation; the harmonic oscillator measure of aromaticity (HOMA); bird aromaticity index; harmonic oscillator stabilization energy (HOSE); aromatic stabilization energy (ASE); magnetic resonance energies (MRE); and electron localization function (ELF).  

Aromaticity is very important for revealing the structures and properties of novel compounds. The aim of this Special Issue is to provide a platform to present the latest research results on aromatic inorganic and metallic species.

Prof. Dr. Jinchang Guo
Dr. Venkatesan S. Thimmakondu
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • aromaticity
  • inorganic compounds
  • metallic compounds
  • stability
  • dynamic properties
  • structure

Published Papers (7 papers)

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Research

13 pages, 4935 KiB  
Article
Synthesis of Ag3PO4/Ag/g-C3N4 Composite for Enhanced Photocatalytic Degradation of Methyl Orange
by Qingwang Liu, Ying Meng, Qiman Liu, Mai Xu, Yunhu Hu and Shikun Chen
Molecules 2023, 28(16), 6082; https://doi.org/10.3390/molecules28166082 - 16 Aug 2023
Cited by 1 | Viewed by 769
Abstract
In this study, we have successfully constructed Ag3PO4/Ag/g-C3N4 heterojunctions via the hydrothermal method, which displays a wide photo-absorption range. The higher photocurrent intensity of Ag3PO4/Ag/g-C3N4 indicates that the separation [...] Read more.
In this study, we have successfully constructed Ag3PO4/Ag/g-C3N4 heterojunctions via the hydrothermal method, which displays a wide photo-absorption range. The higher photocurrent intensity of Ag3PO4/Ag/g-C3N4 indicates that the separation efficiency of the photogenerated electron–hole pairs is higher than that of both Ag3PO4 and Ag/g-C3N4 pure substances. It is confirmed that the efficient separation of photogenerated electron–hole pairs is attributed to the heterojunction of the material. Under visible light irradiation, Ag3PO4/Ag/g-C3N4-1.6 can remove MO (~90%) at a higher rate than Ag3PO4 or Ag/g-C3N4. Its degradation rate is 0.04126 min−1, which is 4.23 and 6.53 times that of Ag/g-C3N4 and Ag3PO4, respectively. After five cycles of testing, the Ag3PO4/Ag/g-C3N4 photocatalyst still maintained high photocatalytic activity. The excellent photocatalysis of Ag3PO4/Ag/g-C3N4-1.6 under ultraviolet-visible light is due to the efficient separation of photogenerated carriers brought about by the construction of the Ag3PO4/Ag/g-C3N4 heterostructure. Additionally, Ag3PO4/Ag/g-C3N4 specimens can be easily recycled with high stability. The effects of hydroxyl and superoxide radicals on the degradation process of organic compounds were studied using electron paramagnetic resonance spectroscopy and radical quenching experiments. Therefore, the Ag3PO4/Ag/g-C3N4 composite can be used as an efficient and recyclable UV-vis spectrum-driven photocatalyst for the purification of organic pollutants. Full article
(This article belongs to the Special Issue Aromatic Inorganic and Metallic Compounds)
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10 pages, 909 KiB  
Article
Main-Group Metal Complexes of Benzene: Predicted Features of Stabilization and Isomerization
by Fedor Y. Naumkin
Molecules 2023, 28(16), 5985; https://doi.org/10.3390/molecules28165985 - 10 Aug 2023
Cited by 1 | Viewed by 704
Abstract
Complexes of metal atoms with organic molecules represent a broad variety of systems with many important applications, e.g., in metal–organic interfaces and organometallic chemistry. One class involves aromatic species like benzene (Bz). Here, such complexes with second-group metals are investigated systematically in terms [...] Read more.
Complexes of metal atoms with organic molecules represent a broad variety of systems with many important applications, e.g., in metal–organic interfaces and organometallic chemistry. One class involves aromatic species like benzene (Bz). Here, such complexes with second-group metals are investigated systematically in terms of structure and shape, stability and isomerization, charge distribution and aromaticity, and polarity and IR spectra. Three groups of isomers are identified, varying from metastable to stable ones, in effect featuring “physisorption” or “chemisorption”. In particular, the high polarity of binary complexes and nonadditive stabilization of ternary systems for some isomers are found. Also, the Bz component’s shape alteration for different isomers and system sizes and related aromaticity variations are predicted to be considerable. Property evolution for the series of metal components is analyzed. Full article
(This article belongs to the Special Issue Aromatic Inorganic and Metallic Compounds)
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15 pages, 4072 KiB  
Article
Boron-Based Inverse Sandwich V2B7− Cluster: Double π/σ Aromaticity, Metal–Metal Bonding, and Chemical Analogy to Planar Hypercoordinate Molecular Wheels
by Peng-Fei Han, Qiang Sun and Hua-Jin Zhai
Molecules 2023, 28(12), 4721; https://doi.org/10.3390/molecules28124721 - 12 Jun 2023
Cited by 1 | Viewed by 1078
Abstract
Inverse sandwich clusters composed of a monocyclic boron ring and two capping transition metal atoms are interesting alloy cluster systems, yet their chemical bonding nature has not been sufficiently elucidated to date. We report herein on the theoretical prediction of a new example [...] Read more.
Inverse sandwich clusters composed of a monocyclic boron ring and two capping transition metal atoms are interesting alloy cluster systems, yet their chemical bonding nature has not been sufficiently elucidated to date. We report herein on the theoretical prediction of a new example of boron-based inverse sandwich alloy clusters, V2B7−, through computational global-minimum structure searches and quantum chemical calculations. This alloy cluster has a heptatomic boron ring as well as a perpendicular V2 dimer unit that penetrates through the ring. Chemical bonding analysis suggests that the inverse sandwich cluster is governed by globally delocalized 6π and 6σ frameworks, that is, double 6π/6σ aromaticity following the (4n + 2) Hückel rule. The skeleton B−B σ bonding in the cluster is shown not to be strictly Lewis-type two-center two-electron (2c-2e) σ bonds. Rather, these are quasi-Lewis-type, roof-like 4c-2e V−B2−V σ bonds, which amount to seven in total and cover the whole surface of inverse sandwich in a truly three-dimensional manner. Theoretical evidence is revealed for a 2c-2e Lewis σ single bond within the V2 dimer. Direct metal–metal bonding is scarce in inverse sandwich alloy clusters. The present inverse sandwich alloy cluster also offers a new type of electronic transmutation in physical chemistry, which helps establish an intriguing chemical analogy between inverse sandwich clusters and planar hypercoordinate molecular wheels. Full article
(This article belongs to the Special Issue Aromatic Inorganic and Metallic Compounds)
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14 pages, 3544 KiB  
Article
Mechanisms in the Catalytic Reduction of N2O by CO over the M13@Cu42 Clusters of Aromatic-like Inorganic and Metal Compounds
by Ziyang Liu, Haifeng Wang, Yan Gao and Jijun Zhao
Molecules 2023, 28(11), 4485; https://doi.org/10.3390/molecules28114485 - 01 Jun 2023
Cited by 3 | Viewed by 947
Abstract
Metal aromatic substances play a unique and important role in both experimental and theoretical aspects, and they have made tremendous progress in the past few decades. The new aromaticity system has posed a significant challenge and expansion to the concept of aromaticity. From [...] Read more.
Metal aromatic substances play a unique and important role in both experimental and theoretical aspects, and they have made tremendous progress in the past few decades. The new aromaticity system has posed a significant challenge and expansion to the concept of aromaticity. From this perspective, based on spin-polarized density functional theory (DFT) calculations, we systematically investigated the doping effects on the reduction reactions of N2O catalyzed by CO for M13@Cu42 (M = Cu, Co, Ni, Zn, Ru, Rh, Pd, Pt) core–shell clusters from aromatic-like inorganic and metal compounds. It was found that compared with the pure Cu55 cluster, the strong M–Cu bonds provide more structural stability for M13@Cu42 clusters. Electrons that transferred from the M13@Cu42 to N2O promoted the activation and dissociation of the N–O bond. Two possible reaction modes of co-adsorption (L-H) and stepwise adsorption (E-R) mechanisms over M13@Cu42 clusters were thoroughly discovered. The results showed that the exothermic phenomenon was accompanied with the decomposition process of N2O via L-H mechanisms for all of the considered M13@Cu42 clusters and via E-R mechanisms for most of the M13@Cu42 clusters. Furthermore, the rate-limiting step of the whole reactions for the M13@Cu42 clusters were examined as the CO oxidation process. Our numerical calculations suggested that the Ni13@Cu42 cluster and Co13@Cu42 clusters exhibited superior potential in the reduction reactions of N2O by CO; especially, Ni13@Cu42 clusters are highly active, with very low free energy barriers of 9.68 kcal/mol under the L-H mechanism. This work demonstrates that the transition metal core encapsulated M13@Cu42 clusters can present superior catalytic activities towards N2O reduction by CO. Full article
(This article belongs to the Special Issue Aromatic Inorganic and Metallic Compounds)
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10 pages, 1688 KiB  
Article
Sc@B28−, Ti@B28, V@B28+, and V@B292−: Spherically Aromatic Endohedral Seashell-like Metallo-Borospherenes
by Ting Zhang, Min Zhang, Xiao-Qin Lu, Qiao-Qiao Yan, Xiao-Ni Zhao and Si-Dian Li
Molecules 2023, 28(9), 3892; https://doi.org/10.3390/molecules28093892 - 05 May 2023
Cited by 2 | Viewed by 1011
Abstract
Transition-metal-doped boron nanoclusters exhibit unique structures and bonding in chemistry. Using the experimentally observed seashell-like borospherenes C2 B28−/0 and Cs B29− as ligands and based on extensive first-principles theory calculations, we predict herein a series of novel [...] Read more.
Transition-metal-doped boron nanoclusters exhibit unique structures and bonding in chemistry. Using the experimentally observed seashell-like borospherenes C2 B28−/0 and Cs B29− as ligands and based on extensive first-principles theory calculations, we predict herein a series of novel transition-metal-centered endohedral seashell-like metallo-borospherenes C2 Sc@B28− (1), C2 Ti@B28 (2), C2 V@B28+ (3), and Cs V@B292− (4) which, as the global minima of the complex systems, turn out to be the boron analogues of dibenzenechromium D6h Cr(C6H6)2 with two B12 ligands on the top and bottom interconnected by four or five corner boron atoms on the waist and one transition-metal “pearl” sandwiched at the center in between. Detailed molecular orbital, adaptive natural density partitioning (AdNDP), and iso−chemical shielding surface (ICSS) analyses indicate that, similar to Cr(C6H6)2, these endohedral seashell-like complexes follow the 18-electron rule in bonding patterns (1S21P61D10), rendering spherical aromaticity and extra stability to the systems. Full article
(This article belongs to the Special Issue Aromatic Inorganic and Metallic Compounds)
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11 pages, 3649 KiB  
Article
CAl4X4 (X = Te, Po): Double Aromatic Molecular Stars Containing Planar Tetracoordinate Carbon Atoms
by Li-Xia Bai and Jin-Chang Guo
Molecules 2023, 28(7), 3280; https://doi.org/10.3390/molecules28073280 - 06 Apr 2023
Cited by 3 | Viewed by 1255
Abstract
Planar tetracoordinate carbon (ptC) species are scarce and exotic. Introducing four peripheral Te/Po auxiliary atoms is an effective strategy to flatten the tetrahedral structure of CAl4 (Td, 1A1). Neutral CAl4X4 (X = Te, [...] Read more.
Planar tetracoordinate carbon (ptC) species are scarce and exotic. Introducing four peripheral Te/Po auxiliary atoms is an effective strategy to flatten the tetrahedral structure of CAl4 (Td, 1A1). Neutral CAl4X4 (X = Te, Po) clusters possess quadrangular star structures containing perfect ptC centers. Unbiased density functional theory (DFT) searches and high-level CCSD(T) calculations suggest that these ptC species are the global minima on the potential energy surfaces. Bonding analyses indicate that 40 valence-electron (VE) is ideal for the ptC CAl4X4 (X = Te, Po): one delocalized π and three σ bonds for the CAl4 core; four lone pairs (LPs) of four X atoms, eight localized Al–X σ bonds, and four delocalized Al–X–Al π bonds for the periphery. Thus, the ptC CAl4X4 (X = Te, Po) clusters possess the stable eight electron structures and 2π + 6σ double aromaticity. Born–Oppenheimer molecular dynamics (BOMD) simulations indicate that neutral ptC CAl4X4 (X = Te, Po) clusters are robust. Full article
(This article belongs to the Special Issue Aromatic Inorganic and Metallic Compounds)
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12 pages, 3964 KiB  
Article
Chemical Bonding and Dynamic Structural Fluxionality of a Boron-Based Na5B7 Sandwich Cluster
by Peng-Fei Han, Ying-Jin Wang, Lin-Yan Feng, Shu-Juan Gao, Qiang Sun and Hua-Jin Zhai
Molecules 2023, 28(7), 3276; https://doi.org/10.3390/molecules28073276 - 06 Apr 2023
Viewed by 1339
Abstract
Doping alkali metals into boron clusters can effectively compensate for the intrinsic electron deficiency of boron and lead to interesting boron-based binary clusters, owing to the small electronegativity of the former elements. We report on the computational design of a three-layered sandwich cluster, [...] Read more.
Doping alkali metals into boron clusters can effectively compensate for the intrinsic electron deficiency of boron and lead to interesting boron-based binary clusters, owing to the small electronegativity of the former elements. We report on the computational design of a three-layered sandwich cluster, Na5B7, on the basis of global-minimum (GM) searches and electronic structure calculations. It is shown that the Na5B7 cluster can be described as a charge-transfer complex: [Na4]2+[B7]3−[Na]+. In this sandwich cluster, the [B7]3− core assumes a molecular wheel in shape and features in-plane hexagonal coordination. The magic 6π/6σ double aromaticity underlies the stability of the [B7]3− molecular wheel, following the (4n + 2) Hückel rule. The tetrahedral Na4 ligand in the sandwich has a [Na4]2+ charge-state, which is the simplest example of three-dimensional aromaticity, spherical aromaticity, or superatom. Its 2σ electron counting renders σ aromaticity for the ligand. Overall, the sandwich cluster has three-fold 6π/6σ/2σ aromaticity. Molecular dynamics simulation shows that the sandwich cluster is dynamically fluxional even at room temperature, with a negligible energy barrier for intramolecular twisting between the B7 wheel and the Na4 ligand. The Na5B7 cluster offers a new example for dynamic structural fluxionality in molecular systems. Full article
(This article belongs to the Special Issue Aromatic Inorganic and Metallic Compounds)
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