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Bonding in Inorganic and Coordination Compounds

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

Deadline for manuscript submissions: closed (31 December 2020) | Viewed by 34924

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Special Issue Editor

Prof. Dr. Catherine Housecroft

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Department of Chemistry, University of Basel, Building 1095, Mattenstrasse 22, Postfach, CH-4002 Basel, Switzerland
Interests: light harvesting using inorganic coordination complexes as dyes in dye-sensitized solar cells (DSCs); development of emissive complexes for application in light-emitting electrochemical cells (LECs); water splitting and water oxidation catalysts; functional coordination polymers and networks; chemical education
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Special Issue Information

Dear Colleagues,

Molecules are defined by the bonds connecting their constituent atoms and ions. Thus, it is appropriate and overdue to dedicate a Special Issue of Molecules to the topic of bonding.

The concept of bonding is almost as old as chemistry itself. As alchemy transformed to chemistry, Newton discussed the forces that held atoms together. In the 19th century, concepts of bonding developed in parallel with those of valency and structure. Our modern understanding of the covalent bond is due to Gilbert Lewis and dates to 1916, whereas ionic bonding is more nebulous, but modern ideas date back to Kossel in the same year.

Pauling's seminal work 'The Chemical Bond' published in 1939 was pivotal in our understanding of bonding in chemical compounds and extended the electronic view of chemical structure from organic chemistry to the whole of chemistry. From an educational standpoint, concepts of bonding typically begin with a Lewis approach for simple covalent molecules and an electrostatic approach for ionic lattices. The picture soon becomes more complex, firstly when the ideas of covalent and ionic contributions to the same bond are introduced, and then when quantum mechanical models with ever more extended basis sets are used. The myriad of exotic structures of inorganic and organic molecules that now graces the literature continues to challenge accepted bonding models, and concepts such as hypervalency go in and out of fashion.

At the research level, the development of theoretical approaches has blossomed over the last few decades, and the application of density functional theory (DFT) to both small and large molecular species has become an integral part of chemical research. Combined theoretical and synthetic investigations have opened the door to both predictive models and the rationalization of structural and physical (e.g., spectroscopic) observations. The development of robust computational methods to investigate the structures of, and bonding in, excited as well as ground state species has been a fundamental breakthrough, giving significant insight into, for example, changes that occur upon photoexcitation of molecules. In the third Millennium, it is difficult to envisage chemical research without input from theoretical investigations.

Single-crystal X-ray diffraction is routinely used to verify the structures of discrete molecules, extended arrays and proteins. In-depth analysis of structural data is key to an understanding of molecular bonding and distributions of electron density. The marriage of crystallographic and theoretical (in particular, DFT) results provides a firm foundation for the further elaboration of bonding models in inorganic, coordination and organometallic chemistry.

The theme of this Special Issue of Molecules is 'Bonding in Inorganic and Coordination Compounds', and I invite both retrospective and current research contributions, as well as manuscripts that contribute towards the development of bonding analysis, and to chemical education.

Prof. Dr. Catherine Housecroft
Guest Editor

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Keywords

chemical bond
covalent
ionic
electron density distribution
coordination
organometallic

Published Papers (10 papers)

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Research

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12 pages, 1241 KiB

Open AccessArticle

1,3,5-Triaza-7-Phosphaadamantane (PTA) as a ³¹P NMR Probe for Organometallic Transition Metal Complexes in Solution

by Ilya G. Shenderovich

Molecules 2021, 26(5), 1390; https://doi.org/10.3390/molecules26051390 - 4 Mar 2021

Cited by 9 | Viewed by 3007

Abstract

Due to the rigid structure of 1,3,5-triaza-7-phosphaadamantane (PTA), its ³¹P chemical shift solely depends on non-covalent interactions in which the molecule is involved. The maximum range of change caused by the most common of these, hydrogen bonding, is only 6 ppm, because the active site is one of the PTA nitrogen atoms. In contrast, when the PTA phosphorus atom is coordinated to a metal, the range of change exceeds 100 ppm. This feature can be used to support or reject specific structural models of organometallic transition metal complexes in solution by comparing the experimental and Density Functional Theory (DFT) calculated values of this ³¹P chemical shift. This approach has been tested on a variety of the metals of groups 8–12 and molecular structures. General recommendations for appropriate basis sets are reported. Full article

(This article belongs to the Special Issue Bonding in Inorganic and Coordination Compounds)

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16 pages, 2925 KiB

Open AccessArticle

Structure Controlling Factors of Oxido-Bridged Dinuclear Iron(III) Complexes

by Ryusei Hoshikawa, Kosuke Yoshida, Ryoji Mitsuhashi, Masahiro Mikuriya, Takashi Okuno and Hiroshi Sakiyama

Molecules 2021, 26(4), 897; https://doi.org/10.3390/molecules26040897 - 8 Feb 2021

Cited by 5 | Viewed by 2126

Abstract

Oxido bridges commonly form between iron(III) ions, but their bond angles and symmetry vary with the circumstances. A large number of oxido-bridged dinuclear iron(III) complexes have been structurally characterized. Some of them belong to the C₂ point group, possessing bent Fe–O–Fe bonds, while some others belong to the C_i symmetry, possessing the linear Fe–O–Fe bonds. The question in this study is what determines the structures and symmetry of oxido-bridged dinuclear iron(III) complexes. In order to gain further insights, three oxido-bridged dinuclear iron(III) complexes were newly prepared with 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) ligands: [Fe₂OCl₂(bpy)₄][PF₆]₂ (1), [Fe₂O(NO₃)₂(bpy)₄][PF₆]₂·0.6MeCN·0.2(2-PrOH) (2), and [Fe₂OCl₂(phen)₄][PF₆]₂·MeCN·0.5H₂O (3). The crystal structures of 1, 2, and 3 were determined by the single-crystal X-ray diffraction method, and all of them were found to have the bent Fe–O–Fe bonds. Judging from the crystal structure, some intramolecular interligand hydrogen bonds were found to play an important role in fixing the structures. Additional density functional theory (DFT) calculations were conducted, also for a related oxido-bridged dinuclear iron(III) complex with a linear Fe–O–Fe bond. We conclude that the Fe–O–Fe bridge tends to bend like a water molecule, but is often stretched by interligand steric repulsion, and that the structures are mainly controlled by the intramolecular interligand interactions. Full article

(This article belongs to the Special Issue Bonding in Inorganic and Coordination Compounds)

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12 pages, 28339 KiB

Open AccessCommunication

Crystallographic and Computational Electron Density of d_x2-y2 Orbitals of Azo-Schiff Base Metal Complexes Using Conventional Programs

by Yuji Takiguchi, Yuika Onami, Tomoyuki Haraguchi and Takashiro Akitsu

Molecules 2021, 26(3), 551; https://doi.org/10.3390/molecules26030551 - 21 Jan 2021

Cited by 2 | Viewed by 1644

Abstract

The crystal structures of two azobenzene derivative Schiff base metal complexes (new C₄₄H₄₀CuN₆O₂ of P-1 and known C₄₄H₃₈MnN₆O₇ of P2₁/c abbreviated as Cu and Mn, [...] Read more.

The crystal structures of two azobenzene derivative Schiff base metal complexes (new C₄₄H₄₀CuN₆O₂ of P-1 and known C₄₄H₃₈MnN₆O₇ of P2₁/c abbreviated as Cu and Mn, respectively) were (re-)determined experimentally using conventional X-ray analysis to obtain electron density using a PLATON program. Cu affords a four-coordinated square planar geometry, while Mn affords a hexa-coordinated distorted octahedral geometry whose apical sites are occupied by an acetate ion and water ligands, which are associated with hydrogen bonds. The π-π or CH-π and hydrogen bonding intermolecular interactions were found in both crystals, which were also analyzed using a Hirshfeld surface analysis program. To compare these results with experimental results, a density functional theory (DFT) calculation was also carried out based on the crystal structures to obtain calculated electron density using a conventional Gaussian program. These results revealed that the axial Mn-O coordination bonds of Mn were relatively weaker than the in-plane M-N or M-O coordination bonds. Full article

(This article belongs to the Special Issue Bonding in Inorganic and Coordination Compounds)

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31 pages, 7002 KiB

Open AccessArticle

Self-Assembly of Antiferromagnetically-Coupled Copper(II) Supramolecular Architectures with Diverse Structural Complexities

by Santokh S. Tandon, Scott D. Bunge, Neil Patel, Esther C. Wang and Laurence K. Thompson

Molecules 2020, 25(23), 5549; https://doi.org/10.3390/molecules25235549 - 26 Nov 2020

Cited by 8 | Viewed by 2356

Abstract

The self-assembly of 2,6-diformyl-4-methylphenol (DFMP) and 1-amino-2-propanol (AP)/2-amino-1,3-propanediol (APD) in the presence of copper(II) ions results in the formation of six new supramolecular architectures containing two versatile double Schiff base ligands (H₃L and H₅L1) with one-, two-, or three-dimensional structures involving diverse nuclearities: tetranuclear [Cu₄(HL²⁻)₂(N₃)₄]·4CH₃OH·56H₂O (1) and [Cu₄(L³⁻)₂(OH)₂(H₂O)₂] (2), dinuclear [Cu₂(H₃L1²⁻)(N₃)(H₂O)(NO₃)] (3), polynuclear {[Cu₂(H₃L1²⁻)(H₂O)(BF₄)(N₃)]·H₂O}_n (4), heptanuclear [Cu₇(H₃L1²⁻)₂(O)₂(C₆H₅CO₂)₆]·6CH₃OH·44H₂O (5), and decanuclear [Cu₁₀(H₃L1²⁻)₄(O)₂(OH)₂(C₆H₅CO₂)₄] (C₆H₅CO₂)₂·20H₂O (6). X-ray studies have revealed that the basic building block in 1, 3, and 4 is comprised of two copper centers bridged through one μ-phenolate oxygen atom from HL²⁻ or H₃L1²⁻, and one μ-1,1-azido (N₃⁻) ion and in 2, 5, and 6 by μ-phenoxide oxygen of L³⁻ or H₃L1²⁻ and μ-O²⁻ or μ₃-O²⁻ ions. H-bonding involving coordinated/uncoordinated hydroxy groups of the ligands generates fascinating supramolecular architectures with 1D-single chains (1 and 6), 2D-sheets (3), and 3D-structures (4). In 5, benzoate ions display four different coordination modes, which, in our opinion, is unprecedented and constitutes a new discovery. In 1, 3, and 5, Cu(II) ions in [Cu₂] units are antiferromagnetically coupled, with J ranging from −177 to −278 cm⁻¹. Full article

(This article belongs to the Special Issue Bonding in Inorganic and Coordination Compounds)

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11 pages, 1082 KiB

Open AccessArticle

Interactions in Model Ionic Dyads and Triads Containing Tetrel Atoms

by Sean A. C. McDowell, Ruijing Wang and Qingzhong Li

Molecules 2020, 25(18), 4197; https://doi.org/10.3390/molecules25184197 - 14 Sep 2020

Cited by 3 | Viewed by 1783

Abstract

The interactions in model ionic YTX₃···Z (Y = NC, F, Cl, Br; X = F, Cl, Br, Z = F⁻, Cl⁻, Br⁻, Li⁺) dyads containing the tetrel atoms, T = C, Si, Ge, [...] Read more.

The interactions in model ionic YTX₃···Z (Y = NC, F, Cl, Br; X = F, Cl, Br, Z = F⁻, Cl⁻, Br⁻, Li⁺) dyads containing the tetrel atoms, T = C, Si, Ge, were studied using ab initio computational methods, including an energy decomposition analysis, which found that the YTX₃ molecules were stabilized by both anions (via tetrel bonding) and cations (via polarization). For the tetrel-bonded dyads, both the electrostatic and polarization forces make comparable contributions to the binding in the C-containing dyads, whereas, electrostatic forces are by far the largest contributor to the binding in the Si- and Ge-containing analogues. Model metastable Li⁺···NCTCl₃···F⁻ (T = C, Si, Ge) triads were found to be lower in energy than the combined energy of the Li⁺ + NCTCl₃ + F⁻ fragments. The pair energies and cooperative energies for these highly polar triads were also computed and discussed. Full article

(This article belongs to the Special Issue Bonding in Inorganic and Coordination Compounds)

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15 pages, 3895 KiB

Open AccessArticle

Computational Study of Methane C–H Activation by Main Group and Mixed Main Group–Transition Metal Complexes

by Carly C. Carter and Thomas R. Cundari

Molecules 2020, 25(12), 2794; https://doi.org/10.3390/molecules25122794 - 17 Jun 2020

Cited by 2 | Viewed by 2533

Abstract

In the present density functional theory (DFT) research, nine different molecules, each with different combinations of A (triel) and E (divalent metal) elements, were reacted to effect methane C–H activation. The compounds modeled herein incorporated the triels A = B, Al, or Ga and the divalent metals E = Be, Mg, or Zn. The results show that changes in the divalent metal have a much bigger impact on the thermodynamics and methane activation barriers than changes in the triels. The activating molecules that contained beryllium were most likely to have the potential for activating methane, as their free energies of reaction and free energy barriers were close to reasonable experimental values (i.e., ΔG close to thermoneutral, ΔG^‡ ~30 kcal/mol). In contrast, the molecules that contained larger elements such as Zn and Ga had much higher ΔG^‡. The addition of various substituents to the A–E complexes did not seem to affect thermodynamics but had some effect on the kinetics when substituted closer to the active site. Full article

(This article belongs to the Special Issue Bonding in Inorganic and Coordination Compounds)

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15 pages, 1886 KiB

Open AccessArticle

The Nature of Triel Bonds, a Case of B and Al Centres Bonded with Electron Rich Sites

by Sławomir J. Grabowski

Molecules 2020, 25(11), 2703; https://doi.org/10.3390/molecules25112703 - 11 Jun 2020

Cited by 34 | Viewed by 2982

Abstract

The second-order Møller–Plesset perturbation theory calculations with the aug-cc-pVTZ basis set were performed on complexes of triel species: BCl₃, BH₃, AlCl₃, and AlH₃ acting as Lewis acids through the B or Al centre with Lewis base units: NCH, N₂, NH₃, and Cl⁻ anion. These complexes are linked by triel bonds: B/Al⋅⋅⋅N or B/Al⋅⋅⋅Cl. The Quantum Theory of ´Atoms in Molecules´ approach, Natural Bond Orbital method, and the decomposition of energy of interaction were applied to characterise the latter links. The majority of complexes are connected through strong interactions possessing features of covalent bonds and characterised by short intermolecular distances, often below 2 Å. The BCl₃⋅⋅⋅N₂ complex is linked by a weak interaction corresponding to the B⋅⋅⋅N distance of ~3 Å. For the BCl₃⋅⋅⋅NCH complex, two configurations corresponding to local energetic minima are observed, one characterised by a short B⋅⋅⋅N distance and a strong interaction and another one characterised by a longer B⋅⋅⋅N distance and a weak triel bond. The tetrahedral triel structure is observed for complexes linked by strong triel bonds, while, for complexes connected by weak interactions, the structure is close to the trigonal pyramid, particularly observed for the BCl₃⋅⋅⋅N₂ complex. Full article

(This article belongs to the Special Issue Bonding in Inorganic and Coordination Compounds)

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Review

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21 pages, 7920 KiB

Open AccessReview

Polyhedral [M₂B₅] Metallaborane Clusters and Derivatives: An Overview of Their Structural Features and Chemical Bonding

by Rini Prakash, Jean-François Halet and Sundargopal Ghosh

Molecules 2020, 25(14), 3179; https://doi.org/10.3390/molecules25143179 - 12 Jul 2020

Cited by 1 | Viewed by 2768

Abstract

A large number of metallaborane clusters and their derivatives with various structural arrangements are known. Among them, M₂B₅ clusters and derivatives constitute a significant class. Transition metals present in these species span from group 4 to group 7. Their structure can vary from oblatonido, oblatoarachno, to arachno type open structures. Many of these clusters appear to be hypoelectronic and are often considered as ‘rule breakers’ with respect to the classical Wade–Mingos electron counting rules. This is due to their unique highly oblate (flattened) deltahedral structures featuring a cross-cluster M−M interaction. Many theoretical calculations were performed to elucidate their electronic structure and chemical bonding properties. In this review, the synthesis, structure, and electronic aspects of the transition metal M₂B₅ clusters known in the literature are discussed. The chosen examples illustrate how, in synergy with experiments, computational results can provide additional valuable information to better understand the electronic properties and electronic requirements which govern their architecture and thermodynamic stability. Full article

(This article belongs to the Special Issue Bonding in Inorganic and Coordination Compounds)

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35 pages, 4854 KiB

Open AccessReview

The Basics of Covalent Bonding in Terms of Energy and Dynamics

by Sture Nordholm and George B. Bacskay

Molecules 2020, 25(11), 2667; https://doi.org/10.3390/molecules25112667 - 8 Jun 2020

Cited by 18 | Viewed by 7527

Abstract

We address the paradoxical fact that the concept of a covalent bond, a cornerstone of chemistry which is well resolved computationally by the methods of quantum chemistry, is still the subject of debate, disagreement, and ignorance with respect to its physical origin. Our aim here is to unify two seemingly different explanations: one in terms of energy, the other dynamics. We summarize the mechanistic bonding models and the debate over the last 100 years, with specific applications to the simplest molecules: H₂⁺ and H₂. In particular, we focus on the bonding analysis of Hellmann (1933) that was brought into modern form by Ruedenberg (from 1962 on). We and many others have helped verify the validity of the Hellmann–Ruedenberg proposal that a decrease in kinetic energy associated with interatomic delocalization of electron motion is the key to covalent bonding but contrary views, confusion or lack of understanding still abound. In order to resolve this impasse we show that quantum mechanics affords us a complementary dynamical perspective on the bonding mechanism, which agrees with that of Hellmann and Ruedenberg, while providing a direct and unifying view of atomic reactivity, molecule formation and the basic role of the kinetic energy, as well as the important but secondary role of electrostatics, in covalent bonding. Full article

(This article belongs to the Special Issue Bonding in Inorganic and Coordination Compounds)

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46 pages, 6144 KiB

Open AccessReview

Chemical Bonding: The Journey from Miniature Hooks to Density Functional Theory

by Edwin C. Constable and Catherine E. Housecroft

Molecules 2020, 25(11), 2623; https://doi.org/10.3390/molecules25112623 - 5 Jun 2020

Cited by 12 | Viewed by 7134

Abstract

Our modern understanding of chemistry is predicated upon bonding interactions between atoms and ions resulting in the assembly of all of the forms of matter that we encounter in our daily life. It was not always so. This review article traces the development of our understanding of bonding from prehistory, through the debates in the 19th century C.E. bearing on valence, to modern quantum chemical models and beyond. Full article

(This article belongs to the Special Issue Bonding in Inorganic and Coordination Compounds)

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