Topological Analysis of the Electron Density in the Carbonyl Complexes M(CO)8 (M = Ca, Sr, Ba)

QTAIM analysis of the bonding in anionic group 6 carbonyl selenide clusters: [Se2M3(CO)10]2- (M=Cr, Mo, W)

CONTEXT

This research aims to offer a deeper understanding of the bonding interactions between M-Se and M-CO and how these interactions change across the group 6 transition metal series: [Se2M3(CO)10]2- (M = Cr, Mo, W). It also seeks to explore the impact of carbonyl groups on M-M interactions within the clusters. Seven criteria, which are based on QTAIM properties, have been considered and compared with the corresponding criteria in other transition metal clusters. The results confirm that no such bond critical points or bond baths occur between transition metals, which instead have 5c-7e bonding interactions delocalized over their five-membered M3(μ-Se)2 ring, as evidenced by the non-negligible nonbonding delocalization indices. The topological properties of three bond clusters, Cr-Se, Mo-Se, and W-Se, resemble those of "intermediate closed shell characters," which combine covalent and electrostatic properties. Source function calculations indicated that the bonded Se atom contributed the most to each Cr-Se and Mo-Se bcp. The OCO atoms and nonbonded Se atoms also contributed to some extent. However, metal atoms act as sinks rather than as sources of electron density. In contrast, the majority of the metal atoms, both bonded and nonbonded, contribute to Cr-W bcps. Analysis of the delocalization indices δ(M…O) in the three clusters indicates that CO significantly contributes to Cr π-back donation in cluster 1. In contrast, no π-back donation occurs from CO to Mo or W in clusters 2 or 3, respectively.

METHODS

The B3P86 hybrid functional was used for computations in the Gaussian 09 software. The LanL2DZ basis set was employed for Cr, Mo, and W, while the 6-31G (d, p) basis set was used for C, O, and Se atoms. We performed QTAIM analysis using the AIM2000 and Multiwfn packages, incorporating B3P86/WTBS for Cr, Mo, and W atoms. The 6-311++G(3df,3pd) basis set was used for C, O, and Se atoms. Additionally, we utilized the ELF and SF.

Open shell versus closed shell bonding interaction in cyclopropane derivatives: EDA-NOCV analyses

Cyclopropane ring is a very common motif in organic/bio-organic compounds. The chemical bonding of this strained ring is taught to all chemistry students. This three-membered cyclic, C3 ring is quite reactive which has attracted both, synthetic and theoretical chemists to rationalize/correlate its stability and bonding with its reactivity and physical properties over a century. There are a few bonding models (mainly the Bent-Bond model and Walsh model) of this C3 ring that are debated to date. Herein, we have carried out energy decomposition analysis coupled with natural orbital for chemical valence (EDA-NOCV) to study the two most reactive bonds of cyclopropane rings of 49 different organic compounds containing different functional groups to obtain a much deeper bonding insight toward a more general bonding model of this class of compounds. The EDA-NOCV analyses of fragment orbitals and susequent bond formation revealed that the nature of the CC bond of the cyclopropane (splitting two bonds at a time out of three CC bonds) ring is preferred to form two dative covalent CC bonds (between a singlet olefin-fragment and an excited singlet carbene-fragment with a vacant sp2 orbital and a filled p-orbital) for the majority (37/49) of compounds over two covalent electron sharing bonds in some (7/49) compounds (between an excited triplet olefin and triplet carbene), while a few (5/49) compounds show flexibility to adopt either the electron sharing or dative covalent bond as both are equally possible. The effects of functional groups on the nature of chemical bond in cyclopropane rings have been studied in detail. Our bonding analyses are in line with the QTAIM analyses which produce small negative values of the Laplacian, significantly positive values of bond ellipticity, and accumulation of electron densities around the ring critical point of C3 -rings. These corresponding QTAIM parameters of C3 -rings are quite different for CC single bonds of normal hydrocarbons as expected. The chemical bonding in the majority of cyclopropane rings can be very similar to those of metal-olefin systems.

Honeycomb Constructs in the La-Ni Intermetallics: Controlling Dimensionality via p-Element Substitution

The new ternary compounds La15Ni13Bi5 and La9Ni8Sn5 were obtained by arc melting under argon from appropriate amounts of the elements and subsequent annealing at 800 °C for 2 weeks. Single-crystal X-ray diffraction reveals that they represent two new structure types: La15Ni13Bi5 crystallizes in the hexagonal space group P62m [hP33, a = 14.995(3), c = 4.3421(10) Å, V = 845.5(4) Å3, Z = 1] and La9Ni8Sn5 in P63/m [hP88, a = 23.870(15), c = 4.433(3) Å, V = 2187(3) Å3, Z = 4]. The crystal structures of both compounds are characterized by hexagonal honeycomb-based motifs formed by Ni and Sn that extend along the c axis. The building motif with its three-blade wind turbine shape is reminiscent of the organic molecule triptycene and is unprecedented in extended solids. First-principles calculations have been performed in order to analyze the electronic structure and provide insight into chemical bonding. They reveal significant electron transfer from La to Ni and the respective p-element, which supports the formation of the polyanionic Ni-p-element network. DFT calculations suggest paramagnetic-like behavior for both compounds, which was confirmed by magnetic measurements.

Quantitative Descriptions of Dewar-Chatt-Duncanson Bonding Model: A Case Study of Zeise and Its Family Ions

Historically, Dewar-Chatt-Duncanson (DCD) model is a heuristic device to advance the development of organometallic chemistry and deepen our understanding of the metal-ligand bonding nature. Zeise's ion, the first man-made organometallic compound and a quintessential transition metal-olefin complex, was qualitatively explained using the DCD bonding scheme in 1950s. In this work, we quantified the explicit contributions of the σ donation and π back-donation to the metal-ligand bonding in Zeise and its family ions, [PtX3 L]- (X=F, Cl, Br, I, and At; L=C2 H4 , CO, and N2 ), using state-of-the-art quantum chemical calculations and energy decomposition analysis. The relative importance of the σ donation and π back-donation depends on both X and L, with [PtCl3 (C2 H4 )]- being a critical case in which the σ donation is marginally weaker than the π back-donation. The changes along this series are controlled by the energy levels of the correlated molecular orbitals of PtX3 - and ligand L. This study deepens our understanding of the bonding properties for transition metal complexes beyond the qualitative description of the DCD model.

Novel synthesis of multicomponent porous nano-hybrid composite, theoretical investigation using DFT and dye adsorption applications: disposing of waste with waste

Extensive studies have shown that doping can enhance the properties of graphene, but the application to real industrial wastewater treatment and theoretical calculations are limited. In this study, the hybrid nanoadsorbent Cu, N co-doped graphene (Cu@NG) was successfully synthesized via green route using carbon rods from waste dry batteries, human urine and copper nitrate, then multiple characterizations, detailed density functional theory (DFT) theoretical calculations and comprehensive actual wastewater tests are performed in environmental applications to investigate the adsorption properties and mechanism. The results showed that Cu@NG surface is mesoporous, decorated with CuO crystals and doped with N atoms. The isotherms and kinetics were simulated by Langmuir and pseudo-second-order models, respectively. The theoretical maximum sorption for MB and CV on Cu@NG is 116.28 mg·g^-1 and CV is 86.96 mg·g^-1, respectively. Pilot tests with Cu@NG on real textile wastewater showed that COD, BOD and color were removed by 54.2%, 55.2% and 86.4%, respectively. The desorption rate of Cu@NG is approximately above 90% for both MB and CV on Cu@NG after six cycles of treatment. The DFT calculations confirmed the experimental results as MB is more reactive than CV molecules. Besides, interactions have been systematically investigated via topology and natural bond orbital (NBO) analyses. The process mechanism involved mainly electrostatic adsorption, π-π stacking interactions and H-bonding interactions and ion exchange.

Clarifying notes on the bonding analysis adopted by the energy decomposition analysis

We discuss the fundamental aspects of the EDA-NOCV method and address some critical comments that have been made recently. The EDA-NOCV method unlike most other methods focuses on the process of bond formation between the interacting species and not just only on the analysis of the finally formed bond. This is demonstrated using LiF as an example. There is a difference between the interactions between the initial species which form the bond and are also the final product of bond cleavage, and the interactions between the fragments in the eventually formed molecule. The flexibility of the method allows the choice of the interacting fragments which helps to identify the charge and electron configuration of the fragments which describe the bond. This is very helpful in cases where the bond may be described with several Lewis structures. We reject the idea that it would be a disadvantage to have "bond path functions" as the energy components in the EDA, which actually indicate the variability of the method. The bonding analysis in a different sequence of the bond formation gives important results for the various questions that can be asked. This is demonstrated by using CH₂, CO₂ and the formation of a guanine quartet as examples. The fact that a bond is always defined by the bound molecule, the fragments, and their states is universal and deeply physical, as we show here again for various examples. The results of the EDA-NOCV method are in full accordance with the physical mechanism of the chemical bond as revealed by Ruedenberg.

Ag2O versus Cu2O in the Catalytic Isomerization of Coordinated Diaminocarbenes to Formamidines: A Theoretical Study

DFT theoretical calculations for the Ag₂O-induced isomerization process of diaminocarbenes to formamidines, coordinated to Mn(I), have been carried out. The reaction mechanism found involves metalation of an N-H residue of the carbene ligand by the catalyst Ag₂O and the formation of a key transition state showing a μ-η²:η² coordination of the formamidinyl ligand between manganese and silver, which allows a translocation process of Mn(I) and silver(I) ions between the carbene carbon atom and the nitrogen atom, before the formation of the formamidine ligand is completed. Calculations carried out using Cu₂O as a catalyst instead of Ag₂O show a similar reaction mechanism that is thermodynamically possible, but highly unfavorable kinetically and very unlikely to be observed, which fully agrees with experimental results.

Transition-Metal Chemistry of the Heavier Alkaline Earth Atoms Ca, Sr, and Ba

ConspectusAlkaline earth elements beryllium, magnesium, calcium, strontium, and barium with an ns² valence-shell configuration are usually classified as main-group elements that belong to the s-block atoms. For a long time, the elements were considered to be rather chemically uninteresting atomic species due to preconceived ideas about bonding, structure, and reactivity. They typically use the two ns valence electrons in forming ionic salt compounds with the metal in a formal oxidation state of +2. For the heavier alkaline earth atoms, calcium, strontium, and barium, their (n - 1)d atomic orbitals (AOs) are empty but lie close in energy to the valence np orbitals. Earlier theoretical investigations have already suggested that these elements can employ the (n - 1)d AOs to some extent to form polar bonds in divalent species in which the alkaline earth metal centers are sufficiently positively charged. The d orbital involvement increases from Ca to Sr and markedly in Ba. Thus, barium has been termed an honorary transition metal.Recently, molecular complexes of Ca, Sr, and Ba were prepared in the gas phase and in a low-temperature solid neon matrix and were detected by infrared spectroscopy. An analysis of the electronic structures of [Ba(CO)]⁺, [Ba(CO)]^-, saturated coordinated octacarbonyls [M(CO)₈] and [M(CO)₈]⁺, isoelectronic dinitrogen complexes [M(N₂)₈] and [M(N₂)₈]⁺, and the tribenzene complexes [M(Bz)₃] (M = Ca, Sr, Ba) revealed that the metal-ligand bonding can be straightforwardly discussed using the traditional Dewar-Chatt-Duncanson (DCD) model as in classical transition-metal complexes. The metal-ligand bonds can be explained with metal → ligand π back donation from occupied metal (n - 1)d AOs to vacant antibonding π molecular orbitals of the ligands with concomitant σ donation from occupied MOs of the ligands to vacant metal d orbitals of the alkaline earth atoms. In addition, heteronuclear Ca-Fe carbonyl cation complexes were also produced in the gas phase. Bonding analysis of the coordination saturated [CaFe(CO)₁₀]⁺ complex implies that it can be described by the bonding interactions between a [Ca(CO)₆]²⁺ fragment and an [Fe(CO)₄]^- anion fragment in forming a Fe → Ca d-d dative bond. The nature of metal-ligand and metal-metal bonding was quantitatively elucidated by the energy decomposition analysis in conjunction with the natural orbitals for the chemical valence (EDA-NOCV) method, which indicate that the (n - 1)d AOs of the alkaline earth metals are the dominant orbitals participating in the covalent interactions, just as typical transition metals. The results indicate that the heavier alkaline earth elements have a much richer covalent chemistry than previously thought. These findings, along with earlier studies, suggest that the heavier alkaline earth atoms Ca, Sr, and Ba should be classified as transition metals rather than main group atoms in the periodic table of the elements. This interesting structural chemistry, together with some recently reported examples of spectacular reactivity, establishes these elements as exciting and promising research targets in current research.

Metal-CO Bonding in Mononuclear Transition Metal Carbonyl Complexes

DFT calculations have been carried out for coordinatively saturated neutral and charged carbonyl complexes [M(CO) _n ] ^q where M is a metal atom of groups 2-10. The model compounds M(CO)₂ (M = Ca, Sr, Ba) and the experimentally observed [Ba(CO)]⁺ were also studied. The bonding situation has been analyzed with a variety of charge and energy partitioning approaches. It is shown that the Dewar-Chatt-Duncanson model in terms of M ← CO σ-donation and M → CO π-backdonation is a valid approach to explain the M-CO bonds and the trend of the CO stretching frequencies. The carbonyl ligands of the neutral complexes carry a negative charge, and the polarity of the M-CO bonds increases for the less electronegative metals, which is particularly strong for the group 4 and group 2 atoms. The NBO method delivers an unrealistic charge distribution in the carbonyl complexes, while the AIM approach gives physically reasonable partial charges that are consistent with the EDA-NOCV calculations and with the trend of the C-O stretching frequencies. The AdNDP method provides delocalized MOs which are very useful models for the carbonyl complexes. Deep insight into the nature of the metal-CO bonds and quantitative information about the strength of the [M] ← (CO)₈ σ-donation and [M(d)] → (CO)₈ π-backdonation visualized by the deformation densities are provided by the EDA-NOCV method. The large polarity of the M-CO π orbitals toward the CO end in the alkaline earth octacarbonyls M(CO)₈ (M = Ca, Sr, Ba) leads to small values for the delocalization indices δ(M-C) and δ(M···O) and significant overlap between adjacent CO groups, but the origin of the charge migration and the associated red-shift of the C-O stretching frequencies is the [M(d)] → (CO)₈ π-backdonation. The heavier alkaline earth metals calcium, strontium and barium use their s/d valence orbitals for covalent bonding. They are therefore to be assigned to the transition metals.

The Valence Orbitals of the Alkaline-Earth Atoms

Quantum chemical calculations of the alkaline-earth oxides, imides and dihydrides of the alkaline-earth atoms (Ae=Be, Mg, Ca, Sr, Ba) and the calcium cluster Ca6 H9 [N(SiMe3 )2 ]3 (pmdta)3 (pmdta=N,N,N',N'',N''-pentamethyldiethylenetriamine) have been carried out by using density functional theory. Analysis of the electronic structures by charge and energy partitioning methods suggests that the valence orbitals of the lighter atoms Be and Mg are the (n)s and (n)p orbitals. In contrast, the valence orbitals of the heavier atoms Ca, Sr and Ba comprise the (n)s and (n-1)d orbitals. The alkaline-earth metals Be and Mg build covalent bonds like typical main-group elements, whereas Ca, Sr and Ba covalently bind like transition metals. The results not only shed new light on the covalent bonds of the heavier alkaline-earth metals, but are also very important for understanding and designing experimental studies.

The X-ray constrained wavefunction of the [Mn(CO)4{(C6H5)2P-S-C(Br2)-P(C6H5)2}]Br complex: a theoretical and experimental study of dihalogen bonds and other noncovalent interactions

The synthesis and X-ray structure determination of the [Mn(CO)₄{(C₆H₅)₂P-S-C(Br₂)-P(C₆H₅)₂}]Br complex (1) are described. The C-Br...Br dihalogen bond present in 1 has been characterized by means of topological studies of the electron density. Both the quantum theory of atoms in molecules and the electron localization function approaches have been applied to several theoretically calculated wavefunctions as well as to an X-ray constrained wavefunction. In addition, a number of theoretical techniques, such as the source function, the reduced density gradient method and the interacting quantum atoms approach, among others, have been used to analyse the dihalogen bond as well as several intramolecular interactions of the type C-H...Br-C which have also been detected in 1. The results show clearly that while bonding in the latter interactions are dominated by electrostatic components, the former has a high degree of covalency.

Substituent Effect Parameters: Extending the Applications to Organometallic Chemistry

Typically, metal complexes are constituted of an acceptor metal ion and one or more Iigands containing the donor atoms. Accordingly, the properties of a metal complex are equally dependent on the nature of the metal ion and the ligands. Minute structural variations in the ligand will may result in linear changes in the respective energetic parameters and such linear relationships have paramount importance in organometallic chemistry. The variation in ligands is virtually limitless and substantial because of the extent of organic chemistry available for the modelling of desirable ligands, apart from the variation in metal ions. Anyhow, there is still a need for new parameters for the design and quantification of new ligands which in turn leads to the synthesis of metal complexes with possibly predictable chemical properties. Previous studies have demonstrated that quantum chemically derived molecular electrostatic potential (MESP) parameters can be listed as one of the superior quantifiers in this regard, which can act as an effective ligand electronic parameter. The interaction between the ligand part and metal-containing part will be crucial in assessing the reactivity of organometallic complexes. Here we are applying MESP based substituent constants derived from substituted benzenes to forecast the interaction energies in (pyr^* )W(CO)₅ , (NHC^* )Mo(CO)₅ and (η⁶ -arene^* )Cr(CO)₃ complexes. Ligands and metal ions are varied in each case for better understanding and transparency.

Principal interacting spin orbital: understanding the fragment interactions in open-shell systems

Due to the recent rise in the interest and research efforts on first-row transition metal catalysis and other radical-related reactions, open-shell systems play a much more important role in modern chemistry. However, the development of bonding analysis tools for open-shell systems is still lagging behind. In this work, we present the principal interacting spin orbital (PISO) analysis, which is an analysis framework developed based on our previously reported principal interacting orbital (PIO) analysis. We will demonstrate the power of our framework to analyse different kinds of open-shell systems, ranging from simple organic radicals to much more complicated coordination complexes, from which we can see how different kinds of odd-electron bonds could be identified. We will also illustrate its advantage when used in the analysis of chemical reactions, through which we can observe subtle patterns that could be helpful for tuning or rational design of related reactions.