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IntroductionDuring the COVID-19 pandemic, digital video conferencing formats temporarily became the new norm at universities. Due to social distancing, these environments were often the only way for students to work together. In the present study, we investigated how first-semester chemistry students dealt with new, challenging content, i.e., quantum theories of chemical bonding such as molecular orbital (MO) theory, in such an unfamiliar collaboration environment. Studies in the field of Computer-Supported Collaborative Learning (CSCL) suggest that small groups working on complex tasks are particularly effective when students actively build on the ideas and reasoning of their peers, i.e., when they engage in transactive talk and when they structure their work on a metacognitive level by following typical problem-solving patterns.MethodsTo operationalize these constructs, we developed a coding manual through quantitative content analysis, that we used to analyze a total of N = 77 students working together in 21 small groups on two consecutive tasks: the creation of glossaries and the construction of concept maps on MO theory. Our manual showed very good characteristics in terms of internal consistency and inter-coder reliability. Based on the data obtained, it was possible to not only describe the student’s transactive communication and problem-solving activities, but to correlate it with other variables such as knowledge development in MO theory, which allowed us to compare the two different collaborative phases as well as different treatment groups.Results and discussionStudents showed a higher proportion of transactivity and problem-solving activities when constructing the concept maps than when creating glossaries. In terms of knowledge gains, a multiple linear regression analysis revealed that students in groups that derived consequences from their collaborative work showed greater improvements than students who did not, although the students’ prior knowledge remained the most influential factor. As for the different treatments, our data did not reveal any noticeable difference when students from a small group worked with either complementary or identical material before collaboration, neither in terms of transactive talk nor problem-solving patterns. All in all, we were able to develop and test a powerful tool to quantify transactive communication and problem-solving activities in a collaborative context.

We present the two‐photon absorption (2PA) spectrum of aqueous thiocyanate calculated using high‐level quantum‐chemistry methods. The 2PA spectrum is compared to the one‐photon absorption (1PA) spectrum computed using the same computational protocol. Although the two spectra probe the same set of electronic states, the intensity patterns are different, leading to an apparent red‐shift of the 2PA spectrum relative to the 1PA spectrum. The presented analysis explains the intensity patterns and attributes the differences between the 1PA and 2PA spectra to the native symmetry of isolated SCN −, which influences the spectra in the low‐symmetry solvated environment. The native symmetry also manifests itself in variations of the polarization ratio (e.g., parallel vs. perpendicular cross sections) across the spectrum. The presented results highlight the potential of 2PA spectroscopy and high‐level quantum‐chemistry methods in studies of condensed‐phase phenomena. [ABSTRACT FROM AUTHOR]

A large number of chemistry students drop out of their studies, often because of high requirements for content knowledge. Quantum chemical models of atomic bonding such as molecular orbital (MO) theory are particularly challenging. We aimed to develop an intervention on MO theory based on the Computer-Supported Collaborative Learning framework. First, students work independently with interactive learning videos. Then, they create concept maps about core concepts of MO theory. In this paper, we present the evaluation of this intervention in terms of content knowledge, considering person-specific characteristics. Additionally, we compare three different treatment groups with varying materials and group arrangements, and prospective chemistry teachers with other first-year students. Our results show that students can answer single-choice questions well with the prior knowledge from their first-year chemistry course. Answering open-ended questions is more difficult. Nevertheless, they can improve significantly in both categories by working with the learning videos; creating concept maps does not lead to significant content knowledge changes. There are also no significant differences between the three treatment groups, or between teacher students and other chemistry freshmen. Regarding prior knowledge, differences depending on gender and school-leaving grades can be measured, whereas the choice of courses in school has no effect.

Recent publications by several leading philosophers of chemistry have focused on the definition, scope, utility, and nomenclature of issues dealing with acidity and basicity. In this paper, molecular orbital theory is used to explain all acid–base reactions, concluding that the interaction of the highest occupied molecular orbital (HOMO) of one substrate, "the base," with the lowest unoccupied molecular orbital (LUMO) of a second substrate, "the acid," determines the reactivity of such systems. This paradigm provides an understanding of all acid–base reactions as well as other reactions which, on the surface, may not seem like acid–base reactions but which have fundamental underpinnings of that kind of chemistry. Rather than being unable to determine a unified understanding of acidity and basicity as suggested in the philosophy of chemistry literature, we propose that acidity and basicity fit securely in a classification of many other reactions that, using classical chemistry knowledge, pre-quantum chemistry, would not be possible. We strongly support the use of all scientific knowledge and experience in the development of the ideas in the philosophy science. We further suggest increased interactions between philosophers of science and scientists, so that all scholars benefit from the values, knowledge, and perspectives of other disciplines. [ABSTRACT FROM AUTHOR]

Halogen bonding (XB) is a potential mechanism for the inhibition of the thyroid‐activating/deactivating iodothyronine deiodinase family of selenoproteins through interactions with halogenated endocrine disrupting compounds (EDCs). Trends in XB interactions were examined using density functional theory for a series of polyhalogenated dibenzo‐1,4‐dioxins, biphenyls, and other EDCs with methylselenolate, a simple model of the Dio active site selenocysteine. The strengths of the interactions depend upon the halogen (Br>Cl), the degree of substitution, and the position of the acceptor. In terms of donor‐acceptor energies, interactions at the meta position are often the strongest, suggesting a link to the topology of THs, especially for outer‐ring deiodination of thyroxine, which occurs at a meta iodine, and produces the active TH. However, relationships between XB interaction strengths and potential for Dio inhibition should be made in the context of the binding to the active sites, the topology of which are not fully characterized. [ABSTRACT FROM AUTHOR]

Context: In 2000, a remarkably simple relationship was introduced, which connected the calculated geometries of isomolecular states of three different multiplicities. These encompass a ground single state, the first excited triplet state, as well as related radical anion and radical cation. The rule allows the prediction of the geometry of one of the species if the three remaining ones are known. Here, we verify the applicability of this bond length rule for two small planar cyclic organic molecules, i.e., benzene and cyclobutadiene, which stand as prototypical examples of, respectively, aromatic and antiaromatic systems. We see that the rule works fairly well to benzene, and it works independently for quinoid as well as for anti-quinoid minima, despite the fact that radical anion species poses challenges for correct theoretical description. Methods: To obtain chosen electronic state equilibrium geometries, three types of computational approaches were utilized: fast and efficient density functional theory DFT, the coupled cluster method CC2, the complete active space self-consistent field (CASSCF) approach, and the most accurate but also resource-consuming perturbation theory with multireference wavefunction (CASPT2) with a default value and without IPEA-shift. Dunning and co-workers correlation-consistent basis sets (aug-)cc-pVXZ (X = D, T, Q) were employed. Gaussian 16 revision A.03, Turbomole 7.1, and Molcas 8.0 computational software were used. [ABSTRACT FROM AUTHOR]

Very few physicists who laid the foundation stone of quantum mechanics have played as important a role in chemistry as Friedrich Hund [1]. The following two significant contributions bear his name. (i) 'Hund's rules' dealing with the electronic configuration of atoms and the atomic term symbols. These rules are now a part of high school chemistry worldwide and have been generalized to diatomic molecules by Hund himself. (ii) 'Hund's coupling cases' called by him as (a) to (d) addressing the ways in which various quantum mechanical angular momenta (electron spin, orbital angular momentum, rotation) couple to form the total angular momentum via vector addition. Another early and pioneering work by Hund was on the quantum mechanical tunneling effect. However, the most significant and long-lasting contribution of Hund, together with Mulliken, was to establish the molecular orbital (MO) theory on a firm footing. In view of this, the MO theory became known as the Mulliken—Hund MO theory. [ABSTRACT FROM AUTHOR]

The electronic structures of charged point defects influence electrical and optical properties of semiconductors. Understanding the orbital interactions responsible for the electronic structures of defects therefore promotes a chemical intuition for defect‐driven mechanisms in semiconductors. In this tutorial, we discuss a molecular orbital theory‐based framework for understanding defect‐induced electronic states based on local chemical interactions between the defect and the atoms surrounding the defect site. By using Mg2Si as a case study, we show how both the chemical interactions and molecular orbitals (i. e., wave functions) responsible for the charge state(s) of a defect can be understood from the bonding symmetry of the defect site. We anticipate that a chemistry‐based perspective of charged defects will enrich defect engineering efforts for electronic and optical materials. [ABSTRACT FROM AUTHOR]

This Rosarium Philosophorum essay tells the story of the author's "conversion" to a theorist, and then the events which led him to stumble over valence bond (VB) theory, and his developments of "VB diagrams" as conceptual tools which enable one to describe all chemical reactions. The story continues to the adventure with the enzyme Cytochrome P450, and how this interest led eventually the author to treat the reactivity of this enzyme using VB diagrams. And finally, the essay describes the author's struggle with complexity through molecular dynamics of these enzymes. This is also a story of interactions between individuals who seek insight and wisdom and how they influence one another through friendships and teacher‐disciples relations. This is the key wisdom one garners through scientific life. [ABSTRACT FROM AUTHOR]

This is Paper 2 in the 27‐paper series on the history of the development of the Woodward‐Hoffmann rules. Paper 2 takes the reader back to the 1950s and early 1960s, before the publication of the first Woodward‐Hoffmann paper in January 1965. The scope of the pericyclic no‐mechanism problem is described along with many of the key "hints" or "clues" to orbital symmetry control that were available in the literature prior to 1965. A chronology of reactions with alternating stereospecificities is provided. A second chronology of alternating theoretical hints is provided, e. g., 4n+2 versus 4n. Another chronology is provided, that of the development of frontier molecular orbital theory, with and without phases and nodes. A tabulation is provided of 36 instances in which the MOs of 1,3‐butadiene were reported in the literature. A knowledge of the MOs of 1,3‐butadiene, plus a knowledge of some of the alternating stereospecific reactions, could have led many chemists to the solution of the pericyclic no‐mechanism problem before Woodward and Hoffmann. [ABSTRACT FROM AUTHOR]

One challenge in chemistry is the plethora of often disparate models for rationalizing the electronic structure of molecules. Chemical concepts abound, but their connections are often frail. This work describes a quantum‐mechanical framework that enables a combination of ideas from three approaches common for the analysis of chemical bonds: energy decomposition analysis (EDA), quantum chemical topology, and molecular orbital (MO) theory. The glue to our theory is the electron energy density, interpretable as one part electrons and one part electronegativity. We present a three‐dimensional analysis of the electron energy density and use it to redefine what constitutes an atom in a molecule. Definitions of atomic partial charge and electronegativity follow in a way that connects these concepts to the total energy of a molecule. The formation of polar bonds is predicted to cause inversion of electronegativity, and a new perspective of bonding in diborane and guanine−cytosine base‐pairing is presented. The electronegativity of atoms inside molecules is shown to be predictive of pKa. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO2RR), and nitrogen reduction reaction (NRR) are important cathodic reactions for renewable fuel production and energy conversion technologies. However, the sluggish kinetics of these reactions hinders the practical applications of the relevant technologies. Perovskite oxides, a promising family of catalysts with great flexibility in composition and structure engineering, exhibit versatility in electrocatalysis of these reactions. In this review, beginning with a brief introduction on the fundamentals of ORR, CO2RR, and NRR, the mechanistic understanding of the electrocatalysis by perovskite oxides is discussed based on both molecular orbital and band theories. The recent advances of perovskite oxide‐based electrocatalysts for ORR, CO2RR, and NRR are then highlighted. Strategies for developing perovskite oxide‐based ORR catalysts are emphasized with representative examples, intending to draw on the experience of developing ORR catalysts to both CO2RR and NRR catalysts. Finally, perspectives on the perovskite oxide‐based electrocatalysis are discussed by paying particular attention to the practical applications and future development of perovskite oxide‐based catalysts. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO2RR), and nitrogen reduction reaction (NRR) are important cathodic reactions for renewable fuel production and energy conversion technologies. However, the sluggish kinetics of these reactions hinders the practical applications of the relevant technologies. Perovskite oxides, a promising family of catalysts with great flexibility in composition and structure engineering, exhibit versatility in electrocatalysis of these reactions. In this review, beginning with a brief introduction on the fundamentals of ORR, CO2RR, and NRR, the mechanistic understanding of the electrocatalysis by perovskite oxides is discussed based on both molecular orbital and band theories. The recent advances of perovskite oxide‐based electrocatalysts for ORR, CO2RR, and NRR are then highlighted. Strategies for developing perovskite oxide‐based ORR catalysts are emphasized with representative examples, intending to draw on the experience of developing ORR catalysts to both CO2RR and NRR catalysts. Finally, perspectives on the perovskite oxide‐based electrocatalysis are discussed by paying particular attention to the practical applications and future development of perovskite oxide‐based catalysts. [ABSTRACT FROM AUTHOR]

A computational study on Pinnick oxidation of aldehydes into carboxylic acids using density functional theory (DFT) calculations has been evaluated with the (SMD)-M06-2X/aug-pVDZ level of theory, leading to an important understanding of the reaction mechanism that agrees with the experimental observations and explaining the substantial role of acid in driving the reaction. The DFT results elucidated that the first reaction step (FRS) proceeds in a manner where chlorous acid reacts with the aldehyde group through a distorted six-membered ring transition state to give a hydroxyallyl chlorite intermediate that undergoes a pericyclic fragmentation to release the carboxylic acid as a second reaction step (SRS). 1H NMR experiments and simulations showed that hydrogen bonding between carbonyl and t-butanol is unlikely to occur. Additionally, it was found that the FRS is a rate-determining and thermoneutral step, whereas SRS is highly exergonic with a low energetic barrier due to the Cl(III) → Cl(II) reduction. Frontier molecular orbital analysis, intrinsic reaction coordinate, molecular dynamics and distortion/interaction analysis further supported the proposed mechanism.

Dative Bond (IUPAC): "The coordination bond formed upon interaction between molecular species, one of which serves as a donor and the other as an acceptor of the electron pair to be shared in the complex formed... The distinctive feature of dative bonds is that their minimum‐energy rupture in the gas phase or in inert solvent follows the heterolytic bond cleavage path." This definition encompasses an immense number of molecules such as Lewis adducts, transition‐metal complexes, supposedly hypervalent or hypovalent systems, and many molecules with multifaceted Lewis structures. Still, there is a large reticence to include dative bonds in the regular depiction of molecules, and even a larger unawareness of the dative bond arrow in many chemical circles. Herein we will discuss in simple chemical terms the past, present and future of such bonds. In addition, we will try to provide cleaner options to represent intricate molecules without sacrificing physical accuracy. [ABSTRACT FROM AUTHOR]

The influence of Linus Pauling on the understanding of chemical bonding is critically examined. Pauling deserves credit for presenting a connection between the quantum theoretical description of chemical bonding and Gilbert Lewis’s classical bonding model of localized electron pair bonds for a wide range of chemistry. Using the concept of resonance that he introduced, he was able to present a consistent description of chemical bonding for molecules, metals, and ionic crystals which was used by many chemists and subsequently found its way into chemistry textbooks. However, his one-sided restriction to the valence bond method and his rejection of the molecular orbital approach hindered further development of chemical bonding theory for a while and his close association of the heuristic Lewis binding model with the quantum chemical VB approach led to misleading ideas until today.

Thermoelectric performance is proportional to the thermal conductivity reciprocal and power-factor, which are impacted by microstructures and electronic band structures, respectively. Herein, we study the effect of nanoscale pores on thermal conductivity. Within Cd-doped SnTe 1-x Se x , electron microscopy characterizations indicate the majority of pores are less than 200 nm, which is comparable to the phonon mean free path. Together with the point defects and nanoprecipitates, an ultra-low lattice thermal conductivity is obtained. Electrically, we find that the slight overdose of cation lone pair s2 character at L point of the first Brillion zone yields the energetically higher valence band edge at L point than at Σ point in rock-salt chalcogenides. As for SnTe 1-x Se x , Cd is a dopant free of lone pair s2 orbital. Cd doping decreases the energy offset of multivalence bands for SnTe 1-x Se x by partially reducing the cation lone pair s2 character. The refined band structures yield an enhanced power-factor. Combined with the decreased thermal conductivity, a figure-of-merit > 1.5 has been obtained. The demonstrated strategies of exploring nanoscale pores with size matching phonon mean free path to decrease lattice thermal conductivity and the computationally screening suitable dopants to modify band structures can enlighten the development of high-performance thermoelectric candidates in wide materials. Image 1 • Nanoscale pores with sizes matching phonon mean free path decrease the thermal conductivity. • The refined band structures lead to enhanced power-factor. • Dual valence band edges in rock-salt chalcogenides are ascribed to the weak contribution of cation lone pair s2 orbital. • Exploring the nanoscale pores extends the nanostructuring strategy for enhancing thermoelectric performance. [ABSTRACT FROM AUTHOR]

The application of photoelectron spectroscopy to metallocenes, tetrahedral molecules, metal dimers and clusters, and lanthanides and actinides, interpreted through molecular orbital theory, reveals periodic trends, which, in turn, help spectral assignments. [ABSTRACT FROM AUTHOR]

Understanding diamagnetism of oxygenated and paramagnetism of deoxygenated hemoglobin, an important topic in (bio) chemistry for medical students, begins with the understanding of the detailed structure of the oxygen molecule. It continues with a short description of the structures of reactive oxygen species: the singlet form of oxygen, the superoxide, and peroxide anions. The article then describes the high spin and low spin form of the iron ion with its d‐orbitals and explains why both forms with different diameters exist in the heme part. At the end, medical applications of the acquired knowledge are presented: the cooperative effect in hemoglobin and the principles of magnetic resonance imagining. © 2018 International Union of Biochemistry and Molecular Biology, 46(6):630–633, 2018. [ABSTRACT FROM AUTHOR]

Furoxan-fused pyrenes and their dinitroso derivatives (obtained by furoxan ring opening) are considered for density functional treatment at the level of B3LYP/6-31G(d,p). Embedded benzofuroxan moiety in the furoxan-fused pyrene system is thought to undergo ring opening and reclosure process analogously to benzofuroxan itself. The stabilities, structural features, NICS(0) values, IR, and UV-VIS spectral aspects, etc., are investigated comparatively for these isomeric furoxan-fused pyrenes and their isomeric dinitroso derivatives. [ABSTRACT FROM AUTHOR]

Abstract: The preference of π‐stacking interactions for parallel‐displaced (PD) and twisted (TW) conformations over the fully eclipsed sandwich (S) in small π‐stacked dimers of benzene, pyridine, pyrimidine, 1,3,5‐trifluorobenzene, and hexafluorobenzene are examined in terms of enhancement of the inter‐ring density through mixing of the monomer orbitals (MOs). PD and/or TW conformations are consistent with a non‐zero “stack bond order” (SBO), defined in analogy to the bond order of conventional MO theory, as the difference in the occupation of bonding and antibonding π‐type dimer MOs. In the S conformation, the equal number of bonding and antibonding MOs cancel overall stack bonding character between the monomers for an SBO of zero and an overall repulsive interaction. PD from the S shifts the character of at least one antibonding combination of monomer π‐type MOs with nodes perpendicular to the coordinate for PD to bonding, leading to an attractive nonzero SBO. The inter‐ring density measured through the Wiberg bond index analysis shows an enhancement at the PD conformations consistent with greater interpenetration of the monomer densities. This intuitive bonding model for π‐stacking interactions is complementary to highly accurate calculations of π‐stacking energies and allows a predictive understanding of relative stability using cheaper quantum chemical methods. [ABSTRACT FROM AUTHOR]

An unconventional cis-cis-cis-trans or (Z,Z,Z,E) structure B of cyclooctatetraene (COT) is calculated to lie only 23 kcal/mol above the well-known tub-shaped (Z,Z,Z,Z) isomer A; one example of this type of structure is known. The barrier for B returning to A is small, 3 kcal/mol. However, by suitable choice of substituents, the (Z,Z,Z,E) isomer can be made to lie in energy below the tub-shaped structure. Steric, clamping, and electronic strategies are proposed for achieving this. In the steric strategy, the C8H4(CH3)2(C(tBu)3)2 structure B is predicted to lie 21 kcal/mol below structure A, which is separated from form B only by a small barrier. A simple clamping strategy, effective for COT planarization, does not influence the A/B isomerization much. But, if the clamping group is aromatic (a fused benzene, pyrrole, thiophene, furan), the subtle interplay of potential aromaticity with clamping can be used to confer persistence if not stability on the (Z,Z,Z,E) isomer. An electronic strategy of a different kind, push-pull substitution on the COT ring, was not very effective in stabilizing the B form. However, it led us to vicinal amine-borane-substituted normal COTs that proved to be quite good at activating H2 in a frustrated Lewis pair scenario. [ABSTRACT FROM AUTHOR]

For the design of adsorptive-separation units, knowledge is required of the multicomponent adsorption behavior. Ideal adsorbed solution theory (IAST) breaks down for olefin adsorption in open-metal site (OMS) materials due to non-ideal donor-acceptor interactions. Using a density-function-theory-based energy decomposition scheme, we develop a physically justifiable classical force field that incorporates the missing orbital interactions using an appropriate functional form. Our first-principles derived force field shows greatly improved quantitative agreement with the inflection points, initial uptake, saturation capacity, and enthalpies of adsorption obtained from our in-house adsorption experiments. While IAST fails to make accurate predictions, our improved force field model is able to correctly predict the multicomponent behavior. Our approach is also transferable to other OMS structures, allowing the accurate study of their separation performances for olefins/paraffins and further mixtures involving complex donor-acceptor interactions. [ABSTRACT FROM AUTHOR]

We return to an old puzzle – the short metal–metal separation and electrical conductivity of the apparently unoxidized one-dimensionally stacked structure of a d 8 Ir(I) complex, Ir(CO) 3 Cl. One would expect neither a short Ir–Ir distance of 2.84 Å, nor metallicity in an unoxidized stacked square-planar d 8 array. We build up dimer, trimer, one-dimensional polymer and model 3-dimensional structures, in both molecular and extended structure plane wave calculations. The short Ir–Ir separation in the polymer, with a substantial contribution of 6 p z – 5 d z 2 bonding to it, is obtained without any oxidation. There is computational evidence for an important level crossing in the polymer. The metallicity remains unexplained, but likely arises from partial oxidation. And that remains an outstanding experimental issue. [ABSTRACT FROM AUTHOR]

Research projects in physical-organic chemistry can go in unpredictable directions. One such project, described herein, began with the discovery of a large, imaginary, calculated vibrational frequency and soon led to the prediction that cyclobutanetetraone (CO)4 had a triplet ground state. Molecular orbital (MO) theory provided the understanding of why (CO)4 was calculated to have a planar triplet ground state and why, in contrast, (SiO)4 was calculated to have a tetrahedral singlet ground state. Qualitative MO theory, as well as calculations, also predicted that (CO)3, (CO)5, and (CO)6 should all be found to have singlet ground states. Testing experimentally these predictions about (CO) n molecules, n=3-6, led to a very fruitful collaboration with Dr. Xuebin Wang, who obtained the negative ion photoelectron (NIPE) spectra of the radical anions of these four molecules and also of (CS)4. Assignments of the signals in these five NIPE spectra required computing the vibrational progressions in them. The necessary acquisition of the ability to simulate the signals in NIPE spectra resulted in the successful analysis of the very complex spectrum of meta-benzoquinone (MBQ) radical anion, which Dr. Wang had already obtained and published. Analysis of this spectrum confirmed the prediction, made more than 20 years previously, that the ordering of the two lowest singlet states in MBQ was reversed from that in meta-benzoquinodimethane (MBQDM). The research described herein illustrates not only the unpredictability of where some research projects will eventually lead, but also the synergy between calculations and experiments in physical-organic chemistry. [ABSTRACT FROM AUTHOR]

A simple, four-step method for better introducing undergraduate students to the fundamentals of molecular orbital (MO) theory of the polyatomic molecules H2O, NH3, BH3 and SiH4 using group theory is reported. These molecules serve to illustrate the concept of ligand group orbitals (LGOs) and subsequent construction of MO energy diagrams on the basis of molecular symmetry requirements.

The geometrical structures, bonding characteristics, Raman spectra, and molecular orbitals of hexagonal and tetrahedral Cr-doped CdX molecules have been investigated using density functional theory calculations at the B3LYP/LANL2DZ level. The structures of Cr-doped CdX molecules had obvious distortions compared with pure CdX clusters, especially CdCr2Se3 and CdCr2S3 clusters. The Mulliken charges of Cr atoms were negative and were lower than those of Cd atoms in the corresponding structures. Raman spectra showed that there was the vibration of the Cr-Cr bond in Cr-doped CdX molecules. Wiberg bond indices (WBI) values show that there were Cr-Cr bonds in some clusters. WBI values have also revealed that bonds between Cr and Te, Se, S were stronger than those between Cd and X atoms. Finally, molecular orbital observations indicate that the transitions in doped structures were from d orbital to d orbital, which is different from undoped structures. [ABSTRACT FROM AUTHOR]

Bonding in six-coordinate complexes based on Group 13 elements (B, Al, Ga, In, Tl) is usually considered to be identical to that in transition-metal analogues. We herein demonstrate through sophisticated electronic-structure analyses that the bonding in these Group 13 element complexes is fundamentally different and better characterized as electron-rich hypervalent bonding with essentially no role for the d orbitals. This characteristic is carried through to the molecular properties of the complex. [ABSTRACT FROM AUTHOR]

We wish to understand how a transition-metal catalyst can be rationally designed so as to selectively activate one particular bond in a substrate, herein, C−H and C−C bonds in ethane. To this end, we quantum chemically analyzed the activity and selectivity of a large series of model catalysts towards ethane and, for comparison, methane, by using the activation strain model and quantitative molecular orbital theory. The model catalysts comprise d10 ML n complexes with coordination numbers n=0, 1, and 2; metal centers M=Co−, Rh−, Ir−, Ni, Pd, Pt, Cu+, Ag+, and Au+; and ligands L=NH3, PH3, and CO. Our analyses reveal that rather subtle electronic differences between bonds can be exploited to induce a lower barrier for activating one or the other, depending, among other factors, on the catalysts electronic regime (i.e., s-regime versus d-regime catalysts). Interestingly, the concepts and design principles emerging from this work can also be applied to the more challenging problem of differentiating between activation of the C−H bonds in ethane versus those in methane. [ABSTRACT FROM AUTHOR]