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The N-(4-nitrophenyl)methacrylamide homopolymer (poly(4NPMA)) and copolymer of limonene with N-(4-nitrophenyl)methacrylamide (4NPMA-co-LIM) have been synthesized and characterized by FT-IR and NMR spectroscopic methods. The spectroscopic properties of poly(4NPMA) and 4NPMA-co-LIM were predicted using Density Functional Theory (DFT) calculations. The results have been compared with observed values, and they match with each other. Frontier orbital analysis (FMOs), global reactivity descriptors, MEP as well as Mulliken atomic charge were calculated with same method for poly(4NPMA) and 4NPMA-co-LIM. The physical properties of homopolymer of NPMA and its copolymer with D-Limonene were compared and evaluated. Thermal stabilities of homo and copolymer were investigated.

A localized bond orbital analysis of the bonding in dioxygen and related species provides a unique fundamental insight into its bonding characteristics. It reveals the coalescence of the molecular orbital and valence bond/Lewis approaches and clearly demonstrates that the often stated inability of valence bond theory to describe the bonding of O2 is a myth. The analysis indicates that the σ-bond strength of 3O2 is not weak as previously believed and accounts for much of its enhanced stability compared with hydroperoxyl. We attribute the stability and persistence of 3O2 to a combination of this attribute and favorable maximization of exchange coupling between the valence electrons.

The first isolable Ge5-spiropentadiene 1 was synthesized via the reduction of (iPr3Si)2NGeCl (3) with potassium. The crystal structure of 1 reveals a spirocyclic Ge5 skeleton containing two Ge-Ge double bonds (avg. 2.34 A), which are fettered in two Ge3 rings with a dihedral angle of 70.193°. The DFT calculations and orbital analysis show that the σ-delocalization of the Ge5 skeleton and the 2π-delocalized aromatic Ge3 rings enhance the stability of molecule 1.

Main group cluster compounds have attracted increasing attention in the past decades. Despite recent developments in their synthesis, the description of their electronic structures is usually limited to simply applying Wade's rule originally developed for borane compounds. This traditional approach is once again challenged by two recently reported group 14 metalloid clusters in the form of [Pd3Ge18R6]2-. In this work, we put forward a modular bonding model for these two clusters, via principal interacting orbital (PIO) analysis. The site preference for six substituents has also been analyzed.

Dinitrogen activation in non-metallic systems has received considerable attention in recent years. Herein, we report the theoretical feasibility of N2 fixation using aminocarbenes (L) or their anionic derivatives. The molecular descriptors of L and anionic L‾, which affect the interaction of L and anionic L‾ with N2, were identified through multiple linear regression analysis. Additionally, the electron flow during C‒N bond formation was confirmed by performing intrinsic reaction coordination calculations with intrinsic bond orbital analysis for the reaction of anionic L‾ with N2.

Photoswitch triads comprising two dihydroazulene (DHA) units in conjugation with a central trans-azobenzene (AZB) unit were prepared in stepwise protocols starting from meta- and para-disubstituted azobenzenes. The para-connected triad had significantly altered optical properties and lacked the photoactivity of the separate photochromes. In contrast, for the meta-connected triad, all three photochromes could be photoisomerized to generate an isomer with two vinylheptafulvene (VHF) units and a cis-azobenzene unit. Ultrafast spectroscopy of the photoisomerizations revealed a fast DHA-to-VHF photoisomerization and a slower trans-to-cis AZB photoisomerization. This meta triad underwent thermal VHF-to-DHA back-conversion with a similar rate of all VHFs, independent of the identity of the neighboring units, and in parallel thermal cis-to-trans AZB conversion. The experimental observations were supported by computation (excitation spectra and orbital analysis of the transitions).

Magnetic response properties of 1,2,3,5-tetrazine derivatives including the newly synthesized 4,6-diphenyl-1,2,3,5-tetrazine have been studied computationally at the density functional theory (DFT) level. Calculations of magnetically induced current densities and induced magnetic fields show that the unsubstituted 1,2,3,5-tetrazine is almost as aromatic as benzene. Separating the magnetic shielding functions into molecular orbital components provided additional insights into the magnetic response. The aromatic character estimated from magnetically induced current densities and induced magnetic fields shows that NICS pi zz(0) values and ring-current strengths yield about the same degree of aromaticity, whereas NICSzz(0) and NICSzz(1) values are contaminated by sigma electron contributions. The studied 1,2,3,5-tetrazine derivatives are less aromatic than the unsubstituted one. Calculations of magnetic response properties of 4,6-diphenyl-1,2,3,5-tetrazine showed that it is the least aromatic among the studied molecules according to the ring-current criterion, while 4,6-[1,2,3,5]-ditetrazinyl-1,2,3,5-tetrazine is as aromatic as 4,6-dimethyl-1,2,3,5-tetrazine and slightly less aromatic than the unsubstituted 1,2,3,5-tetrazine.

A series of heterometallic formate framework templated by amines were solvothermally prepared. They feature the formula of [AI][CrMII(HCO2)6] (AI = NH4H2OI and M = Mn for 1, AI = CH3NH3I and M = Fe for 2, AI = CH3NH2CH3I and M = Co for 3, AI = CH3NH3I and M = Ni for 4). The title compounds exhibit isostructural niccolite architectures with differences only in the host metal ions and guest amines. Tunable ferromagnetic (FO) strength was realized in the resulting framework under the guidance of orthogonal magnetic orbital analysis of CrIII (t2g3eg) and MII (t2g3eg2 for MnII, t2g4eg2 for FeII, t2g5eg2 for CoII, t2g6eg2 for NiII) ions. The magnetic ordering temperatures derived from the experimental magnetic measurements for 1–4 are lower than 2, 10.3, 7.6, and 22.0 K, respectively. Notably, thanks to the weak FO coupling between CrIII and MnII ions, compound 1 displays a large magnetocaloric effect bearing the maximum of magnetic entropy change (−ΔSmmax) up to 43.9 J kg–1 K–1 with ΔH = 7 T and T = 3.5 K, lar...

This study was conducted to investigate the effect of various substituents on the Cr=C bond in the [(OC)5Cr=C(OEt)-para-C6H4X] complexes using B3LYP*-based quantum mechanical calculations. In this respect, the study evaluates the influence of electron withdrawing and donating groups on the Cr=C bond distances and topological properties and correlates the calculated parameters with the Hammett and Brown constants for the para-substituted (σp and σ p + , respectively) functional groups. Also, the frontier orbital analysis was used to show the electronic structure of complexes and the percentage composition in terms of the defined groups of frontier orbitals was evaluated. To obtain insight into the physical nature of Cr=C bond bonds, we extensively used energy decomposition analysis and Bader’s Quantum Theory of Atoms-in-Molecules (QTAIM). With this aim, in addition to examining the bond critical points properties, we apply Pendas’ Interacting Quantum Atoms (IQA) scheme, which enables the rigorous and physical study of Cr=C bonds in these complexes.

The gas phase proton transfer process in 1,2,4-triazolium dinitramide (TD) was studied using second-order perturbation theory to determine how the presence of one and two water molecules modifies the potential energy surface that connects the ion pair to the neutral pair. The presence of one water molecule can introduce small proton transfer energy barriers that separate the ion pair from the lower-energy neutral pair. These energy barriers are easily surmounted. Reaction paths were determined for single proton transfers and double proton transfers via one water molecule. In the presence of two water molecules, the global minimum is an ion pair, as are most of the lower-energy local minima. Energy barriers for single, double, and triple proton transfers were also found for TD in the presence of two water molecules. One TD ion pair structure with two water molecules has no corresponding neutral pair energy minimum. A quasi-atomic orbital analysis is used to understand the nature of the bonding in the various species studied in this work.

A detailed analysis of the C(sp3)−H activation process by vinylidene AuI complexes is described based on an intrinsic bond orbital analysis. Based on our analysis this event can be divided into three phases: (i) hydride transfer, (ii) C−C bond formation, and (iii) σ to π rearrangement of the lone pair coordinated to Au. Small perturbations of the system lead to either a concerted asynchronous reaction, or a stepwise reaction featuring an intermediate with a C-H-C three-centre two-electron (3c–2e) bond. The role of π-donating substituents is highlighted and provides a way of controlling reactions of this type in future experimental studies.

In this study, we report the substituent effect on the structures, frontier orbital analysis, and spectroscopic properties (IR, 13C, 29Si NMR) in the molybdenum silylidyne complexes CpMo(CO)2(≡Si-para-C6H4X) (X = H, F, Cl, CN, NO2 , Me, OMe, NH2 , NHMe) using MPW1PW91 quantum chemical calculations. The calculated structural parameters and spectral parameters are compatible with the experimental values in similar complexes. The nature of the chemical bond between the [Cp(OC) 2Mo]− and [Si-para-C6H4X]+ fragments was explored with energy decomposition analysis (EDA). The percentage composition in terms of the defined groups of frontier orbitals for CpMo(CO)2(≡Si-para-C6H4X) complexes was investigated to explore the character of the metal–ligand bonds. The linear correlations between the properties and Hammett constants (σ p) were illustrated. Natural bond orbital analysis (NBO) was used to illustrate the electronic structure of the complexes.

We introduce Li+ involving cycloadditions between acetylene and ring-like cycloparaphenylenes (CPPs) in theory. Orbital analysis suggests an inverse electron-demand mechanism in which the diene CPP acts as an electron acceptor. Partial electron transfer to Li+ results in a reduced and localized π* orbital of CPP, giving rise to a site-selective reaction with a much smaller barrier.

Cu–S heteroadamantanes are of great interest owing to their relevance to bioproteins. New copper(I) thiolate compounds with additional N-donor functions from phenanthroline ligands have been synthesised. These complexes feature heteroadamantane cage structures with minor deviations in their construction and, therefore, a strong structural relationship. Furthermore, a decanuclear copper–sulfur cluster complex was isolated and shows known structural motifs arranged in a new fashion. Metallothioneins are natural counterparts to these complexes due to their thiolate-rich and polynuclear d10 character. In addition to the structural characterisation, theoretical studies with a triple-zeta basis set have been performed to further understand the building patterns of the reported complexes and their relevance to copper-rich metalloproteins. This includes a Wiberg bond analysis and a full orbital analysis of selected heteroadamantanes to highlight the bonding interactions that connect the copper–sulfur skeletons.

The effect of methanol group on absorption of SO2 by diamine compound was investigated via density functional theory. It was observed that the presence of methanol group increases the binding energy of absorption. According to the result of binding energy, the di-methanol-diamine (D-b) structure can be the best diamine for SO2 absorption and the results of Gibbs energy verified the most thermodynamically favorable structure. According to the weak energy analysis, the absorption interactions in D-b are both vdW and HB interactions. The result of second-order perturbation energy showed that the interaction of the donor atom of diamine with antibonding orbital of S-O (BD*S) in D-b is the highest which points to the most stable structure. According to molecular frontier orbital analysis, it can be concluded that the absorption of SO2 on the diamines is not very strong and desorption of SO2 would be easier than that the strong chemical absorption.

Often have you heard that complexes containing close Au(I) contacts are strongly influenced by what has come to be known as aurophilic interactions. In this work, local orbital analysis is carried out to separate competing metallophilic and other weak interactions at the correlated level in three selected molecular crystals. We carefully separate and discuss the different contributions to the total interaction energy of dimers and trimers according to their spatial location, and identify the relative weight in binding. Changes according to the orientation of the monomers have also been computed. Our results show that although metallophilic contacts contribute to the overall stability and the structure of the crystals, they are not at all dominant, and ligand–ligand interactions can easily outweigh the latter.

Decomposing chemical interactions into bonds and other higher order interactions is a common practice to analyse chemical structures, and gave birth to many chemical concepts, despite the fact that the decomposition itself might be subjective in nature. Fragment molecular orbitals (FMOs) offer a more rigorous alternative to such intuition, but might be less interpretable due to extensive delocalisation in FMOs. Inspired by the Principal Component Analysis in statistics, we hereby present a novel framework, Principal Interacting Orbital (PIO) analysis, that can very quickly identify the "dominant interacting orbitals" that are semi-localised and easily interpretable, while still maintaining mathematical rigor. Many chemical concepts that are often taken for granted, but could not be easily inferred from other computational techniques like FMO analysis, can now be visualised as PIOs. We have also illustrated, through various examples covering both organic and inorganic chemistry, how PIO analysis could help us pinpoint subtle features that might play determining roles in bonding and reactions.

In this comprehensive study on unsaturated phosphorus compounds of the type R-P=CR2, R-P=N-R, and R-P=P-R, we investigated how the electronic, spectroscopic, and geometric parameters are influenced by different substituents by means of ab initio and DFT methods. The parent systems are studied with highly accurate theoretical methods and used to benchmark DFT methods. The substituent effects are rationalized based on orbital analysis of DFT calculations for phos-phaalkenes, iminophosphanes, and diphosphenes in comparison with their analogous alkenes and imines. Theoretical data are also compared to experimental data if available. This study provides a broad picture of the use of DFT methods for unsaturated main group systems. Trends obtained from this study will enable a rational molecule design for selective manipulation of electronic and geometric properties.

A detailed orbital analysis of two seemingly ordinary classes of complexes of group 12 dications, [M(NH3)4]2+ and [M(PH3)4]2+, M = Zn, Cd, Hg, holds a surprise. The PH3 complexes are text-book examples of tetrahedral bonding, but in the ammine complexes calculations reveal a remarkable degree of mixing between occupied M (n-1)d and NH3 σπ orbitals. A perturbation-based Fock matrix examination traces the origin of this mixing to an energy resonance and improved overlap of interacting orbitals for NH3 ligands. The possibility of probing this anomalous mixing with valence-to-core X-ray emission spectroscopy (V2C XES) is discussed.

This chapter deals with cheletropic reactions and higher order and multicomponent cycloadditions. The orbital mechanisms of cheletropic reactions are described and selection rules are provided. Singlet carbene cycloadditions including periselectivity and site selectivity, and cheletropic addition and extrusion of sulphur dioxide are presented. The cheletropic extrusions of nitrogen and carbon monoxide are also exemplified. Higher order cycloadditions involving more than 6 electrons are described which include 8-electron [4 + 4] photodimerizations and 10-electron [6 + 4] and [8 + 2] cycloadditions. The stereoselectivity of [6 + 4] cycloadditions has been shown mechanistically. Examples of cycloadditions involving more than 10 electrons including [14 + 2] cycloaddition are provided. Multicomponent cycloadditions with reference to [2 + 2 + 2] and [2 + 2 + 2 + 2] cycloadditions are described. Finally a frontier orbital analysis of cycloaddition involving more than two components is presented.

We report the synthesis and X-ray characterization of several oxaphosphirane tungsten(0) complexes especially designed to analyse the intramolecular W–CO(lone pair)⋯π(arene) interaction. The unexpected behaviour of this interaction in the solid state of oxaphosphirane complexes with different degrees of fluorination is rationalized by means of DFT calculations using orbital analysis and Bader's theory of “atoms-in-molecules”.

Ever since the proposal of the exotic concept “planar tetra-coordinate carbon” (ptC), continuous endeavors have been hotly devoted to the design and characterization of molecules with planar tetra- or hyper-coordinate atomic centers. In sharp contrast to the big ptC family, examples with the planar penta-coordinate carbon (ppC) have remained very scarce, only including CAl 5 + , CAl 4 Be, CAl 3 Be 2 , CAl 2 Be 3 2 and CBe 5 E (E = Al, Ga). To enrich the member of ppC, in this work, we report our global isomeric characterization of CAl 4 X + (X = Al, Ga, In and Tl) at the CCSD(T)/def2-TZVPP//B3LYP/def2-TZVP level with zero-point energy correction, among which, to our knowledge, systems with X = Ga, In and Tl have not been considered previously. For CAl 5 + , besides confirming previous computational study that ppC is the ground structure, we find a new isomer (4th) among the former seven species here. Promisingly, by means of the structural and orbital analysis, CAl 4 Ga + is a novel ppC structure though the penta-coordinate ligands of C are not average due to the Al → Ga substitution. For the heavier CAl 4 X + (X = In and Tl), there does not exist a ppC structure and the global isomer can formally be considered as an X + adsorbed to the neutral T d -like CAl 4 . In the order of X = Al, Ga, In and Tl, the preference of ppC over the T d -C decreases for CAl 4 X + , which could be interpreted by the decreased covalent ability. The newly disclosed CAl 4 Ga + awaits future mass spectrometry characterization.

Bacterial resistance to standard (i.e., β-lactam-based) antibiotics has become a global pandemic. Simultaneously, research into the underlying causes of resistance has slowed substantially, although its importance is universally recognized. Key to unraveling critical details is characterization of the noncovalent interactions that govern binding and specificity (DD-peptidases, antibiotic targets, versus β-lactamases, the evolutionarily derived enzymes that play a major role in resistance) and ultimately resistance as a whole. Herein, we describe a detailed investigation that elicits new chemical insights into these underlying intermolecular interactions. Benzylpenicillin and a novel β-lactam peptidomimetic complexed to the Stremptomyces R61 peptidase are examined using an arsenal of computational techniques: MD simulations, QM/MM calculations, charge perturbation analysis, QM/MM orbital analysis, bioinformatics, flexible receptor/flexible ligand docking, and computational ADME predictions. Several key molecular level interactions are identified that not only shed light onto fundamental resistance mechanisms, but also offer explanations for observed specificity. Specifically, an extended π–π network is elucidated that suggests antibacterial resistance has evolved, in part, due to stabilizing aromatic interactions. Additionally, interactions between the protein and peptidomimetic substrate are identified and characterized. Of particular interest is a water-mediated salt bridge between Asp217 and the positively charged N-terminus of the peptidomimetic, revealing an interaction that may significantly contribute to β-lactam specificity. Finally, interaction information is used to suggest modifications to current β-lactam compounds that should both improve binding and specificity in DD-peptidases and their physiochemical properties.

TcO3 + and TcO3(OH) along with their S and Se analogs, TcS3 +, TcSe 3 + ,TcS3(OH) and TcSe3(OH), have been analyzed employing the hybrid meta-GGA functional TPSS. Charge, geometry, frontier orbital analysis based on the optimized structure have been done as a function of type of an atom bonded to Tc. The effect of addition of OH− group to TcS3 +, TcSe 3 + and TcO3 + on geometrical and electronic properties is discussed. Rotational barrier of the O–H bond for title molecules are calculated and discussed.

We present a method to analyze the origin of molecular optical activity in terms of orbital contributions and rotatory strength in configuration space. The method uses quantities already available at completion of standard linear-response calculations of specific rotation and requires minimal manipulation. Preliminary application to (1S,4S)-norborne-none and (P)-2,3-pentadiene shows that only a few orbitals (6 and 4, respectively) contribute significantly to the specific rotation and can be used directly for a qualitative interpretation of this fundamental property.

A combination of computational techniques was used to study the phosphorescent emission of complexes with general formula [Cu 3 ( μ -dppm) 3 ( μ 3 - η 1 -C≡CAr) 2 ]BF 4 , with Ar = aryl. The calculated S 0 –T 1 transition energies are in good agreement with the experimental emission maxima. Natural Transition Orbital analysis of the lowest triplet states indicates that the emission largely originates from a π → π* excitation on one of the two acetylide ligands with only a marginal participation of the trinuclear copper(I) cluster, unlike previously proposed.

The binding behaviors of eight bivalent metalloporphyrins (MPs) (MZn, Mg, Cu, Mn, Fe, Co, Ni, and Cd) with NH3 were investigated by density functional theory. For both MPs and corresponding complexes MPs-NH3, good linear correlations are found between the partial charge on metal M and that on atom N (nitrogen of porphyrin) as well as the MN bond length. Natural population and frontier orbital analysis demonstrate that charge transfer in CoP-NH3 is much easier and greater. As a consequence of the charge transfer and the hybridization of molecular energy levels, striking disparities of electronic properties of MPs-NH3 are observed. Particularly, a modest linear relationship is obtained between the magnitude of charge transfer and the binding energy. The much greater Fukui functions of CoP, together with its larger binding strength, suggest that CoP is more favorable to the interaction with NH3, which might be a promising sensing material to response NH3. © 2013 Wiley Periodicals, Inc.

The nature of the Ga-Ga bonding in Na2[Arx*GaGaArx*] (Arx* = C6H3-2,6-(C6H5)2) has been investigated and compared with that of in H2[Arx*GaGaArx*] using electron localization function (ELF) and orbital analysis. The calculation results show that in Na2[Arx*GaGaArx*], the Ga-Ga interaction is a non-classical triple bond, the heart of Na2[Arx*GaGaArx*] is the Ga2Na2 cluster rather than a simple Ga-Ga bond, and the contribution of the sodium atoms to the short Ga-Ga bond length is considerable. As the two sodium atoms are substituted by two hydrogen atoms, the Ga-Ga bond is replaced by two 3-center, 2-electron (3c-2e) Ga-H-Ga covalent bridged bonding.

We report results of hyperpolarizability calculations on CdnXn (X: S, Se and Te; n = 1–10) clusters. Our results show that the geometric configurations of different types of clusters under investigation are quite similar at specific values of n. Both static and frequency dependent components of first and second order hyperpolarizability tensors of CdnSn, CdnSen and CdnTen are compared. It is observed that in general nonlinear optical coefficients show identical variation in all the cluster materials. The present investigation also manifests the improvement of these coefficients due to the introduction of asymptotically correct generalized gradient approximation functional over the local density functional and normal gradient corrected functional. Symmetrized fragment orbital analysis has been performed to provide explanation of the observed hyperpolarizability variation. We also analyse how geometries with closely lying energy values influence the hyperpolarizabilities of these cluster materials.

Using hybrid density functional theory and a relatively large basis set, the lowest energy equilibrium structure, vibrational spectrum, and natural orbital analysis were obtained for magnesium diboride clusters [(MgB2)x for x=1,2, and 3]. For comparison, boron clusters [Bx for x=2,4, and 6] were also considered. The MgB2 and (MgB2)2 showed equilibrium structures with the boron atoms in arrangements similar to what was obtained for pure boron atoms, whereas, for (MgB2)3 a different arrangement of boron was obtained. From the population analysis, large electron density in the boron atoms forming the clusters was observed.

Six groups of diastereomeric 2,4-disubstituted adamantanes were studied with DFT–GIAO–NBO (natural orbital analysis) methods. The calculated 13C chemical shifts reproduce well the experimental data. It was found that among all diastereomers, those bearing substituents in δ-syn-axial positions showed the largest overall deshielding, i.e. the sum of all 13C chemical shifts [Σδ(13C)] was the greatest and also had the highest delocalization contribution to the molecular energy evaluated with NBO. The higher delocalization energy is proposed to be the origin of the deshielding δ-syn-axial effect. Copyright © 2008 John Wiley & Sons, Ltd.

The reactions of 1-pentenyl decomposition system have been studied extensively at the B3LYP/6-311++G∗ ∗ level with Gaussion 98 package. The potential energy surface with zero-point energy correction was drawn. All reaction channels were fully investigated with the vibrational mode analysis, frontier orbital analysis and electron population analysis to confirm the transition states and reveal the reaction mechanism.

To better understand the origin and difference associated with chemical stability, water resistance, and shearing viscosity of three types of different oxidized modified starch-based adhesives, a detailed theoretical investigation from a molecular viewpoint has been performed using the AM1 semiempirical level and the DFT-B3LYP level, respectively. As a result, our findings suggest that, by Mulliken population analysis (MPA), frontier orbital analysis, and electrostatic potential (EP) analysis based on B3LYP/6-31G calculations, the chemical stability, water resistance, and shearing viscosity of the oxidized modified starch-based adhesives are uniformly improved and corresponding difference for each property presents an identical order: the oxidized grafted cross-linked starch-based adhesive > the oxidized grafted starch-based adhesive > the oxidized starch-based adhesive, which is well consistent with experimental results.

The equilibrium geometries, energies, harmonic vibrational frequencies, stability, and aromaticities for the [Formula: see text], E 4 Fe , and [ Fe (η4 - E 4)2]2- ( E = N, P, As, Sb, and Bi ) species are studied using density functional theory (DFT). The ground states of the E 4 Fe and [ Fe (η4 - E 4)2]2- systems are predicted to be Cs and D4d structures, respectively. Orbital analysis indicates that the orbital interactions between the π orbitals of the ligands and the atomic orbitals of the d 6 iron center are the main bonding scheme for these [ Fe (η4 - E 4)2]2- (D4d) complexes. The stability of the [ Fe (η4 - E 4)2]2- complexes exhibits the order P > As > Sb > Bi > N for E. On the basis of comparison with the known ferrocene, the NICS analysis confirms that the [ Fe (η4 - E 4)2]2- (D4d) as well as ferrocene are aromatic. The dissected NICS reveals that the aromaticities of the [ Fe (η4 - E 4)2]2- (D4d) are primarily attributed to the effects of their E–E π bonds and Fe lone pairs.

By using broken-symmetry hybrid-DFT (UB3LYP and UB2LYP) calculation, the effective exchange integrals (J values) of [Cr(C5(CH3)5)2]+[TCNE]−[Cr(C5(CH3)5)2]+ and [Mn(C5(CH3)5)2]+[TCNQ]−[Mn(C5(CH3)5)2]+ were determined theoretically. Those calculated models were reduced to 3-spin-sites models from X-ray crystallographic data of charge transfer 3D crystal. The calculated results showed that effective exchange integrals were positive and the signs of spin densities on the cyclopentadienyl rings were negative. These results supported the so-called McConnell I mechanism for ferromagnetism proposed by Kollmar et al. and our previous calculations. Natural orbital analysis made it clear that the orbital overlap between SOMO on metals and SOMO on TCNE or TCNQ cations was nearly zero. These results indicated that orbital orthogonality was an important key factor for explaining the ferromagnetism of those systems.

Density functional theory as well as Møller-Plesset investigations has been carried out on tetrafluoro cyclobutadiene, C4F4, to explore the origin of its nonplanarity. Although Petersson et al. (Petersson, E. J.; Fanuele, J. C.; Nimlos, M. R.; Lemal, D. M.; Ellison, G. B.; Radziszewski, J. G. J. Am. Chem. Soc. 1997, 119, 11122-11123) had earlier predicted a nonplanar geometry of this compound on the basis of spectral and bond orbital analysis, the explanation of the same from a more fundamental point of view is still missing. In the present study, we provide a heuristic explanation for the origin of nonplanarity of C4F4. The two major driving forces behind this nonplanar geometry are the unusual aromaticity of this cyclic homoatomic 4pi electron system and the second-order Jahn-Teller effect (SOJTE). These driving forces can well be explained by various energy and density parameters and also by nucleus-independent chemical shift (NICS) values. Aromaticity of a cyclic homoatomic 4pi electron system is quite remarkable. The enhancement of pi- delocalization as evidenced from molecular orbital analysis may be attributed to s-ppi mixing in nonplanar C4F4.

Studying the interaction of some atmospheric gases (H2O, HCN, NH3, SO3 and H2S) with 3PT oligomers is important in the development of polymeric sensors for gas detection. In the present study, we studied the relaxed geometries, interaction energies, charge analysis, HOMO-LUMO orbital analysis, and UV-vis spectra of all interacted systems using first-principles density functional theory (DFT). All these analyses indicated the potential of polythiophene as an inexpensive polymeric sensor for the analytes mentioned. Interaction energy values of -19.90, -19.66, -14.01, -8.70, and -4.76 kJ mol(-1) were achieved for adsorption of SO3, H2O, NH3, HCN, and H2S on 3PT, respectively. Consequently, clarification of their physical parameters became the major focus of this study.

Very recently, a series of endohedral fullerenes Sc2O@C2n (n = 35-47) were facilely produced. However, only two of them have been further characterized so far. Theoretically, we studied another discandium oxide endohedral fullerene without any characterizations, Sc2O@C84, which is the second most-abundant species in terms of relative heights of all mass spectrum peaks. Two thermodynamically stable isomers with isolated pentagon rule-obeying cages were found, namely, Sc2O@C2v(51575)-C84 and Sc2O@C1(51580)-C84. This is the first case that an endohedral fullerene containing the C2v(51575)-C84 cage acts as the lowest-energy isomer, and it is the first report of a clusterfullerene containing the C1(51580)-C84 cage. The endohedral Sc2O cluster can keep its ideal structure after encapsulation, while both C84 cages have deformed dramatically. Orbital analysis suggests that nucleophilic and oxidization reactions of both isomers should take place on the cage, while regioselectivity of Sc2O@C2v(51575)-C84 and Sc2O@C1(51580)-C84 is different due to their different characteristics of the highest occupied orbital distribution. Two-dimensional electron localization function and Laplacian of electron density maps unambiguously indicate strong electrostatic interactions exist between one scandium atom and the oxygen one. Meanwhile, overlaps of occupied metal atom orbitals and the cage ones along with Mayer bond order analysis identify that covalent interactions between a scandium atom and each C84 cage cannot be neglected. At last, (13)C NMR, UV-vis-NIR, and IR spectra of both Sc2O@C84 isomers were simulated theoretically. Because of their structural difference, all spectra between two isomers are significantly divergent. Consequently, these spectra are helpful to distinguish Sc2O@C2v(51575)-C84 and Sc2O@C1(51580)-C84 in further experimental characterizations.

A detailed computational study is performed on the radical-molecule reactions between HCO/HOC and ethylene ( C 2 H 4) at the Gaussian-3//B3LYP/6-31G(d) level. For the HCO + C 2 H 4 reaction, the most favorable pathway is the direct C -addition forming the intermediate H 2 CCH 2 CHO , followed by a 1,2- H -shift leading to H 3 CCHCHO . Subsequently, there are two highly competitive dissociation pathways for H 3 CCHCHO : one is the formation of the direct H -extrusion product H 2 CCHCHO + H , and the other is the formation of C 2 H 5 + CO via the intermediate H 3 CCH 2 CO . The overall reaction barrier is 14.1 and 14.6 kcal/mol respectively, at the G3B3 level. The quasi-direct H -donation process to produce C 2 H 5 + CO with the barrier 16.5 kcal/mol is less competitive. Thus, only at higher temperatures, the HCO + C 2 H 4 reaction could play a role. In contrast, the HOC + C 2 H 4 reaction just need to overcome a small barrier 2.0 kcal/mol to generate C 2 H 5 + CO via the quasi-direct H -donation mechanism. This is suggestive of the potential importance of the HOC + C 2 H 4 reaction in combustion processes. However, the direct C -addition channel is much less competitive. The present kinetic data and orbital analysis show that the HCO radical has much higher reactivity than HOC , although the latter is more energetic. Till now, no kinetic study on the HOC radical has been reported, the present study can provide useful information on understanding the reactivity and depletion mechanism of the energetic HOC radical.

The doubly Si-bridged ansa -tungstenocene, [W(η 5 -C 5 H 3 ) 2 (SiMe 2 ) 2 ], ( a -Si 2 Cp 2 W) is calculated to have singlet and triplet states of comparable energy, in contrast to other tungstenocenes which have triplet ground states. Therefore, on an SCF energy surface there is no barrier to formation of a sigma complex with methane, and formation of a methyl hydride is exo-energetic by −125 kJ mol −1 . Orbital analysis of the tungstenocenes shows that the singlet ground state is favoured by a ring conformation that stabilizes the 2b 1 orbital by back donation, and that a double ansa bridge promotes this ring conformation.

In this work, we present a theoretical study (based on DFT-calculations) of the electronic properties of compounds crystallising in a NH4Pb2Br5 type structure in a wide pressure range. The main focus of this study is to elucidate the nature of bonding of the ns2-cations at ambient and elevated pressure. For a better understanding of the structure and bonding, the DOS of these compounds are evaluated and discussed on the basis of a simple model assuming mainly ionic interactions. The calculations are complemented by an orbital analysis using the crystal orbital Hamilton population (COHP) and an analysis of the electronic density topology with the electron localisation function (ELF). Structural and theoretical investigations give results that are in excellent agreement: The DFT-calculations confirm the existence of bonding interactions between the ns2-cations at elevated pressure. Our study indicates that the “character” of the additional electron pair changes with increasing pressure from nonbonding to bonding in agreement with a simple model system of two interacting ns2-cations. Hochdruckuntersuchungen an Verbindungen mit NH4Pb2Br5-Struktur Teil II: Elektronische Struktur und ihre Anderung unter hohem Druck Auf der Basis von DFT-Rechnungen werden theoretische Untersuchungen an Verbindungen, die im NH4Pb2Br5-Strukturtyp kristallisieren, in einem grosen Druckbereich durchgefuhrt. Das Hauptziel dieser Untersuchungen ist die Charakterisierung des Bindungszustandes der ns2-Kationen bei niedrigem und hohem Druck. Zum besseren Verstandnis der Struktur dieser Verbindungen und der Bindungssituation, wird die Zustandsdichte dieser Verbindungen anhand eines einfachen Modells diskutiert, das vorwiegend ionische Wechselwirkungen postuliert. Die Rechnungen werden durch Analysen der COHP und der Topologie der Elektronendichte mit der Elektronenlokalisierungsfunktion (ELF) vervollstandigt. Theoretische Untersuchungen und die Auswertung experimenteller Daten liefern Ergebnisse, die sehr gut miteinander ubereinstimmen: Die DFT-Rechnungen bestatigen die Existenz bindender Wechselwirkungen zwischen nah benachbarten ns2-Kationen bei hohem Druck. Der Charakter des zusatzlichen Elektronenpaares am ns2-Kation andert sich also von nahezu nichtbindend zu bindend in Ubereinstimmung mit einem einfachen Modellsystem fur zwei miteinander wechselwirkende ns2-Kationen.

Density functional theory has been used to explore the energetics and bonding of the symmetric and unsymmetric isomeric sandwich complexes (η 5 -C 5 H 5 ) 2 M, (η 4 -C 4 H 4 )M(η 6 -C 6 H 6 ), and (η 3 -C 3 H 3 )M(η 7 -C 7 H 7 ) (M = Fe, Ru, Os). For each metal atom, the symmetric “5–5” metallocene was found to be the most stable isomer, with the “4–6” and “3–7” isomers ca. 40 and 80 kcal/mol higher in energy, respectively. Bonding analysis shows that (η 4 -C 4 H 4 )Fe(η 6 -C 6 H 6 ) is best considered as a (η 4 -C 4 H 4 )Fe fragment interacting with a C 6 H 6 ligand, although the interactions become less separable as the metal is changed to Ru and Os. Similarly, the dominant bonding in (η 3 -C 3 H 3 )M(η 7 -C 7 H 7 ) is that of a M(η 7 -C 7 H 7 ) perturbed by the interaction with a C 3 H 3 ligand.

A complete orbital analysis of two isoelectronic complexes of trifluorobenzene (TFB), TFB ⋯ F − and TFB ⋯ Na + , as models for anion-π and cation-π interactions, respectively, has been performed at the MP2/6-31++G** level of theory. There are important orbital differences between both interactions, which are discussed in detail herein.

A first-principles study of the dissociative adsorption of water on Ge(100)-(2 x 1) is described, on the basis of density functional theory with a cluster model of the surface. Experiments have shown that water incident on the Ge(100)-(2 x 1) surface has a very small probability of dissociative adsorption, indicating the presence of an activation barrier. This is in contrast to the analogous reaction on Si(100)-(2 x 1), which is unactivated. This difference is reproduced in the calculations, demonstrating the predictive capability of the methods used, though some caveats about basis sets are necessary. A frontier orbital analysis is used to identify the interactions that determine the transition state energy and underlie the difference between reactivity on Si and Ge.

Maps of induced current density are computed with the coupled Hartree–Fock, distributed-gauge, CTOCD-DZ method for the trannulene isomers of the hydrogenated fullerenes C20H10 and C24H12. Orbital analysis identifies ‘in-plane’ ring currents in trannulenes that obey equivalent selection rules to those for conventional annulenes. Thus, in systems of either type, 4-electron diatropicity is associated with electron counts of 4n + 2, 2-electron paratropicity with 4n.

The unrestricted Hartree-Fock (UHF) and hybrid density functional theory (HDFT) calculations have been carried out for manganese oxides. In order to elucidate magnetic properties of the species, the effective exchange integrals ( J ab ) have been obtained by the total energy difference between the highest and lowest spin states. The natural orbital analysis has also been performed for elucidation of symmetry and occupation numbers of the magnetic orbitals.

A novel Au19 nanocluster with a composition of [Au19(PhC≡C)9(Hdppa)3](SbF6)2 was synthesized (Hdppa = N,N-bis(diphenylphosphino)amine). Single crystal X-ray structural analysis reveals that the cluster comprises a centered icosahedral Au13 core hugged by three V-shaped PhC≡C–Au–C≡C(Ph)–Au–C≡CPh motifs. Such motif is observed for the first time in an alkynyl-protected gold nanocluster. The Au19 cluster shows two main optical-absorption bands at 1.25 and 2.25 eV, confirmed by time-dependent density functional theory. Orbital analysis indicates that PhC≡C– groups can actively participate in the frontier orbitals of the whole cluster. The new Au19 cluster and the novel alkynyl–gold motif open the door to understanding the alkynyl–gold interface and discovering many potential members of this new class of gold clusters.