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In the present work, the lowest energy structures and electronic properties of Pt15 clusters are investigated using first-principles calculations. The catalytic activity for the oxygen reduction reaction is analyzed and discussed.

Total energy computations using density functional theory are typically carried out at a zero temperature; thus, entropic and thermic contributions to the total energy are neglected, even though functional materials work at finite temperatures. This book chapter investigates the Boltzmann populations of the fluxional Be6B11− and chiral Be4B8 isomers at finite temperature estimated within the framework of density functional theory, CCSD(T), and statistical thermodynamics. A couple of steps are taken into account to compute the Boltzmann populations. First, to identify a list of all possible low-energy chiral and achiral structures, an exhaustive and efficient exploration of the potential/free energy surfaces is carried out using a multi-level and multi-step global hybrid genetic algorithm search coupled with Gaussian code. Second, the thermal or so-called Boltzmann populations were computed in the framework of statistical thermodynamics for temperatures ranging from 20 to 1500 K at DFT and CCSD(T) theoretical levels. The results show the effects of temperature on the distribution of isomers define the putative global minimum at finite temperature due to the minimization of the Gibbs free energy and maximization of entropy. Additionally, we found that the fluxional Be6B11− cluster is strongly dominant at hot temperatures, whereas the chiral Be4B8 cluster is dominant at room temperature. The methodology and results show the thermal effects in the relative population hence molecular properties.

Correction for ‘Structure effects of Pt15 clusters for the oxygen reduction reaction: first-principles calculations’ by Peter L. Rodríguez-Kessler et al., Phys. Chem. Chem. Phys., 2023, https://doi.org/10.1039/d2cp05188e.

Density functional theory (DFT) is currently one of the most utilized theoretical approaches to analyze physical and chemical properties of metal clusters, which are of interest in economically important applications such as catalysis. In this respect, the important role of temperature has been scarcely considered mainly because this variable is not part of the DFT model and other theoretical ab initio schemes. In this work, we present an ab initio molecular dynamics study of Pd8 and Pd7Au1 clusters to understand, to a degree, the effect of doping on the structural stability of palladium clusters as a function of temperature. A combined strategy using both empirical potential and DFT calculations is employed to obtain lowest-energy configurations for Pd8 and Pd7Au1 clusters, which are later subject to Born–Oppenheimer molecular dynamics simulations at finite temperatures. The structural stability as a function of temperature is evaluated through an analysis of the total energy dispersion with respect to the average energy of clusters at different thermodynamic states. Results show that the effect of doping Pd cluster with one Au atom gives rise to a decreasing of the structural stability. In the range of temperatures studied, atomic diffusion is not observed for Pd8 cluster, while Pd7Au1 cluster shows Pd-Au dimer diffusion at 300 K toward different faces of the 6-atom Pd octahedron structural motif. Preliminary data suggest that melting transition is about 250 K for this bimetallic cluster.

Herein we introduce a strategy employing lithium atoms as a scaffold to stabilize an embryo for boron tubes. The systematical exploration of the potential energy surface via evolutionary algorithms allowed us to find that Li2B24 adopts a tubular structure formed by three stacked rings of eight borons each with two lithium atoms capping the tube. The lithium atoms are essential for stabilization because of the strong electrostatic interaction between the Li cations and the boron framework, and concomitantly, they compensate for the energy cost of distorting a quasi-planar or double ring B24 cluster.

The starting point to understanding cluster properties is the putative global minimum and all the nearby local energy minima, however, locating them is computationally expensive and difficult. The relative populations and spectroscopic properties that are a function of temperature can be approximately computed by employing statistical thermodynamics. Here, we investigate entropy-driven isomers distribution on Be6B11&minus, clusters and the effect of temperature on their infrared spectroscopy and relative populations. We identify the vibration modes possessed by the cluster that significantly contribute to the zero-point energy. A couple of steps are considered for computing the temperature-dependent relative population: First, using a genetic algorithm coupled to density functional theory, we performed an extensive and systematic exploration of the potential/free energy surface of Be6B11&minus, clusters to locate the putative global minimum and elucidate the low-energy structures. Second, the relative populations&rsquo, temperature effects are determined by considering the thermodynamic properties and Boltzmann factors. The temperature-dependent relative populations show that the entropies and temperature are essential for determining the global minimum. We compute the temperature-dependent total infrared spectra employing the Boltzmann factor weighted sums of each isomer&rsquo, s infrared spectrum and find that at finite temperature, the total infrared spectrum is composed of an admixture of infrared spectra that corresponds to the spectra of the lowest-energy structure and its isomers located at higher energies. The methodology and results describe the thermal effects in the relative population and the infrared spectra.

The starting point to understanding cluster properties is the putative global minimum and all the nearby local energy minima; however, locating them is computationally expensive and difficult. The relative populations and spectroscopic properties that are a function of temperature can be approximately computed by employing statistical thermodynamics. Here, we investigate entropy-driven isomers distribution on Be6B11− clusters and the effect of temperature on their infrared spectroscopy and relative populations. We identify the vibration modes possessed by the cluster that significantly contribute to the zero-point energy. A couple of steps are considered for computing the temperature-dependent relative population: First, using a genetic algorithm coupled to density functional theory, we performed an extensive and systematic exploration of the potential/free energy surface of Be6B11− clusters to locate the putative global minimum and elucidate the low-energy structures. Second, the relative populations’ temperature effects are determined by considering the thermodynamic properties and Boltzmann factors. The temperature-dependent relative populations show that the entropies and temperature are essential for determining the global minimum. We compute the temperature-dependent total infrared spectra employing the Boltzmann factor weighted sums of each isomer’s infrared spectrum and find that at finite temperature, the total infrared spectrum is composed of an admixture of infrared spectra that corresponds to the spectra of the lowest-energy structure and its isomers located at higher energies. The methodology and results describe the thermal effects in the relative population and the infrared spectra.

We computed the optical properties and the folded and unfolded band structure of Cu-doped KCl crystals. The calculations use the plane-wave pseudo-potential approach implemented in the ABINIT electronic structure package within the first-principles density-functional theory framework. Cu substitution into pristine KCl crystals requires calculation by the supercell (SC) method from a theoretical perspective. This procedure shrinks the Brillouin zone, resulting in a folded band structure that is difficult to interpret. To solve this problem and gain insight into the effect of cuprous ion (Cu+) on electronic properties; We unfolded the band structure of SC KCl:Cu to directly compare with the band structure of the primitive cell (PC) of pristine KCl. To understand the effect of Cu substitution on optical absorption, we calculated the imaginary part of the dielectric function of KCl:Cu through a sum-over-states formalism and broke it down into different band contributions by partially making an iterated cumulative sum (ICS) of selected valence and conduction bands. As a result, we identified those interband transitions that give rise to the absorption peaks due to the Cu ion. These transitions include valence and conduction bands formed by the Cu-3d and Cu-4s electronic states. To investigate the effects of doping position, we consider different doping positions, where the Cu dopant occupies all the substitutional sites replacing host K cations. Our results indicate that the doping position's effects give rise to two octahedral shapes in the geometric structure. The distorted-twisted octahedral square bipyramidal geometric-shape induces a difference in the crystal field splitting energy compared to that of the perfect octahedral square bipyramidal geometric-shape.

The structure, bonding, and stability of clusters with the empirical formula CE5- (E=Al-Tl) have been analyzed by means of high-level computations. The results indicate that, whereas aluminum and gallium clusters have C2v structures with a planar tetracoordinate carbon (ptC), their heavier homologues prefer three-dimensional C4v forms with a pentacoordinate carbon center over the ptC one. The reason for such a preference is a delicate balance between the interaction energy of the fifth E atom with CE4 and the distortion energy. Moreover, bonding analysis shows that the ptC systems can be better described as CE4- , with 17-valence electrons interacting with E. The ptC core in these systems exhibits double aromatic (both σ and π) behavior, but the σ contribution is dominating.

An intriguing structural transition from the quasi-planar form of B12 cluster upon the interaction with lithium atoms is reported. High-level computations show that the lowest energy structures of LiB12 , Li2 B12 , and Li3 B12 have quasi-planar (Cs ), tubular (D6d ), and cage-like (Cs ) geometries, respectively. The energetic cost of distorting the B12 quasi-planar fragment is overcompensated by an enhanced electrostatic interaction between the Li cations and the tubular or cage-like B12 fragments, which is the main reason of such drastic structural changes, resulting in the smallest tubular (Li2 B12 ) and cage-like (Li3 B12 ) boron structures reported to date.

We report a family of systems having a planar pentacoordinate carbon (ppC) based on the next heavier analogue of CAl5+, the ppC system par excellence. Although because of the larger size of Ga, the ppC isomer is not even a local minimum in CGa5+, a single isoelectronic substitution of Ga by smaller sized Be maximizes the bonding in the ppC form. Retaining the 18 valence electron rule, the global minimum structures of CGa4Be, CGa3Be2−, CGa2Be32−, and CGaBe43− clusters and their corresponding lithium salts have a ppC.

Herein we propose a general mechanism for the racemization of [n]helicenes up to n = 24. It is a concerted process for n = 4–7, but a multi-step mechanism is followed for n ≥ 8, involving 2n − 14 intermediates. The changes in the barriers are a delicate consequence of the steric hindrance and the π-interactions.

In this study, we report the lowest energy structure of bare Cu13 nanoclusters as a pair of enantiomers at room temperature. Moreover, we compute the enantiomerization energy for the interconversion from minus to plus structures in the chiral putative global minimum for temperatures ranging from 20 to 1300 K. Additionally, employing nanothermodynamics, we compute the probabilities of occurrence for each particular isomer as a function of temperature. To achieve that, we explore the free energy surface of the Cu13 cluster, employing a genetic algorithm coupled with density functional theory. Moreover, we discuss the energetic ordering of isomers computed with various density functionals. Based on the computed thermal population, our results show that the chiral putative global minimum strongly dominates at room temperature.

Lowest-energy structures, the distribution of isomers, and their molecular properties depend significantly on geometry and temperature. Total energy computations using DFT methodology are typically carried out at a temperature of zero K, thereby, entropic contributions to the total energy are neglected, even though functional materials work at finite temperatures. In the present study, the probability of the occurrence of one particular Be4B8 isomer at temperature T is estimated by employing Gibbs free energy computed within the framework of quantum statistical mechanics and nanothermodynamics. To identify a list of all possible low-energy chiral and achiral structures, an exhaustive and efficient exploration of the potential/free energy surfaces is carried out using a multi-level multistep global genetic algorithm search coupled with DFT. In addition, we discuss the energetic ordering of structures computed at the DFT level against single-point energy calculations at the CCSD(T) level of theory. The total VCD/IR spectra as a function of temperature are computed using each isomer’s probability of occurrence in a Boltzmann-weighted superposition of each isomer’s spectrum. Additionally, we present chemical bonding analysis using the adaptive natural density partitioning method in the chiral putative global minimum. The transition state structures and the enantiomer–enantiomer and enantiomer–achiral activation energies as a function of temperature evidence that a change from an endergonic to an exergonic type of reaction occurs at a temperature of 739 K.

Structural properties of AgnRh (n ≤ 15) clusters are investigated using a successive growth algorithm coupled with density functional theory computations. The structures of the clusters are revisited, including a detailed discussion of their electronic properties. In contrast to these previous contributions, the lowest energy structures of the clusters are planar for n = 3–6, while three-dimensional for n = 7 onward. Our present searches identify new lowest energy structures for n = 3–6 and 9–13. The most stable isomers are selected to study the adsorption of NO. The size-dependent reactivity of the clusters indicates that Rh atom acts as a more effective adsorption site for NO than Ag. Since the transition from Rh-exposed to Rh-encapsulated structures occurs at n = 9, the reactivity toward NO for AgnRh clusters with n ≤ 8 is considerably higher than that for the larger homologues. Further, the results show that doping Agn clusters with Rh increases the reactivity toward NO adsorption.

Extensive potential energy surface explorations of 25 clusters with formula E3M3+ (E = Group 14 element and M = Group 1 element) via density functional theory and high level ab initio computations reveal that the lowest energy isomer for all these systems corresponds to a nonclassical D3h star-like structure in singlet state, where three M atoms interact electrostatically with the triangular E3 core, occupying three bridging positions around it. More than 18,200 calculations were done in the search for the minima structures, starting with a first phase at PBE0/LANL2DZ and ending with an analysis of the most representative clusters at CCSD(T)/def2-TZVP//PBE0/def2-TZVP level. The title clusters represent the smallest molecular stars with three planar tetracoordinate C to Pb atoms. All these E3M3+ clusters behave like superalkali cations with small vertical electron affinity (smaller than Cs), large vertical electron detachment energy, and HOMO-LUMO energy gap. Their energetics, bonding, and electron delocalization are discussed in detail. The high stability of these clusters is reflected from the large dissociation energy needed through different dissociation channels. The electron delocalization is confirmed by the presence of two delocalized pi-electrons over the E3 core and strong diatropic response.

Two novel low-lying structures are unveiled for the Be6B11- nanocluster system: a triple-layered isomer versus a boron helix-type one, which are virtually isoenergetic and the former apes the motions of the earth-moon system. For the triple-layered cluster the B11 ring revolves like a flexible chain at room temperature, gliding freely around the Be6 prism. At elevated temperatures (1000 K), the Be6 core itself also rotates. The rotational movement has a higher energy barrier than revolution: 4.70 versus 0.22 kcal mol-1 at single-point CCSD(T). Bonding analyses suggest four-fold (π and σ) aromaticity, unprecedented for a molecular system, which offer a dilute and fluxional electron cloud that lubricates the dynamics. In contrast, the helix-type cluster contains a B11 helical skeleton encompassing a distorted Be6 prism. A large electron transfer occurs from Be6 to boron, making a boron core of formal [B11]9− charge state or higher, which presumably underlies the helical arrangement.

The preference for concave mode binding of the CpM unit with sumanene in CpM(η6-sumanene)+ (M = Fe, Ru, Os) over the convex mode is analyzed by various density functional theory based methods including (or not) dispersion and solvent effects. In the case of the iron complex, the concave-bound isomer becomes energetically more favorable than the convex form only after the proper inclusion of dispersion effects, highlighting the importance of such contributions to stabilize the former arrangement. For the ruthenium complex, both the dispersion and solvent effects should be taken into account to provide a correct trend. The noncovalent interaction index corroborates the role of dispersion in concave selectivity. Our computations also show that the presence of the counterion is not relevant for this selectivity, discarding the previously reported argument made by Okumura et al.

The lowest energy isomers of alkali-metal pentalenides, E2C8H6 (E = Li, Na, K, Rb, Cs), are inverted sandwiches. Along Li to Cs, the location of the E atoms shifts toward the points over the center of the pentalene moiety even in the presence of solvent molecules such as dimethoxyethane. Adaptive natural density partitioning analysis reveals the equivalent 10 π-bonding frameworks in the C8H62– and E2C8H6 systems. The stability of these complexes practically originates from the electrostatic interaction (84–92%) between C8H62– and [E···E]2+. While the sharp drop in interaction energy in Na complex, in comparison to that in the Li analogue, is due to the lower contribution from both electrostatic (by 31.6 kcal mol–1) and orbitalic (by 48.1 kcal mol–1) terms, for the rest of the complexes the obtained trend of interaction energy originates from the reduced ionic contacts. Although the orbital interaction is less important in these complexes, it plays an important role in deciding their geometries. The obtain...

Herein we introduce a strategy employing lithium atoms as a scaffold to stabilize an embryo for boron tubes. The systematical exploration of the potential energy surface via evolutionary algorithms allowed us to find that Li2B24 adopts a tubular structure formed by three stacked rings of eight borons each with two lithium atoms capping the tube. The lithium atoms are essential for stabilization because of the strong electrostatic interaction between the Li cations and the boron framework, and concomitantly, they compensate for the energy cost of distorting a quasi-planar or double ring B24 cluster.

Detailed knowledge of the minimum energy and low-lying structures of metal clusters is crucial to understand their physicochemical properties. In this work, the effect of van der Waals (vdW) interactions on the structure and stability of Cu-Pd clusters is investigated. With this aim, a global search algorithm that combines the basin-hopping method and density functional theory is used to explore the potential energy surface of Cu8-xPdx (x = 0, 4, 8) clusters. We present the structural motifs adopted by the low-energy isomers obtained with the PBE gereralized gradient exchange-correlation functional, and with PBE supplemented by dispersion energy corrections as given by Grimme’s D3 method. The isomeric structures obtained by PBE and PBE-D3 methods are in general quite similar, except for minor changes in some particular isomers. Global structural explorations were also performed with the meta-GGA TPSS and the hybrid PBE0 functionals, showing a reasonable agreement with the results obtained with the PBE and corrected PBE-D3 functionals. The energetics of the clusters is investigated by analyzing the binding energy per atom. Binding ;1;energies become larger when vdW forces are included, and this contribution increases from Cu8 to Pd8 and then to Cu4Pd4. Mixing between Cu and Pd atoms to form nanoalloys is favorable, a feature consistent with the well-known formation of intermetallic compounds in the bulk Cu-Pd alloys. The HOMO-LUMO gap indicates that some isomers in Cu8 and Cu4Pd4 are more reactive than the lowest energy isomer, a feature that gives a hint into the importance that low-lying isomers may have in catalytic reactions. Binding energies and HOMO-LUMO gaps present a stronger dependence on the exchange-correlation functional than the cluster structures.

We have performed a global minimum search for the multicharged ruthenium-doped germanium clusters with the formula RuGenq (n = 2–12, q = −2, – 3) using a particle swarm optimization metaheuristic coupled with density functional theory computations. Leading candidates for the lowest energy forms have been identified. Among the global minimum geometries, going from the size of n = 2 to n = 12, it is perceived that the cluster growth is directed toward the formation of an endohedral aggregate. Particularly, the half-encapsulated structures of RuGe7q and RuGe8q made the bridge between small open-shell (n = 2–6) geometries and the endohedral (n = 9–12) geometries. The endohedral constructions contain the Ru atoms at their interstitial positions. Particularly, the 10-vertex endohedral cluster RuGe102– has an unprecedented 3-connected C3v polyhedral geometry. The positive values of highest occupied molecular orbital energies of global minimum anions depict the electronic instability. The countercation effect is ...

The regioselective opening of the ring E in spirostan sapogenins provides new dihydropyran derivatives. This novel side chain is obtained after a Lewis acid mediated acetolysis followed by an alkaline workup. The reaction mechanism is analyzed via density functional theory computations, and both experimental and computational data support the formation of an oxacarbenium intermediate. The behavior of the title skeletons under acidic conditions is also investigated.

In this paper, we provide solid evidence to show that among an overwhelming structural diversity, alkaline earth metals (Ca, Sr, Ba) have the ability to form inverted sandwich compounds with C6H6, C7H7(+), and C8H8(2+) of Dnh symmetry and general formula [E-(CnHn)-E](n-6) (n = 6-8) with planar 10-π-electron aromatic cores by virtue of transferring two electrons per metal atom to the ring. However, the origin of the orbital interaction between the metals and the carbon ring is quite different; while [E-(C6H6)-E] complexes are dominated by δ-interactions, both π- and δ-interactions are important in [E-(C7H7)-E](+) and [E-(C8H8)-E](2+) complexes.

Exploration of the potential energy surfaces (PESs) of various microsolvated species associated with the microsolvation of the nitrate anion using density functional theory methods uncovers a rich and complex structural diversity previously unnoticed in the scientific literature for the [NO3(H2O)n]−, n = 1–6 clusters. Two types of interactions are at play in stabilizing the clusters: traditional water to water and charge assisted nitrate to water hydrogen bonds (HBs). The formal negative charge on oxygen atoms in nitrate strengthens hydrogen bonding among water molecules. There is outstanding agreement between available experimental data (sequential hydration enthalpies, IR spectra, and vertical detachment energies) and the corresponding expectation values obtained from our structures. Each PES is heavily populated in the vicinities of the corresponding global minimum with multiple structures contributing to the experimental properties. The last two statements, in conjunction with results from other works (see for example Phys. Chem. Chem. Phys. 2014, 16, 19241) place a warning on the generalized and naive practice of assigning experimental observations to individual structures.

The mechanism of methylation of Vaska's complex trans-[ClIr(CO)(PPh3)2] by trimethylgallium was studied and the identification of the spectroscopically detected intermediates was achieved with the aid of computational methods. The reaction pathway, computed by means of density functional theory (M05-2X-D3/def2-SVP), involves the initial formation of a chloride-bridged adduct trans-[(Cl·GaMe3)Ir(CO)(PPh3)2] to then proceeds to a transition state [(μ2-Cl,C-ClMeGaMe2)Ir(CO)(PPh3)2]. This transition state subsequently evolves to the methylated adduct [MeIr(CO)(PPh3)2·(GaMe2Cl)] to finally release the alkylated product trans-[MeIr(CO)(PPh3)2] together with GaMe2Cl.

The thermochemical behavior of four sorghum procyanidin trimers (SPT) with C4−C8 and C4−C6 interflavan bonds, in the reaction with O2− via the concerted double proton-transfer electron-transfer (CDPTET) and sequential proton-loss electron-transfer (SPLET) mechanisms, as well as with a H2O2-forming NADH-oxidase flavoenzyme, were analyzed by computational methods. Our results revealed that both CDPTET and SPLET mechanisms could be viable to develop in an aqueous medium. However, the free energies and rate constants of reaction showed that SPLET could be more favored. The SPT2 with interflavan bonds C4–C8 and C4–C6 in its most stable and predominant conformation (Compact-Extended), reached apparent rate constants of 1.07 × 106 (CDPTET) and 9.8 × 106 (SPLET) to scavenge the O2 − in aqueous media. Likewise, SPT2 could prevent binding of NAD(P)H to the NADH-oxidase flavoenzyme, suggesting the greatest potential of this procyanidin to prevent the production and activity of the O2 − in aqueous media.

As an effort to search for paramagnetic probing agents toward specific substrates, 1H NMR studies were carried out on the Dy3+ complex of a chelating cyclophane derived from DTPA (diethylenetriaminepentaacetate) and p-xylylenediamine, and the paramagnetic effects were examined on coexisting d -histidine and histamine. The lanthanide metal complex exhibits well-defined paramagnetic shifts of the psuedocontact term, owing to the highly rigid macrocyclic framework. Coexisting histamine and histidine also show sharp NMR peaks with small but significant shifts, in contrast to the spectra in the coexistence of the free metal ion. The metal chelate molecule has a large open space, in which a substrate molecule is captured and exchanged with nearby molecules. Through this exchange process, the spatial paramagnetic effect of the metal chelate extends in a long range so that coexisting substrate molecules can be probed by NMR.

The electronic and optical properties of KCl and Cu doped KCl (KCl:Cu) were calculated within full potential augmented plane wave method based on Density Functional Theory (DFT), as implemented in WIEN2k software. Calculations were carried out using two energy functional approximations, the exchange-correlation functional of Perdew, Burke and Ernzerhof (PBE96) to optimize the KCl lattice parameter, and the modified Becke-Johnson (mBJ) exchange potential in combination with the local density approximation (LDA) for correlation, to obtain the band structure. The energy bands reveal the insulating properties of KCl with a direct band gap of 8.6 eV, and the semiconductor nature of KCl:Cu with a direct band gap of 3.4 eV. From the analysis of the total and partial density of states, it is apparent that the KCl and KCl:Cu states at the Fermi level arise from Cl p states and Cu d states, respectively. Also, the optical properties reported here (dielectric function and absorption spectra) show that Cu atoms are responsible of electronic excitations occurring from Cu d valence bands to conduction bands of Cu, Cl and K with p character.

A genetic algorithm has been used to perform a global sampling of the potential energy surface in the search for the lowest-energy structures of unsupported 38-atom Cu–Pt clusters. Structural details of bimetallic Cu–Pt nanoparticles are analyzed as a function of their chemical composition and the parameters of the Gupta potential, which is used to mimic the interatomic interactions. The symmetrical weighting of all parameters used in this work strongly influences the chemical ordering patterns and, consequently, cluster morphologies. The most stable structures are those corresponding to potentials weighted toward Pt characteristics, leading to Cu–Pt mixing for a weighting factor of 0.7. This reproduces density functional theory (DFT) results for Cu–Pt clusters of this size. For several weighting factor values, the Cu30Pt8 cluster exhibits slightly higher relative stability. The copper-rich Cu32Pt6 cluster was reoptimized at the DFT level to validate the reliability of the empirical approach, which predicts a Pt@Cu core-shell segregated cluster. A general increase of interatomic distances is observed in the DFT calculations, which is greater in the Pt core. After cluster relaxation, structural changes are identified through the pair distribution function. For the majority of weighting factors and compositions, the truncated octahedron geometry is energetically preferred at the Gupta potential level of theory.

We report a family of systems having a planar pentacoordinate carbon (ppC) based on the next heavier analogue of CAl5+, the ppC system par excellence. Although because of the larger size of Ga, the ppC isomer is not even a local minimum in CGa5+, a single isoelectronic substitution of Ga by smaller sized Be maximizes the bonding in the ppC form. Retaining the 18 valence electron rule, the global minimum structures of CGa4Be, CGa3Be2-, CGa2Be32-, and CGaBe43- clusters and their corresponding lithium salts have a ppC.

The structure, bonding, and stability of clusters with the empirical formula CE

An intriguing structural transition from the quasi-planar form of B

The possible existence of H

Extensive potential energy surface explorations of twenty-five clusters with the formula E

The possible existence of H4SO5 in aqueous sulfuric acid is analyzed in detail. For bare H4SO5, the computed free energy barrier for the exergonic transformation of H4SO5 into the H2SO4⋯H2O complex is only 3.8 kcal mol−1. The presence of water or sulfuric acid catalyzes the dehydration to such an extent that it becomes almost a barrierless process. In the gas phase, dehydration of H4SO5 is an autocatalytic reaction as the water molecule produced by the decomposition of one H4SO5 molecule induces further dissociation. Thus, in solution, the surrounding water molecules make the para-sulfuric acid a very vulnerable species to exist. The simulated Raman spectra also corroborate the absence of H4SO5 in solution.

On-surface chemistry for atomically precise sp2 macromolecules requires top-down lithographic methods on insulating surfaces in order to pattern the long-range complex architectures needed by the semiconductor industry. Here, we fabricate sp2-carbon nanometer-thin films on insulators and under ultrahigh vacuum (UHV) conditions from photocoupled brominated precursors. We reveal that covalent coupling is initiated by C–Br bond cleavage through photon energies exceeding 4.4 eV, as monitored by laser desorption ionization (LDI) mass spectrometry (MS) and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) gives insight into the mechanisms of C–Br scission and C–C coupling processes. Further, unreacted material can be sublimed and the coupled sp2-carbon precursors can be graphitized by e-beam treatment at 500 °C, demonstrating promising applications in photolithography of graphene nanoarchitectures. Our results present UV-induced reactions on insulators for the formation of all sp2-carbon architectures, thereby converging top-down lithography and bottom-up on-surface chemistry into technology., We acknowledge financial support from the European Research Council Advanced Grant DYNamo (ERC-2010-AdG-267374) Spanish Grants (FIS2010-21282-C02-01 and PIB2010US-00652), Grupos Consolidados UPV/EHU del Gobierno Vasco (IT578-13), Ikerbasque and the European Commission projects CRONOS (Grant 280879-2 CRONOS CP-FP7). C.-A.P. and K.D. were funded through the ERC Advanced Grant MolArt (no. 247299). D.J.M. acknowledges funding through the Spanish “Juan de la Cireva” program (JCI-2010-08156). J.L.C acknowledges funding through the Mexican CONACyT program.

Viable planar pentacoordinate carbon (ppC) systems with a ppC bonded to a transition metal and embedded in a metallocene framework are reported. Our detailed global minima search shows that CAl4MX2 (M = Zr and Hf; X = F–I and C5H5) clusters with ppCs are appropriate candidates for experimental realization in the gas phase. The fulfillment of the 18 electron rule and electron delocalization is found to be crucial for the stabilization of these ppC arrangements.

Several of the lowest energy structures of small and medium sized boron clusters are two-dimensional systems made up of a pair of concentric rings. In some cases, the barriers to the rotation of one of those rings relative to the other are remarkably low. We find that a combination of electronic and geometrical factors, including apparently the relative sizes and symmetries of the inner and outer rings, are decisive for the diminished barriers to in-plane rotation in these two dimensional clusters. A sufficiently large outer ring is important; for instance, expansion of the outer ring by a single atom may reduce the barrier significantly. A crucial factor for an apparent rotation is that the σ-skeleton of the individual rings remains essentially intact during the rotation. Finally, the transition state for the rotation of the inner ring comprises the transformation of a square into a diamond, which may be linked to a mechanism suggested decades ago for the isomerization of carboranes and boranes.

Density functional theory computations at the BP86-D3/def2-TZVP level are reported for the CpE–Cr(CO)5 complexes (E = Group 13 element). In principle, we have answered two important facts: first the nature and trend of the E–Cr bonding along B to Tl complexes; second, the deviation of Cp (centroid)-E–Cr angle in In and Tl from linearity. The bonding situation in the complexes is examined via the natural bond orbital, adaptive natural density partitioning, and energy decomposition analysis schemes. Our results reveal that the E–Cr bonding in the lighter compounds is mainly ionic, while this bonding in the In and Tl complexes is dominated by an orbitalic contribution. We also clarify the origin of deviation of Cp (centroid)-E–Cr angle for the In and Tl complexes using simple molecular orbital arguments and find that the repulsive intermolecular contacts in the crystals are not the real source of this deviation as was claimed.

Stochastic explorations of the configurational spaces for WC n (n = 2–5) clusters lead to densely populated spin states at each molecularity. We found 8, 16, 42, and 68 well-defined minima for n = 2, 3, 4, 5, respectively, in spin states ranging from singlets to quintuplets. The lowest energy isomers are triplets in all cases, except for n = 2 where there is competition between a quintuplet and a triplet state for the global minimum. The transition from planar to 3D structural preferences occurs between n = 4 and n = 5. For the global minima, the structures may be considered as the result of the interaction between two fragments: a tungsten cation and a covalently bonded anionic carbon chain. We found that spin–orbit (SO) effects reduce energy differences among isomers. Likewise, SO effects diminish as a function of the carbon content in the clusters to the point that for n = 5 they become negligible.

The degenerate rearrangement in the 21-homododecahedryl cation (1) has been studied via density functional theory computations and Born-Oppenheimer Molecular Dynamics simulations. Compound 1 can be described as a highly fluxional hyperconjugated carbocation. Complete scrambling of 1 can be achieved by the combination of two unveiled barrierless processes. The first one is a "rotation" of one of the six-membered rings via a 0.8 kcal·mol(-1) barrier, and the second one is a slower interconvertion between two hyperconjomers via an out-of-plane methine bending (ΔG(⧧) = 4.0 kcal·mol(-1)).

An exhaustive exploration of the potential energy surfaces of ferrocene, ruthenocene and osmocene dimers has been performed. Our computations involving dispersion show that only four different isomers are present in each metallocene dimer. The collective action of small interaction energies of dispersive nature leads to a dissociation energy of 7.5 kcal mol(-1) for the ferrocene dimer. Dispersion has strong effects on the geometrical parameters, reducing the M···M distances by almost 1 Å. Our results also reveal that inclusion of entropic factors modifies the relative stability of the complexes. The nature of bonding is examined using the energy decomposition analysis and the non-covalent interaction index. Both analyses indicate that dispersion is the major contributing factor in stabilizing a metallocene dimer.