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A new computational tool enables associating the changes in IR spectra occurring upon complex formation with individual types of intermolecular interactions (electrostatic, exchange, induction, and dispersion).

Cobalt-catalyzed C–H amination via M-nitrenoid species is spiking the interest of the research community. Understanding this process at a molecular level is a challenging task, and here we report a well-defined macrocyclic system featuring a pseudo-Oh aryl-CoIII species that reacts with aliphatic azides to effect intramolecular Csp2–N bond formation. Strikingly, a putative aryl-Co═NR nitrenoid intermediate species is formed and is rapidly trapped by a carboxylate ligand to form a carboxylate masked-nitrene, which functions as a shortcut to stabilize and guide the reaction to productive intramolecular Csp2–N bond formation. On one hand, several intermediate species featuring the Csp2–N bond formed have been isolated and structurally characterized, and the essential role of the carboxylate ligand has been proven. Complementarily, a thorough density functional theory study of the Csp2–N bond formation mechanism explains at the molecular level the key role of the carboxylate-masked nitrene species, which is essential to tame the metastability of the putative aryl-CoIII═NR nitrene species to effectively yield the Csp2–N products. The solid molecular mechanistic scheme determined for the Csp2–N bond forming reaction is fully supported by both experimental and computation complementary studies This work was financially supported by MICINN (CTQ2016- 77989-P and PID2019-104498GB-I00 to X.R., PGC2018- 098212-B-C22 to J.M.L. and PGC2018-095808-B-I00 to T.P.) and Generalitat de Catalunya (2017SGR264 to X.R. and 2017SGR39 to J.M.L.) Open Access funding provided thanks to the CRUE-CSIC agreement with ACS

Two oxoiron(IV) isomers (R2a and R2b) of general formula [FeIV(O)(RPyNMe3)(CH3CN)]2+ are obtained by reaction of their iron(II) precursor with NBu4IO4. The two isomers differ in the position of the oxo ligand, cis and trans to the pyridine donor. The mechanism of isomerization between R2a and R2b has been determined by kinetic and computational analyses uncovering an unprecedented path for interconversion of geometrical oxoiron(IV) isomers. The activity of the two oxoiron(IV) isomers in hydrogen atom transfer (HAT) reactions shows that R2a reacts one order of magnitude faster than R2b, which is explained by a repulsive noncovalent interaction between the ligand and the substrate in R2b. Interestingly, the electronic properties of the R substituent in the ligand pyridine ring do not have a significant effect on reaction rates. Overall, the intrinsic structural aspects of each isomer define their relative HAT reactivity, overcoming changes in electronic properties of the ligand.

The popularity of the Infrared (IR) spectroscopy is due to its high interpretive power. This study presents a new computational tool for analyzing the IR spectra of molecular complexes in terms of intermolecular interaction energy components. In particular, the proposed scheme enables to associate the changes in IR spectra occurring upon the complex formation with individual types of intermolecular interactions (electrostatic, exchange, induction, dispersion), thus providing a completely new insight into the relations between the spectral features and the nature of interactions in molecular complexes. To demonstrate its interpretive power, we analyze for selected vibrational modes which interaction types rule the IR intensity changes upon the formation of two different types of complexes, namely π...π stacked (benzene...1,3,5-trifluorobenzene) and hydrogen-bonded (HCN...HNC) systems. The exemplary applications of the new scheme to these two molecular complexes revealed that the interplay of interaction energy components governing their stability might be very different from that behind the IR intensity changes. For example, in the case of the dispersion-bound π...π-type complex, dispersion contributions to the interaction induced IR intensity of the selected modes are notably smaller than their first-order (electrostatic and exchange) counterparts.

We have studied the halogen-bonding interactions of a pyridine-functionalized fluoroborate dye with perfluorohaloarenes (C

Herein we explore the intrinsic organometallic reactivity of iron embedded in a tetradentate N

Cobalt-catalyzed C-H amination via M-nitrenoid species is spiking the interest of the research community. Understanding this process at a molecular level is a challenging task, and here we report a well-defined macrocyclic system featuring a pseudo

The tuning of the spectroscopic signatures of boron-carrying fluorescent dyes is achieved by subtle chemical modifications. In more detail, we propose a new series of compounds incorporating up to three electron-donating moieties around the central accepting core, using various positions for the donating moieties, including the central boron atom. For all dyes, a thorough experimental and computational investigation of the absorption and emission properties is presented, with specific emphasis on two-photon absorption. Our key finding is that the two-photon absorption cross section, a property vital for bioimaging applications, can be tuned to a large extent (eightfold increase) by changing the topology of the molecule and using an optimal substitution pattern, while mainly conserving the position of the absorption/emission band and fluorescence quantum yield. In addition, these dyes combine significant values of two-photon absorption cross sections (exceeding 500 GM) to significant fluorescence quantum yields - a beneficial feature for several applications J. M. L. is grateful for the financial support from the Spanish MICIN PGC2018-098212-B-C22 and the Catalan DIUE 2017SGR39

The shift towards renewable energy is one of the main challenges of this generation. Dye-sensitized solar cells (DSSC), based on donor-acceptor architectures, can help on this transition as they present excellent photovoltaic efficiencies yet cheap and simple manufacturing. For molecular heterojunctions DSSCs, donor-acceptor pairs are linked in a covalent manner, which facilitates their tailoring and rational design. Nevertheless, reliable computational characterization of charge transfer rate constants (kCT) is needed to speed this development process up. In this context, the performance of time-dependent density functional theory for the calculation of kCT's in donor-acceptor fullerene-based dyads has not been benchmarked yet. Herein, we present a detailed analysis on the performance of seven well-known density functional approximations (DFAs) for this type of systems, focusing on several parameters as the reorganization energies (λ), electronic couplings (VDA), and Gibbs energies (ΔG^0_CT), as well as in the final rate constants. The amount of exact exchange at short range (SR) and long range (LR) electron-electron distances (and the transition from SR to LR) turned out to be key for the success of the prediction. The tuning of these parameters improves significantly the performance of current DFAs This work was supported with funds from the Ministerio de Economía y Competitividad (MINECO) of Spain (project CTQ2017- 85341-P to M.S. and A.A.V.), the Spanish government MICINN (project PGC2018-098212-B-C22 to J.M.L), and the Generalitat de Catalunya (project 2017SGR39 to M.S. and J.M.L.). We thank the Spanish government for the predoctoral grant to P.B.-S. (FPU17/02058)

C-F bonds are one of the most inert functionalities. Nevertheless, some [Cu_2O_2]^2+ species are able to defluorinate-hydroxylate ortho-fluorophenolates in a chemoselective manner over other ortho-halophenolates. Albeit it is known that such reactivity is promoted by an electrophilic attack of a [Cu_2O_2]^2+ core over the arene ring, the crucial details of the mechanism that explain the chemo- and regioselectivity of the reaction remain unknown, and it has not being determined either if Cu^II_2(η_2:η_2-O_2) or Cu^III_2(μ-O)_2 species are responsible for the initial attack on the arene. Herein, we present a combined theoretical and experimental mechanistic study to unravel the origin of the chemoselectivity of the ortho-defluorination-hydroxylation of 2-halophenolates by the [Cu_2(O)_2(DBED)_2]2+ complex (DBED = N,N′-di-tert-butylethylenediamine). Our results show that the equilibria between (side-on)peroxo (P) and bis(μ-oxo) (O) isomers plays a key role in the mechanism, with the latter being the reactive species. Furthermore, on the basis of quantum-mechanical calculations, we were able to rationalize the chemoselective preference of the [Cu_2(O)_2(DBED)_2]^2+ catalyst for the C-F activation over C-Cl and C-H activations. This work was supported with funds from the Spanish government MICINN (PGC2018-098212-B-C22 to JML, PGC2018-101737-BI00 to M.C., CTQ2016-77989-P to A.C.), and the Generalitat de Catalunya (2017SGR39 to J.M.L, 2017 SGR 00264 and ICREA Academia to M.C. and A.C.). We thank the Spanish government for the predoctoral grant to P.B.-S. (FPU17/02058)

In the last 30 years, fullerene-based materials have become popular building blocks for devices with a broad range of applications. Among fullerene derivatives, endohedral metallofullerenes (EMFs, M@Cx) have been widely studied owing to their unique properties and reactivity. For real applications, fullerenes and EMFs must be exohedrally functionalized. It has been shown that encapsulated metal cations facilitate the Diels-Alder reaction in fullerenes. Herein, the Bingel-Hirsch (BH) addition of ethyl bromomalonate over a series of ion-encapsulated M@C60 (M=O, Li+, Na+, K+, Mg2+, Ca2+, and Cl-; O@C60 stands for C60 without any endohedral metal) is quantum mechanically explored to analyze the effect of these ions on the BH addition. The results show that the incarcerated ion has a very important effect on the kinetics and thermodynamics of this reaction. Among the systems studied, K+@C60 is the one that leads to the fastest BH reaction, whereas the slowest reaction is given by Cl-@C60.

The optimization of nonlinear optical properties for “real-life” applications remains a key challenge for both experimental and theoretical approaches. In particular, for two-photon processes, maximizing the two-photon action cross section (TPACS), the figure of merit for two-photon bioimaging spectroscopy, requires simultaneously controlling all its components. In the present Letter, a series of difluoroborates presenting various heterocyclic rings as an electron acceptor have been synthesized and their absorption, fluorescence, photoisomerization, and two-photon absorption features have been analyzed using both experimental and theoretical approaches. Our results demonstrate that the TPACS values can be fine-tuned by changing the position of a single heteroatom, which alters the fluorescence quantum yields without changing the intrinsic two-photon absorption cross section. This approach offers a new strategy for optimizing TPACS J.M.L. is grateful for financial support from the Spanish MICIN PGC2018-098212-B-C22 and the Catalan DIUE 2017SGR39

Reactions that enable selective functionalization of strong aliphatic C-H bonds open new synthetic paths to rapidly increase molecular complexity and expand chemical space. Particularly valuable are reactions where site-selectivity can be directed toward a specific C-H bond by catalyst control. Herein we describe the catalytic site- and stereoselective γ-lactonization of unactivated primary C-H bonds in carboxylic acid substrates. The system relies on a chiral Mn catalyst that activates aqueous hydrogen peroxide to promote intramolecular lactonization under mild conditions, via carboxylate binding to the metal center. The system exhibits high site-selectivity and enables the oxidation of unactivated primary γ-C-H bonds even in the presence of intrinsically weaker and a priori more reactive secondary and tertiary ones at α- and β-carbons. With substrates bearing nonequivalent γ-C-H bonds, the factors governing site-selectivity have been uncovered. Most remarkably, by manipulating the absolute chirality of the catalyst, γ-lactonization at methyl groups in gem-dimethyl structural units of rigid cyclic and bicyclic carboxylic acids can be achieved with unprecedented levels of diastereoselectivity. Such control has been successfully exploited in the late-stage lactonization of natural products such as camphoric, camphanic, ketopinic, and isoketopinic acids. DFT analysis points toward a rebound type mechanism initiated by intramolecular 1,7-HAT from a primary γ-C-H bond of the bound substrate to a highly reactive MnIV-oxyl intermediate, to deliver a carbon radical that rapidly lactonizes through carboxylate transfer. Intramolecular kinetic deuterium isotope effect and 18O labeling experiments provide strong support to this mechanistic picture This work was supported by the Spanish Ministry of Science, Innovation, and Universities (PGC2018-101737-B-I00 to M.C., PGC2018-098212-B-C22 to J.M.L., IJC2020-046115-I to A.C.; and PhD grants FPU16/04231 to L.V., FPU17/02058 to P.B.-S., and PRE2019-090149 to A.P.), the University of Rome “Tor Vergata” (Project E84I20000250005), the European Research Council, (AdvG 883922 to M.C.), and Generalitat de Catalunya (ICREA Academia Award and 2017-SGR00264 to M.C. and X.R., and 2017SGR39 to J.M.L.)

Following our study on hydrogen-bonded (HB) complexes [Phys. Chem. Chem. Phys., 2018, 20, 19841], the physical nature of interaction-induced (non)linear optical properties of another important class of molecular complexes, namely halogen-bonded (XB) systems, was analyzed in this study. The excess electronic and nuclear relaxation (hyper)polarizabilities of nine representative XB complexes covering a wide range of halogen-bond strengths were computed. The partitioning of the excess properties into individual interaction-energy components (electrostatic, exchange, induction, dispersion) was performed by using the variational-perturbational energy decomposition scheme at the MP2/aug-cc-pVTZ level of theory and further supported by calculations with the SCS-MP2 method. In the case of the electronic interaction-induced properties, the physical composition of Δαel and Δγel was found to be very similar for the two types of bonding, despite the different nature of the binding. For Δβel, the XB complexes exhibit a more systematic interplay of interaction-energy contributions compared to the HB systems studied in the previous work. Our analysis revealed that the patterns of interaction-energy contributions to the interaction-induced nuclear-relaxation contributions to the linear polarizability and the first hyperpolarizability are very similar. For both properties the exchange repulsion term is canceled out by the electrostatic and delocalization terms. The physical composition of these contributions is analogous to those observed for the HB complexes J. M. L. is grateful for financial support from the Spanish MICIN PGC2018-098212-B-C22 and the Catalan DIUE 2017SGR39

Nickel-catalyzed C-F activations enabled chemodivergent C-C formation with alkynes by chelation assistance. The judicious choice of the alkyne electronic properties allowed the selective synthesis of double-insertion aromatic homologation or alkyne monoannulation products by C-F/C-H activation. On the basis of the unambiguous crystallographic characterization of an unprecedented nine-membered nickelacyclic intermediate and extensive DFT studies, a plausible mechanistic rationale was established for the selective C-F activation and the chemodivergent catalysis This work was financially supported by grants from the European Research Council (ERC-2011-StG-277801 to XR), the DFG (GottfriedWilhelm-Leibniz award to LA), MICINN (CTQ2016-77989-P to XR), and Generalitat de Catalunya (2017SGR264). XR is thankful for an ICREA Acadèmia award. We thank COST Action CHAOS (CA15106) and Dr. L. Gómez and STR from UdG for technical support

This work reports on an extensive assessment of the performance of a wide palette of density functional approximations in predicting the (high-order) electric properties of hydrogen-bonded complexes. To this end, we compute the electronic and vibrational contributions to the electric polarizability and the first and second hyperpolarizabilities, using the CCSD(T)/aug-cc-pVTZ level of theory as reference. For all the studied properties, the average absolute errors below 20% can only be obtained using the CAM-B3LYP functional, while LC-BLYP and MN15 are shown to be only slightly less accurate (average absolute errors not exceeding 30%). Among Minnesota density functionals, i.e., M06, M06-2X, and MN15, we only recommend the latter one, which quite accurately predicts the electronic and vibrational (hyper)polarizabilities. We also analyze the optimal tuning of the range-separation parameter μ for the LC-BLYP functional, finding that this approach does not bring any systematic improvement in the predictions of electronic and vibrational (hyper)polarizabilities and the accuracy of computed properties is largely system-dependent. Finally, we report huge errors in predicting the vibrational second hyperpolarizability by ωB97X, M06, and M06-2X functionals. Based on the explicit evaluation of anharmonic terms contributing to the second hyperpolarizability, this failure is traced down to a poor determination of third- and fourth-order energy derivatives with respect to normal modes. These results reveal serious flaws of some density functional approximations and suggest caution in selecting the appropriate functional to calculate not only electronic and vibrational (hyper)polarizabilities but also other molecular properties that contain vibrational anharmonic contributions.

Electrides are very peculiar ionic compounds where electrons occupy the anionic positions. In a crystal lattice, these isolated electrons often group forming channels or surfaces, furnishing electrides with a plethora of traits with promising technological applications. Despite their huge potential, thus far, only a few stable electrides have been produced because of the intricate synthesis they entail. Due to the difficulty in assessing the presence of isolated electrons, the characterization of electrides also poses some serious challenges. In fact, their properties are expected to depend on the arrangement of these electrons in the molecule. Among the criteria that we can use to characterize electrides, the presence of a non-nuclear attractor (NNA) of the electron density is both the rarest and the most salient feature. Therefore, a correct description of the NNA is crucial to determine the properties of electrides. In this paper, we analyze the NNA and the surrounding region of nine molecular electrides with the goal of determining the number of isolated electrons that are held in the electride. We have seen that the correct description of a molecular electride hinges on the electronic structure method employed for the analyses. In particular, one should employ a basis set with sufficient flexibility to describe the region close to the NNA and a density functional approximation that does not suffer from large delocalization errors. Finally, we have classified these nine molecular electrides according to the most likely number of electrons that we can find in the NNA. We believe this classification highlights the strength of the electride character and will prove useful in the design of new electrides.

Real-space analysis tools afford additive and transferable contributions of atoms to molecular properties. In the case of the molecular (hyper)polarizabilities, the atomic contributions that have been derived so far include a charge-transfer term that is origin-dependent. In this letter, we present the first genuinely origin-independent energy-based (OIEB) methodology for the decomposition of the static (hyper)polarizabilities that benefits from real-space molecular energy decomposition schemes, focusing on the static polarizability and showing that extension to static hyperpolarizabilities is straightforward. The numerical realization of the OIEB method shows the expected origin independence, atomic additivity, and transferability of atomic and functional group polarizability tensors. Furthermore, the OIEB atomic (fragment) polarizability tensors are symmetric by definition.

Herein we explore the intrinsic organometallic reactivity of iron embedded in a tetradentate N3C macrocy-clic ligand scaffold that allows the stabilization of aryl-Fe species, which are key intermediates in Fe-catalyzed cross-coupling and C-H functionalization processes. This study covers C-H activation reactions using MeLH and FeCl2, biaryl C-C coupling product formation through reaction with Gri-gnard reagents, and cross-coupling reactions using MeLBr or HLBr in combination with Fe0(CO)5. Synthesis under light irradiation and moderate heating (50 ºC) affords aryl-FeII complexes [FeII(Br)(MeL)(CO)] (1Me) and [FeII(HL)(CO)2]Br (1H). Exhaustive spectroscopic characterization of these rare low spin diamagnetic species, including their crystal struc-tures, allowed the investigation of their intrinsic reactivity We acknowledge financial support from MINECO-Spain for projects PID2019-104498GB-I00 to X.R., PID2019-106699GBI00 to A.C. and PGC2018-098212-B-C22 to J.M.L. Generalitat de Catalunya is also acknowledged for projects 2017SGR264 and 2017SGR39

In the oriented external electric-field-driven catalysis, the reaction rates and the selectivity of chemical reactions can be tuned at will. The activation barriers of chemical reactions within external electric fields of several strengths and directions can be computationally modeled. However, the calculation of all of the required field-dependent transition states and reactants is computationally demanding, especially for large systems. Herein, we present a method based on the Taylor expansion of the field-dependent energy of the reactants and transition states in terms of their field-free dipole moments and electrical (hyper)polarizabilities. This approach, called field-dependent energy barrier (FDBβ), allows systematic one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) representations of the activation energy barriers for any strength and direction of the external electric field. The calculation of the field-dependent FDBβ energy barriers has a computational cost several orders of magnitude lower than the explicit electric field optimizations, and the errors of the FDBβ barriers are within the range of only 1-2 kcal·mol-1. The achieved accuracy is sufficient for a fast-screening tool to study and predict potential electric-field-induced catalysis, regioselectivity, and stereoselectivity. As illustrative examples, four cycloadditions (1,3-dipolar and Diels-Alder) are studied This work was supported with funds from the Ministerio de Economía y Competitividad (MINECO) of Spain (project CTQ2017-85341-P to M.S.), the Spanish government MICINN (projects PGC2018-098212-B-C22 to J.M.L, PID2020-113711GB-I00 to M.S., and PID2019-104772GBI00 to M.T.S.), the Generalitat de Catalunya (project 2017SGR39 to M.S. and J.M.L.), and Gobierno Vasco (project IT1346-19 to M.T.S.). The authors thank the Spanish government for the predoctoral grant to P.B.-S. (FPU17/ 02058)

Electrides are very peculiar ionic compounds where electrons occupy the anionic positions. In a crystal lattice, these isolated electrons often form channels or surfaces, furnishing electrides with many traits with promising technological applications. Despite their huge potential, thus far, only a few stable electrides have been produced because of the intricate synthesis they entail. Due to the difficulty in assessing the presence of isolated electrons, the characterization of electrides also poses some serious challenges. In fact, their properties are expected to depend on the arrangement of these electrons in the molecule. Among the criteria that we can use to characterize electrides, the presence of a non-nuclear attractor (NNA) of the electron density is both the rarest and the most salient feature. Therefore, a correct description of the NNA is crucial to determine the properties of electrides. In this paper, we analyze the NNA and the surrounding region of nine molecular electrides to determine the number of isolated electrons held in the electride. We have seen that the correct description of a molecular electride hinges on the electronic structure method employed for the analyses. In particular, one should employ a basis set with sufficient flexibility to describe the region close to the NNA and a density functional approximation that does not suffer from large delocalization errors. Finally, we have classified these nine molecular electrides according to the most likely number of electrons that we can find in the NNA. We believe this classification highlights the strength of the electride character and will prove useful in designing new electrides This work has been supported by grants from the Spanish government MICINN (PGC2018-098212−B-C21, PGC2018-098212−B-C22, CTQ2016-80375-P, and EUR2019-103825), Generalitat de Catalunya (2017SGR39), Diputación Foral de Gipuzkoa (2019-CIEN-000092-01). and Gobierno Vasco-Eusko Jaurlaritza (IT1254-19, PRE_2020_2_0015 and PIBA19-0004). E.R.- C. acknowledges funding from the Juan de la Cierva Program IJCI-2017-34658. We are also grateful for the computational time from the Consorci de Serveis Universitaris de Catalunya (CSUC), DIPC, and the SGI/IZO-SGIker UPV/EHU

A novel hydroperoxoiron(III) species [Fe III (OOH)(MeCN)(PyNMe 3 )] 2+ (3) has been generated by reaction of its ferrous precursor [Fe II (CF 3 SO 3 ) 2 (PyNMe 3 )] (1) with hydrogen peroxide at low temperatures. This species has been characterized by several spectroscopic techniques and cryospray mass spectrometry. Similar to most of the previously described low-spin hydroperoxoiron(III) compounds, 3 behaves as a sluggish oxidant and it is not kinetically competent for breaking weak C−H bonds. However, triflic acid addition to 3 causes its transformation into a much more reactive compound towards organic substrates that is capable of oxidizing unactivated C−H bonds with high stereospecificity. Stopped-flow kinetic analyses and theoretical studies provide a rationale for the observed chemistry, a triflic-acid-assisted heterolytic cleavage of the O−O bond to form a putative strongly oxidizing oxoiron(V) species. This mechanism is reminiscent to that observed in heme systems, where protonation of the hydroperoxo intermediate leads to the formation of the high-valent [(Porph . )Fe IV (O)] (Compound I) Financial support for this work was provided by the European Commission (2011-CIG-303522 to A.C., 675020-MSCA-ITN-2015-ETN to M.C.), the Spanish Ministry of Science (CTQ2015-70795-P to M.C., CTQ2016-77989-P to A.C., CTQ2014-52525-P to J.M.L., CTQ2015-65707-C2-2-P to M.G.B., and CSD2010-00065 to M.C and M.G.B.) and Generalitat de Catalunya (ICREA Academia Award to M.C. and 2014 SGR 862). The Spanish Ministry of Science is also acknowledged for a Ram n y Cajal contract to A.C. (RYC-2011–08683). The work conducted at the University of Minnesota has been supported by the US National Science Foundation (grant CHE1665391 to L.Q.). XAS data was collected at the SOLEIL synchrotron SAMBA beamline (proposal 20150413)

Understanding the effects of different fundamental intermolecular interactions on nonlinear optical properties is crucial for proposing efficient strategies to obtain new materials with tailored properties. In this study, we computed the electronic and vibrational (hyper)polarizabilities of ten hydrogen-bonded molecular complexes employing the MP2, CCSD and CCSD(T) methods combined with the aug-cc-pVTZ basis set. The vibrational contributions to hyperpolarizabilities included nuclear-relaxation anharmonic corrections. The effect of intermolecular interactions was analyzed in terms of excess properties, which are defined as the difference between a property of the complex and the net properties of the noninteracting subsystems. Considering systems covering a wide range of hydrogen bond strengths, the electronic and vibrational excess (hyper)polarizabilities were decomposed into different interaction energy contributions (electrostatic, exchange, induction and dispersion). This systematic study, the very first of this kind, revealed that the physical origins of the electronic and vibrational excess properties are completely different. In the case of vibrational contributions, the decomposition pattern is very similar for the polarizability and first and second hyperpolarizabilities. The exchange contributions to excess vibrational properties are the largest and they have an opposite sign to the electrostatic, induction and dispersion terms. On the other hand, no general patterns can be established for the electronic excess properties.

The macrocyclic ring of expanded porphyrins presents a conformational versatility that leads to original structural motifs and generates unique Hückel-to-Möbius topological switches. These systems can act as optoelectronic materials, and their range of applicability depends on the high values of the nonlinear optical properties (NLOPs) and the large differences between the Hückel and Möbius structures. With the aim to design new topological switches with the optimum NLOPs, we have performed a DFT computational study on the effect of three different geometric and electronic factors of the meso-substituents: (i) their electron-withdrawing and -releasing character; (ii) their distribution along the porphyrin ring; and (iii) the length of the conjugation path. In this work, we report the electronic and vibrational contributions to static and dynamic NLOPs of the Hückel and Möbius conformations of 18 meso-substituted [28]-hexaphyrins. These systems can achieve first and second hyperpolarizability values around 1 × 10^5 and 2 × 10^7 au, respectively, and differences between the Möbius and Hückel conformations around 4 × 10^4 and 5 × 10^6 au, respectively. From our results, we conclude that efficient NLOP topological switches can be obtained from push-pull porphyrins with a π-conjugated spacer and strong electron-withdrawing and -releasing groups located on opposite sides of the skeleton ring Financial support was provided by the Ministerio de Economía y Competitividad (MINECO) of Spain and FEDER (projects CTQ2016-80375-P and CTQ2014-52525-P) and the Generalitat de Catalunya (Grant 2014SGR139)

A nonheme iron catalyst catalyzed stereoselective oxidation of alkanes with H2O2 with remarkable efficiency and exhibiting an unprecedented high incorporation of water into the oxidized products. The present results challenge the canonical description of oxygenases, the standard oxo-hydroxo tautomerism that applies to heme systems and serves as a precedent for alternative pathways for the oxidation of hydrocarbons at nonheme iron oxygenases Financial support from MCYT of Spain (CTQ2006–05367 to MC) and from US-DOE (DE-FG02-03ER15455 to LQ) is gratefully acknowledged

In this work a new method to calculate anharmonic vibrational ground and excited state energies is proposed. The method relies on the auto-adjusting perturbation theory (APT) which has been successfully used to diagonalize square matrices. We use as zeroth order correction the self-consistent vibrational energies, and with the APT approach we calculate the vibrational anharmonic correlation correction to any desired order. In this paper we present the methodology and apply it to a model system and formaldehyde. Vibrational APT approach shows a robust convergent behavior even for the states where the standard (Rayleigh-Schr¨odinger) vibrational Møller-Plesset perturbation theory is clearly divergent E.B. and J.M.B. thank the project CTQ2006-04410/BQU of the Spanish Ministerio de Ciencia y Tecnología. O.C. acknowledges support from the Danish Center for Scientific Computing (DCSC), the Danish national research foundation, the Lundbeck Foundation, and EUROHORCs for a EURYI award. J.M.L thanks the project CTQ2008-06696/BQU of the Spanish Ministerio de Ciencia y Tecnología

The IUPAC has recently clarified the term oxidation state (OS), and provided algorithms for its determination based on the ionic approximation (IA) of the bonds supported by atomic electronegativities (EN). Unfortunately, there are a number of exceptions and ambiguities in IUPAC's algorithms when it comes to practical applications. Our comprehensive study reveals the critical role of the chemical environment on establishing the OS, which cannot always be properly predicted using fix atomic EN values. By identifying what we define here as subsystems of enhanced stability within the molecular system, the OS can be safely assigned in many cases without invoking exceptions. New insights about the effect of local aromaticity upon OS are revealed. Moreover, we prove that there are intrinsic limitations of the IA that cannot be overcome. In this context, the effective oxidation state (EOS) analysis arises as a robust and general scheme to derive an OS without any external guidance Ministerio de Educación, Cultura y Deporte. Grant Numbers: CTQ2014-59212-P, CTQ2014-52525-P, BES-2012-052801 Agència de Gestió d'Ajuts Universitaris i de Recerca. Grant Numbers: 2014SGR1202, 2014SGR931 Universitat de Girona. Grant Number: GdRCompet-UdG2017 European Regional Development Fund. Grant Number: UNGI104E-801

The influence of the spatial confinement on the electronic and vibrational contributions to longitudinal electric-dipole properties of model linear molecules including HCN, HCCH and CO2 is discussed. The effect of confinement is represented by two-dimensional harmonic oscillator potential of cylindrical symmetry, which mimics the key features of various types of trapping environments like, for instance, nanotubes or quantum well wires. Our results indicate that in general both (electronic and vibrational) contributions to (hyper)polarizabilities diminish upon spatial confinement. However, since the electronic term is particularly affected, the relative importance of vibrational contributions is larger for confined species. This effect increases also with the degree of anharmonicity of vibrational motion.

Vibrational motions can play an important role in determining electrical, magnetic, and spectroscopic properties through so-called nuclear relaxation, zero-point vibrational averaging, or a combination of the two. Recent advances in the analysis and computational treatment of these phenomena include the finite field/nuclear relaxation technique and field-induced coordinates. These methodologies, which were originally developed for non-resonant electric dipole (hyper)polarizabilities, are reviewed and extended to magnetic properties as well as properties involving simultaneous electric and magnetic fields. In addition, spectroscopic applications such as two-photon absorption, circular dichroism, and infrared/Raman vibrational intensities are considered. With the finite field/nuclear relaxation technique and field-induced coordinates computations are now feasible for much larger molecules than before The authors are indebted to Prof. D. M. Bishop for helpful discussions. J. M. L. acknowledges the financial assistance provided through Spanish DGICYT Project No. PB98-0457-C02-1

Nonlinear optical properties (NLOPs) play a major role in photonics, electro-optics and optoelectronics, and other fields of modern optics. The design of new NLO molecules and materials has benefited from the development of computational tools to analyze the relationship between the electronic structure of molecules and their optical response. In this paper, we present a new means to analyze the response property through the partition of NLOPs in terms of orbital contributions (PNOC). This tool can be used to obtain a real-space representation of the NLOPs, providing a powerful visualization aid to connect the magnitude of the optical property with some parts of the molecule. Unlike other methods to analyze NLOPs, the PNOC decomposes the optical property into orbitals of the unperturbed system, furnishing this method with the ability to assess the performance of single- and multi-determinant electronic structure methods. PNOC can be also used to design small basis sets for an accurate description of large systems, saving a substantial amount of computer time for the calculation of optical properties This research has been funded by Spanish MINECO/FEDER Projects CTQ2014-52525-P and EUIN2017-88605, the Catalan DIUE 2014SGR931 and IKERBASQUE

The zero-point static vibrational averaging (ZPVA) correction to the (hyper)polarizability is written in first-order as the sum of two contributions, one involving electric field derivatives, and the other a sum over normal coordinate derivatives of the zero point energy. It is shown that the sum over 3N-6 normal modes can be replaced by a single term using field-induced coordinates (FICs). A computational strategy that takes advantage of this simplification is presented and applied to a typical push-pull polyene NH2-(CH=CH)3-NO2. From the dependence of the first-order ZPVA on the field-dependent equilibrium geometry we also obtain other loworder static and dynamic vibrational curvature contributions to the (hyper)polarizabilities. The entire set of electronic and vibrational terms is partitioned into two different sequences, each of which exhibits rapid initial convergence for NH2(CH=CH)3NO2 at the Hartree-Fock/6-31G+p level. Including electron correlation at the MP2 level and the frequency-dependence of the ZPVA correction is discussed Support for this work under Grant PB98- 0457-C02-01 from the Dirección General de Enseñanza Superior e Investigación Científica y Técnica (MEC-Spain) is acknowledged

The calculation of nonlinear optical properties (NLOPs) using density functional theory (DFT) remains a challenge in computational chemistry. Although the existing range-separated functionals display the best performance for the calculation of this type of properties, their errors strongly depend on the family of molecules studied. Herein, we have explored a new strategy to empirically tune the range-separated LC-BLYP method to improve the accuracy of the calculation of the second hyperpolarizabilities (γ), which are poorly described by current density functional approximations. First, we benchmarked nine of the most accurate commonly used range-separated hybrid and optimally tuned functionals (i.e. B3LYP, PBE0, BH&HLYP, M06-2X, MN15, ωB97X-D, CAM-B3LYP, LC-BLYP and OT-LC-BLYP) for the calculation of γ using as a reference the CCSD(T) values of a chemically diverse set of 60 molecules. Among these nine functionals, LC-BLYP gives the lowest average errors. We determined the value of the range-separation parameter ω required to reproduce the CCSD(T) second hyperpolarizabilities with the LC-BLYP functional (ωCC) for the set of 60 molecules. Our new tuned range-separated functional, Tα-LC-BLYP, uses a quadratic correlation between ωCC and a molecular descriptor in terms of the linear polarizability and the number of electrons in the molecule. The average error of the γ values obtained with Tα-LC-BLYP is reduced by half or more as compared with the most accurate among the nine density functional approximations benchmarked.

A mechanistic understanding of electro- and photocatalytic CO

This study focuses on the theoretical description of the influence of spatial confinement on the electronic and vibrational contributions to (hyper)polarizabilities of two dimeric hydrogen bonded systems, namely HCN···HCN and HCN···HNC. A two-dimensional analytical potential is employed to render the confining environment (e.g. carbon nanotube). Based on the results of the state-of-the-art calculations, performed at the CCSD(T)/aug-cc-pVTZ level of theory, we established that: (i) the influence of spatial confinement increases with increasing order of the electrical properties, (ii) the effect of spatial confinement is much larger in the case of the electronic than vibrational contribution (this holds for each order of the electrical properties) and (iii) the decrease in the static nuclear relaxation first hyperpolarizability upon the increase of confinement strength is mainly due to changes in the harmonic term, however, in the case of nuclear relaxation second hyperpolarizability the anharmonic terms contribute more to the drop of this property This work was supported by the Polish National Science Centre (Grant No. 2015/19/B/ST4/01881). J.M.L. is grateful for financial support from the Spanish MINECO CTQ2014-52525-P and the Catalan DIUE 2014SGR931

The selective annulation reaction of alkynes with substrates containing inert C-H bonds using cobalt as catalyst is currently a topic attracting significant interest. Unfortunately, the mechanism of this transformation is still relatively poorly understood, with little experimental evidence for intermediates, although an organometallic Co(III) species is generally implicated. Herein, we describe a rare example of the preparation and characterization of benchtop-stable organometallic aryl-Co(III) compounds (NMR, HRMS, XAS, and XRD) prepared through a C(sp2)-H activation, using a model macrocyclic arene substrate. Furthermore, we provide crystallographic evidence of an organometallic aryl-Co(III) intermediate proposed in 8-aminoquinoline-directed Co-catalyzed C-H activation processes. Subsequent insights obtained from the application of our new organometallic aryl-Co(III) compounds in alkyne annulation reactions are also disclosed. Evidence obtained from the resulting regioselectivity of the annulation reactions and DFT studies indicates that a mechanism involving an organometallic aryl-Co(III)-alkynyl intermediate species is preferred for terminal alkynes, in contrast to the generally accepted migratory insertion pathway We acknowledge financial support from the European Research Council for the Starting Grant Project ERC-2011-StG-277801 to X.R. and from MINECO of Spain for project CTQ2013-43012-P to A.C. and X.R., CTQ2014-52525-P to J.M.L and CTQ2015-64436-P to T.P. We also thank Generalitat de Catalunya for projects 2014SGR862 and 2014SGR931. We thank the MECD of Spain for a FPU PhD grant to O.P. and MINECO for a Ramón y Cajal contract to A.C. X.R. also thanks Generalitat de Catalunya for an ICREA-Acadèmia Award. In addition, the research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 312284

Data de publicació online és 30 de novembbre de 2018, malgrat que apareix publicat en una revista del 2019 The nature of the oxidizing species in water oxidation reactions with chemical oxidants catalyzed by α-[Fe(OTf)2(mcp)] (1α; mcp = N,N′-dimethyl-N,N′-bis(pyridin-2-ylmethyl)cyclohexane-1,2-diamine, OTf = trifluoromethanesulfonate anion) and β-[Fe(OTf)2(mcp)] (1β) has been investigated. Mössbauer spectroscopy provides definitive evidence that 1α and 1β generate oxoiron(IV) species as the resting state. Decomposition paths of the catalysts have been investigated by identifying and quantifying ligand fragments that form upon degradation. This analysis correlates the water oxidation activity of 1α and 1β with stability against oxidative damage of the ligand via aliphatic C-H oxidation. The site of degradation and the relative stability against oxidative degradation are shown to be dependent on the topology of the catalyst. Furthermore, the mechanisms of catalyst degradation have been rationalized by computational analyses, which also explain why the topology of the catalyst enforces different oxidation-sensitive sites. This information has served in creating catalysts where sensitive C-H bonds have been replaced by C-D bonds. The deuterated analogues D4-α-[Fe(OTf)2(mcp)] (D4-1α), D4-β-[Fe(OTf)2(mcp)] (D4-1β), and D6-β-[Fe(OTf)2(mcp)] (D6-1β) were prepared, and their catalytic activity has been studied. D4-1α proves to be an extraordinarily active and efficient catalyst (up to 91% of O2 yield); it exhibits initial reaction rates identical with those of its protio analogue, but it is substantially more robust toward oxidative degradation and yields more than 3400 TON (n(O2)/n(Fe)). Altogether this evidences that the water oxidation catalytic activity is performed by a well-defined coordination complex and not by iron oxides formed after oxidative degradation of the ligands We acknowledge the Spanish Ministry of Science CTQ2015-70795-P (M. C.), CTQ2016- 80038-R (J. LL. F.), CTQ2014-59212-P (J. M. Lluis). We would like to thank the European Commission for the ERC-CG-2014-648304 (J.Ll.-F) project

To extend the interesting new concept of the all-metal electride, a series of endohedral all-metal electride cages 2e-Mg2+(M@E12)2-Ca2+ (E = Ge, Sn, and Pb; M = Ni, Pd, and Pt) has been designed and investigated theoretically using the exchange-correlation functional CAM-B3LYP. In these electride cage molecules with excess electrons, interesting pull-push electron transfer relay occurs. The metal cage M@E12 first pulls valence electrons from Ca atom forming a polyanion (M@E12)2-, and then the formed polyanion pushes valence electrons of Mg atom out of its valence shell generating the isolated excess electrons that characterize this species as all-metal electrides. These endohedral all-metal electride cages display a large electronic first hyperpolarizability (beta^e_0) and so they could have a potential application as a new kind of second-order nonlinear optical (NLO) material. We have explored the structure-property relationships, which are significant. It is shown that, for a given central atom, the all-metal electrides with a Sn-cage correspond to the largest beta^e_0, whereas, for a given metal cage, the all-metal electrides with Ni as the central atom correspond to the largest beta^e_0. Owing to the two effects, the endohedral all-metal electride cage 2e-Mg2+(Ni@Sn12)2-Ca2+ exhibits the largest beta^e_0 value (16 893 a.u.). The same conclusions are also valid for the frequency-dependent be(2omega; omega, omgea) and be(2omea; omega, 0). Moreover, we have also explored the role of the vibrational contribution in the largest components (in x-axis) of static b for endohedral all-metal electride cages. The vibrational contributions are significant for new all-metal electride NLO properties and therefore should be considered in the design of new NLO all-metal electrides This study was supported by the National Natural Science Foundation of China (Grant No. 21573089, 21603032), the Graduate Innovation Fund of Jilin University (Grant No. 2017011), the Spanish Ministerio de Economıa y competividad (MINECO, CTQ2014-52525-P), and the Generalitat de Catalunya (project number 2014SGR931)