Non-covalent interactions can usually be described accurately at the coupled-cluster level of the... more Non-covalent interactions can usually be described accurately at the coupled-cluster level of theory using single, double and triple excitations, the latter within a perturbation-theory framework. However, since the computations with the corresponding coupled-cluster model, CCSD(T), are computationally very demanding, they can often not be carried out in large enough basis sets. This leads to a basis-set truncation error. To correct this error, a basis-set correction can be computed at the level of second-order Møller–Plesset (MP2) perturbation theory in the limit of a complete basis set, but such a correction tends to overestimate the magnitude of the basis-set truncation error. In the present work, we suggest to damp the basis-set correction obtained at the complete-basis-set MP2 level using interference factors for individual occupied orbital pairs. The approach is applied to the non-covalent interactions of the S22B database, where the interference correction turns out to be very small.
The air-free reaction of CoCl 2 with 1,3,5-tri(1H-1,2,3-triazol-5-yl)benzene (H 3 BTTri) in N,N-d... more The air-free reaction of CoCl 2 with 1,3,5-tri(1H-1,2,3-triazol-5-yl)benzene (H 3 BTTri) in N,N-dimethylforma-mide (DMF) and methanol leads to the formation of Co-BTTri (Co 3 [(Co 4 Cl) 3 (BTTri) 8 ] 2 ·DMF), a sodalite-type metal− organic framework. Desolvation of this material generates coordinatively unsaturated low-spin cobalt(II) centers that exhibit a strong preference for binding O 2 over N 2 , with isosteric heats of adsorption (Q st) of −34(1) and −12(1) kJ/ mol, respectively. The low-spin (S = 1/2) electronic configuration of the metal centers in the desolvated framework is supported by structural, magnetic susceptibility, and computational studies. A single-crystal X-ray structure determination reveals that O 2 binds end-on to each framework cobalt center in a 1:1 ratio with a Co−O 2 bond distance of 1.973(6) Å. Replacement of one of the triazolate linkers with a more electron-donating pyrazolate group leads to the isostructural framework Co-BDTriP (Co 3 [(Co 4 Cl) 3 (BDTriP) 8 ] 2 ·DMF; H 3 BDTriP = 5,5′-(5-(1H-pyrazol-4-yl)-1,3-phenylene)bis(1H-1,2,3-triazole)), which demonstrates markedly higher yet still fully reversible O 2 affinities (Q st = −47(1) kJ/mol at low loadings). Electronic structure calculations suggest that the O 2 adducts in Co-BTTri are best described as cobalt(II)−dioxygen species with partial electron transfer, while the stronger binding sites in Co-BDTriP form cobalt(III)−superoxo moieties. The stability, selectivity, and high O 2 adsorption capacity of these materials render them promising new adsorbents for air separation processes.
Metal−organic frameworks (MOFs) are versatile nanoporous materials that have gained significant i... more Metal−organic frameworks (MOFs) are versatile nanoporous materials that have gained significant interest as low heat capacity, high selectivity sorbents for CO 2 capture applications. Large-scale atomistic simulations for identifying high-performance MOFs are possible, but are limited to systems for which existing molecular mechanics force fields describe the interactions between the guest and framework atoms with sufficient accuracy. However, standard force fields are not applicable to cases involving coordinatively unsaturated metal centers that can strongly bind specific sorbate molecules. It has been previously shown that improved force fields can be derived from quantum mechanical calculations. In this work, we derived force fields for an isostructural series of MOFs, M-MOF-74, where M = Mn, Co, Ni, and Cu, from first principles. Monte Carlo calculations in the Gibbs ensemble were used to calculate the CO 2 adsorption isotherms in order to assess the quality of the derived force field parameters and to determine a generally applicable procedure for obtaining a reliable force field for a targeted MOF and adsorbate system. The computed CO 2 adsorption isotherms for the different M-MOF-74 members agree with experimental measurements at low loading and show that Ni-MOF-74 possesses the highest affinity toward CO 2 and Cu-MOF-74 the weakest. In addition, we explored the source of open metal site and pore inaccessibility in these materials and quantified its impact on adsorption, especially the discrepancies often observed between experiments and simulations at high loadings.
A dicobalt complex catalyzes N 2 silylation with Me 3 SiCl and KC 8 under 1 atm N 2 at ambient te... more A dicobalt complex catalyzes N 2 silylation with Me 3 SiCl and KC 8 under 1 atm N 2 at ambient temperature. Tris(trimethylsilyl)amine is formed with an initial turnover rate of 1 N(TMS) 3 /min, ultimately reaching a turnover number of ∼200. The dicobalt species features a metal−metal interaction, which we postulate is important to its function. Although N 2 functionalization occurs at a single cobalt site, the second cobalt center modifies the electronics at the active site. Density functional calculations reveal that the Co−Co interaction evolves during the catalytic cycle: weakening upon N 2 binding, breaking with silylation of the metal-bound N 2 and reforming with expulsion of [N 2 (SiMe 3) 3 ] −. T he N−Si bond has long been recognized as a useful linkage in organic synthesis for masking primary and secondary amines. Catalytic schemes to construct such bonds directly from N 2 are underdeveloped and could revolutionize the manufacturing of silylamines, which are increasingly important as industrial chemicals. For example, trisilylamines are used to fabricate silicon-nitride semiconductors in front-end electronic applications , and Si−N based polymers are incorporated into ceramic materials to impart thermal resistance. 1 Developing N 2 silylation catalysts 2 also complements ongoing research in N 2 fixation to ammonia, as they share the challenge of functionalizing N 2 , a molecule that is both thermodynamically stable and kinetically inert, in an efficient and selective manner. 3 A known catalyst for N 2 silylation is Mo(depf) 2 (N 2) 2 (depf =1,1′-bis(diethylphosphino)ferrocene), which produces N-(SiMe 3) 3 from N 2 (1 atm), Me 3 SiCl, and Na (s) , with a turnover number (TON) of 150. 2d Efforts to surpass the Mo catalyst with a first-row transition metal have met with limited success. 2b A survey of iron coordination complexes showed subdued TONs, attaining a maximum of 34. 2e,g We report a dicobalt catalyst that achieves relatively high TON of N(SiMe 3) 3 at 299 K. The catalyst features a hemilabile metal−metal interaction, which is an unusual hallmark in catalytic N 2 functionalization. 3g,4 The precatalyst, Co 2 L (1) comprises a (Co 2) 3+ core within the trisphosphino(triamido)amine ligand (L 3−) framework (Figure 1, SI). 5 Under N 2 , the cyclic voltammogram of 1 showed two one-electron transfer processes at −2.11 and −2.54 V (vs Fc + /Fc, SI Figure 6). The first reduction is irreversible with ΔE p of 0.4 V and an i pc /i pa ratio of 0.64. The electrochemical behavior is consistent with an ECE mechanism, where the chemical reaction (C) following the first electron transfer (E) is most likely dinitrogen binding. 6 Indeed, reduction of 1 with 1 equiv KC 8 in the presence of N 2 and 2.2.2-cryptand (abbreviated as crypt-222) led to the isolation of K(crypt-222)[Co 2 (N 2)L] (2) containing an end-on N 2 ligand (Figure 1). Infrared spectroscopy of 2 revealed an N−N stretching frequency of 1994 cm −1 , which is consistent with slight weakening of the N 2 triple bond. 7 The molecular structures of 1 and 2 are shown in Figure 1b,c, respectively (SI Tables 1−2). The Co−Co bond distance elongates substantially from 2.32 to 2.68 Å upon reduction of Co 2 3+ 1 to Co 2 2+ 2. As the sum of the metallic radii of two cobalt atoms is 2.314 Å, the former is consistent with a Co−Co single bond, while the latter is a weak Co−Co interaction. 8 The magnetic susceptibilities of 1 and 2 were measured from 2 to 290 K and are consistent with S = 5/2 and S = 1 ground states, respectively (SI Figures 9−11). The effective magnetic moment for sextet 1 decreases slightly from 6.1 to 5.8 μ B from 50 to 290 K. To fit the data, a two-spin model is needed with ferromagnetic coupling (J = 60 cm −1) between Co(II), S = 3/2, and Co(I), S = 1, centers. The triplet state of 2 is energetically isolated, with a g-Figure 1. (a) Reduction of Co 2 L (1) to generate K(crypt-222)-[Co 2 (N 2)L] (2). (b,c) Molecular structures of 1 and 2, respectively, shown with 50% thermal ellipsoids. Hydrogen atoms (and counterion for 2) were removed for clarity. Communication pubs.acs.org/JACS
The interactions of H2, CO, CO2, and H2O with the undercoordinated metal centers of the trimetall... more The interactions of H2, CO, CO2, and H2O with the undercoordinated metal centers of the trimetallic oxo-centered M3(III)(μ3-O)(X) (COO)6 moiety are studied by means of wave function and density functional theory. This trimetallic oxo-centered cluster is a common building unit in several metal-organic frameworks (MOFs) such as MIL-100, MIL-101, and MIL-127 (also referred to as soc-MOF). A combinatorial computational screening is performed for a large variety of trimetallic oxo-centered units M3(III)O (M = Al(3+), Sc(3+), V(3+), Cr(3+), Fe(3+), Ga(3+), Rh(3+), In(3+), Ir(3+)) interacting with H2O, H2, CO, and CO2. The screening addresses interaction energies, adsorption enthalpies, and vibrational properties. The results show that the Rh and Ir analogues are very promising materials for gas storage and separations.
ABSTRACT Using explicitly-correlated coupled-cluster theory with single and double excitations, t... more ABSTRACT Using explicitly-correlated coupled-cluster theory with single and double excitations, the intermolecular distances and interaction energies of the T-shaped imidazole...benzene and pyrrole...benzene complexes have been computed in a large augmented correlation-consistent quadruple-zeta basis set, adding also corrections for connected triple excitations and remaining basis-set-superposition errors. The results of these computations are used to assess other methods such as Moller-Plesset perturbation theory (MP2), spin-component-scaled MP2 theory, dispersion-weighted MP2 theory, interference-corrected explicitly-correlated MP2 theory, dispersion-corrected double-hybrid density-functional theory (DFT), DFT-based symmetry-adapted perturbation theory, the random-phase approximation, explicitly-correlated ring-coupled-cluster-doubles theory, and double-hybrid DFT with a correlation energy computed in the random-phase approximation.
ABSTRACT Interference-corrected explicitly correlated second-order perturbation theory (INT-MP2-F... more ABSTRACT Interference-corrected explicitly correlated second-order perturbation theory (INT-MP2-F12) is applied to accelerate the convergence to the complete-basis-set limit of coupled-cluster computations. Adding energy terms obtained from INT-MP2-F12 theory to the energies obtained from coupled-cluster singles-and-doubles (CCSD) computations yields a mean absolute deviation (MAD) from explicitly correlated CCSD results below 1 kJ/mol for a test set of 106 molecules. A composite scheme for the computation of atomization energies is assessed. This scheme is denoted as CCSD(T)+F12+INT and consists of the CCSD model with perturbative triples (CCSD(T)) supplemented with INT-MP2-F12 corrections, using a quadruple-zeta quality basis set (cc-pVQZ-F12). The composite scheme achieves chemical accuracy with respect to experimentally derived or computed reference values. Using Boys localized molecular orbitals, the MAD of the CCSD(T)+F12+INT/cc-pVQZ-F12 atomization energies from the reference values is below 1 kJ/mol for the G2/97 test set.
Journal of the American Chemical Society, Jan 11, 2015
A dicobalt(II) complex, [Co2(mBDCA-5t)](2-) (1), demonstrates a cofacial arrangement of trigonal ... more A dicobalt(II) complex, [Co2(mBDCA-5t)](2-) (1), demonstrates a cofacial arrangement of trigonal monopyramidal cobalt(II) ions with an inter-metal separation of 6.2710(6) Å. Reaction of 1 with potassium superoxide generates an encapsulated Co-O-Co core in the dianionic complex [Co2O(mBDCA-5t)](2-) (2); to form the linear Co-O-Co core, the inter-metal distance has diminished to 3.994(3) Å. Co K-edge X-ray absorption spectroscopy data are consistent with a +2 oxidation state assignment for cobalt in both complexes 1 and 2. Multireference complete active space calculations followed by second order perturbation theory, CASPT2, support this assignment, with hole equivalents residing on the bridging oxygen atom and on the cryptand ligand for the case of 2. Complex 2 acts as a two-electron oxidant towards substrates including CO and H2, in both cases efficiently regenerating 1 in what represent net oxygen atom transfer (OAT) reactions. This dicobalt system also functions as a catalase upon...
The applicability and accuracy of the generalized active space self-consistent field, (GASSCF), a... more The applicability and accuracy of the generalized active space self-consistent field, (GASSCF), and (SplitGAS) methods are presented. The GASSCF method enables the exploration of larger active spaces than with the conventional complete active space SCF, (CASSCF), by fragmentation of a large space into subspaces and by controlling the interspace excitations. In the SplitGAS method, the GAS configuration interaction, CI, expansion is further partitioned in two parts: the principal, which includes the most important configuration state functions, and an extended, containing less relevant but not negligible ones. An effective Hamiltonian is then generated, with the extended part acting as a perturbation to the principal space. Excitation energies of ozone, furan, pyrrole, nickel dioxide, and copper tetrachloride dianion are reported. Various partitioning schemes of the GASSCF and SplitGAS CI expansions are considered and compared with the complete active space followed by second-order perturbation theory, (CASPT2), and multireference CI method, (MRCI), or available experimental data. General guidelines for the optimum applicability of these methods are discussed together with their current limitations.
The separation, capture and storage of carbon dioxide from the flue gas is an environmental and e... more The separation, capture and storage of carbon dioxide from the flue gas is an environmental and economical problem of significant importance. Zeolites and activated carbons have been used from the industries in order to reduce the emissions of CO2. A new family of materials, the metal-organic frameworks (MOFs), has been recently proposed as an efficient substitute of the abovementioned materials.
Journal of the American Chemical Society, Jan 17, 2015
The catalytic properties of the metal-organic framework Fe2(dobdc), containing open Fe(II) sites,... more The catalytic properties of the metal-organic framework Fe2(dobdc), containing open Fe(II) sites, include hydroxylation of phenol by pure Fe2(dobdc) and hydroxylation of ethane by its magnesium-diluted analogue, Fe0.1Mg1.9(dobdc). In earlier work, the latter reaction was proposed to occur through a redox mechanism involving the generation of an iron(IV)-oxo species, which is an intermediate that is also observed or postulated (depending on the case) in some heme and non-heme enzymes and their model complexes. In the present work, we present a detailed mechanism by which the catalytic material, Fe0.1Mg1.9(dobdc), activates the strong C-H bonds of ethane. Kohn-Sham density functional and multireference wave function calculations have been performed to characterize the electronic structure of key species. We show that the catalytic non-heme-Fe hydroxylation of the strong C-H bond of ethane proceeds by a quintet single-state σ-attack pathway after the formation of highly reactive iron-o...
Non-covalent interactions can usually be described accurately at the coupled-cluster level of the... more Non-covalent interactions can usually be described accurately at the coupled-cluster level of theory using single, double and triple excitations, the latter within a perturbation-theory framework. However, since the computations with the corresponding coupled-cluster model, CCSD(T), are computationally very demanding, they can often not be carried out in large enough basis sets. This leads to a basis-set truncation error. To correct this error, a basis-set correction can be computed at the level of second-order Møller–Plesset (MP2) perturbation theory in the limit of a complete basis set, but such a correction tends to overestimate the magnitude of the basis-set truncation error. In the present work, we suggest to damp the basis-set correction obtained at the complete-basis-set MP2 level using interference factors for individual occupied orbital pairs. The approach is applied to the non-covalent interactions of the S22B database, where the interference correction turns out to be very small.
The air-free reaction of CoCl 2 with 1,3,5-tri(1H-1,2,3-triazol-5-yl)benzene (H 3 BTTri) in N,N-d... more The air-free reaction of CoCl 2 with 1,3,5-tri(1H-1,2,3-triazol-5-yl)benzene (H 3 BTTri) in N,N-dimethylforma-mide (DMF) and methanol leads to the formation of Co-BTTri (Co 3 [(Co 4 Cl) 3 (BTTri) 8 ] 2 ·DMF), a sodalite-type metal− organic framework. Desolvation of this material generates coordinatively unsaturated low-spin cobalt(II) centers that exhibit a strong preference for binding O 2 over N 2 , with isosteric heats of adsorption (Q st) of −34(1) and −12(1) kJ/ mol, respectively. The low-spin (S = 1/2) electronic configuration of the metal centers in the desolvated framework is supported by structural, magnetic susceptibility, and computational studies. A single-crystal X-ray structure determination reveals that O 2 binds end-on to each framework cobalt center in a 1:1 ratio with a Co−O 2 bond distance of 1.973(6) Å. Replacement of one of the triazolate linkers with a more electron-donating pyrazolate group leads to the isostructural framework Co-BDTriP (Co 3 [(Co 4 Cl) 3 (BDTriP) 8 ] 2 ·DMF; H 3 BDTriP = 5,5′-(5-(1H-pyrazol-4-yl)-1,3-phenylene)bis(1H-1,2,3-triazole)), which demonstrates markedly higher yet still fully reversible O 2 affinities (Q st = −47(1) kJ/mol at low loadings). Electronic structure calculations suggest that the O 2 adducts in Co-BTTri are best described as cobalt(II)−dioxygen species with partial electron transfer, while the stronger binding sites in Co-BDTriP form cobalt(III)−superoxo moieties. The stability, selectivity, and high O 2 adsorption capacity of these materials render them promising new adsorbents for air separation processes.
Metal−organic frameworks (MOFs) are versatile nanoporous materials that have gained significant i... more Metal−organic frameworks (MOFs) are versatile nanoporous materials that have gained significant interest as low heat capacity, high selectivity sorbents for CO 2 capture applications. Large-scale atomistic simulations for identifying high-performance MOFs are possible, but are limited to systems for which existing molecular mechanics force fields describe the interactions between the guest and framework atoms with sufficient accuracy. However, standard force fields are not applicable to cases involving coordinatively unsaturated metal centers that can strongly bind specific sorbate molecules. It has been previously shown that improved force fields can be derived from quantum mechanical calculations. In this work, we derived force fields for an isostructural series of MOFs, M-MOF-74, where M = Mn, Co, Ni, and Cu, from first principles. Monte Carlo calculations in the Gibbs ensemble were used to calculate the CO 2 adsorption isotherms in order to assess the quality of the derived force field parameters and to determine a generally applicable procedure for obtaining a reliable force field for a targeted MOF and adsorbate system. The computed CO 2 adsorption isotherms for the different M-MOF-74 members agree with experimental measurements at low loading and show that Ni-MOF-74 possesses the highest affinity toward CO 2 and Cu-MOF-74 the weakest. In addition, we explored the source of open metal site and pore inaccessibility in these materials and quantified its impact on adsorption, especially the discrepancies often observed between experiments and simulations at high loadings.
A dicobalt complex catalyzes N 2 silylation with Me 3 SiCl and KC 8 under 1 atm N 2 at ambient te... more A dicobalt complex catalyzes N 2 silylation with Me 3 SiCl and KC 8 under 1 atm N 2 at ambient temperature. Tris(trimethylsilyl)amine is formed with an initial turnover rate of 1 N(TMS) 3 /min, ultimately reaching a turnover number of ∼200. The dicobalt species features a metal−metal interaction, which we postulate is important to its function. Although N 2 functionalization occurs at a single cobalt site, the second cobalt center modifies the electronics at the active site. Density functional calculations reveal that the Co−Co interaction evolves during the catalytic cycle: weakening upon N 2 binding, breaking with silylation of the metal-bound N 2 and reforming with expulsion of [N 2 (SiMe 3) 3 ] −. T he N−Si bond has long been recognized as a useful linkage in organic synthesis for masking primary and secondary amines. Catalytic schemes to construct such bonds directly from N 2 are underdeveloped and could revolutionize the manufacturing of silylamines, which are increasingly important as industrial chemicals. For example, trisilylamines are used to fabricate silicon-nitride semiconductors in front-end electronic applications , and Si−N based polymers are incorporated into ceramic materials to impart thermal resistance. 1 Developing N 2 silylation catalysts 2 also complements ongoing research in N 2 fixation to ammonia, as they share the challenge of functionalizing N 2 , a molecule that is both thermodynamically stable and kinetically inert, in an efficient and selective manner. 3 A known catalyst for N 2 silylation is Mo(depf) 2 (N 2) 2 (depf =1,1′-bis(diethylphosphino)ferrocene), which produces N-(SiMe 3) 3 from N 2 (1 atm), Me 3 SiCl, and Na (s) , with a turnover number (TON) of 150. 2d Efforts to surpass the Mo catalyst with a first-row transition metal have met with limited success. 2b A survey of iron coordination complexes showed subdued TONs, attaining a maximum of 34. 2e,g We report a dicobalt catalyst that achieves relatively high TON of N(SiMe 3) 3 at 299 K. The catalyst features a hemilabile metal−metal interaction, which is an unusual hallmark in catalytic N 2 functionalization. 3g,4 The precatalyst, Co 2 L (1) comprises a (Co 2) 3+ core within the trisphosphino(triamido)amine ligand (L 3−) framework (Figure 1, SI). 5 Under N 2 , the cyclic voltammogram of 1 showed two one-electron transfer processes at −2.11 and −2.54 V (vs Fc + /Fc, SI Figure 6). The first reduction is irreversible with ΔE p of 0.4 V and an i pc /i pa ratio of 0.64. The electrochemical behavior is consistent with an ECE mechanism, where the chemical reaction (C) following the first electron transfer (E) is most likely dinitrogen binding. 6 Indeed, reduction of 1 with 1 equiv KC 8 in the presence of N 2 and 2.2.2-cryptand (abbreviated as crypt-222) led to the isolation of K(crypt-222)[Co 2 (N 2)L] (2) containing an end-on N 2 ligand (Figure 1). Infrared spectroscopy of 2 revealed an N−N stretching frequency of 1994 cm −1 , which is consistent with slight weakening of the N 2 triple bond. 7 The molecular structures of 1 and 2 are shown in Figure 1b,c, respectively (SI Tables 1−2). The Co−Co bond distance elongates substantially from 2.32 to 2.68 Å upon reduction of Co 2 3+ 1 to Co 2 2+ 2. As the sum of the metallic radii of two cobalt atoms is 2.314 Å, the former is consistent with a Co−Co single bond, while the latter is a weak Co−Co interaction. 8 The magnetic susceptibilities of 1 and 2 were measured from 2 to 290 K and are consistent with S = 5/2 and S = 1 ground states, respectively (SI Figures 9−11). The effective magnetic moment for sextet 1 decreases slightly from 6.1 to 5.8 μ B from 50 to 290 K. To fit the data, a two-spin model is needed with ferromagnetic coupling (J = 60 cm −1) between Co(II), S = 3/2, and Co(I), S = 1, centers. The triplet state of 2 is energetically isolated, with a g-Figure 1. (a) Reduction of Co 2 L (1) to generate K(crypt-222)-[Co 2 (N 2)L] (2). (b,c) Molecular structures of 1 and 2, respectively, shown with 50% thermal ellipsoids. Hydrogen atoms (and counterion for 2) were removed for clarity. Communication pubs.acs.org/JACS
The interactions of H2, CO, CO2, and H2O with the undercoordinated metal centers of the trimetall... more The interactions of H2, CO, CO2, and H2O with the undercoordinated metal centers of the trimetallic oxo-centered M3(III)(μ3-O)(X) (COO)6 moiety are studied by means of wave function and density functional theory. This trimetallic oxo-centered cluster is a common building unit in several metal-organic frameworks (MOFs) such as MIL-100, MIL-101, and MIL-127 (also referred to as soc-MOF). A combinatorial computational screening is performed for a large variety of trimetallic oxo-centered units M3(III)O (M = Al(3+), Sc(3+), V(3+), Cr(3+), Fe(3+), Ga(3+), Rh(3+), In(3+), Ir(3+)) interacting with H2O, H2, CO, and CO2. The screening addresses interaction energies, adsorption enthalpies, and vibrational properties. The results show that the Rh and Ir analogues are very promising materials for gas storage and separations.
ABSTRACT Using explicitly-correlated coupled-cluster theory with single and double excitations, t... more ABSTRACT Using explicitly-correlated coupled-cluster theory with single and double excitations, the intermolecular distances and interaction energies of the T-shaped imidazole...benzene and pyrrole...benzene complexes have been computed in a large augmented correlation-consistent quadruple-zeta basis set, adding also corrections for connected triple excitations and remaining basis-set-superposition errors. The results of these computations are used to assess other methods such as Moller-Plesset perturbation theory (MP2), spin-component-scaled MP2 theory, dispersion-weighted MP2 theory, interference-corrected explicitly-correlated MP2 theory, dispersion-corrected double-hybrid density-functional theory (DFT), DFT-based symmetry-adapted perturbation theory, the random-phase approximation, explicitly-correlated ring-coupled-cluster-doubles theory, and double-hybrid DFT with a correlation energy computed in the random-phase approximation.
ABSTRACT Interference-corrected explicitly correlated second-order perturbation theory (INT-MP2-F... more ABSTRACT Interference-corrected explicitly correlated second-order perturbation theory (INT-MP2-F12) is applied to accelerate the convergence to the complete-basis-set limit of coupled-cluster computations. Adding energy terms obtained from INT-MP2-F12 theory to the energies obtained from coupled-cluster singles-and-doubles (CCSD) computations yields a mean absolute deviation (MAD) from explicitly correlated CCSD results below 1 kJ/mol for a test set of 106 molecules. A composite scheme for the computation of atomization energies is assessed. This scheme is denoted as CCSD(T)+F12+INT and consists of the CCSD model with perturbative triples (CCSD(T)) supplemented with INT-MP2-F12 corrections, using a quadruple-zeta quality basis set (cc-pVQZ-F12). The composite scheme achieves chemical accuracy with respect to experimentally derived or computed reference values. Using Boys localized molecular orbitals, the MAD of the CCSD(T)+F12+INT/cc-pVQZ-F12 atomization energies from the reference values is below 1 kJ/mol for the G2/97 test set.
Journal of the American Chemical Society, Jan 11, 2015
A dicobalt(II) complex, [Co2(mBDCA-5t)](2-) (1), demonstrates a cofacial arrangement of trigonal ... more A dicobalt(II) complex, [Co2(mBDCA-5t)](2-) (1), demonstrates a cofacial arrangement of trigonal monopyramidal cobalt(II) ions with an inter-metal separation of 6.2710(6) Å. Reaction of 1 with potassium superoxide generates an encapsulated Co-O-Co core in the dianionic complex [Co2O(mBDCA-5t)](2-) (2); to form the linear Co-O-Co core, the inter-metal distance has diminished to 3.994(3) Å. Co K-edge X-ray absorption spectroscopy data are consistent with a +2 oxidation state assignment for cobalt in both complexes 1 and 2. Multireference complete active space calculations followed by second order perturbation theory, CASPT2, support this assignment, with hole equivalents residing on the bridging oxygen atom and on the cryptand ligand for the case of 2. Complex 2 acts as a two-electron oxidant towards substrates including CO and H2, in both cases efficiently regenerating 1 in what represent net oxygen atom transfer (OAT) reactions. This dicobalt system also functions as a catalase upon...
The applicability and accuracy of the generalized active space self-consistent field, (GASSCF), a... more The applicability and accuracy of the generalized active space self-consistent field, (GASSCF), and (SplitGAS) methods are presented. The GASSCF method enables the exploration of larger active spaces than with the conventional complete active space SCF, (CASSCF), by fragmentation of a large space into subspaces and by controlling the interspace excitations. In the SplitGAS method, the GAS configuration interaction, CI, expansion is further partitioned in two parts: the principal, which includes the most important configuration state functions, and an extended, containing less relevant but not negligible ones. An effective Hamiltonian is then generated, with the extended part acting as a perturbation to the principal space. Excitation energies of ozone, furan, pyrrole, nickel dioxide, and copper tetrachloride dianion are reported. Various partitioning schemes of the GASSCF and SplitGAS CI expansions are considered and compared with the complete active space followed by second-order perturbation theory, (CASPT2), and multireference CI method, (MRCI), or available experimental data. General guidelines for the optimum applicability of these methods are discussed together with their current limitations.
The separation, capture and storage of carbon dioxide from the flue gas is an environmental and e... more The separation, capture and storage of carbon dioxide from the flue gas is an environmental and economical problem of significant importance. Zeolites and activated carbons have been used from the industries in order to reduce the emissions of CO2. A new family of materials, the metal-organic frameworks (MOFs), has been recently proposed as an efficient substitute of the abovementioned materials.
Journal of the American Chemical Society, Jan 17, 2015
The catalytic properties of the metal-organic framework Fe2(dobdc), containing open Fe(II) sites,... more The catalytic properties of the metal-organic framework Fe2(dobdc), containing open Fe(II) sites, include hydroxylation of phenol by pure Fe2(dobdc) and hydroxylation of ethane by its magnesium-diluted analogue, Fe0.1Mg1.9(dobdc). In earlier work, the latter reaction was proposed to occur through a redox mechanism involving the generation of an iron(IV)-oxo species, which is an intermediate that is also observed or postulated (depending on the case) in some heme and non-heme enzymes and their model complexes. In the present work, we present a detailed mechanism by which the catalytic material, Fe0.1Mg1.9(dobdc), activates the strong C-H bonds of ethane. Kohn-Sham density functional and multireference wave function calculations have been performed to characterize the electronic structure of key species. We show that the catalytic non-heme-Fe hydroxylation of the strong C-H bond of ethane proceeds by a quintet single-state σ-attack pathway after the formation of highly reactive iron-o...
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Papers by Konstantinos Vogiatzis