Adsorption and Catalytic Reduction of Nitrogen Oxides (NO, NO) on Disulfide Cluster Complexes of Cobalt and Iron-A Density Functional Study.

The reactivity of nitrogen oxide, NO, as a ligand in complexes with [Fe2-S2] and [Co2-S2] non-planar rhombic cores is examined by density functional theory (DFT). The cobalt-containing nitrosyl complexes are less stable than the iron complexes because the Co-S bonds in the [Co2-S2] core are weakened upon NO coordination. Various positions of NO were examined, including its binding to sulfur centers.

Cation binding of Li(I), Na(I) and Zn(II) to cobalt and iron sulphide clusters - electronic structure study.

The binding of alkaline (Li and Na) and zinc (Zn) cations to mononuclear disulphides MS and to persulphides, containing an S-S bond, M(S), to binuclear disulphides MS and persulphides M(S) and to cubic tetranuclear sulphides MS where M = Fe, Co, is examined by density functional theory with the B3LYP functional, and dispersion corrections were applied. For the small-sized clusters (up to two transition metal centres), the energy gaps between different configurations were verified by CCSD(T) calculations. Persulphides M(S) are more stable than disulphides MS as bare clusters, upon carbonyl and chloride ligand coordination and upon cation binding (Li, Na, Zn).

Cation pair formation in copper and palladium exchanged MFI zeolite frameworks - a theoretical study.

The coordination of copper and palladium cations in the channels of MFI frameworks is examined by the QM/MM approach within the ONIOM method. Density functional theory is applied to the high layer of the ONIOM models, and different rings and ring associations are considered with the aim to find the optimal positions for cation pair formation. The Al atoms were located at tetrahedral sites which are known to have high occupancy factors from crystal structure studies.

A theoretical study of nitric oxide adsorption and dissociation on copper-exchanged zeolites SSZ-13 and SAPO-34: the impact of framework acid-base properties.

The adsorption of nitric oxide as dinitrosyls and the deNOx proton-mediated reaction mechanism are assessed using electronic structure methods and transition state theory. Dinitrosyls bind to copper cations either via a N-atom or via an O-atom, with N-binding being more stable. In their ground states, dinitrosyls reach a planar configuration with the metal cation.

CO2 conversion to methanol on Cu(I) oxide nanolayers and clusters: an electronic structure insight into the reaction mechanism.

The mechanism of carbon dioxide reduction to methanol on Cu(I) oxide nanolayers and clusters using water as the source of hydrogen was traced using density functional theory. The nature of the active sites is revealed, namely the role of surface copper dimers, which are present on the Cu2O(001) surface and in the nanoclusters of size Cu32O16 and Cu14O7. The major difference between metal catalysts and Cu2O is outlined: the CO2 molecule interacts strongly with the oxide and undergoes bending prior to hydrogenation.

Electronic, magnetic structure and water splitting reactivity of the iron-sulfur dimers and their hexacarbonyl complexes: A density functional study.

The iron sulfide dimers (FeS)2 and their persulfide isomers with S-S bonds are studied with the B3LYP density functional as bare clusters and as hexacarbonyls. The disulfides are more stable than the persulfides as bare clusters and the persulfide ground state lies at 3.2 eV above the global minimum, while in the hexacarbonyl complexes this order is reversed: persulfides are more stable, but the energy gap between disulfides and persulfides becomes much smaller and the activation barrier for the transition persulfide → disulfide is 1.

Electronic structure and reactivity in water splitting of the iron oxide dimers and their hexacarbonyls: a density functional study.

The iron oxide dimers (FeO)2 and their peroxide isomers are studied with the B3LYP density functional as bare clusters and as hexacarbonyls. Among the bare clusters the planar four-member ring structures are more stable than the non-planar ones and the rhombic dioxide Fe2O2 with antiferromagnetically ordered electrons on iron centers is the global minimum. Water adsorption on the bare diiron dioxide is exothermic, but dissociation does not occur.

Electronic structure and reactivity of cobalt oxide dimers and their hexacarbonyl complexes: a density functional study.

The dimers of cobalt oxide (CoO)(2) with cyclic and open bent structure are studied with the B1LYP density functional; the ordering of states is validated by the CCSD(T) method. The D(2h)-symmetry rhombic dioxide Co(2)O(2) with antiferromagnetically ordered electrons on cobalt centers is the global minimum. The cyclic peroxide Co(2)(O(2)) with side-on-bonded dioxygen in (7)B(2) ground state is separated from the global minimum by an energy gap of 3.

Density functional study of the stable oxidation states and the binding of oxygen in MO4 clusters of the 3d elements.

The tetraoxide clusters with stoichiometry MO(4), and the structural isomers with side-on and end-on bonded dioxygen, are studied by DFT with the B1LYP functional. Diperoxides M(O(2))(2) are the most stable clusters at the beginning (Sc, Ti) and at the end of the row (Co-Cu), the latter being planar. For V, Cr, and Mn, the dioxoperoxides O(2)M(O(2)) are the most stable isomers.

Electronic structure of trioxide, oxoperoxide, oxosuperoxide, and ozonide clusters of the 3d elements: density functional theory study.

The trioxide clusters with stoichiometry MO3, and the structural isomers with side-on and end-on bonded oxygen atoms, are studied by DFT with the B1LYP functional. For the first half of the 3d elements row (Sc to Cr), pyramidal or distorted pyramidal structures dominate among the trioxide and oxoperoxide ground states, while the remaining elements form planar trioxides, oxoperoxides, oxosuperoxides, and ozonides. Low-lying trioxide clusters are formed by Ti, V, Cr, and Mn, among which the distorted pyramidal VO3 in the (2)A'' state, the pyramidal CrO3 in the (1)A1 state, and the planar MnO3 in the (2)A1' state are global minima.

Intersystem crossings of the triplet and singlet States in cobalt and copper mononitrosyls.

Local minima on the singlet, triplet, and quintet potential energy surfaces (PES) of cobalt and copper mononitrosyls are studied by DFT with the B3LYP functional. While quintet states are separated from the triplet and singlet states by a high energy gap, the linear singlet local minimum and the triplet transition state of CoNO lie close together. The ordering of local minima by relative stability of low-lying excited states with respect to the ground state was assessed by B3LYP, the coupled-cluster method CCSD(T), and complete active space calculations (CAS MP2).

Electronic structure of oxide, peroxide, and superoxide clusters of the 3d elements: a comparative density functional study.

The 3d-element transition metal dioxide MO(2), peroxide M(O(2)), and superoxide MOO clusters (M=Sc-Zn), are studied by density functional theory with the B1LYP functional. The reliability of the methods and basis sets employed was tested by a reinvestigation of the monoxides, for which a database of experimental data is available. The global minima on the M+O(2) potential energy surfaces correspond to dioxide structure, the only exception being CuOO, with a superoxide structure.

Interaction of molecular nitrogen and oxygen with extraframework cations in zeolites with double six-membered rings of oxygen-bridged silicon and aluminum atoms: a DFT study.

The interaction of N(2) and O(2) with extraframework cations of zeolite frameworks was studied by DFT, using the B3LYP method. The extraframework cation sites located in the vicinity of the double six-member rings (D6R) of FAU zeolites (SI, SI', SIII') were considered and clusters with composition (M(n)(+))(2/)(n)()H(12)Si(10)Al(2)O(18), M = Li(+), Na(+), K(+), Ca(2+), were selected to represent the adsorption centers. The cation sites SII in the center of single six-membered rings (S6R) were modeled by [M(I)H(12)Si(4)Al(2)O(6)](-) and M(II)H(12)Si(4)Al(2)O(6) clusters.

Manganese, iron, cobalt, and nickel oxo-, peroxo-, and superoxoclusters: a density functional theory study.

The 3d-transition-metal dioxo-, peroxo-, and superoxoclusters with the general composition MO2, M(O2), and MOO (M = Mn, Fe, Co, and Ni) were studied by DFT by the B1LYP functional. The dioxides in their ground states represent the global minima for the M + O2 system. Both ground-state dioxides and the lowest-energy peroxides are in their (d-only) highest spin states.