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1.
Inorg Chem ; 58(23): 15751-15757, 2019 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-31710211

RESUMO

The performance of MnII/III-monosubstituted heteropolytungstates [MnIII(H2O)GeW11O39]5- ([GT-MnIII-OH2]5-, where GT = GeW11O39) and [MnII(H2O)GeW11O39]6- ([GT-MnII-OH2]6-) as water oxidation catalysts at pH 9 was explored using density functional theory calculations. The counterion effect was fully considered, in which five and six Na+ ions were included in the calculations for water oxidation catalyzed by [GT-MnIII-OH2]5- and [GT-MnII-OH2]6-, respectively. The process of water oxidation catalysis was divided into three elemental stages: (i) oxidative activation, (ii) O-O bond formation, and (iii) O2 evolution. In the oxidative activation stage, two electrons and two protons are removed from [Na5-GT-MnIII-OH2] and three electrons and two protons are removed from [Na6-GT-MnII-OH2]. Therefore, the MnIV-O• species [Na5-GT-MnIV-O•] is obtained. Two mechanisms, (i) water nucleophilic attack and (ii) oxo-oxo coupling, were demonstrated to be competitive in O-O bond formation triggered from [Na5-GT-MnIV-O•]. In the last stage, the O2 molecule could be readily evolved from the peroxo or dinuclear species and the catalyst returns to the ground state after the coordination of a water molecule(s).

2.
Inorg Chem ; 58(24): 16518-16523, 2019 Dec 16.
Artigo em Inglês | MEDLINE | ID: mdl-31774665

RESUMO

The design and synthesis of polynuclear metal cluster-based coordination cages is of considerable interest due to their appealing structural characteristics and potential applications. Herein, we report a calix[4]resorcinarene-based [Co12] coordination cage, [Co12(TPC4R-I)2(1,3-BDC)10(µ3-OH)4(H2O)10(DMF)2]·7DMF·23H2O (1), assembled with 2 bowl-shaped calix[4]resorcinarenes (TPC4R-I), 10 angular 1,3-benzenedicarboxylates (1,3-BDC), and 12 Co(II) cations. Remarkably, it is shown to be a highly efficient recyclable heterogeneous catalyst for CO2 conversion due to its exposed Co(II) Lewis acid sites.

3.
Chem Commun (Camb) ; 54(57): 7959-7962, 2018 Jul 12.
Artigo em Inglês | MEDLINE | ID: mdl-29956695

RESUMO

Dual catalysis has become a desirable alternative because of the synergetic effect of two distinct catalysts, but little is known about the mechanism of dual catalysis and its effect on the high reactivity and selectivity. Here, a novel Ullmann C-C cross-coupling of bromobenzene and 4-methoxyphenyltriflate via nickel/palladium dual catalysis has been investigated using density functional theory. The orthogonal reactivity of NiI/Pd0 combination is the precondition and foundation of achieving such a Ullmann cross-coupling reaction. In the present dual catalysis, the NiI complex acts as the primary catalyst, while the Pd0 catalyst plays a decisive role in the cross-selectivity.

4.
Chem Commun (Camb) ; 54(47): 5968-5971, 2018 Jun 08.
Artigo em Inglês | MEDLINE | ID: mdl-29770395

RESUMO

A novel oxidation state modulation mechanism, merging oxidative quenching (IrIII-*IrIII-IrIV-IrIII) and nickel catalytic (NiII-NiI-NiIII-NiI-NiII) cycles, has been illuminated unambiguously for photoredox-mediated iridium(iii)/nickel(ii) dual catalyzed C-O cross-coupling of aryl bromide and alcohol. Quinuclidine participates in a crucial proton-coupled electron transfer process to accelerate the reaction and regulate C-O coupling selectivity.

5.
Dalton Trans ; 46(46): 16145-16158, 2017 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-29130092

RESUMO

Density functional theory calculations combined with the energy and building-block decomposition analyses have been carried out to investigate the structures, stability orders, redox potentials and proton binding of the six Baker-Figgis isomers (α, ß, γ, α*, ß* and γ*) of [(SbO6)W18O54(OH)2]9- {H2SbW18} and [(NaF6)W18O54(OH)2]7- {H2NaW18} anions at the level of PBEsol-D3/TZP. Both bonding energy and Gibbs free energy analyses exhibit that the two non-classical Wells-Dawson (WD) species behave quite differently from each other. The pyroanimonate {H2SbW18}, with a stability order of γ* > ß* > α > α* > ß > γ, is a non-classical WD species, while the hexafluoride {H2NaW18} (α > ß > γ > γ* > ß* > α*) is a transition intermediate between classical and non-classical WD types, possessing both non-classical ([XW18O60(OH)2]n-, X = I, Te and W) and classical [Si2W18O62]8- properties. Energy decomposition analyses (EDA) reveal that spatial arrangement (Ehost), host-guest fragment interaction energy (FIE), and structural distortion energy (DE) are three key factors governing the relative stability of isomers; among these, DE is always dominant, while FIE and Ehost are subordinated but are still important. Building-block decomposition analyses (BDA) disclose that the octahedral {MO6} units of the equatorial belt, particularly the staggered belt, are always more distorted than those of the two polar caps inside each structure. The theoretical redox potentials demonstrate that the oxidizing power increases with a trend of α < ß < γ and α* < ß* < γ* for both species, and the first redox potential is closely related to the energy level of the LUMO of each anion. Evaluation of the proton inclusion energies suggests that {H2NaW18} can only embed two protons, while {H2SbW18} may encapsulate four; the number of embedded protons is controlled by both the charge of the heteroatom X and the volume of the tetrahedral {O4}/{OF3} cavity.

6.
J Am Chem Soc ; 138(35): 11069-72, 2016 09 07.
Artigo em Inglês | MEDLINE | ID: mdl-27549571

RESUMO

The cleavage of inert C-C bonds is a central challenge in modern chemistry. Multinuclear transition metal complexes would be a desirable alternative because of the synergetic effect of multiple metal centers. In this work, carbon-carbon bond cleavage and rearrangement of benzene by a trinuclear titanium hydride were investigated using density functional theory. The reaction occurs via a novel "two-state reactivity" mechanism. The important elementary steps consist of hydride transfer, benzene coordination, dehydrogenation, oxidative addition, hydride-proton exchange, and reductive elimination. Most importantly, the ground-state potential energy surface switches from nearly degenerate triplet and antiferromagnetic singlet states to a closed-shell singlet state in the dearomatization of benzene, which effectively decreases the activation barrier. Furthermore, the roles of the transition metal centers and hydrides were clarified.

7.
Dalton Trans ; 44(19): 9063-70, 2015 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-25894867

RESUMO

A thorough theoretical analysis was carried out on the sulfoxidation with H2O2 catalyzed by a tetranuclear peroxotungstate [SiO4{WO(O2)2}4](4-). The active species is the [SiO4{WO(O2)2}4(H2O2)](4-) (SiW4(H2O2)) complex rather than [SiO4{WO(O2)2}4](4-) (SiW4). The catalytic cycle consists of three elementary processes: oxygen transfer, sulfoxide dissociation, and catalyst regeneration. The oxygen transfer occurs from the peroxo oxygen atom O1 of SiW4(H2O2) to the sulfur center of dimethyl sulfide with a moderate Gibbs activation energy (ΔG°(‡)) of 17.1 kcal mol(-1). By comparing potential energy surfaces and condensed Fukui functions (ƒ(+)), the electrophilicity of the outer peroxo atoms in SiW4(H2O2) determines which oxygen transfers to the dimethyl sulfide. Then, the sulfoxide dissociation proceeds with a small ΔG°(‡) value of 2.3 kcal mol(-1) by elongation of the peroxo O1-O4 distance and elimination of the product dimethylsulfoxide. Finally, the catalyst regeneration is found to occur via two successive proton transfers from H2O2 to the oxygen atoms of peroxotungstates with the ΔG°(‡) values of 15.9 and 15.3 kcal mol(-1), which has been firstly examined in the present study. All of these steps occur easily with moderate ΔG°(‡) values, but the oxygen transfer is the rate-determining step of this catalytic reaction. In addition, the catalytic activity of peroxotungstates can be effectively tuned by changing the heteroatom X of [XO4{WO(O2)2}4(H2O2)](n-) in the order: Se(VI) ≈ S(VI) > As(V) ≈ P(V) > Si(IV).


Assuntos
Peróxido de Hidrogênio/química , Teoria Quântica , Sulfóxidos/síntese química , Compostos de Tungstênio/química , Arsênico/química , Catálise , Fósforo/química , Selênio/química , Silício/química , Sulfóxidos/química , Enxofre/química , Termodinâmica
8.
Chem Commun (Camb) ; 50(80): 11934-7, 2014 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-25157800

RESUMO

An ultrastable [Ag55(MoO4)6](43+) ({Ag55Mo6} for short) nanocluster with a Ag-centered multishell structure in compound [Ag55(MoO4)6(C≡C(t)Bu)24(CH3COO)18](OAc)·2H2O (1) has been obtained. The ultrastability of 1 was demonstrated by Mulliken population analysis. In addition, the potential wide gap semiconductor property and electrochemical properties of 1 were investigated.

9.
Phys Chem Chem Phys ; 16(33): 18017-22, 2014 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-25050910

RESUMO

Density functional theory (DFT) calculations and natural bond orbital (NBO) analysis were carried out to investigate the electronic structures and bonding features between the ruthenium(ii) atom and the SO2 molecule in two ruthenium-sulfur dioxide (SO2) adducts, trans-Ru(NH3)4(SO2)Cl(+) and [{SiW11O39}Ru(II)(SO2)](6-). In addition, the bonding interactions between SO2 and the metal-ruthenium fragment were determined by binding energy (ΔEabs) calculation and electronic structures. The results indicate that the η(1)-S-planar model in both trans-Ru(NH3)4(SO2)Cl(+) and [{SiW11O39}Ru(II)(SO2)](6-) are more favorable. NBO analysis of the bonding interaction between ruthenium and sulfur centers in the [{SiW11O39}Ru(II)(SO2)](6-) complex shows that it possesses a σ and a π bond. It predicts that the polyoxometalate [SiW11O39Ru](6-) can serve as a potential adsorbent for the SO2 molecule because of the strong Ru-S bond relative to Ru(NH3)4Cl(+).

10.
Dalton Trans ; 43(28): 10695-9, 2014 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-24921974

RESUMO

We report a rare all-thiol-stabilized [Ag28(S(t)Bu)23](5+) ({Ag28S23} for short) nanocluster with a "crab-like" shape in compound [Ag28(S(t)Bu)23](CF3COO)5·8CH3OH (1), which has been synthesized by the self-assembly of AgS(t)Bu with CF3COOH, Et3N and KBr/KI in methanol. The diffuse reflection spectrum and luminescence spectra of 1 were investigated.

11.
Dalton Trans ; 43(26): 9847-50, 2014 Jul 14.
Artigo em Inglês | MEDLINE | ID: mdl-24867456

RESUMO

A new organic-inorganic hybrid titaniobate compound, [Cu(en)2][Cu(en)2(H2O)2]3[Ti2Nb8O28]·8H2O (1) (en = ethylenediamine), was successfully synthesized, characterized by single-crystal X-ray diffraction, IR spectroscopy, thermogravimetric analysis (TGA) and UV-Vis diffuse reflectance spectroscopy and its photoluminescence studied.


Assuntos
Cobre/química , Nióbio/química , Óxidos/química , Titânio/química , Estrutura Molecular , Difração de Pó , Análise Espectral/métodos , Termogravimetria , Difração de Raios X
12.
Dalton Trans ; 43(13): 5069-75, 2014 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-24413566

RESUMO

The rotary motion based on metallacarboranes around a molecular axis can be controlled by simple electron transfer processes, which provides a basis for the structure-property relationship for the nonlinear optical (NLO) switching. However, this phenomenon has not been previously reported in the development of NLO properties of metallacarboranes. In this work, the metallacarboranes [Ni(III/IV)(C2B9H11)2](-/0) and their C-,B-functionalized derivatives are studied by the density functional theory (DFT) method. By calculating relative energies, we obtained the stable states before and after rotation controlled by simple electron transfer. Then, the static and frequency-dependent second-order NLO properties were calculated by several DFT functionals. According to the TDDFT results, the large NLO responses of the studied compounds are mainly caused by substituent group-to-carborane cage charge transfer (L'LCT) and substituent group-to-metal charge transfer (L'MCT) processes. The order of first hyperpolarizabilities (ß values) illustrates that the NLO response can be enhanced by introducing a strong electron-donating group. Significantly, the geometric interconversions resulting from the redox reaction of 1C/1T-6C/6T allow the NLO responses to be switched "ON" or "OFF". The B(9,9')-methoxyphenyl-functionalized derivative of nickelacarborane, having low energetic cost and large different NLO responses between two states (from 0 to 20 998 a.u.), can be an excellent switchable NLO material.

13.
J Phys Chem A ; 117(41): 10783-9, 2013 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-24099065

RESUMO

The switchable second-order nonlinear optical (NLO) properties on two-dimensional (2D) molecules based on Lindqvist-type [Mo6O19](2-) and dithienylperfluorocyclopentene (DTE) have been investigated at density functional theory (DFT) level. The CAM-B3LYP and M06-2X functionals were employed to study the switching behavior on NLO properties by photoisomerization reaction. The ßtot value of system 2c (closed-ring form) is 15920.5 au, which is 150.1 times larger than that of the corresponding open-ring form (system 2o). The time-dependent DFT calculations predict that the charge transfer from DTE to polyoxometalate, and DTE intramolecular charge transfer in closed-ring systems effectively improve the static first hyperpolarizability. Furthermore, the Λ-shaped systems possess a larger u value than those of W-shaped systems owing to different orientation for substituent groups.

14.
Sci Rep ; 3: 2616, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-24019078

RESUMO

A novel 3D hexadecanuclear heteropolyoxozincate organic framework, IFMC-200, has been successfully synthesized based on a late transition metal-oxygen cluster. IFMC-200 not only represents the first example of (3,4,24)-connected framework but also contains the first 24-connected single metal cluster in a crystal structure. It exhibits superior thermal stability, good water-stability, and even insensitivity to the existence of acid and base within a certain range of pH values. Furthermore, it performs as a heterogeneous crystalline Lewis acid catalyst with good activity for the conversion of long-chain fatty acids rather than short-chain ones, and high recycling efficiency for esterification reaction of fatty acids with alcohols to produce biodiesel.

15.
J Mol Graph Model ; 44: 26-32, 2013 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-23732303

RESUMO

The ultraviolet-visible and electronic circular dichroism (UV-vis/ECD) spectra of diphosphonate-functionalized asymmetric cantilever-type chiral polyoxomolybdate (POM) enantiomer R-{Mo2O5[(Mo2O6)NH3CH2CH2CH2C(O)(PO3)2]2}(6-) (R) were systematically investigated using time-dependent density functional theory (TDDFT) method. From the view of molecular structure and relative energy, we inferred that there is likely a structural conversion from enantiomers R to S-{Mo2O5[(Mo2O6)NH3CH2CH2CH2C(O)(PO3)2]2}(6-) (S) via the intermediate configuration (IN). The ECD spectra of the enantiomer R were produced over the range of 3.0-6.3eV. The UV-vis and ECD spectra of enantiomer R in the gas phase and different solvents were calculated. The results reveal that the UV-vis and ECD spectra of the chiral POM in gas phase, polar solvent, or non-polar solvent are different. The calculated electron density difference maps (EDDMs) display that the POM cluster is a chiroptical chromophore in studied compound.


Assuntos
Dicroísmo Circular , Difosfonatos/química , Elétrons , Modelos Moleculares , Molibdênio/química , Polímeros/química , Solventes/química , Conformação Molecular
16.
Dalton Trans ; 42(29): 10617-25, 2013 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-23765391

RESUMO

Water oxidation is a key half reaction in the energy conversion scheme. The reaction mechanism for the oxidation of H2O to O2 catalyzed by single-Ru-substituted polyoxometalates, [Ru(III)(H2O)XW11O39](n-) (X = Si(IV), Ge(IV)), was investigated by means of density functional calculations. The electronic structure of the pre-activation intermediates indicates that the aqua ligand is prone to accommodate the proton coupled electron transfer (PCET) process to achieve the active group [Ru(V)=Oa], and the high valent oxo-ruthenium(V) species are responsible for the O-O forming event. Three possible proton acceptors were designed for the rate-determining step (Ob, Oa, and H2O), the calculated results support that the bridge Ob atom of the polytungstate ligand will act as the most favorable proton acceptor in the O-O bond formation, with an energy barrier of 28.43 kcal mol(-1). A detailed information of the peroxidic intermediates in the oxidation process was also characterized, both the peroxo-species [Ru(IV)(OO)SiW11O39](6-) and [Ru(V)(OO)SiW11O39](5-) show the six-coordinate isomer with an open terminal geometry is more favorable than the close seven-coordinate ones. In addition, the replacement of the heteroatom in XO4(n-) can effectively tune the catalytic activity of polyoxometalates, in the order of Ge(IV) > Si(IV).

17.
J Phys Chem A ; 117(12): 2492-8, 2013 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-23452254

RESUMO

The electronic circular dichroism (ECD) and UV-visible absorption (UV-vis) spectra of Strandberg-type polyoxometalates (POMs) (R, R)-[(R*PO3)2M5O15](2-) (R* = CH3CH(NH3), (M = Mo, W)) have been explored using the time-dependent density functional theory (TDDFT) method. It demonstrates that the absolute configurations of chiral systems can be determined by chiroptical spectroscopic methods combined with DFT calculations. The calculated ECD spectra of the Strandberg-type molybdate were produced over the range of 3.3-6.5 eV, which are generally in agreement with the experimental spectra. In addition, the ECD spectra of (R, R)-[(R*PO3)2W5O15](2-) (R* = CH3CH(NH3)) were produced over the range of 4.5-8.5 eV. The Becke's half-and-half hybrid exchange-correlation functional (BHandHLYP) with the HF exchange fraction to 55% hybrid functional was found to well predict the excitation energies of studied systems. The origins of the ECD bands of two systems are mainly ascribed to charge-transfer (CT) transitions from oxygen atoms to metal atoms in polyanion. The results suggest that the polyanion are chiroptical chromophores. The polyanion plays a role as an optically active chromophore and contribute to the absorptions of ECD spectra. The difference of the UV-vis/ECD spectra between two systems shows that the transition metal atom significantly influences on the chiroptical properties of the studied Strandberg-type POMs.

18.
J Mol Graph Model ; 40: 110-5, 2013 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-23419765

RESUMO

The switchable second-order nonlinear optical (NLO) responses of the photoisomerized chromophore dithienylperfluorocyclopentene (DTE) derivatives, organic-inorganic systems of Lindqvist-type [Mo6O19]²â», have been investigated by tuning open-ring and the closed-ring form. In the present paper, we performed density functional theory (DFT) combined with finite field (FF) methods to calculate the second-order NLO coefficients for these organic-inorganic compounds. The calculations with three functionals (B3LYP/CAM-B3LYP/LC-BLYP) confirm the switching behavior on NLO properties by the photoisomerization reaction. The ß(tot) value of system 2c (closed-ring form) is 10 times larger than that of its open-ring form (system 2o). And the other two pairs of systems also show good tuning properties. The ampliative ratio on second-order NLO coefficients between systems 2o and 2c (ß(2c)/ß(2o)) is 13 times as large as that of DTE (ß(DTEc)/ß(DTEo)). It suggests that introduction of [Mo6O19]²â» and organic groups to the DTE monomer effectively improve the conversion ratio of second-order NLO coefficients between the open-ring and closed-ring forms.


Assuntos
Modelos Teóricos , Compostos de Tungstênio/química , Isomerismo , Conformação Molecular
19.
Chem Commun (Camb) ; 49(11): 1088-90, 2013 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-23282415

RESUMO

Two S-containing MOFs, interpenetrating and non-interpenetrating , were synthesized by altering solvent size. The nanoporous reveals high selective adsorption for Cu(2+) ions and has been applied as a chromatographic column for separating transition metal ions for the first time.


Assuntos
Metais/química , Compostos Organometálicos/química , Enxofre/química , Adsorção , Solventes/química
20.
Dalton Trans ; 41(37): 11361-8, 2012 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-22886001

RESUMO

The formation mechanism is always a fundamental and confused issue for polyoxometalate chemistry. Two formation mechanisms (M1 and M2) of the Lindqvist anion [W(6)O(19)](2-) have been adopted to investigate it's self-assembly reaction pathways at a density functional theory (DFT) level. The potential energy surfaces reveal that both the mechanisms are thermodynamically favorable and overall barrierless at room temperature, but M2 is slightly dominant to M1. The formation of the pentanuclear species [W(5)O(16)](2-) and [W(5)O(15)(OH)](-) are recognized as the rate-determining steps in the whole assembly polymerization processes. These two steps involve the highest energy barriers with 30.48 kcal mol(-1) and 28.90 kcal mol(-1), respectively, for M1 and M2. [W(4)O(13)](2-) and [W(4)O(12)(OH)](-) are proved to be the most stable building blocks. In addition, DFT results reveal that the formation of [W(3)O(10)](2-) experiences a lower barrier along the chain channel.


Assuntos
Teoria Quântica , Compostos de Tungstênio/química , Água/química , Ânions , Modelos Moleculares , Soluções
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