Distribution by Scientific Domains
Distribution within Chemistry

Kinds of DFT

  • hybrid dft
  • time-dependent dft

  • Terms modified by DFT

  • dft analysis
  • dft calculation
  • dft computation
  • dft functional
  • dft level
  • dft method
  • dft methods
  • dft studies
  • dft study
  • dft testing

  • Selected Abstracts

    Generality with specificity: the dynamic field theory generalizes across tasks and time scales

    Vanessa R. Simmering
    A central goal in cognitive and developmental science is to develop models of behavior that can generalize across both tasks and development while maintaining a commitment to detailed behavioral prediction. This paper presents tests of one such model, the Dynamic Field Theory (DFT). The DFT was originally proposed to capture delay-dependent biases in spatial recall and developmental changes in spatial recall performance. More recently, the theory was generalized to adults' performance in a second spatial working memory task, position discrimination. Here we use the theory to predict a specific, complex developmental pattern in position discrimination. Data with 3- to 6-year-old children and adults confirm these predictions, demonstrating that the DFT achieves generality across tasks and time scales, as well as the specificity necessary to generate novel, falsifiable predictions. [source]

    Macrocyclic Receptor Showing Improved PbII/ZnII and PbII/CaII Selectivities

    Raquel Ferreirós-Martínez
    Abstract Herein we report on the macrocyclic receptor N,N,-bis[(6-carboxy-2-pyridyl)methyl]-1,10-diaza-15-crown-5 (H2bp15c5) and its coordination properties towards ZnII, CdII, PbII, and CaII. The stability constants of these complexes determined by pH-potentiometric titration at 25 °C in 0.1 M KNO3 vary in the following order: PbII > CdII >> ZnII > CaII. As a result, bp15c5 presents very important PbII/ZnII and PbII/CaII selectivities. These results are in contrast to those reported for the related receptor derived from 1,7-diaza-12-crown-4, which provides very similar complex stabilities for ZnII and PbII. The X-ray crystal structure of [Cd(Hbp15c5)]+ shows heptadentate binding of the ligand to the metal ion, with two oxygen atoms of the macrocyclic unit remaining uncoordinated. The 1H NMR spectra of the complexes formed with PbII, ZnII, and CaII (D2O) show very broad peaks in the region 2,5 ppm, indicating an important degree of flexibility of the crownmoiety in these complexes. On the contrary, the 1H and 13C NMR spectra recorded for the CdII complex are well resolved and could be fully assigned. A detailed conformational investigation using theoretical calculations performed at the DFT (B3LYP) level predict a minimum energy conformation for [Cd(bp15c5)] that is very similar to that observed in the solid state. Analogous calculations performed on the [M(bp15c5)] (M = Zn or Pb) systems predict hexadentate binding of the ligand to these metal ions. In the case of the PbII complex our calculations indicate that the 6s lone pair is stereochemically active, which results in a hemidirected coordination geometry around the metal ion. The minimum energy conformations calculated for the ZnII, CdII, and PbII complexes are compatible with the experimental NMR spectra obtained in D2O solution. [source]

    Synthesis, Structures, and Magnetic Properties of N -Trialkylsilyl-8-amidoquinoline Complexes of Chromium, Manganese, Iron, and Cobalt as well as of Wheel-Like Hexanuclear Iron(II) and Manganese(II) Bis(8-amidoquinoline)

    Astrid Malassa
    Abstract The transamination of 8-(tert -butyldimethylsilylamino)quinoline with (thf)2Cr[N(SiMe3)2]2 yields monomeric bis[8-(tert -butyldimethylsilylamido)quinoline]chromium(II) (1). Similar reactions of M[N(SiMe3)2]2 (M = Mn, Fe, Co) with 8-(trialkylsilylamino)quinoline lead to the formation of monomeric bis[8-(trialkylsilylamido)quinoline]metal(II) [M = Mn, SiR3 = SiMe2tBu (2a), SiiPr3 (2b); M = Fe, SiR3 = SiMe2tBu (3a),SiiPr3 (3b); M = Co, SiR3 = SiMe2tBu (4a), SiiPr3 (4b)]. The transamination of 8-aminoquinoline with M[N(SiMe3)2]2 (M = Mn, Fe, Co) allows the isolation of the heteroleptic 1:1 and homoleptic 2:1 products. The 1:1 complexes bis[8-amidoquinoline metal(II)bis(trimethylsilyl)amide] [M = Mn (5), Fe (6), Co (7)] are dimeric with bridging 8-amidoquinoline moieties. The 2:1 complexes of Mn and Fe, bis(8-amidoquinoline)manganese(II) (8) and bis(8-amidoquinoline)iron(II) (9), form hexamers with wheel-like molecular structures consisting of metal-centered nitrogen octahedra interconnected by common N···N edges. The cobalt complex, bis(8-amidoquinoline)cobalt(II) (10), precipitates as a microcrystalline powder. Investigations of the magnetic properties by DFT corroborate the experimental data for the Mn derivative 8, where an antiferomagnetic coupling is observed. By contrast, calculations on the Fe6 -wheel 9 yield very close-lying ferromagnetically and antiferromagnetically coupled states. [source]

    A Dinuclear Double-Stranded Oxido Complex of ReV with a Bis(benzene- o -dithiolato) Ligand

    Jorge S. Gancheff
    Abstract The reaction of [ReOCl3(PPh3)2] with 1,2-bis(2,3-dimercaptobenzamido)ethane (H4 - 1) in the presence of Na2CO3 in methanol under anaerobic conditions affords the dinuclear ReV oxido complex [PPh4]2[ReO(1)]2 containing two distorted square-pyramidal {ReVOS4} units bridged by the ligand strands in a double-stranded fashion. The coordinationgeometry around the metal centers is similar to the one observed for [ReO(bdt)2],. The ReS4 planes are arranged in a coplanar fashion and are not twisted around the metal,metal vector, which prevents the complex to adopt a helical structure. Luminescence studies show the presence of emission bands, which are assigned to singlet-singlet transitions exhibiting very fast decays (ca. 10 ns). Theoretical Density Functional (DFT) studies on geometry and electronic properties were performed employing the hybrid B3LYP and PBE1PBE functionals. While the general trends observed in the experimental data are well reproduced in all cases, a good agreement was obtained using PBE1PBE, in particular for the Re,S bonds. Natural Bond Orbitals (NBO) analysis indicates the presence of polarized Re,O and Re,S bonds, both of them polarized toward the non-metal. The calculation show that the molecular orbitals of the ReV are doubly degenerated, the occupied 5d orbital of rhenium lying beneath occupied sulfur-based MOs due to the rigid geometry imposed by the C,C backbone of the bis(benzene- o -dithiolato) ligands. The origin of all absorption bands is ascribed to a ligand-to-metal charge transfer (LMCT), in which occupied sulfur-based orbitals and unoccupied rhenium-centered orbitals are involved.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Nickel Complexes of N/O -Functionalized N-Heterocyclic Carbenes as Precatalysts for Michael Reactions in Air at Room Temperature Under the Much Preferred Base-Free Conditions

    Sriparna Ray
    Abstract A series of several new nickel precatalysts supported overN/O -functionalized N-heterocyclic carbenes (NHC) for the Michael reactions of ,-dicarbonyl, ,-keto ester, ,-diester, and ,-cyano ester compounds with ,,,-unsaturated carbonyl compounds in air at ambient temperature under the much preferred base-free conditions are reported. Specifically, the nickel complexes, [1-(R1 -aminocarbonylmethyl)-3-R2 -imidazol-2-ylidene]2Ni [R1 = 2-C6H4(OMe); R2 = Me (1b), iPr (2b), CH2Ph (3b) and R1 = 2-CH2C4H3O; R2 = Me (4b), CH2Ph (5b)] carried out the highly convenient base-free Michael addition of the activated C,H compounds across ,,,-unsaturated carbonyl compounds in air at room temperature. The complexes 1b,5b were synthesized by the direct reaction of the respective imidazolium chloride salt with NiCl2·6H2O in CH3CN in the presence of K2CO3 as a base. The exceptional stability of 1b,5b has been attributed to the deeply buried nickel,NHC ,-bonding molecular orbitals as evidenced from the density functional theory (DFT) studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Vanadium Carbonyl Nitrosyl Compounds: The Carbonyl Nitrosyl Chemistry of an Oxophilic Early Transition Metal

    Hongyan Wang
    Abstract The vanadium carbonyl nitrosyl compounds V(NO)(CO)n (n = 5, 4, 3) and V2(NO)2(CO)n (n = 9, 8, 7) have been examined by density functional theory in order to assess the effect of the oxophilicity of vanadium on its metal carbonyl nitrosyl chemistry. The expected octahedral structure for the experimentally known, but surprisingly unstable, V(NO)(CO)5, is confirmed by DFT. The optimized structures of the unsaturated derivatives V(NO)(CO)4 and V(NO)(CO)3 can be derived from the octahedral V(NO)(CO)5 structure by loss of one or two carbonyl groups, respectively. This leads to anearly square-planar predicted structure for V(NO)(CO)3. The lowest energy structures for the binuclear derivatives V2(NO)2(CO)n (n = 9, 8, 7) have exclusively two-electron donor carbonyl groups and three-electron donor linear nitrosyl groups with metal,metal distances corresponding to the formal bond orders required for the favored 18-electron configurations. Bridging carbonyl groups appear to be preferred energetically over bridging nitrosyl groups in the V2(NO)2(CO)n structures in contrast to the similar carbonyl nitrosyl compounds of later transition metals. The saturated V2(NO)2(CO)9, with a relatively long V,V distance of 3.583 Å (B3LYP) or 3.205 Å (BP86), is thermodynamically unstable with respect to dissociation into V(NO)(CO)5 + V(NO)(CO)4.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Sulfur Dioxide and Water: Structures and Energies of the Hydrated Species SO2·nH2O, [HSO3],·nH2O, [SO3H],·nH2O, and H2SO3·nH2O (n = 0,8)

    Ralf Steudel
    Abstract The structures of a large number of hydrates of sulfur dioxide (SO2·nH2O), of the sulfonate ion ([HSO3],·nH2O), of the tautomeric hydrogensulfite anion ([SO3H],·nH2O), and of sulfurous acid (H2SO3·nH2O) with up to eight water molecules attached to these species have been optimized at the B3LYP/6-31G(2df,p) level of theory (DFT). The calculated vibrational frequencies allow the definite assignment of certain characteristic modes, and in this way a convincing interpretation of published spectra of aqueous SO2 as well as of SO2 adsorbed on very cold ice crystals has been achieved for the first time. Single-point calculations at the G3X(MP2) level of theory were used to calculate the binding energies of the water molecules in SO2·nH2O as well as the relative stabilities of the isomeric anionic species [HSO3],·nH2O and [SO3H],·nH2O. Generally, the water molecules tend to stick together forming clusters, whereas the particular sulfur-containing molecule remains at the surface of the water cluster, but it is always strongly hydrogen-bonded. Only when there are more than six water molecules are the anions more or less completely surrounded by water molecules. DFT calculations erroneously predict that the gaseous hydrated sulfonate ions are more stable than the isomeric hydrogensulfite ions, even when hydrated with six water molecules. However, if these hydrated species are calculated as being embedded in a polar continuum simulating the aqueous phase, the hydrogensulfite ions are more stable than the sulfonate ions, in agreement with various spectroscopic observations on aqueous sulfite solutions. On the other hand, at the higher G3X(MP2) level, the gaseous hydrated hydrogensulfite anions are more stable than the corresponding sulfonate ions only if the number of water molecules is larger than four, whereas for the weakly hydrated anions the order of relative energies is reversed. The possible implications of these results for the enzymatic oxidation of "sulfite ions" ([HSO3], and [SO3H],) by sulfite oxidase are discussed. The conversion of SO2·6H2O into its isomer H2SO3·5H2O is predicted to be exothermic (,H°298 = ,56.1 kJ,mol,1) and exergonic (,G°298 = ,22.5 kJ,mol,1). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Solid-State and Solution Structure of Lanthanide(III) Complexes with a Flexible Py-N6 Macrocyclic Ligand

    Cristina Núñez
    Abstract Lanthanide complexes of a hexaaza macrocyclic ligand containing a pyridine head unit (L) were synthesized (Ln = La,Lu, except Pm). The solid-state structures of the corresponding La, Ce, Pr, Nd, and Lu complexes were determined by single-crystal X-ray crystallography, and they reveal the presence of three different mononuclear complexes with three different conformations of the macrocycle and coordination environments around the metal ions. In all complexes the lanthanide ion is coordinated in an endomacrocyclic manner to the six nitrogen donor atoms of the ligand. In the La, Ce, and Pr complexes the metal ions show a 12-coordinate mononuclear environment in which 3 nitrate anions coordinate in a bidentate fashion. However, in the Nd analogue the metal ion displays a 10-coordinated environment with the coordination of 2 bidentate nitrate groups, whereas Lu shows a 9-coordinate environment interacting with 2 nitrate ligands, one of them acting as bidentate and the second one coordinating in a monodentate fashion. The 1H and 13C NMR spectra of the complexes recorded in CD3CN suggest that the complexes adopt in solution a similar structure to that observed for the Nd complex in the solid state. The [Ln(L)(NO3)3] and [Ln(L)(NO3)2]+ complexes were characterized by density functional theory (DFT) calculations (B3LYP model). The structures obtained from these calculations for La, Ce, Pr, and Nd are in good agreement with the experimental solid-state structures. The relative stabilities of the [Ln(L)(NO3)2]+ complexes with respect to the [Ln(L)(NO3)3] ones (Ln = La, Nd, Gd, Ho, or Lu) were studied both in vacuo and in acetonitrile solution (PCM model) at the same computational level. Our calculations indicate that in solution the [Ln(L)(NO3)2]+ species is the most stable one along the whole lanthanide series, in agreement with the NMR spectroscopic data.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Synthesis, Protonation and CuII Complexes of Two Novel Isomeric Pentaazacyclophane Ligands: Potentiometric, DFT, Kinetic and AMP Recognition Studies

    Andrés G. Algarra
    Abstract The synthesis and coordination chemistry of two novel ligands, 2,6,9,12,16-pentaaza[17]metacyclophane (L1) and 2,6,9,12,16-pentaaza[17]paracyclophane (L2), is described. Potentiometric studies indicate that L1 and L2 form a variety of mononuclear complexes the stability constants of which reveal a change in the denticity of the ligand when moving from L1 to L2, a behaviour that can be qualitatively explained by the inability of the paracyclophanes to simultaneously use both benzylic nitrogen atoms for coordination to a single metal centre. In contrast, the formation of dinuclear hydroxylated complexes is more favoured for the paraL2 ligand. DFT calculations have been carried out to compare the geometries and relative energies of isomeric forms of the [CuL]2+ complexes of L1 and L2 in which the cyclophane acts either as tri- or tetradentate. The results indicate that the energy cost associated with a change in the coordination mode of the cyclophane from tri- to tetradentate is moderate for both ligands so that the actual coordination mode can be determined not only by the characteristics of the first coordination sphere but also by the specific interactions with additional nearby water molecules. The kinetics of the acid promoted decomposition of the mono- and dinuclear CuII complexes of both cyclophanes have also been studied. For both ligands, dinuclear complexes convert rapidly to mononuclear species upon addition of excess acid, the release of the first metal ion occurring within the mixing time of the stopped-flow instrument. Decomposition of the mononuclear [CuL2]2+ and [CuHL2]3+ species occurs with the same kinetics, thus showing that protonation of [CuL2]2+ occurs at an uncoordinated amine group. In contrast, the [CuL1]2+ and [CuHL1]3+ species show different decomposition kinetics indicating the existence of significant structural reorganisation upon protonation of the [CuL1]2+ species. The interaction of AMP with the protonated forms of the cyclophanes and the formation of mixed complexes in the systems Cu,L1 -AMP, Cu,L2 -AMP, and Cu,L3 -AMP, where L3 is the related pyridinophane containing the same polyamine chain and 2,6-dimethylpyridine as a spacer, is also reported. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Beyond the Icosahedron: A Density Functional Theory Study of 14-Atom Germanium Clusters

    R. Bruce King
    Abstract Density functional theory (DFT) at the hybrid B3LYP level has been applied to the germanium clusters Ge14z (z = ,8, ,6, ,4, ,2, 0, +2, +4) starting from seven different initial configurations. An Oh omnicapped cube structure is the most stable for Ge142, followed by a hexagonal antiprism structure with a relative energy of 42.7 kcal/mol. The lowest-energy structure for neutral Ge14 is a triplet omnicapped cube with full Oh symmetry followed by a singlet omnicapped cube compressed to D4h symmetry through Jahn,Teller distortion. The lowest energy Ge142+ structure is also an Oh structure derived from the omnicapped cube through elongation of the 12 edges of the underlying cube to give a rhomboidal dodecahedron with 12 rhombus faces. The lowest-energy Ge124+ structure is a bicapped icosahedron. Some D6h hexagonal wheel structures at higher energies are also found for the hypoelectronic systems Ge14, Ge142+, and Ge144+. The lowest-energy structures for the hyperelectronic Ge144,, Ge146,, and Ge148, are relatively unsymmetrical not readily recognizable open structures typically with some pentagonal or hexagonal faces. The D6d bicapped hexagonal antiprism found in 14-vertex C2B12 carborane and M2C2B10 dimetallacarborane structures is not the lowest-energy structure for any of the Ge14z clusters.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Luminescent Gold(I) and Copper(I) Phosphane Complexes Containing the 4-Nitrophenylthiolate Ligand: Observation of ,,,* Charge-Transfer Emission

    Cheng-Hui Li
    Abstract Gold(I) and copper(I) phosphane complexes containing the 4-nitrophenylthiolate ligand, namely [(PCy3)Au(SC6H4NO2 -4)] (1) (PCy3 = tricyclohexylphosphane), [Au2(,-dcpm)(SC6H4NO2 -4)2] (2) [dcpm = bis(dicyclohexylphosphanyl)methane], [Au2(,-dppm)(SC6H4NO2 -4)2] (3) [dppm = bis(diphenylphosphanyl)methane], and [(,2 -SC6H4NO2 -4)2(,3 -SC6H4NO2 -4)2(CuPPh3)4] (4), were prepared and characterized by X-ray crystal analysis. All of these complexes show an intense absorption band with ,max at 396,409 nm attributed to the intraligand (IL) ,(S),,*(C6H4NO2 -4) charge-transfer transition. The assignment is supported by the results of DFT and TDDFT calculations on the model complexes [PH3Au(SC6H4NO2 -4)] and [(,2 -SC6H4NO2 -4)2(,3 -SC6H4NO2 -4)2(CuPH3)4]. The emissions of solid samples and glassy solutions (methanol/ethanol, 1:4, v/v) of 1,4 at 77 K are assigned to the [,(S),,*(C6H4NO2 -4)] charge-transfer excited state. Metallophilic interactions are not observed in both solid state and solutions of complexes 1,3. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Cleavage of CO by Mo[N(R)Ar]3 Complexes

    Gemma Christian
    Abstract The reaction of MoL3 [L = NH2 and N(tBu)Ar] with CO was explored using DFT in order to rationalize why CO cleavage is not observed experimentally for this system in contrast to the corresponding N2 reaction which results in spontaneous cleavage of the N,N bond. The binding of CO to MoL3 was found to be both kinetically and thermodynamically favored over the binding of N2, with the formation of the encounter complex, L3Mo,CO, calculated to be without barrier and exothermic. While the overall reaction to form the C,MoL3 and O,MoL3 products was calculated to be energetically favorable, both the encounter complex and intermediate dimer, L3Mo,CO,MoL3, were found to be lower in energy than the products, with the final C,O cleavage step calculated to be endothermic by 169 kJ,mol,1 and 163 kJ,mol,1 for L = NH2 and N(tBu)Ar, respectively. The unfavorable CO cleavage step can be attributed to the fact that Mo does not possess the optimum d-electron configuration to sufficiently stabilise the carbide and oxide products relative to the CO-bridged intermediate dimer.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Electronic Structure of Linearly Coordinated EQ Complexes of the Type [(N3N)W(EQ)] [N3N = N(CH2CH2NSiMe3)3; E = P, As, Sb, Bi; Q = O, S, Se, Te]: A DFT Study

    Gábor Balázs
    Abstract Density functional theory (DFT) calculations were carried out on the terminal EQ complexes [(N3N)W(EQ)] {N3N = N(CH2CH2NSiMe3)3; E = P, As, Sb, Bi; Q = O, S, Se Te} to clarify the bonding situation within the linear Nax,W,E,Q core. This unusual structural motif gives rise to a bonding arrangement in which the ,-electron density is delocalised over the three atoms of the W,E,Q unit. Fragment calculations and natural bond order (NBO) data indicated that the ,-bonding component of the Nax,W,E,Q unit comprises two occupied , orbitals, while the , component of bonding comprises two sets of degenerate , orbitals. In general, the , orbitals of the Nax,W,E,Q core are higher in energy compared to the , orbitals. The phosphorus monoxide (EQ = PO) complexes provide an exception to this rule, with the 1, orbitals of the W,P,O core lower in energy than the , orbitals. Generally, as the atomic number of either the pnicogen (E) or chalcogen (Q) atom increases the extent of ,-orbital delocalisation decreases, whereas the ,-orbital delocalisation increases. Fractional bond orders and Wiberg bond indices were used to establish whether localisation of the ,-electron density gives rise to a W,E or an E,Q double or triple bond. Both methods indicate a W,E as well as an E,Q double bond. The ionic nature of the complexes were analysed by inspection of the Hirschfeld charge distribution which shows only a moderate ionic character. Exceptions are the pnicogen monoxide complexes, which are more ionic. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Metal Ion Complementarity: Effect of Ring-Size Variation on the Conformation and Stability of Lead(II) and Cadmium(II) Complexes with Pendant-Armed Crowns

    Martín Regueiro-Figueroa
    Abstract The binding tendencies of the pendant-armed crown ethers L1,L3 [L1 = N,N, -bis(benzimidazol-2-ylmethyl)-1,7-diaza-12-crown-4, L2 = N,N, -bis(benzimidazol-2-ylmethyl)-1,10-diaza-15-crown-5) and L3 = N,N, -bis(benzimidazol-2-ylmethyl)-4,13-diaza-18-crown-6] towards PbII and CdII have been investigated. The X-ray crystal structure of [Cd(L3)](ClO4)2·EtOH shows that, in the solid state, the CdII ion is eight-coordinate and fits quite well into the crown hole, favouring an anti arrangement of the organic receptor. NMR measurements recorded in acetonitrile solution indicate that increasing the crown size induces a conformational change in the series of CdII complexes. The conformation goes from a syn arrangement for L1 to an anti arrangement for L3, passing through a syn [lrarr2] anti equilibrium in the complex derived from L2. On the contrary, no conformational change was observed for the corresponding PbII complexes, which have a syn conformation in all cases. These results have been confirmed by means of density functional theory (DFT) calculations performed by using the B3LYP model. The binding constants obtained from UV/Vis titration experiments in DMSO solution demonstrate that a decrease in the crown size provokes a 102 -fold enhancement of the stability for this series of CdII complexes, whereas for PbII a gradual decrease of the binding constants is observed. Receptor L1 shows a certain degree of selectivity for CdII over PbII, with a selectivity factor > 102. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Mechanisms of H2, H2C=CH2, and O=CH2 Insertion into Cp2Zr(,2 -SiMe2=NtBu)(PMe3)

    Siwei Bi
    Abstract In this paper, the mechanisms for the insertion of H2, H2C=CH2, and O=CH2 into the Zr,Si bond of Cp2Zr(,2 -SiMe2=NtBu)(PMe3) (R) are theoretically investigated with the aid of density functional theory (DFT) calculations. The structure of the H2 insertion product P is discussed on the basis of our calculations, and its bonding features are rationalized in terms of molecular orbital theory. The regiochemistry for insertion of O=CH2 has also been theoretically investigated. It is found that the relative stabilities of the three insertion products of R are in the order P < P, < P,. For the reactions of R with H2 and CH2=CH2, the rate-determining steps are the insertions of H2 and CH2=CH2 into the Zr,Si bond of Cp2Zr(,2 -SiMe2=NtBu) (Int1), whereas PMe3 dissociation is the rate-determining step for the reaction of R with O=CH2. Only the precursor Int2,, formed by the coordination of O=CH2 to the Zr atom, is located; those formed by the coordination of H2 and CH2=CH2 to Int1 are not found.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Pentafluorosulfanyl (SF5) Containing Energetic Salts

    Haixiang Gao
    Abstract New quaternary salts of pentafluorosulfanyl-substituted (SF5) N -methylimidazole (1), 4-amino-1,2,4-triazole (3) or pyridine (5) were prepared and characterized. Most of the salts exhibit good thermal stabilities and low melting points placing them in the ionic liquid class. Their densities range between 1.4 and 1.8 g/cm3. The standard enthalpies of formation for the new salts were calculated by the use of computationally feasible DFT(B3LYP) and MP2 methods in conjunction with an empirical approach based on densities of salts. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

    Polymers or Supramolecules Generated From a New V-Shaped Bis-monodentate Ligand and the Effect of Steric Hindrance on Coordination Modes of the Ligand

    Caihua Zhou
    Abstract A new V-shaped bis-monodentate ligand L (L = 2,3,-dipyridylamine) (1) has been designed and synthesized by alkylation reaction of pyridylamine. An investigation of the charge distributions of the coordination atoms and single-point energy calculations of four conformers of ligand L based on the geometry of conformers optimized by the DFT (density functional theory) method was carried out. The results show that the four conformers of ligand L take on two stable and two less stable configurations. Theory forecasts that two relatively stable configurations present in complexes as probable coordination motifs of the ligand, and that steric hindrance of pyridine nitrogen atoms in isomers will affect its coordination ability together with the electronic factor. This forecast has been demonstrated by the coordination chemistry of ligand L, that is, configuration (a) and (b) of the ligand occur in the following reported complexes, which combines with AgI or CuII through two coordination modes (bidentate bridging or a monodentate mode) resulting in coordination polymers {[Ag (L)2]NO3}n (2), [Cu2(L)2(maa)4]n (maa = methacrylic acid) (3), and the mononuclear molecule [Cu(L)4](ClO4)2·2CH3CH2OH (4). The ligand assumes different coordination modes in the three complexes because of different levels of steric hindrance of the pyridine nitrogen atoms in the conformers. Interestingly, polymers 2 and 3 assume a 1D helical structure and a linear framework, respectively, and 4 has a 2D supramolecular architecture induced from hydrogen bond interactions. In addition, the magnetic properties of 3 have been explored, which shows a strong antiferromagnetic interaction.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

    N -Methylation Effects on the Coordination Chemistry of Cyclic Triamines with Divalent Transition Metals and Their CoII Dioxygen Carriers

    Silvia Del Piero
    Abstract The thermodynamics of complex formation of CoII and CdII ions with the triaza macrocyclic ligand 1,4,7-triazacyclononane (tacn) and its N -methylated derivative 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3tacn) has been studied in dimethyl sulfoxide (DMSO) at 298.1 K and in an ionic medium (0.1 M Et4NClO4) by means of potentiometric, UV/Vis, calorimetric and FT-IR techniques. The results are discussed by taking into account electronic and steric effects as well as solvation of the species concerned. Computational methods based on density functional theory (DFT) have been used to obtain structural information about the ligands and their complexes in order to provide further, independent insights into the effect of N -methylation on the coordination affinity of the ligands towards the metal ions. The computational suggestions are of great help to correlate steric effects and thermodynamic results. The kinetics of dioxygen uptake for the formation of the Co(tacn)2O2 superoxo adduct has also been studied by means of UV/Vis measurements. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

    The Additive Nature of Energy Penalties in 10-Vertex nido -(Car)boranes

    Farooq A. Kiani
    Abstract A structural increment system, i.e. quantitative rules that govern the relative stabilities of 10-vertex nido -boranes and-carboranes, has been determined. Density functional theory computations at the B3LYP/6-311+G(d,p)//B3LYP/6-31G(d) level with ZPE corrections were carried out for 81 different boron hydride and carborane structures from [B10H12]2, to C3B7H11 to determine their relative stabilities. A set of eleven disfavored geometrical features that destabilize a cluster structure relative to a hypothetical ideal situation were identified and weighted by so-called energy penalties. The latter show good additive behavior and allow us to reproduce the DFT computed relative energies mostly with an accuracy of 6.0 kcal,mol,1. Some unknown 10-vertex nido- carboranes that are thermodynamically more stable than their known isomers are also identified. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

    Syntheses, Structures, and Magnetic Properties of Copper(II) Complexes with 1,3-[Bis(2-pyridylmethyl)amino]benzene (1,3-tpbd) as Ligand

    Simon P. Foxon
    Abstract The dinuclear copper(II) complexes {[Cu2(1,3-tpbd)(H2O)(OAc)2](ClO4)2}0.23{[Cu2(1,3-tpbd)(H2O)2(OAc)](ClO4)3}0.77·0.77H2O (1), [Cu2(1,3-tpbd)(H2O)2(OAc)2](ClO4)2·2H2O (2), and the tetranuclear copper(II) complex [Cu4(1,3-tpbd)2(H2O)2(SO4)4]·8H2O (3) {1,3-tpbd = 1,3-bis[bis(2-pyridylmethyl)amino]benzene} were synthesised and structurally characterised by X-ray diffraction. Variable-temperature (2.0,290 K) magnetic susceptibility measurements on these complexes as well as on the dinuclear copper(II) complex [Cu2(1,3-tpbd)(H2O)2(ClO4)3]ClO4 (4) (whose structure was published earlier) were performed. In contrast to 2 and 3, significant ferromagnetic coupling with J = +9.3 cm,1 was observed for 4 (the Hamiltonian being defined as H, = ,J S,1·S,2). Density functional theory (DFT) calculations were used successfully for the interpretation of the ferromagnetic coupling observed in 4. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

    Density Functional Study of the Complexation Reaction of Sn(CH3)3X (X = F, Cl, Br and I) with Halide Anions

    Frank De Proft
    Abstract The Lewis acid-base reaction between Sn(CH3)3X and Y, (with X, Y = F, Cl, Br and I) has been studied using quantum chemical calculations. Complexation energies were calculated at the Density Functional Theory (DFT) level and rationalized on the basis of a local application of the hard and soft acids and bases principle. It was observed that smaller differences in the local softness of the interacting sites in the Lewis acid and base correspond to stronger interactions. Moreover, the calculated sequences in complexation energies can be reproduced using equations containing chemical concepts introduced within the framework of conceptual density functional theory and rooted in the hard and soft acids and bases principle and referring only to the reactants. A method of treating the electronegativity and softness of the halide anions is presented based on a Taylor expansion of the electronegativity of the neutral halogens and the softness-polarizability proportionality. Experimental evidence for the calculated sequences was gathered from measured 117Sn chemical shifts and 1J (13C- 119/117Sn) coupling constant changes upon complexation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

    Calculated Enthalpies for Dimerisation of Binary, Unsaturated, Main-Group Element Hydrides as a Means to Analyse Their Potential for Multiple Bonding

    Hans-Jörg Himmel
    Abstract Herein, the dimerisation of subvalent, binary, main-group element hydrides with the potential for multiple bonding is studied using both hybrid DFT (B3LYP) and ab initio [MP2 and CCSD(T)] methods. The [2+2] cycloaddition is an important and characteristic reaction of derivatives of ethylene. A comparison of dimerisation reactions for several compounds with the potential for multiple bonding should, therefore, shed light on the properties of these species. Our study includes the hydrides E2H2 (E = B, Al, Ga, N P or As), E2H4 (E = C, Si or Ge) and ENH4 (E = B, Al or Ga) and their dimers. Several isomeric forms of the monomers and dimers have to be considered. The trends within a group and a period are established and the factors responsible for them are discussed. It turns out that, generally, the enthalpies for dimerisation increase for heavier homologues, reflecting that the most important factor is the reduced strength of the E,E bonds in the monomers prior to dimerisation and, to some degree, also the reduced ring strain in the cyclic dimers. The exceptions are the dimerisations of B2H2 and Al2H2, both of which lead to the tetrahedral E4H4 species (E = B or Al). Dimerisation of Al2H2 is associated with a smaller enthalpy than that for the dimerisation of B2H2. Comparisons and analyses are made complicated because of the changes in the structures of the isomeric global minima between homologues. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

    Ab Initio Guided Design of bcc Ternary Mg,Li,X (X,=,Ca, Al, Si, Zn, Cu) Alloys for Ultra-Lightweight Applications

    William Art Counts
    Abstract Ab initio calculations are becoming increasingly important for designing new alloys as these calculations can accurately predict basic structural, mechanical, and functional properties using only the atomic composition as a basis. In this paper, fundamental physical properties (like formation energies and elastic constants) of a set of bcc Mg,Li and Mg,Li-based compounds are calculated using density functional theory (DFT). These DFT-determined properties are in turn used to calculate engineering parameters such as (i) specific Young's modulus (Y/,) or (ii) shear over bulk modulus ratio (G/B) differentiating between brittle and ductile behavior. These parameters are then used to identify those alloys that have optimal mechanical properties for lightweight structural applications. First, in case of the binary Mg,Li system, an Ashby map containing Y/, versus G/B shows that it is not possible to increase Y/, without simultaneously increasing G/B (i.e., brittleness) by changing only the composition of a binary alloy. In an attempt to bypass such a fundamental materials-design limitation, a set of Mg,Li,X ternaries (X,=,Ca, Al, Si, Cu, Zn) based on stoichiometric Mg,Li with CsCl structure was studied. It is shown that none of the studied ternary solutes is able to simultaneously improve both specific Young's modulus and ductility. [source]

    Theoretical Study on Hetero-Diels,Alder Reaction of Butadiene with Benzaldehyde Catalyzed by Chiral InIII Complexes

    Xiuli Cao
    Abstract The mechanism of the hetero-Diels,Alder reaction of butadiene with benzaldehyde catalyzed by chiral N,N, -dioxide/In(OTf)3 complexes was studied theoretically by using density functional theory (DFT) and model system. The computational results indicate that the catalyzed reaction proceeded through a concerted mechanism via a highly zwitterionic transition state. The lowest energy barrier was 11.8 kJ,mol,1, which is 63.0 kJ,mol,1 lower than that of the uncatalyzed reaction. The results indicate that the endo approach is advantageous over the exo approach, because exo transitions states suffer from more steric hindrance than the endo transitions states as a result of interactions among the substrates, the trifluoromethanesulfonic group and the R4 groups of the ligand. The (S) configuration was observed predominantly over the (R) form, because there is no distinguishable repulsion between butadiene and the exo amino side or the endo amino side of the ligand. Besides, the interactions between the terminal hydrogen atoms of butadiene and the oxygen atoms of the trifluoromethanesulfonic group make the structure more stable. Thus, the experimental results were explained well by calculation of the chiral N,N, -dioxide/In(OTf)3 complex catalyzed hetero-Diels,Alder reaction at the molecular level. [source]

    Theoretical Description of Substituent Effects in Electrophilic Aromatic Substitution Reactions

    Tobias Schwabe
    Abstract The ability of the current Kohn,Sham density functional theory (DFT) to compute the change of the proton affinity (PA) of phenol derivatives due to substitution is investigated. These systems can be used as models to predict reactivities in electrophilic aromatic substitution reactions. The complexity of the problem is increased systematically by introducing successively up to four substituents in five typical cases (methyl, cyano, fluorine, chlorine, and bromine). Our investigation can be regarded as representative for an important class of problems consistently encountered in the DFT modeling of organic reactions. High-level theoretical reference data from CCSD(T) and SCS-MP2 wave-function calculations are presented, and the PAs are compared to those obtained by a series of density functionals (DFs). It is shown that not all DFs are capable of quantitatively reproducing the substituent effects. These can be simply linear in the number of substituents or show more complicated patterns. Especially for halogens, some DFs even fail completely. In these cases, linearly increasing errors with the number of groups are observed. Reliable results are obtained with hybrid DFs or the even more accurate double-hybrid DF approach. The errors are attributed to the common self-interaction (over-delocalization) error in part of the DFs. Comparison with Hartree,Fock results shows that a reliable account of electron correlation is necessary to compute the PA of unsaturated and highly substituted molecules with chemical accuracy.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    J -Based Analysis and DFT,NMR Assignments of Natural Complex Molecules: Application to 3,,7-Dihydroxy-5,6-epoxycholestanes

    Jesús Javier Poza
    Abstract In order to reproduce the stereochemical dispositions of the epoxy and hydroxy functionalities, four 3,,7-hydroxy-5,6-epoxycholestanes were easily prepared from cholesterol, and their NMR spectroscopic data were experimentally obtained from 1D and 2D NMR experiments. An exhaustive QM- J -based analysis was then performed to replicate the experimental H,H and C,H coupling constants as well as the 13C NMR chemical shifts. The B3LYP GIAO methodology with the 6-311-G(d,p) basis set was chosen and showed that the data obtained from rings A and B were sufficient to calculate the correct stereochemistry of the 5,6-epoxy and 7-hydroxy groups. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Superacid-Catalyzed Dimerization/Cyclization of Isopropenyl-PAHs , Novel Pathways to PAH Dimers, Phenalenes and Their Stable Carbocations

    Cédric Brulé
    Abstract The isopropenyl derivatives of representative classes of polycyclic aromatic hydrocarbons (PAHs) having four and five fused-ring systems, namely pyrene, chrysene, benzo[c]phenanthrene (BcPh), dibenzo[a,c]anthracene (benzo[f]tetraphene) and perylene, were synthesized by Wittig olefination from the corresponding acetyl-PAHs. Under the influence of triflic acid (TfOH), the isopropenyl derivatives were converted to novel PAH dimers and/or phenalenes in a simple one-pot procedure. A plausible mechanism for this process has been outlined, and the synthetic scope of this chemistry has been explored. Structural features in the PAH dimers were examined by DFT. As representative initial and final carbocation intermediates in the reaction sequence, stable carbocations derived from 3-isopropenylperylene and from 4,6,6-trimethyl-6H -dibenzo[a,kl]anthracene were generated and studied directly by NMR spectroscopy. The NMR characteristics and charge delocalization modes in the resulting benzylic carbocations are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    One-Pot Synthesis of Core-Modified Rubyrin, Octaphyrin, and Dodecaphyrin: Characterization and Nonlinear Optical Properties

    Rajeev Kumar
    Abstract Modified 26, rubyrin, 36, octaphyrin, and 54, dodecaphyrin systems have been synthesized in moderately good yields through acid-catalyzed condensations of terthiophene diols and tripyrranes. The product distributions are decided both by the acid catalyst concentration and by the nature of the meso substituents. For example, a new isomer of [26]hexaphyrin( (rubyrin) was obtained with 0.3 equiv. of p -toluenesulfonic acid, when the meso substituent was mesityl in at least one of the precursors. A change of the mesityl substituent for a p -methoxy substituent in terthiophene diol resulted in the formation of a [3,+,3,+,3,+,3] condensation product , [54]dodecaphyrin( , in addition to the expected rubyrin. Furthermore, an increase in the acid concentration to 0.6 equiv. resulted in the formation of a new [36]octaphyrin(, in addition to the rubyrin and dodecaphyrin. A single-crystal X-ray analysis of octaphyrin represents the first example of a planar conformation of an octaphyrin with six meso links. In rubyrin 19, one thiophene ring, opposite to the terthiophene subunit, is inverted, while in octaphyrin 30 one pyrrole ring and two thiophene rings are inverted. The various conformational possibilities tested for the unsubstituted dodecaphyrin 28, at semiempirical level, suggest that the most stable conformation is a figure-eight. The final geometry optimization of figure-eight dodecaphyrin was done at the B3LYP/6-31G* level of DFT. Octaphyrins and dodecaphyrins bind trifluoroacetate anion effectively in their diprotonated forms, the binding constants (K) being 638 M,1 for dodecaphyrin 28, and 415 M,1 for octaphyrin 30. Electrochemical data reveal HOMO destabilization with increasing , electron conjugation, consistently with the large red shifts of the absorption bands. Preliminary studies on the use of these expanded porphyrins as third-order NLO materials were followed by measurements of their two-photon absorption (TPA) cross-sections [,(2)]. The ,(2) values increase upon going from the 26, rubyrins to the 54, dodecaphyrins, confirming our earlier observation that increases in ,-conjugated electrons increase the TPA values.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Radical Cation and Dication Derived from 4,8-Diethylbenzo[1,2- d:4,5- d,]bis[1,2,3]trithiole [DEBBT]: Change of Electronic State from Singlet-State Dication DEBBT(2+)- S to Triplet-State Dimer 2DEBBT(2+)- T in D2SO4 and CD3CN Solutions

    Takeshi Kimura
    Abstract 4,8-Diethylbenzo[1,2- d:4,5- d,]bis[1,2,3]trithiole [DEBBT] was oxidized using concentrated D2SO4, leading to the generation of the radical cation DEBBT(·+) which was verified by ESR spectroscopy. DEBBT(·+) in the solution was further oxidized to produce the dication DEBBT(2+), as determined by 1H and 13C NMR spectroscopy. DEBBT(2+) was also prepared by treating DEBBT 1-oxide [DEBBT 1-O] with concentrated D2SO4, and was verified by 1H and 13C NMR spectroscopy. The 13C NMR chemical shifts of DEBBT(2+), calculated by the density functional theoretical (DFT) method at the B3LYP6-31G** level, correlated well with those obtained experimentally. The ESR signal of DEBBT(2+) generated from DEBBT 1-O was observed in solution, which implies that the singlet-state dication DEBBT(2+)- S isomerizes to the triplet-state dication DEBBT(2+)- T, and that two molecules of DEBBT(2+)- T further form a spin pair at one trithiole ring with significant distance between the two radical centers. The oxidation of DEBBT with one or two equivalents of single-electron oxidizing reagents produced DEBBT(·+) and DEBBT(2+), and the salts were isolated in a stable form. However, the DEBBT(2+) that was prepared by oxidation with NOPF6 proved silent for NMR in CD3CN, while ESR was active. The stability, electronic state, and NMR and ESR spectroscopy of the dication are affected by solvation with D2SO4 and CD3CN. The optimized structures and the total energy of the singlet- and triplet-state dication were calculated using the DFT method at the B3LYP6-31G** level, which shows that the structures of the singlet- and triplet-state dications have a completely planar form with 1.7 kcal/mol as the total energy difference between them. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

    The 15N-CPMAS spectra of simazine and its metabolites: measurements and quantum chemical calculations

    A. E. Berns
    Summary DFT calculations are a powerful tool to support NMR studies of xenobiotics such as decomposition studies in soil. They can help interpret spectra of bound residues, for example, by predicting shifts for possible model bonds. The described bound-residue models supported the hypothesis of a free amino side chain already suspected by comparison with the experimental data of the standards. No match was found between the calculated shifts of amide bondings of the amino side chains (free or substituted) and the experimental NMR shifts of a previous study. In the present paper, first-principles quantum chemical calculations were used to support and check the interpretation of the 15N cross polarization-magic angle spinning nuclear magnetic resonance (15N-CPMAS NMR) spectra of simazine and its metabolites. Density functional theory (DFT) calculations were performed using Gaussian 03 and the nuclear magnetic shielding tensors were calculated using the Gauge-Independent Atomic Orbital (GIAO) method and B3LYP/6,311+G(2d,p) model chemistry. Good agreement was reached between the calculated and measured chemical shifts of the core nitrogens and the lactam and lactim forms of the hydroxylated metabolites could be clearly distinguished. The calculated spectra showed that these metabolites exist preferentially in the lactam form, an important fact when considering the possible interactions of such hydroxylated metabolites with the soil matrix. Although the calculated bound-residue models in the present study only partly matched the experimental data, they were nevertheless useful in helping to interpret the experimental NMR results of a previous study. To get a better match between the calculated and the measured shifts of the side-chain nitrogens the calculations need to be further developed, taking into account the influence of neighbouring molecules in the solid state. Altogether, quantum chemical calculations are very helpful in the interpretation of NMR spectra. In the future, they can also be very useful for the prediction of NMR shifts, in particular when it is not possible to measure the metabolites due to a lack of material or in cases where practical experiments cannot be conducted. [source]