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  • 11
    Electronic Resource
    Electronic Resource
    A density functional theory study of the conformational properties of 1,2-ethanediamine: protonation and solvent effects (2000)
    Springer
    Theoretical chemistry accounts 105 (2000), S. 39-45 
    Details
    ISSN: 1432-2234
    Keywords: Key words: Density functional theory – Solvation – Protonation – Electron localisation function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract.  The structures and the conformational energies of nonprotonated, monoprotonated and diprotonated 1,2-ethanediamine have been investigated through density functional theory. The relative performance of local and gradient-corrected functionals is discussed. The existence of hydrogen-bond formation has been determined with electron localisation function calculations. Proton affinities for nonprotonated and monoprotonated 1,2-ethanediamine have been calculated and are in agreement with experimental data. The influence of solvation has been accounted for through the self-consistent isodensity polarisable continuum model. The results for the nonprotonated conformers show that solvation stabilises those conformers which have the lone pair in an antiperiplanar conformation. Solvation of the monoprotonated conformer stabilises significantly the “anti” conformation, which is unstable in the gas phase. For the di-protonated species, solvation stabilises slightly the gauche conformer, which is unstable in the gas phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002140000177
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  • 12
    Electronic Resource
    Electronic Resource
    The modelling of nucleophilic and electrophilic additions to organometallic complexes using molecular graphics techniques (1988)
    Springer
    Journal of computer aided molecular design 2 (1988), S. 235-253 
    Details
    ISSN: 1573-4951
    Keywords: Intermolecular interactions ; Extended Hückel ; Dot surfaces ; Molecular properties ; Reactivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new formalism has been developed in order to evaluate intermolecular interaction energies for inorganic and organometallic complexes in the framework of the extended Hückel method. In order to provide the shortest possible response time on an interactive computer graphics facility, this model should require the minimum amount of computer time, which explains why approximate procedures are used to evaluate electrostatic, charge transfer and exchange repulsion components. When applying this model to typical examples of electrophilic addition reactions to organometallic complexes, it is found that it is essential to take account of charge transfer interactions, the electrostatic component alone being not sufficient, even qualitatively, for a proper description of the reaction mechanism. The results, presented as color-coded dot molecular surfaces, show a very good agreement with experiment as to the site of attack, namely (i) on metal for the electrophilic attack on Fe(cp)2, Fe(CO)5 and X(cp)(CO)2, X=Co, Rh; (ii) on the cp ligand for the nucleophilic attack on Co(cp)2 + and Rh(cp)2 +; (iii) on bz for the nucleophilic attack on Fe(cp)(bz)+. Finally, modellizations of the nucleophilic attack on a coordinated olefin and of the relation between structure and acidic properties of zeolites are presented and discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01531997
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  • 13
    Electronic Resource
    Electronic Resource
    Density-functional investigation of the excited state properties and the Jahn—Teller effect in [CrX6]3- (X=Cl-, Br-) (1995)
    Springer
    Theoretica chimica acta 91 (1995), S. 215-224 
    Details
    ISSN: 0040-5744
    Keywords: Key words: Density functional theory ; Excited states ; Jahn ; Teller effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary.  The luminescence of [CrX6]3- X=Br-, Cl- has been studied through density functional theory (DFT) using both deMon and ADF codes. Multiplet energies 4A2, 2E, 4T2, and 4T1 have been expressed as energies of non-redundant single determinants and calculated as in Ref. [1]. The influence of the metal ligand distance on the multiplet energies has been investigated. Of particular interest to this work is the Jahn–Teller effect distortion. We found that the system moves to a more stable geometry when the axial bond length is compressed and the equatorial one elongated in agreement with the experimental value.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01114988
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  • 14
    Electronic Resource
    Electronic Resource
    Base Hydrolysis of (Acidato)(Pentaamine) Complexes with Inert Metal Centers: Electronic Structure of the Intermediates, Requirements for Their Formation, and the Unique Reactivity of the Complexes of Cobalt(III) (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1247-1263 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular-orbital calculations have been performed for the conjugate base cis-[Co(NH3)4(NH2)Cl]+ and trans-[M(NH3)4(NH2)Cl]+ (M = CrIII, CoIII, and RhIII), the hexacoordinated intermediates cis- and trans-[Co(NH3)4(NH2)…Cl]+, the square-pyramidal and trigonal bipyramidal pentacoordinated intermediates apical-[Co(NH3)4(NH2)]2+, basal-[Co(NH3)4(NH2)]2+, and equatorial-[M(NH3)4(NH2)]2+ (M = Co and Rh), respectively, using modified extended Hückel and SCF MS-Xα methods. The LUMO of the conjugate bases is an antibonding metal centered dρ* orbital which is stabilized during the dissociative activation of the M—Cl bond. For the above conjugate bases, separations of the highest doubly occupied MO (HDOMO) and the LUMO of 1.3, 2.5, 1.8, and 2.5 eV, respectively, have been calculated using the SCF MS-Xα model. Only in the conjugate base cis-[Co(NH3)4(NH2)Cl]+ with the smallest HDOMO  -  LUMO gap, the singlet electronic structure of the ground state may be stabilized by changing into a triplet when the Co—Cl bond is activated. This situation is unique to (acidato)(pentaamine)cobalt(III) complexes with deprotonated amine ligand cis to the leaving group and the reason for the existence of intermediates and their reactivity as well. Base hydrolysis of the analogues CrIII and RhIII complexes - the latter taken to represent the second- and third-row transition-metal amines - is unlikely to proceed via intermediates; a concerted substitution process is expected to take place.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740613
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  • 15
    Electronic Resource
    Electronic Resource
    Density functional theory applied to the excited states of coordination compounds (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 867-877 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Coordination compounds are usually symmetrical molecules with degenerate orbitals. Hence, the individual multiplet states arising from open-shell configurations can, in general, not be expressed by a single determinant. We have therefore exploited symmetry to the largest possible extent in order to simplify the relation between the multiplet splitting and single-determinant energies and thus developed a new method based on vector coupling to keep the computational effort to a minimum. A system of computer programs working on both mainframe and personal computers has been developed, carrying out for any desired point group the required group theoretical manipulations. The description of the method is illustrated by considering three practical examples. © 1994 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520414
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  • 16
    Electronic Resource
    Electronic Resource
    Komplexe von Kupfer(I) mit Glyoxal-bis-N-t.-butylimin (1975)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 58 (1975), S. 1732-1735 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Formation of strongly colored complexes of Cu+ with glyoxal-bis-(N-t-butylimin) (GLI) is observed in acetonitrile. Optical measurements reveal two complexes, Cu(GLI)+ (ṽmax = 26.0 kK, δ = 2800) and Cu(GLI)2+ (ṽmax = 19.3 kK, ε = 8530). The equilibrium constants (0.1M tetraethylammoniumperchlorate) are logK1 = 3.9 and logK2 = 2.5. The equilibrium data are confirmed by potentiometric measurements with a copper electrode. In O-donor solvents, only the 1:2 complex is observed. Cu(GLI)2CIO4 can be crystallized as a dark red solid which is stable towards atmospheric oxygen.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19750580626
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  • 17
    Electronic Resource
    Electronic Resource
    Molecular-Graphics Modelling of the Acid Strength in Zeolites: Influence of the Aluminium Distribution in Offretite (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 112-121 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using extended Hückel wave functions, molecular electrostatic potentials (MEP's) have been calculated for several model clusters representative of zeolites of offretite type. The clusters studied, which are all made of a central unit comprising 2 AlO4 and 16 SiO4 tetrahedra, differ only by the relative positions of the Al-atoms occupying the same crystallographic sites (T2) within the zeolite framework. using the MEP values as a color-coded acidity index for the various clusters, three-dimensional representations of their molecular surfaces are generated as solid models on a performing computer graphics system. Important differences in acidity are predicted for the clusters which can he classified into two types according to the distribution of Al-atoms: the first one is characterized by nearly independent acid sites localized around the main channel of zeolite (Figs. 3 and 6) whereas the second one exhibits interacting acid sites located longitudinally along the channel of the same gmelinite cage (Figs. 4 and 5). The possible relationship between the structure of the clusters and their catalytic activity towards organic species is discussed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730112
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  • 18
    Electronic Resource
    Electronic Resource
    The modeling of nucleophilic and electrophilic additions and substitutions using extended Hückel-based reaction potentials (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 623-640 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new formalism has been developed in order to evaluate intermolecular interaction energies for organometallic complexes including electrostatic, polarization, and orbital contributions based on extended Hückel molecular orbital (EHMO) theory. The electrostatic interaction is evaluated using (i) a multipolar expansion of EHMO charge density, or (ii) by calculating directly the electrostatic integrals in the basis of atomic orbitals. The polarization effects are evaluated by introducing a perturbation into the Hamiltonian. The orbital interaction is calculated by considering a supermolecule made of the organometallic substrate and a model electrophile or nucleophile. To provide the shortest possible response time on an interactive computer graphics facility, this model should require the minimum amount of computer time, which explains why approximate procedures are used to evaluate the dominant contributions to the interaction energies. Preliminary results show that these interaction energies lead to reaction potentials in good agreement with experiment for a broad series of nucleophilic and electrophilic addition or substitution reactions involving organometallic complexes. In addition, it is shown that the method can easily be extended for the calculation of solvent effects. To this end, developments considering the supermolecule surrounded by a polarizable continuum are in progress.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380505
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  • 19
    Electronic Resource
    Electronic Resource
    The Electronic Fine Structure of Co (11)-Complexes with Schiff-Base Ligands (1982)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 65 (1982), S. 2486-2497 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Multiple-scattering-Xα MO-calculations are reported for Co (acacen). The results are essentially in agreement with extended Hückel calculations and EPR. data. Particular emphasis has been placed on the calculation of the electronic structure and one-electron properties, i.e. state energies diagram, spin-orbit coupling and hyperfine coupling based on a ligand field interpretation of the Xα-results, which allow to rationalize the main features of the EPR. spectra.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19820650818
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  • 20
    Electronic Resource
    Electronic Resource
    Symmetrical “nonproduct” quadrature rules for a fast calculation of multicenter integrals (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 219-230 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A complete method of numerical integration, designed especially for density functional theory, is presented. We first refer to already known methods and then present a new development of the angular integration. A set of symmetrical quadrature rules which is equivalent to the popular Lebedev scheme has been developed for any arbitrary point group. In case of octahedral symmetry our method turns out to be exactly identical to Lebedev's. These formulas integrate exactly spherical harmonics of the highest possible order with, most probably, the least possible number of grid points. Nevertheless a rigorous mathematical proof of this statement has not yet been found. Examples of quadrature rules for noncubic point groups (not covered by Lebedev's grid), e.g., the icosahedral, pentagonal, or hexagonal ones are given. The application of this method to the resolution of the Poisson's equation is also presented. © 1997 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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