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Hermann Stoll

Publications and source records attributed to Hermann Stoll.

5 recordsLinked to original sources
PubMed2003

Replacement of 2,2'-bipyridine by 1,4-diazabutadiene acceptor ligands: why the bathochromic shift for [(N empty set N)IrCl(C5Me5)]+ complexes but the hypsochromic shift for (N empty set N)Ir(C5Me5)?

Replacement of 2,2'-bipyridine (bpy) by substituted 1,4-diazabutadiene (R-DAB) alpha-diimine ligands N empty set N leads to a substantial hypsochromic shift of about 0.8 eV for the long-wavelength absorption band in compounds (N empty set N)Ir(C(5)Me(5)) but to a bathochromic absorption shift of about 0.4 eV for the complex ions [(N empty set N)IrCl(C(5)Me(5))](+). DFT calculations on model complexes based on experimental (R-DAB compounds) and geometry-optimized structures (bpy systems) reveal that the low-energy transitions of the cationic chloro complexes are largely of ligand-to-ligand charge-transfer character L'LCT (L = alpha-diimine, L' = Cl) whereas the neutral compounds exhibit pi --> pi transitions between the considerably mixed metal d(pi) and alpha-diimine pi orbitals. The much more pronounced metal-ligand orbital interaction for the R-DAB complexes causes the qualitatively different shifts on replacing the stronger basic bpy by the better pi-acceptors R-DAB. Only the LUMO of the neutral compounds is destabilized on replacement of bpy by R-DAB whereas the LUMO of [(N empty set N)IrCl(C(5)R'(5))](+) and both HOMOs are stabilized through this change.

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PubMed2002

Relativistic energy-consistent pseudopotentials--recent developments.

The direct adjustment of two-component pseudopotentials (scalar-relativistic + spin-orbit potentials), to atomic total energy valence spectra derived from four-component multiconfiguration Dirac-Hartree-Fock all-electron calculations based on the Dirac-Coulomb-Breit Hamiltonian, has been made a routine tool for an efficient treatment of heavy main-group elements. Both large-core (nsp valence shell) and small-core ((n - 1)spd nsp valence shell) potentials have been generated for all the post-d elements of groups 13-17. At the example of lead and bismuth compounds (PbHal, BiH, BiO, BiHal (Hal = F, Cl, Br, I)), we show how small-core and large-core potentials can be combined in accurate, yet computationally economic, spin-free-state-shifted relativistic electronic structure calculations of molecular ground and excited states.

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PubMed1999

The d(0), d(1) and d(2) Configurations in Known and Unknown Tetrathiometal Compounds MS(4)(n)()(-) (M = Mo, Tc, Ru; W, Re, Os). A Quantum Chemical Study.

The known tetrathiometalates MoS(4)(2)(-)(/3)(-), WS(4)(2)(-)(/3)(-), ReS(4)(-)(/2)(-)(/3)(-), and the unknown species TcS(4)(-)(/2)(-), RuS(4)(0/)(-), and OsS(4)(0/)(-)(/2)(-) were calculated using ab initio and DFT methods. The one-electron reduced species with d(1) configuration were shown to exhibit a slight Jahn-Teller distortion (T(d)() --> D(2)(d)()); the largest corresponding stabilization energy was obtained for MoS(4)(3)(-) with -4.17 kcal/mol. Trends in vacuum bonding energies involve a destabilization on going from 5d(n)() to 4d(n)() systems and on reduction from d(0) to d(1) species, with the exception of Ru and Os complexes where the d(1) configurations are more stable than the d(0) forms. The d(2) species ReS(4)(3)(-) and OsS(4)(2)(-) have vacuum bonding energies similar to those of d(1) analogues. The metal contribution to the lowest unoccupied MO (e) of d(0) forms is lowest for the neutral RuS(4) and OsS(4) and highest for the dianions MoS(4)(2)(-) and WS(4)(2)(-). The DFT approach supported by correlated ab initio calculations describes the main features of the electronic spectra of the d(0) complexes. For the experimentally best accessible ReS(4)(n)()(-) system the absorption energies and stretching frequencies were well reproduced, and the related but hitherto unknown OsS(4)(-) ion is predicted to be a fairly stable paramagnetic species.

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PubMed1996

CpIr(dab) (dab = 1,4-Bis(2,6-dimethylphenyl)-1,4-diazabutadiene): A Coordinatively Unsaturated Six-pi-Electron Metallaheteroaromatic Compound?

1,4-Bis(2,6-dimethylphenyl)-1,4-diaza-1,3-butadiene (dab) forms the structurally characterized iridium(III) complex [CpIrCl(dab)](PF(6)): C(28)H(35)ClF(6)IrN(2)P, orthorhombic, space group Pnma, a = 16.187(2) Å, b = 15.823(2) Å, c = 11.677(1) Å, V = 2990.8(6) Å(3), Z = 4, and R = 0.0588. On reaction with NaBH(3)CN this compound does not form an iridium(III) hydride but the coordinatively unsaturated reduced product CpIr(dab): C(28)H(35)IrN(2), monoclinic, space group P2(1)/n, a = 8.484(2) Å, b = 14.535(3) Å, c = 20.956(4) Å, beta = 98.88(3) degrees, V = 2553.2(9) Å(3), Z = 4, and R = 0.0586. The inverted relation d(CC) (=1.334(15) Å) < d(CN) (=1.379(13) and 1.366(14) Å) in the dab ligand of CpIr(dab) suggests that the reduction has occurred primarily at that ligand to form an ene-1,2-diamido/iridium(III) moiety or, alternatively, a six-pi-electron metallaheteroaromatic system. Ab initio pseudopotential calculations of model complexes [CpIr(HNCHCHNH)](0/2+) support this description of the bonding.

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