Tilo Söhnel

Nuclear Quadrupole Moment of 57Fe from Microscopic Nuclear and Atomic Calculations

The nuclear quadrupole moment (NQM) of the Ipi = 3/2(-) excited nuclear state of 57Fe at 14.41 keV, important in Mössbauer spectroscopy, is determined from the large-scale nuclear shell-model calculations for 54Fe, 57Fe, and also from the electronic ab initio and density functional theory calculations including solid state and electron correlation effects for the molecules Fe(CO)(5) and Fe(C5H5)(2). Both independent methods yield very similar results. The recommended value is 0.15(2) e b. The NQM of the isomeric 10+ in 54Fe has also been calculated. The new NQM values for 54Fe and 57Fe are consistent with the perturbed angular distribution data.

Comparison of ab initio and density functional calculations of electric field gradients: The 57Fe nuclear quadrupole moment from Mössbauer data

The difficulty in accurate determination of the nuclear quadrupole moment of the first I=3/2 excited nuclear state of 57Fe from electronic structure calculations of the iron electric field gradient combined with Mossbauer measurements of the nuclear quadrupole splitting in the isomer shift is addressed by comparing ab initio with density functional calculations for iron pentacarbonyl, Fe(CO)5, ferrocene, Fe(C5H5)2, and the 5Δg electronic ground states of FeCl2 and FeBr2. While the ligand field gradient tensor components change relatively little with the method applied, the iron electric field gradient is sensitive to the specific density functional used. Single reference many-body perturbation theory for electron correlation also performs poorly for the iron electric field gradient and shows extreme oscillatory behavior with a change in the order of the perturbation series. Even with larger basis sets and coupled cluster techniques a precise value for the iron electric field gradient could not be determin...

The quadrupole moment of the 3∕2+ nuclear ground state of Au197 from electric field gradient relativistic coupled cluster and density-functional theory of small molecules and the solid state

An attempt is made to improve the currently accepted muonic value for the 197Au nuclear quadrupole moment [+0.547(16)x10(-28) m2] for the 3/2+ nuclear ground state obtained by Powers et al. [Nucl. Phys. A230, 413 (1974)]. From both measured Mossbauer electric quadrupole splittings and solid-state density-functional calculations for a large number of gold compounds a nuclear quadrupole moment of +0.60x10(-28) m2 is obtained. Recent Fourier transform microwave measurements for gas-phase AuF, AuCl, AuBr, and AuI give accurate bond distances and nuclear quadrupole coupling constants for the 197Au isotope. However, four-component relativistic density-functional calculations for these molecules yield unreliable results for the 197Au nuclear quadrupole moment. Relativistic singles-doubles coupled cluster calculations including perturbative triples [CCSD(T) level of theory] for these diatomic systems are also inaccurate because of large cancellation effects between different field gradient contributions subsequently leading to very small field gradients. Here one needs very large basis sets and has to go beyond the standard CCSD(T) procedure to obtain any reliable field gradients for gold. From recent microwave experiments by Gerry and co-workers [Inorg. Chem. 40, 6123 (2001)] a significantly enhanced (197)Au nuclear quadrupole coupling constant in (CO)AuF compared to free AuF is observed. Here, these cancellation effects are less important, and relativistic CCSD(T) calculations finally give a nuclear quadrupole moment of +0.64x10(-28) m2 for 197Au. It is argued that it is currently very difficult to improve on the already published muonic value for the 197Au nuclear quadrupole moment.

Ground-state properties and static dipole polarizabilities of the alkali dimers from K2n to Fr2n(n=0,+1) from scalar relativistic pseudopotential coupled cluster and density functional studies

The newly adjusted energy-consistent nine-valence-electron pseudopotentials for K to Fr are used to calculate spectroscopic properties for the neutral and positively charged alkali dimers using coupled cluster and density functional theory. For the neutral dimers the static dipole polarizability was calculated. The coupled cluster results are all in excellent agreement with experimental values. The density functionals used can give quite different spectroscopic properties especially for the dipole polarizability, with the Perdew-Wang PW91 functional performing best.

Transmissionsoptimierte Einkristallstrukturbestimmung und elektronische Struktur von Bi3Ni / Transmission-Optimized Single-Crystal Structure Determination and Electronic Structure of Bi3Ni

Crystals of Bi3Ni were synthesized using iodine as mineralizer. X-ray diffraction on a single-crystal including transmission-optimized measurement and optimized absorption correction (μ(Mo-Kα) = 1302 cm−1) results in a structure model (Pnma; a = 887.96(7), b = 409.97(3), c = 1147.8(1) pm) with significant deviations in interatomic distances compared with previous data from X-ray and neutron investigations. From quantum chemical calculations and from the structural chemistry of the subhalides related to Bi3Ni the chemical structure of the intermetallic compound can be derived. In the crystal structure the Ni atoms have a capped trigonal prismatic coordination of Bi atoms with strong bonds Ni-Bi and Ni-Ni. The prisms constitute rods 1∞ [NiBi1/1Bi6/3] by sharing the non-capped square faces. The bonding between the intermetallic rods is clearly weaker than inside them, leading to a preservation of this structural fragment in the subhalides of Bi3Ni. In accordance with the low temperature superconductivity of the compound, its electronic band structure shows steep and flat bands at the Fermi level. DFT and ELF calculations reveal a separation of delocalized conduction electrons inside the prism rods and largely localized valence electrons between them.

The stability of gold iodides in the gas phase and the solid state.

The stability of gold iodides in the oxidation state +I and +III is investigated at the ab initio and density functional level using relativistic and nonrelativistic energy-adjusted pseudopotentials for gold and iodine. The calculations reveal that relativistic effects stabilize the higher oxidation state of gold as expected, that is Au2I6 is thermodynamically stable at the relativistic level, whilst at the nonrelativistic level the complex of two iodine molecules weakly bound to both gold atoms in Au2I2 is energetically preferred. The rather low stability of AuI3 with respect to dissociation into AuI and I2 will make it difficult to isolate this species in the solid state as (possibly) Au2I6 or detect it by matrix-isolation techniques. The monomer AuI3 is Jahn-Teller distorted from the ideal trigonal planar (D3h) form, but adopts a Y-shaped structure (in contrast to AuF3 and AuCl3), and in the nonrelativistic case can be described as I2 weakly bound to AuI. Relativistic effects turn AuI3 from a static Jahn-Teller system to a dynamic one. For the yet undetected gas-phase species AuI accurate coupled-cluster calculations for the potential energy curve are used to predict vibrational-rotational constants. Solid-state density functional calculations are performed for AuI and Au2I6 in order to predict cohesive energies.

Origin and effect of In–Sn ordering in InSnCo3S2: a neutron diffraction and DFT study

The solid solution In2−xSnxCo3S2 is attractive due to a variety of interesting properties depending on the In/Sn content, i.e. half metal ferromagnetic Sn2Co3S2, low dimensional metal In2Co3S2, and semiconducting thermoelectric InSnCo3S2. For the latter, crystal structure effects and a metal to insulator transition are not only related to electron counting but also to ordering of In and Sn within and between Co Kagome nets. These observations have not been adequately understood to date. The degree of ordering is now evaluated from neutron diffraction data to distinguish In and Sn. The origin and effects on crystal and electronic structures are studied by DFT calculations on a superstructure model. Relations of local bonding (electron localization function ELF and Baders AIM theory), In/Sn site preference, crystal structure distortions, and the opening of the gap are explored. Results are generalised from predictions on isoelectronic compounds.

Darstellung, Eigenschaften und Kristallstruktur von RuSn6[(Al1/3–xSi3x/4)O4]2 (0 ≤ x ≤ 1/3) – einem Oxid mit isolierten RuSn6-Oktaedern

RuSn6[(Al1/3–xSi3x/4)O4]2 wird bei Festkorperreaktionen von RuO2, SnO2, Sn und Si im Korundtiegel bei 1273 bis 1373 K erhalten. Die Verbindung kristallisiert kubisch in der Raumgruppe Fm 3 m (a = 9.941(1) A, Z = 4, R1 = 0.0277, wR2 = 0.0619), ist halbleitend und an der Luft stabil. Mosbaueruntersuchungen und Bindungslange–Bindungsstarke-Betrachtungen rechtfertigen eine ionische Grenzformulierung Ru2+Sn62+[(Al1/3–x3+Si3x/44+)O42–]2. Zentrales Strukturmotiv der Kristallstruktur sind voneinander isoliert angeordnete RuSn6-Oktaeder. Diese sind nur uber Sauerstoffatome, die tetraedrisch uber den Flachen der Oktaeder angeordnet und partiell mit Al bzw. Si besetzt sind, miteinander verbunden. Damit stellt diese Verbindung eine Variante des Pentlandit-Strukturtyps dar. Preparation, Properties, and Crystal Structure of RuSn6[(Al1/3–xSi3x/4)O4]2 (0 ≤ x ≤ 1/3) – an Oxide with isolated RuSn6 Octahedra RuSn6[(Al1/3–xSi3x/4)O4]2 is obtained by the solid state reaction of RuO2, SnO2, Sn, and Si in an Al2O3-crucible at 1273 to 1373 K. The compound is cubic with the space group Fm 3 m (a = 9.941(1) A, Z = 4, R1 = 0.0277, wR2 = 0.0619), a semiconductor and stable in air. Results of Mosbauer measurements as well as bond length-bond strength calculations justify the ionic formulation Ru2+Sn62+[(Al1/3–x3+Si3x/44+)O42–]2. The central motif of the crystal structure are separated RuSn6-octahedrea. These are interconnected by oxygen atoms, arranged tetrahedrely above the surfaces of the RuSn6-octahedrea and partialy filled with Al and Si, respectively. Because of these features the compound can be considered as a variant of the crystal structure type of pentlandite.

Anticancer activity of Ru- and Os(arene) compounds of a maleimide-functionalized bioactive pyridinecarbothioamide ligand

With the aim of increasing the accumulation of Ru anticancer agents in the tumor, a targeted delivery strategy based on a maleimide anchor for the biological vector human serum albumin (HSA) was developed. A group of piano stool Ru- and Os(η6-arene) complexes carrying a maleimide-functionalized N-phenyl-2-pyridinecarbothioamide (PCA) ligand was designed allowing for covalent conjugation to biological thiols. The complexes were characterized by NMR spectroscopy, ESI-MS, elemental analysis and single-crystal X-ray diffraction analysis. The compounds were shown to undergo halido/aqua ligand exchange reactions in aqueous solution, depending mainly on the metal center and the nature of the halide. In vitro cytotoxicity studies revealed low potency which is explained by the observed high reactivity of the maleimide to the thiol of l-cysteine (Cys), while the metal center itself shows little affinity to amino acids of the model protein lysozyme.

Pressure dependent stability and structure of carbon dioxide--a density functional study including long-range corrections.

First-principles density functional theory (DFT) is used to study the solid-state modifications of carbon dioxide up to pressures of 60 GPa. All known molecular CO2 structures are investigated in this pressure range, as well as three non-molecular modifications. To account for long-range van der Waals interactions, the dispersion corrected DFT method developed by Grimme and co-workers (DFT-D3) is applied. We find that the DFT-D3 method substantially improves the results compared to the uncorrected DFT methods for the molecular carbon dioxide crystals. Enthalpies at 0 K and cohesive energies support only one possibility of the available experimental solutions for the structure of phase IV: the R3c modification, proposed by Datchi and co-workers [Phys. Rev. Lett. 103, 185701 (2009)]. Furthermore, comparing bulk moduli with experimental values, we cannot reproduce the quite large--rather typical for covalent crystal structures--experimental values for the molecular phases II and III.