RESUMO
The changes in the mean-square charge radius (relative to ^{209}Bi), magnetic dipole, and electric quadrupole moments of ^{187,188,189,191}Bi were measured using the in-source resonance-ionization spectroscopy technique at ISOLDE (CERN). A large staggering in radii was found in ^{187,188,189}Bi^{g}, manifested by a sharp radius increase for the ground state of ^{188}Bi relative to the neighboring ^{187,189}Bi^{g}. A large isomer shift was also observed for ^{188}Bi^{m}. Both effects happen at the same neutron number, N=105, where the shape staggering and a similar isomer shift were observed in the mercury isotopes. Experimental results are reproduced by mean-field calculations where the ground or isomeric states were identified by the blocked quasiparticle configuration compatible with the observed spin, parity, and magnetic moment.
RESUMO
We present a density-functional-theory study of transition-metal atoms (Sc-Zn, Pt, and Au) embedded in single and double vacancies (SV and DV) in a graphene sheet. We show that for most metals, the bonding is strong and the metal-vacancy complexes exhibit interesting magnetic behavior. In particular, an Fe atom on a SV is not magnetic, while the Fe@DV complex has a high magnetic moment. Surprisingly, Au and Cu atoms at SV are magnetic. Both bond strengths and magnetic moments can be understood within a simple local-orbital picture, involving carbon sp(2) hybrids and the metal spd orbitals. We further calculate the barriers for impurity-atom migration, and they agree well with available experimental data. We discuss the experimental realization of such systems in the context of spintronics and nanocatalysis.
RESUMO
Multiconfiguration Dirac-Fock models have been employed to compute the electric field gradient in the ground state of the neutral bismuth atom. Combined with the experimental electric quadrupole hyperfine interaction constant, one obtains for (209)Bi the nuclear quadrupole moment Q = -516 (15) mb, which is almost 40% away from the previously accepted standard value [ -370 (26) mb], and narrows by over an order of magnitude the long-standing, extremely broad array of various results ranging from -370 to -710 mb. The recent Q values of (202-208,210(m)-213)Bi by Pearson et al. suffer a consequent change.
RESUMO
There is no experimental proof documented in the literature for the existence of any beryllium peroxide compound. All recent pertinent preparative attempts described in this work, using a range of beryllium salts with various peroxides as reagents under mild conditions, were equally unsuccessful. (1)H and (9)Be NMR investigations of aqueous solutions containing beryllium salts and hydrogen peroxide in a broad pH range also gave no definite evidence for the presence of peroxoberyllates as components of the manifold equilibria in such solutions. Quantum chemical calculations have therefore been carried out to delineate the energetics and structures of various beryllium peroxide model compounds. Standard Hartree-Fock and density functional methods were employed at various levels of sophistication. The series of prototypes considered consists of [BeOH](+), Be(OH)(2), Be(OH)(OOH), Be(OOH)(2), [Be(O(2))(2)](2-), [BeO(2)(OH(2))(2)], and [Be(2)(O(2))(2)(OH(2))(4)] (all in the gas phase). Surprisingly, the triatomic cation [BeOH](+) has been found to have a linear structure. All the Be-O(peroxide) bonds are found to be rather long, suggesting weaker bonding compared to the Be-O bonds in aquo, hydroxo, or oxo complexes. Hydrogen peroxide or anions derived therefrom are therefore not able to compete successfully with water (hydroxide anions) in aqueous solution. In the mononuclear beryllium peroxide molecules, the peroxide groups form chelating units at tetrahedrally 4-coordinate metal atoms. The binuclear compound [Be(2)(O(2))(2)(OH(2))(4)] has a puckered six-membered-ring structure, close to the standard chair conformation. A significant lengthening of the O-O bonds upon coordination to the Be(2+) centers has been calculated, but it is unlikely that the polarization of the peroxide group by the high positive charge density at Be(2+) is significant to cause an intrinsic instability of beryllium peroxides. All structures represent distinct local minima on the potential energy surface and are predicted to be (meta)stable species in nonaqueous media. The field of aluminum peroxides is a similar gray area on the map of metal and metalloid peroxides and is reminiscent of the well-established "diagonal-relation" of Be and Al in the periodic table of the elements.
RESUMO
A theory for the magnetic-field-dependent quadrupole splitting in the 131Xe NMR spectra in isotropic media is presented and tested by ab initio electronic structure calculations. Evidence exists only for even-power magnetic field dependence. The dominant mechanism is verified to be the electric field gradient caused by the diamagnetic distortion of the atomic electron cloud, quadratic in the magnetic field. The computed results are in excellent agreement with the recent experiment by Meersmann and Haake.
RESUMO
Ab initio calculations on the experimentally known anions [POn(NCN)4-n]3- are used to show that intramolecular forces are sufficient to determine their existence and structure. Structures are predicted for the analogous cyanamidosulphates and perchlorates. If one of the oxygens of the XO4q group is replaced by nitrogen or fluorine, further new anions are obtained. An example is NSO3(3)-. Remarkably, the NArO3- anion is predicted to have strong inner bonding and is, together with ArO4, a candidate for an argon species.
RESUMO
The reaction between thioether phosphine gold(I) precursors such as [AuCl(Ph2PCH2SPh)], 1, or [Au(Ph2PCH2SPh)2]CF3SO3 and PdCl2(NCPh)2 affords the new compounds [(AuCl(Ph2PCH2SPh)2PdCl2], 2, and [AuPdCl2(Ph2PCH2SPh)2]CF3SO3, 3. The crystal structure of complex 2 has the sterically unhindered Pd(II) and Au(I) at a distance of 314 pm. Quasirelativistic pseudopotential calculations on [AuPdCl3(PH2CH2SH)(SH2)] models give short Au-Pd distances at the second-order Møller-Plesset (MP2) level and long Au-Pd distances at Hartree-Fock (HF) level. A detailed analysis of the Au-Pd interaction shows dominant dispersion, some ionic contributions, and no net charge transfer between the metals.
