Nino Runeberg

A stable argon compound

The noble gases have a particularly stable electronic configuration, comprising fully filled s and p valence orbitals. This makes these elements relatively non-reactive, and they exist at room temperature as monatomic gases. Pauling predicted in 1933 that the heavier noble gases, whose valence electrons are screened by core electrons and thus less strongly bound, could form stable molecules. This prediction was verified in 1962 by the preparation of xenon hexafluoroplatinate, XePtF6, the first compound to contain a noble-gas atom. Since then, a range of different compounds containing radon, xenon and krypton have been theoretically anticipated and prepared. Although the lighter noble gases neon, helium and argon are also expected to be reactive under suitable conditions, they remain the last three long-lived elements of the periodic table for which no stable compound is known. Here we report that the photolysis of hydrogen fluoride in a solid argon matrix leads to the formation of argon fluorohydride (HArF), which we have identified by probing the shift in the position of vibrational bands on isotopic substitution using infrared spectroscopy. Extensive ab initio calculations indicate that HArF is intrinsically stable, owing to significant ionic and covalent contributions to its bonding, thus confirming computational predictions that argon should form a stable hydride species with properties similar to those of the analogous xenon and krypton compounds reported before.

Predicted ligand dependence of the Au(I)…Au(I) attraction in (XAuPH3)2

Abstract The dependence of the “aurophilic” attraction in the perpendicular model system (XAuPH 3 ) 2 on the substituent X is studied using 19-valence electron quasirelativistic pseudopotentials for Au. It increases along the series F 3 3 , reaching 25 kJ/mol for the softest ligand, X. The calculated range, R e , depth, V ( R e ), and Au…Au force constant are comparable with available experimental values.

THE AUROPHILIC ATTRACTION AS INTERPRETED BY LOCAL CORRELATION METHODS

The nature of the aurophilic interaction is studied by applying local second-order Mo/ller–Plesset perturbation theory (LMP2) on model dimers of [X–Au–PH3]2 (X=H, Cl) type. The possibility to decompose the correlation contribution of the interaction energy in the dimer (A–B) into different excitation classes reveals that the dispersion contribution (A→A′,B→B′) is accompanied by an almost equally important ionic component (A→A′,B→A′), at shorter distances. Double excitations where at least one electron originates from the gold 5d orbitals account for almost 90% of the attraction. Relativistic effects amount to 28% of the binding energy and can be traced to arise almost exclusively from the relativistic expansion of gold d-shells.

A theoretical study of HArF, a newly observed neutral argon compound

Computational results up to the CCSD(T)/aug-cc-pV5Z level are presented as support for the newly observed argon containing compound, hydrido argonfluoride (HArF). The molecule is calculated to be linear with R(H–Ar)=132.9 pm and R(Ar–F)=196.9 pm. The calculated vibrational frequencies, corrected for anharmonicity and matrix effects, are 462 (Ar–F stretch), 686 (bend) and 1916 cm−1 (Ar–H stretch). These are in good agreement with the corresponding experimentally observed frequencies of 435.7, 687.0, and 1969.5 cm−1 for the matrix isolated species [Nature 406, 874 (2000)]. Including corrections for the finite basis set as well as for the zero-point energy, the new molecule is stable by 0.15 eV compared to the dissociated atoms. HArF is further stabilized by an additional barrier of 0.18 eV, arising from the avoided crossing between the states corresponding to the ionic (HArδ+)(Fδ−) equilibrium structure and the covalent (HAr⋅)(F⋅) dissociation limit. The dissociation of HArF via bending into the thermodynam...

Ab initio studies of bonding trends: Part 9. The dicyanamide-carbon suboxide-dicyanoether-cyanogen azide isoelectronic series ABCDE1

Abstract The isoelectronic analogs of the title molecules are screened for possible unknown species using ab initio HF or MP2 6-31G ∗ calculations. Some candidates are the bent cations OCNCO + and OCPCO + , the linear anions OBCBO 2− and OBNBO − , and the bent NBNBN 3− and NBOBN 2− . The known NC-NNN is predicted to have a CN 4 ( D 2d ) di(diazirine) isomer, only 2.7 eV above the cyanogen azide at HF level. The analogous BN 4 − is also found to have a local minimum. The predicted neutral species include the linear OCNBO and ONNBN and the bent OCPCN, rather resembling the experimentally known NCPCN − anion.

Calculated properties of XeH2

Abstract Relativistic pseudopotential calculations (including spin-orbit (SO) effects) are reported for XeH 2 at levels up to MRCISD and CCSD(T). Three relativistic and one non-relativistic pseudopotential are tested. The 18-valence-electron (Xe) CCSD(T) results, including BSSE and SO, give R e and D e of 191.6 pin and 0.32 eV, respectively. Adding estimates of 0.03 eV for a MRCI dissociation threshold and 0.03 eV for matrix quadrupole stabilisation, the ground-state well depth obtained is comparable with the sum of the zero-point vibrations and one observed vibration. The calculated σ g and π u frequencies are comparable with the observed ones. Test results for XeH + are reported.

Chemical bonds between noble metals and noble gases.: Ab initio study of the neutral diatomics NiXe, PdXe and PtXe

Abstract The lowest potential-energy curves are calculated for the species MXe, M=Ni, Pd, Pt. No bound states are found for NiXe. For PdXe the ground state is bound by 41.6 kJ/mol. The PtXe ground-state curve dissociates to an excited Pt( 1 S 0 ) state but remains bound by 67.9 kJ/mol with respect to the Pt( 3 D 3 ) ground state. Of this D e value, 9.2 kJ/mol is due to the stabilization caused by spin–orbit coupling. The calculated quasirelativistic Pt–Xe distance is 242 pm. Both PdXe and PtXe are possible new gas-phase or matrix species.

Aurophilic attraction: the additivity and the combination with hydrogen bonds

Abstract The coexistence of gold–gold contacts and hydrogen bonding is studied in the model system [H 2 P(OH)AuCl] 2 and [H 2 P(OH)AuPH 2 (O)] 2 . The two interactions are found to be comparable. The possible non-additivity of the aurophilic, Au(I)–Au(I) interaction is studied at MP2 level for the pentagonal [Au(SH) 2 (AuSH) 5 )] − and hexagonal [Au(SH) 2 (AuSH) 6 ] − clusters. The possibilities of ‘mechanical cooperativity’ between different aurophilic attractions and of Au…S attractions are also considered.

Calculation of binary magnetic properties and potential energy curve in xenon dimer: Second virial coefficient of 129Xe nuclear shielding

Quantum chemical calculations of the nuclear shielding tensor, the nuclear quadrupole coupling tensor, and the spin-rotation tensor are reported for the Xe dimer using ab initio quantum chemical methods. The binary chemical shift delta, the anisotropy of the shielding tensor Delta sigma, the nuclear quadrupole coupling tensor component along the internuclear axis chi( parallel ), and the spin-rotation constant C( perpendicular ) are presented as a function of internuclear distance. The basis set superposition error is approximately corrected for by using the counterpoise correction (CP) method. Electron correlation effects are systematically studied via the Hartree-Fock, complete active space self-consistent field, second-order Møller-Plesset many-body perturbation, and coupled-cluster singles and doubles (CCSD) theories, the last one without and with noniterative triples, at the nonrelativistic all-electron level. We also report a high-quality theoretical interatomic potential for the Xe dimer, gained using the relativistic effective potential/core polarization potential scheme. These calculations used valence basis set of cc-pVQZ quality supplemented with a set of midbond functions. The second virial coefficient of Xe nuclear shielding, which is probably the experimentally best-characterized intermolecular interaction effect in nuclear magnetic resonance spectroscopy, is computed as a function of temperature, and compared to experiment and earlier theoretical results. The best results for the second virial coefficient, obtained using the CCSD(CP) binary chemical shift curve and either our best theoretical potential or the empirical potentials from the literature, are in good agreement with experiment. Zero-point vibrational corrections of delta, Delta sigma, chi (parallel), and C (perpendicular) in the nu=0, J=0 rovibrational ground state of the xenon dimer are also reported.

A Study of the Interactions in an Extended Unsupported Gold-Silver Chain

The complex [Ag(Py)3][Au(C6F5)2]·Py (1) (Py = pyridine) has been prepared by the reaction of NBu4[Au(C6F5)2] with AgClO4 in the presence of pyridine. The crystallographic measurements indicate the presence of an extended unsupported one-dimensional chain of alternating gold and silver atoms. This arrangement is due to the formation of molecular Au−Ag ion pairs, to the π-stacking of C6F5 and pyridine arene ligands and to the packing effects that lead to molecular ion pairs at short distance. Theoretical calculations based on approximate experimental distances and angles reveal the presence of both metallophilic AuI−AgI and aromatic C6F5-pyridine interactions. From a theoretical point of view the nature of the intermetallic attraction arises from both an ionic contribution and from dispersion-type correlation effects; the aromatic interaction is mainly due to dispersion-type correlation effects.