Pekka Pyykkö

Molecular Double‐Bond Covalent Radii for Elements Li–E112

The previous systems of triple-bond and single-bond self-consistent, additive covalent radii, R(AB)=r(A)+ r(B), are completed with a fit for sigma(2)pi(2) double-bonds.The primary bond lengths, R, are taken from experimental or theoretical data corresponding to chosen group valencies. All r(E) values are obtained from the same, self-consistent fit. Many of the calculated primary data came from E=CH(2) and H-E=CH(2) models. Homonuclear LE=EL, formaldehyde-type Group 14-Group 16 and open-shell, X (3) Sigma Group-16 dimer data are included. The standard deviation for the 316 included data points is 3 pm.

Spectroscopic nuclear quadrupole moments

A ‘year-2001’ set of nuclear quadrupole moments, Q, is presented. Compared to the previous, ‘year-1992’ set, a major revision of the value or a considerable improvement of the accuracy is reported for 6 3Li, 7N, 19 9F (197 keV, I = 5/2), 11Na, 13Al, 21Sc, 22Ti, 26Fe (14 keV, I = 3/2 Mössbauer state), 31Ga, 32Ge, 77 34Se (250 keV, I = 5/2 state), 35Br, 36Kr, 37Rb, 39Y, 40Zr, 100 45Rh, 50Sn (24 keV, I = Mössbauer state), 53I, 54Xe, 55Cs and 83Bi.

Relativistic Quantum Chemistry

Publisher Summary This chapter provides a summary of the relativistic calculations on multielectron or multicenter problems. The Dirac–Fock Hamiltonian and the main quantum electrodynamical (QED) corrections are discussed and the atomic and bandstructure calculations are reviewed. Then the construction of relativistic molecular orbitals and the solvable one-electron molecular and solid-state models are described. The simplest possible system for studying relativistic effects in chemical bonding is H 2 + . Several variational linear combinations of atomic orbitals (LCAO)-type solutions of the Dirac equation for H 2 + show that the relativistic effects decrease the electronic energy by about –7 ╳ 10 –6 a.u. The Dirac-Fock and Dirac-Slater molecular calculations, the relativistic semiempirical methods, and the perturbation treatments of relativistic effects are also described. In relativistic treatments of several spectroscopic properties, the entire formulation must be changed if relativistic wavefunctions are used. Some of its examples are considered. The chapter also presents a preliminary account of the relativistic effects on the chemical properties of the periodic system of elements.

Year-2008 nuclear quadrupole moments

A ‘year-2008’ set of nuclear quadrupole moments, Q, is presented. Compared to the previous, ‘year-2001’ set, a major revision of the value or an improvement of the accuracy is reported for 38Sr, 49In, 50Sn (Mössbauer state), 51Sb, 57La, 80Hg and 88Ra. Slight improvements or valuable reconfirmations exist for 7N, 11Na, 13Al, 53I, 56Ba and 71Lu.

How Do Spin–Orbit-Induced Heavy-Atom Effects on NMR Chemical Shifts Function? Validation of a Simple Analogy to Spin–Spin Coupling by Density Functional Theory (DFT) Calculations on Some Iodo Compounds

Spin–orbit coupling is responsible for many heavy-atom effects on NMR chemical shifts, for example, normal halogen dependence. A simple but general model for spin–orbit-induced substituent effects has now been developed by analogy to the Fermi contact spin–spin coupling mechanism (see below). DFT calculations on some simple iodo compounds illustrate the scope and validity of the model.

Relativistic Effects in Chemistry: More Common Than You Thought

Relativistic effects can strongly influence the chemical and physical properties of heavy elements and their compounds. This influence has been noted in inorganic chemistry textbooks for a couple of decades. This review provides both traditional and new examples of these effects, including the special properties of gold, lead-acid and mercury batteries, the shapes of gold and thallium clusters, heavy-atom shifts in NMR, topological insulators, and certain specific heats.

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.

Relativity, Gold, Closed-Shell Interactions, and CsAu⋅NH3

The chemical properties of gold are strongly influenced by relativistic effects. One example is the large electronegativity of Au, which qualitatively explains the stability of (solid or liquid) cesium auride, Cs(+)Au(-), and other systems with Au(-) ions. An especially impressive compound is CsAu.NH(3), the structure and bonding of which are discussed. Future possibilities for finding further aurides are outlined.

A transparent interpretation of the relativistic contribution to the N.M.R. ‘heavy atom chemical shift’

The N.M.R. chemical shift problem is formulated so that a correct nonrelativistic limit is obtained for the paramagnetic term using Extended Huckel level wavefunctions. Then the relativistic contributions are identified from a REX-EHT comparison in second-order perturbation theory. The results obtained for hydrogen halides, HX, agree with the observed experimental trend. The main mechanisms are the spin-orbit induced proton spin density in the π1/2 MO and the spin-orbit induced Zeeman term in the 3σ MO. The results obtained for 13C shifts in haloacetylenes and methyl halides are qualitatively correct, but too small. Possible reasons are discussed.

Additive Covalent Radii for Single-, Double-, and Triple-Bonded Molecules and Tetrahedrally Bonded Crystals: A Summary

The recent fits of additive covalent radii R(AB) = r(A) + r(B) for the title systems are reviewed and compared with alternative systems of radii by other authors or with further experimental data. The agreement of the predicted R with experiment is good, provided that the A-B bond is not too ionic, or the coordination numbers of the two atoms too different from the original input data, used in the fit. Bonds between transition metals and halides are not included in the single-bond set, because of their partial multiple-bond character.