OPTIMIZED QUASIPARTICLE DENSITY FUNCTIONAL AND GREEN’S FUNCTIONS METHOD TO COMPUTING BOND ENERGIES OF DIATOMIC MOLECULES

It is presented an advanced approach to computing the energy and spectral parameters of the diatomic molecules, which is based on the hybrid combined density functional theory (DFT) and the Green’s-functions (GF) approach. The Fermi-liquid quasiparticle version of the density functional theory is modified and used. The density of states, which describe the vibrational structure in photoelectron spectra, is defined with the use of combined DFT-GF approach and is well approximated by using only the first order coupling constants in the optimized one-quasiparticle approximation. Using the combined DFT-GF approach to computing the spectroscopic factors of diatomic molecules leads to significant simplification of the calculation procedure and increasing an accuracy of theoretical prediction. As illustration, the results of computing the bond energies in a number of known diatomic molecules are presented and compared with alternative theoretical results, obtained within discrete-variational , muffin-tin orbitals and other methods.

A Comprehensive Analysis of the Metal–Nitrile Bonding in an Organo-Diiron System

Nitriles (N≡CR) are ubiquitous in coordination chemistry, yet literature studies on metal–nitrile bonding based on a multi-technique approach are rare. We selected an easily-available di-organoiron framework, containing both π-acceptor (CO, aminocarbyne) and donor (Cp = η5−C5H5) ligands, as a suitable system to provide a comprehensive description of the iron–nitrile bond. Thus, the new nitrile (2–12)CF3SO3 and the related imine/amine complexes (8–9)CF3SO3 were synthesized in 58–83% yields from the respective tris-carbonyl precursors (1a–d)CF3SO3, using the TMNO strategy (TMNO = trimethylamine-N-oxide). The products were fully characterized by elemental analysis, IR (solution and solid state) and multinuclear NMR spectroscopy. In addition, the structures of (2)CF3SO3, (3)CF3SO3, (5)CF3SO3 and (11)CF3SO3 were ascertained by single crystal X-ray diffraction. Salient spectroscopic data of the nitrile complexes are coherent with the scale of electron-donor power of the R substituents; otherwise, this scale does not match the degree of Fe → N π-back-donation and the Fe–N bond energies, which were elucidated in (2–7)CF3SO3 by DFT calculations.

Thermochemistry

Thermochemistry explores the basic principles of energy changes in chemical reactions. Calorimetry is described as a tool to measure the quantity of heat involved in a chemical or physical change. Quantitative overviews of enthalpy and the stoichiometry of thermochemical equations are provided, including the concepts of endothermic and exothermic reactions. Standard conditions are defined to allow comparison of enthalpies of reactions and determine how the enthalpy change for any reaction can be obtained. Hess"s Law, which allows the enthalpy change of any reaction to be calculated, is discussed with illustrative examples. A presentation of bond energies and bond dissociation enthalpies is offered along with the use of bond enthalpy to estimate heats of reactions.

Solid-state electronegativity of atoms: new approaches

Electronegativities (EN) of 65 elements (H to Bi, except lanthanides and noble gases, plus U and Th) in solids were derived from various observed parameters, namely, bond energies in solids, structural geometry, work functions and force constants, yielding a set of internally consistent values. The solid-state electronegativities are generally lower than the conventional (`molecular') values, due to different coordination numbers and electronic structure in a solid versus a molecule; the decrease is stronger for metals than for non-metals, hence binary compounds have a wider EN difference and higher bond polarity (ionicity) in the solid than in the molecular (gaseous) state. Under high pressure, the ENs of metals increase and those of non-metals decrease, the binary solid becomes less polar and can ultimately dissociate into elements.

From Electronegativity towards Reactivity—Searching for a Measure of Atomic Reactivity

Pauling introduced the concept of electronegativity of an atom which has played an important role in understanding the polarity and ionic character of bonds between atoms. We set out to define a related concept of atomic reactivity in such a way that it can be quantified and used to predict the stability of covalent bonds in molecules. Guided by the early definition of electronegativity by Mulliken in terms of first ionization energies and Pauling in terms of bond energies, we propose corresponding definitions of atomic reactivity. The main goal of clearly distinguishing the inert gas atoms as nonreactive is fulfilled by three different proposed measures of atomic reactivity. The measure likely to be found most useful is based on the bond energies in atomic hydrides, which are related to atomic reactivities by a geometric average. The origin of the atomic reactivity is found in the symmetry of the atomic environment and related conservation laws which are also the origin of the shell structure of atoms and the periodic table. The reactive atoms are characterized by degenerate or nearly degenerate (several states of the same or nearly the same energy) ground states, while the inert atoms have nondegenerate ground states and no near-degeneracies. We show how to extend the use of the Aufbau model of atomic structure to qualitatively describe atomic reactivity in terms of ground state degeneracy. The symmetry and related conservation laws of atomic electron structures produce a strain (energy increase) in the structure, which we estimate by use of the Thomas-Fermi form of DFT implemented approximately with and without the symmetry and conservation constraints. This simplified and approximate analysis indicates that the total strain energy of an atom correlates strongly with the corresponding atomic reactivity measures but antibonding mechanisms prevent full conversion of strain relaxation to bonding.