Relativistic effects on chemical properties

Relativistic effects on chemical properties have been reviewed by many authors For the present purpose, these may be briefly summarized on the basis of the review... 

There are several relatively accessible articles on relativistic effects in atoms. L.J. Nor-rby.Why Is Mercury Liquid Journal of Chemical Education, 68,110-113,1991 M.S. Banna, Relativistic Effects at the Freshman Level, Jouraa/ of Chemical Education, 62,197—198,1985 D.R. McKelvey, Relativistic Effects on Chemical Properties, JcMma/ of Chemical Education, 60, 112—116, 1983. For a more technical account, see P. Pyykko, Relativistic Efects in Structural Chemistry, Chemical Reviews, 88, 563-594,1988. 

It has been well known for a long time that relativity becomes increasingly important as one descends to heavier elements in the periodic table. What has been less well known is the magnitude of relativistic effects on chemical properties. Pyykkb states that pseudopotentials have been more widely used than any other computational method to probe relativistic effects. This is not surprising because ECPs are designed to facilitate calculations on heavier elements (i.e., those for which relativistic effects are most apparent). Additionally, the way in which ECPs are derived can be used to shed further light on relativistic effects in chemical bonding. One can choose to have the ECP model the core of an atom or atomic ion as determined by a relativistic or nonrelativistic calculation.A standard HF calculation can be used instead of a relativistic DHF calculation as the basis for ECP derivation hence differences in calculated properties can be ascribed to relativity. 

System of Elements, (b) P. Pyykko, Chem. Rev., 88, 563 (1988). Relativiestic Effects in Structural Chemistry, (c) K. S. Pitzer, Acc. Chem. Res., 12,271 (1979). Relativistic Effects on Chemical Properties, (d) W. Kutzelnigg, Physica Scripta, 36, 416 (1987). The Relativistic Many Body Problem in Molecular Theory. 

Because atomic titanium has low-lying electronic excited states, potential energy surfaces of Ti compounds, especially unsaturated compounds, often cross. When such crossings occur, nonradiative transitions can occur via spin-orbit coupling. In such cases, spin-orbit coupling probabilities must be evaluated. Such calculations usually are performed with MCSCF-based wavefunctions. In addition, relativistic effects can have a significant effect on chemical properties, even for compounds containing elements in the first transition series. Fortunately, new models have been developed to treat relativistic effects for all-electron basis sets... 

A detailed presentation of relativistic effects on magnetic properties is found in Ref. [60], especially for the H-atom in a homogeneous magnetic field in Ref. [61] Application of DPT to first-order magnetic properties were published by Hennum, et al. [62]. An earlier, more intuitive formulation, especially for NMR chemical shifts was given by Nomura et al. [63]. The fully relativistic theory has been studied by Pyykko [64] and Pyper [65]. 

Most of the molecular relativistic calculations were performed for compounds studied experimentally various halides, oxyhalides and oxides of elements 104 through 108 and of their homologs in the chemical groups. The aim of those works was to predict stability, molecular geometry, type of bonding (ionic/covalence effects) and the influence of relativistic effects on those properties. On their basis, predictions of experimental behavior were made (see Section 3). A number of hydrides and fluorides of elements 111 and 112, as well as of simple compounds of the 7p elements up to Z=118 were also considered with the aim to study scalar relativistic and spin-orbit effects for various properties. 

The discovery and identification of element 101 (mendelevium, Md) was a landmark experiment in many ways [ 1 ]. It was the first new transuranium element to be produced and identified on the basis of one-atom-at-a-time chemistry and it is also the heaviest element (to date) to be chemically identified by direct chemical separation of the element itself. All of the higher Z elements have been first identified by physical/nuclear techniques prior to study of their chemical properties. In fact, one of the criteria for chemical studies is that an isotope with known properties be used for positive identification of the element being studied. Due to relativistic effects [1] chemical properties cannot be reliably predicted and a meaningful study of chemical properties cannot be conducted with both unknown chemistry and unknown, non-specific nuclear decay properties ... 

Another notable difference in properties down groups is the inert psiir effect > as demonstrated by the chemical behaviour of Tl, Pb and Bi. The main oxidation states of these elements are + I, + 2 and + 3, respectively, which are lower by two units than those expected from the behaviour of the lighter members of each group. There is a smaller, but similar, effect in the chemistry of In, Sn and Sb. These effects are partially explained by the relativistic effects on the appropriate ionization energies, which make the achievement of the higher oxidation states (the participation of the pair of s-electrons in chemical bonding) relatively more difficult. 

In recent years, relativistic effects on the chemical properties of atoms have received considerable attention. In the theory of relativity, when an electron is traveling with high velocity v, its mass m is related to its rest mass m0 in the following way,... 

One century after the beginning of most dramatic changes in physics and chemistry, after the advent of quantum theory and in the year of the 100th anniversary of Paul A.M. Dirac, modern relativistic atomic and molecular calculations clearly show the very strong influence of direct and indirect relativistic effects not only on electronic configurations but also on chemical properties of the heaviest elements. The actual state of the theoretical chemistry of the heaviest elements is comprehensively covered in Chapter 2. It does not only discuss most recent theoretical developments and results, where especially up to date molecular calculations dramatically increased our insights over the last decade, but it also relates these results to experimental observations. 

Achievements in the area of the theoretical chemistry of the heaviest elements are overviewed. The influence of relativistic effects on properties of the heaviest elements is elucidated. An emphasis is put on the predictive power of theoretical investigations with respect to the outcome of "one-atom-at-a-time" chemical experiments. 

Investigations of chemical properties of the heaviest elements belong to the most fundamental and important areas of chemical science. They seek to probe the uppermost reaches of the Periodic Table of the elements where the nuclei become extremely unstable and relativistic effects on electronic shells are very strong. This makes both theoretical and experimental research in this area extremely exciting and challenging. 

The influence of relativistic effects on the electronic structures and properties of the 6d compounds and on trends in a chemical group was analyzed in detail for MCI5 (M = V, Nb, Ta and Db) [148]. Opposite trends in the relativistic and nonrelativistic energies of the molecular orbitals (MO) from the 5d to the 6d elements were established (Fig. 14), which is explained by the opposite trends in the relativistic versus nonrelativistic energies of the 6d AOs predominantly contributing to those MOs. Thus, the highest occupied MO (HOMO) of 3p(Cl)... 

The current volume presents the compilation of splendid contributions distributed over 21 chapters. The very first chapter contributed by Istvan Hargittai presents the historical account of development of structural chemistry. It also depicts some historical memories of scientists presented in the form of their pictures. This historical description covers a vast period of time. Intruder states pose serious problem in the multireference formulation based on Rayleigh-Schrodinger expansion. Ivan Hubac and Stephen Wilson discuss the ciurent development and future prospects of Many-Body Brillouin-Wigner theories to avoid the problem of intruder states in the next chapter. The third chapter written by Vladimir Ivanov and collaborators reveals the development of multireference state-specific coupled cluster theory. The next chapter from Maria Barysz discusses the development and application of relativistic effects in chemical problems while the fifth chapter contributed by Manthos Papadopoulos and coworkers describes electronic, vibrational and relativistic contributions to the linear and nonlinear optical properties of molecules. 

There are several review articles (Pitzer 1979, Pyykko and Desclaux 1979, Krauss and Stevens 1984, Balasubramanian and Pitzer 1987, Malli 1982a, b, Christiansen etal. 1985, Pyykko 1986, 1988, Balasubramanian 1989a, b, 1990a, b) which deal with the importance of relativistic effects on the chemical and spectroscopic properties of molecules containing very heavy atoms. For a detailed description of these effects and a survey of the literature, the reader is referred to these reviews. However, in this chapter... 

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