Mercury relativistic effects

Relativistic effects are cited for changes in energy levels, resulting in the yellow color of gold and the fact that mercury is a liquid. Relativistic effects are also cited as being responsible for about 10% of lanthanide contraction. Many more specific examples of relativistic effects are reviewed by Pyykko (1988). 

The growing importance of quantum-chemical calculations is dealt with in a short section, with emphasis on the consideration of relativistic effects, especially in systems containing mercury. These calculations aim at optimization of structures, determination of bond energies, simulation of spectra, and estimation of spectral parameters, independent of but complementary to experiments. 

Apart from the gold(i) system, bis(mesityl)mercury(ii), which also possesses a heavy metal center with strong relativistic effects, has been used for the synthesis of the mixed metal silver(i) aryl complexes, [HgAg2(mes)X2]2 (X = OTf 13a (Figure 7), C104 13b).33 X-ray crystal structure analysis of 13a revealed its hexanuclear nature with the... 

The colour of gold adds to the attractiveness of the metal, and the liquid state of mercury allows the metal to be used over a wide range of temperatures in thermometers and electrical contact switches. These unusual properties are explicable in terms of relativistic effects. The relativistic effects on the 6s orbital are at a maximum in gold and are considerable in mercury. 

Relativistic effects increase the building energies of the electrons and so they contribute to the irregularities in group trends and make appreciable contribution to high I.E. and hence chemical inertness of some heavy element (e.g. Gold and mercury). 

However, deviations from straightforward extrapolations within the Periodic Table were also considered [19]. As a consequence of relativistic effects on the electronic structure, the, v- andp-orbitals of heavy elements should shrink whereas higher lying orbitals should expand. Consequently, the two, v electrons in element 112 and also the two pm electrons in element 114 could form closed electron shells, and eka-mercury and eka-lead could both be chemically inert gases like element 118, eka-radon. 

It has been proposed that the contraction of the electron orbitals in mercury due to Relativistic Effects are important contributors to the element s unusual physical, chemical, and spectroscopic properties. " Some of these properties include the so-called Inert Pair Effect, the difficulty of oxidation of the metal, its unusually low-melting point and electrical conductivity, and the low Enthalpy of vaporization, which at 59.1kJmor is about one-half those of cadmium (100 kJ mol" ) and zinc (114 kJ mol" ). Both NMR shieldings... 

Thus it is the unusually low energy of the 6s orbitals apparently caused by relativistic effects that causes gold to behave like a halogen atom and mercury to behave like a noble gas. ... 

Apart from primary structural and energetic data, which can be extracted directly from four-component calculations, molecular properties, which connect measured and calculated quantities, are sought and obtained from response theory. In a pilot study, Visscher et al. (1997) used the four-component random-phase approximation for the calculation of frequency-dependent dipole polarizabilities for water, tin tetrahydride and the mercury atom. They demonstrated that for the mercury atom the frequency-dependent polarizability (in contrast with the static polarizability) cannot be well described by methods which treat relativistic effects as a perturbation. Thus, the varia-tionally stable one-component Douglas-Kroll-Hess method (Hess 1986) works better than perturbation theory, but differences to the four-component approach appear close to spin-forbidden transitions, where spin-orbit coupling, which the four-component approach implicitly takes care of, becomes important. Obviously, the random-phase approximation suffers from the lack of higher-order electron correlation. 

The mercury atom is frequently chosen as a test system for relativistic methods because it has a simple closed-shell electronic structure (5d 6s ) and exhibits strong relativistic effects. In Table 3.1, we compare results obtained with two variants of the two-component second-order DKH approach [18,19] to results of a four-component DKS method [53]. All calculations presented were obtained with the LDA-VWN functional [130]. 

Another interesting subject is the equilibrium structure of mercury (rhom-bohedral) that deviates from the structure of the other group IIB elements (hep). This peculiarity also has been found to originate from (scalar) relativistic effects [45]. 

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