Energy lanthanide contraction

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). 

Mono- and bimetallic lanthanide complexes of the tren-based macrobicyclic Schiff base ligand [L58]3- have been synthesized and structurally characterized (Fig. 15), and their photophysical properties studied (90,91). The bimetallic cryptates only form with the lanthanides from gadolinium to lutetium due to the lanthanide contraction. The triplet energy of the ligand (ca. 16,500 cm-1) is too low to populate the terbium excited state. The aqueous lifetime of the emission from the europium complex is less than 0.5 ms, due in part to the coordination of a solvent molecule in solution. A recent development is the study of d-f heterobimetallic complexes of this ligand (92) the Zn-Ln complexes show improved photophysical properties over the homobinuclear and mononuclear complexes, although only data in acetonitrile have been reported to date. 

Owing to lanthanide contraction, niobium and tantalum have virtually identical atomic rad (1.47 A) and close ionization energies (Nb6.67, Ta7.3eV), and usually display very similt chemical behavior. Some definite differences can however be noted these can usually be trace to the lower sensitivity of tantalum to reduction and to its higher affinity for dioxygen. lb tantalum-element multiple bonds are usually stabler, while MfiXg arrangements are so ft known only for niobium. 

The relativistic effect goes approximately as Z2, and this is the reason for its importance in the heavier elements. In terms of energy and size, it starts to become important in the vicinity of Z = 60-70. contributing perhaps an additional 10% to the nonrelativistic lanthanide contraction (see Chapter I4).39 As we have seen, this results in an almost exact cancellation of the expected increase in size with increase in n from zirconium to hafnium. 

As we traverse the series, the lattice energies of LnX2 and LnX3 increase steadily in magnitude, a consequence of the lanthanide contraction since UL is always a little more than twice as great for LnX3 as for LnX2 (as... 

The second chapter deals with quantum chemical considerations, s, p, d and f orbitals, electronic configurations, Pauli s principle, spin-orbit coupling and levels, energy level diagrams, Hund s mles, Racah parameters, oxidation states, HSAB principle, coordination number, lanthanide contraction, interconfiguration fluctuations. This is followed by a chapter dealing with methods of determination of stability constants, stability constants of complexes, thermodynamic consideration, double-double effect, inclined w plot, applications of stability constant data. 

Effective nuclear charge Ionization energy Electronegativity Ionic radius Oxidation state Lanthanide contraction... 

It has been realized in recent years that the lanthanide contraction is only part of the explanation for the behavior of the heavier elements. An equally important factor is relativity. On a fundamental level, relativity actually plays an integral role in quantum theory, beginning with the space-time and momentum-energy symmetric which suggested the form of the time-dependent Schrixlinger equation [cf. Sei tion 2.3]. Electron spin and the Pauli exclusion principle are, in fact, implication ... 

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