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The Jahn–Teller effect (JT effect or JTE) is an important mechanism of spontaneous symmetry breaking in molecular and solid-state systems which has far-reaching consequences in different fields, and is responsible for a variety of phenomena in spectroscopy, stereochemistry, crystal chemistry, molecular and solid-state physics, and materials science.
Second-order Jahn-Teller distortion provides a rigorous and first-principles approach to the distortion problem. The interactions between the HOMOs and LUMOs to afford a new set of molecular orbitals is an example of second-order Jahn-Teller distortion.
In their early 1957 paper on what is now called pseudo Jahn–Teller effect (PJTE), Öpik and Pryce [2] showed that a small splitting of the degenerate electronic term does not necessarily remove the instability and distortion of a polyatomic system induced by the Jahn–Teller effect (JTE), provided that the splitting is sufficiently small (the two split states remain "pseudo degenerate ...
A d 1 octahedral metal complex, such as [Ti(H 2 O) 6] 3+, shows a single absorption band in a UV-vis experiment. [7] The term symbol for d 1 is 2 D, which splits into the 2 T 2g and 2 E g states. The t 2g orbital set holds the single electron and has a 2 T 2g state energy of -4Dq.
For example, the d-d transitions for [Cr(NH 3) 5 Cl] 2+ are weak (ε < 100) even though the complex is only of C 4v symmetry. [5] The Laporte rule helps explain the intense colors often observed for the tetrahedral complexes. The tetrahedral point group lacks the inversion operation, so the Laporte rule does not apply. [6]
Complexes such as this are called "low spin". For example, NO 2 − is a strong-field ligand and produces a large Δ. The octahedral ion [Fe(NO 2) 6] 3−, which has 5 d-electrons, would have the octahedral splitting diagram shown at right with all five electrons in the t 2g level. This low spin state therefore does not follow Hund's rule.
the Jahn-Teller effect is a pretty advanced topic in chemistry and a reader would really benefit from some groundwork, octahedral complex would be preferable over octahedral complex. See also the AXE method, most molecular geometries are still missing. V8rik 20:07, 12 July 2005 (UTC)
English: A conceptual comparison of the Jahn-Teller and pseudo Jahn-Teller effects, showing the mutual relation of two potential energy surfaces (PES) in the two cases. . The number of PES is two in this picture but it can be more in actual molecular or solid-state syst