Transition metal complexes Jahn-Teller effect

Stable Mn(HI) compounds, Mn(R2r fc)3, have been known for a long time (42, 46). The structure of Mn(Et2C tc)3 is elucidated (47). The inner geometry of the Mn(CS2)3 core does not conform to the usual D3 point symmetry of transition metal complexes of this type, but shows a strong distortion attributed to the Jahn-Teller effect. The electronic spectrum (48, 49) and the magnetic properties of this type of complexes are well studied (50). 

In geochemistry, the Jahn-Teller effect is relevant for metals Fe and in octahedral complexes and for Cr + and Ni in tetrahedral complexes. Other transition ions (e.g., Cr and Co ) require unusual oxidation or low-spin conditions that can be reached only under extreme pressure. 

Jahn, H. A. Teller, E. Proc. Roy. Soc. bond. A 1937, 161, 220-235. Mckinlay, R. G. Paterson, M. J. The Jahn-Teller Effect in Binary Transition Metal Carbonyl Complexes. In The Jahn-Teller Effect Fundametals and Implications for Physics and Chemistry , Eds. Koppel, H. Yarkony,... 

Two additional factors that can contribute to line breadth and shape are spin-orbil coupling, which is particularly prevalent in complexes of the heavier transition metals, and departures from cubic symmetry, such as through the Jahn-Teller effect. This latter effect, which will be discussed later in this chapter, is believed to be responsible for the low-frequency shoulder observed on the absorption line for [TKH30)6)2 (Fig. 11.8). 

An example of the conflict between stabilization from the Jahn-Teller effect and chelate geometrical requirements is found in the ethylenediamme complexes of Cu2+. Most divalent transition metal ions form complexes with elhylencdiaminc (en) by stepwise replacement of water ... 

There remains the possibility of g-values which depart substantially from 2.00 but are isotropic because of cubic symmetry. In practice such conditions are rare for transition metal complexes, as the Jahn-Teller theorem ensures departure from cubic symmetry in the electronic structure. However, for the lanthanoid and actinoid elements, where the spin—orbit coupling constant is very much larger than kT, the Jahn—Teller theorem may not be relevant and effective cubic symmetry certain. For the lanthanoids, g-values often depart considerably from 2.00, although some anisotropy arising from ligand field splittings is common. For the actinoids, direct observation of ESR is less common but there is evidence of a similar situation. 

Metals that form relatively stable aqua ions in solntion have generally been well characterized. The hydration nnmbers of the transition metals, for example, have commonly been found to be six, consistent with the results of solid-state studies of crystalline hydrates. Exceptions inclnde Ag+, which has a hydration number of four, and Cn +, which has been found to have four short M-0 interactions and two longer ones, consistent with a Jahn-Teller distortion (see Jahn - Teller Effect) of the complex. The hydration numbers of the lanthanide ions in solution have been the subject of many investigations and some controversy recent resnlts snggest a decrease from nine to eight across the series from Ta + to... 

The Jahn-Teller effect and its implications for the structures of transition metal complexes... 

The first attempt to clarify the physical basis of the Jahn-Teller theorem was due to Ruch, [3] in an introductory presentation to the 1957 annual meeting of the Bunsen-Gesellschaft in Kiel, which was organised by H. Hartmann. Ruch discussed the general connection between symmetry and chemical bonding, and also touched upon the Jahn-Teller effect in transition-metal complexes. He explained that degeneracy can always be related to the existence of a higher than twofold rotational axis and a wave function which is not totally symmetric under a rotation around this axis. Provided that the wave function is real the electron densities for such a wave function are bound to be anisotropic. The combination of an anisotropic distribution of the electron cloud and a symmetric nuclear frame leads to electrostatic distortion forces where the nuclear frame adapts itself to the anisotropic attraction force. 

The Jahn-Teller Effect in Binary Transition Metal Carbonyl Complexes... 

Binary transition metal complexes have been the subject of a wide range of studies regarding their structure and spectroscopy for many years beginning with Mond et al. [4] who first reported Ni(CO)4 whilst investigating the Action of Carbon Monoxide on Nickel in 1890. A wide range of spectroscopic methods and techniques has subsequently been utilised, including X-ray and electron diffraction, IR, and UV/Vis spectroscopy. In almost all cases the Jahn-Teller effect has been invoked to explain certain spectroscopic features. Due to a wide breadth of smd-ies reported in the literature, this review will not be comprehensive. Instead it is... 

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