Jahn-Teller effect distortion

The co-ordination number in ionic compounds is determined by the radius ratio - a measure of the necessity to minimize cationic contacts. More subtle effects are the Jahn-Teller effect (distortions due to incomplete occupancy of degenerate orbitals) and metal-metal bonding. 

As we have seen in Sect. 2. the molecular Jahn-Teller effect distorts the molecule into either or Ds symmetry. It is not impossible to place such distorted anions in a lattice so that the overall symmetry remains tetragonal, but the main axis of these distortions cannot coincide with the principal crystallographic axis of the A4C60 crystals. In line with the suggestions by Fabrizio and Tosatti [16], the main distortion axis of the molecule could be disordered or ordered in some way, but the average structure has to be that found by diffraction. 

The stoi7 begins with studies of the molecular Jahn-Teller effect in the late 1950s [1-3]. The Jahn-Teller theorems themselves [4,5] are 20 years older and static Jahn-Teller distortions of elecbonically degenerate species were well known and understood. Geomebic phase is, however, a dynamic phenomenon, associated with nuclear motions in the vicinity of a so-called conical intersection between potential energy surfaces. 

Non-adiabatic coupling is also termed vibronic coupling as the resulting breakdown of the adiabatic picture is due to coupling between the nuclear and electi onic motion. A well-known special case of vibronic coupling is the Jahn-Teller effect [14,164-168], in which a symmetrical molecule in a doubly degenerate electronic state will spontaneously distort so as to break the symmetry and remove the degeneracy. 

Vibrational stmcture is, at best, only partially resolved. The stmcture in the first and second systems is complex which could be due, in part, to there being a Jahn-Teller effect in each of them. Such an effect may arise when a molecule is in an orbitally degenerate E (or T) state. The Jahn-Teller effect involves a distortion of the molecule in order to destroy the... 

J-aggregation Jahn-Teller distortion Jahn-Teller effect J ai Osh Jalaric acid Jameson cell Jams... 

The complex ion (Figure 2.32) contains Rh2 bound cis to two phosphorus atoms (2.216 A) and more distantly to four oxygens (2.201—2.398 A), exhibiting a distortion ascribed to the Jahn-Teller effect it is paramagnetic (fi = 1.80 fiB) and exhibits an ESR spectrum (Figure 2.33) showing rhodium hyperfine coupling as the doublet for g. ... 

Jahn-Teller distortions cobalt and copper complexes, 2, 91 hydrates, 2, 308 Jahn-Teller effect, 5, 535 Jahn-Teller theorem, 1, 247 Jarosites... 

A minor success is also seen in complexes of d and d" ions, in which the distorted octahedral geometries observed may be rationalized (and indeed predicted) in terms of the Jahn-Teller effect, and ultimately in terms of the steric activity of the open d shell. This is a common feature in copper(n) chemistry, and you will... 

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). 

The high lability of cP [Cu(H20)6]2+ is coincident with the operation of a dynamic Jahn-Teller effect which causes its tetragonal distortion to randomly reorientate, or invert, about the x, y, and z axes very rapidly (Fig. 8) so that the lifetime of a given distortion, r, is much less than the lifetime of a given coordinated H20 molecule, THa0 (99,... 

In Fig. 9.4 the additional stabilization by the Jahn-Teller effect has not been taken into account. Its inclusion brings the point for the (distorted) octahedral coordination for Cu2+ further down, thus rendering this arrangement more favorable. 

Distortions due to the Jahn-Teller effect. For example CdBr2 (Cdl2 type) —t CuBr2 (distorted Cdl2 type). 

In the limit of strong vibronic coupling, F4S = 0, c = 5 /3, s=, c2 - s2 =, and the dynamic Jahn-Teller effect thus renders nugatory the orbital contributions to the angular momentum, and reduces the splitting, A, by a factor of two. Note in addition that the c and s quantities used in the vibronic treatment do not correspond to those of the adiabatic case, although the expressions are formally similar, so that the static distortion, A, cannot accurately be calculated from the c and s values deduced from the and 4 data. 

---