Jahn-Teller-distortion

Although the application of elementary ligand field theory is adequate to explain many properties of complexes, there are other factors that come into play in some cases. One of those cases involves complexes that have structures that are distorted from regular symmetry. Complexes of copper(II) are among the most common ones that exhibit such a distortion. 

One experimental verification of this phenomenon comes in the form of bond lengths. In CuCl2, the Cu2+ is surrounded by six Cl- ions, and the equatorial Cu-Cl bonds are 230 pm in length, whereas 

Energy of the d orbitals of a d9 ion in a field with z elongation produced by Jahn-Teller distortion. 

Population of d orbitals for a d9 complex with octahedral or distorted octahedral structure. 

Because of Jahn-Teller distortion, it is normally expected that octahedral complexes of Cu2+ will exhibit distortion. However, this is not the only case of this type. Note that a d4 high-spin complex would have one electron in each of the four orbitals of lowest energy. That means that the orbitals obtained by splitting the upper states would be unequally populated because there is only one electron to be placed in the dz2 orbital. Therefore, splitting the orbitals by distorting the octahedral structure would also lead to an overall reduction in energy in this case. 

It is important to remember that the splitting of the t2g orbitals also occurs, but the splitting is smaller than that of the eg orbitals. Although it might be expected that complexes of dl and d2 ions would undergo Jahn-Teller distortion, such distortion would be extremely small. In fact, there are some other problems in studying this type of distortion because of the short lifetimes of excited states and rearrangement of the complexes. 

This chapter has presented an overview of several important aspects of the chemistry of coordination compounds. In addition to the elementary ideas related to bonding presented here, there is an extensive application of molecular orbital concepts to coordination chemistry. However, most aspects of the chemistry of coordination compounds treated in this book do not require this approach, so it is left to more advanced texts. The references at the end of this chapter should be consulted for more details on bonding in complexes. 

Bailar, J. C. (Ed.). (1956). The Chemistry of Coordination Compounds. New York Reinhold Publishing Co. The book contains 23 chapters written by the late Professor Bailar and his former students. A classic work. Cotton, F. A., Wilkinson, G., Murillo, C. A., Bochmann, M. F. (1999). Advanced Inorganic Chemistry (6th ed.). New York John Wiley. Several chapters in this monumental book give excellent, detailed treatment of topics in coordination chemistry. This book is a standard first choice. 

The orbital energy diagram in Fig. 12.1 may be used to investigate what would happen if we add another electron to the ion to form the neutral H3 molecule. The electron might enter either of the two antibonding MOs or 1 3. As long as the molecule remains trigonal, 

Imagine that the electron is added to 1 2. This would lead to antibonding, that is to repulsion between hydrogen atoms 1 and 2, and we would expect the H(l)-H(2) bond distance to increase. An increase of this distance would in turn reduce the antibonding interactions and the I 2 orbital energy would fall. 

If we add the electron to I i we get bonding between H(l) and H(2), but antibonding between both these atoms and H(3). As a consequence we would expect the bond distance H(l)-H(2) to decrease and the distances H(l)-H(3) and H(2)-H(3) to increase. These distortions would in turn increase the bonding and decrease the antibonding interactions, and the 3 orbital energy would fall. The eonclusion is that it does not matter to which of 

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Copper(II) salts (blue in aqueous solution) are typical M(II) salts but generally have a distorted co-ordination (Jahn-Teller distortion, 4 near plus 2 far neighbours). Extensive ranges of complexes are known, particularly with /V-ligands. 

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. 

The electronic spectrum of the radical has been recorded long before a satisfactory theoretical explanation could be provided. It was realized early on that the system should be Jahn-Teller distorted from the perfect pentagon symmetry (D5/, point group). Recently, an extensive experimental study of the high-resolution UV spectrum was reported [76], and analyzed using Jahn-Teller formalism [73],... 

It was shown by several workers that in this case the first-order Jahn-Teller distortion is due to an ej vibration, and that the second-order distortion vanishes. Therefore, in terms of simple Jahn-Teller theoi, the moat around the symmetric point should be a Mexican hat type, without secondary minima. This expectation was borne out by high-level quantum chemical calculations, which showed that the energy difference between the two expected C2v structures ( A2 and Bi) were indeed very small [73]. 

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

Ab initio molecular orbital calculations for the model systems RCN3S2 (R = H, NH2) show that these dithiatriazines are predicted to be ground state singlets with low-lying triplet excited states (Section 4.4). The singlet state is stabilized by a Jahn-Teller distortion from C2v to Cj symmetry. In this context the observed dimerization of these antiaromatic (eight r-electron) systems is readily understood. 

If Li[Mn2]04 is heated above -780 °C, oxygen-deficient spinels LiMn204 (S <0.14) are produced [132, 144, 145]. The loss of oxygen lowers the manganese oxidation state below 3.5 and triggers a mild Jahn-Teller distortion the da ratio in the tetragonal LiMn204 (7 phase varies between 1.02 and 1.07. 

Jahn-Teller distortions 309 ff Japanese separators 264, 267 Joule effect, heat losses 13 jump frequency, solid electrolytes 532 Jungner nickel cadmium batteries 22... 

Complexes of the divalent metals [M(ttcn)2]2+ undergo electrochemical oxidation to paramagnetic [M(ttcn)2]3+. Red [Pd(ttcn)2]3+ has a tetragonally distorted octahedral structure (d7, Jahn-Teller distortion) with Pd—S 2.356-2.369 A (equatorial) and 2.545 A (axial) in keeping with the ESR spectrum (gj = 2.049, gy = 2.009) which also displays 105Pd hfs. Similarly, electrochemical oxidation of the palladium(II) tacn complex (at a rather lower... 

Stable compounds of silver(II) are found with N, O and F as donor atoms macrocycles are, as elsewhere, able to support the higher oxidation state. As a d9 system, Ag2+ imitates Cu2+ in displaying Jahn-Teller distortion. 

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

The driving force for Jahn-Teller distortions in transition-metal complexes is the open d shell. It is likely that explanations for them along the lines given above would have come about even if the theorem of Jahn and Teller had not been discovered. We make this remark not to denigrate that powerful piece of work, but as an attempt to defuse any mystery that might otherwise attach to OrgeTs application of that group-theoretical construction. 

The data for the 1,2-diaminoethane complexes now parallels the trends in ionic radius and LFSE rather closely, except for the iron case, to which we return shortly. What is happening Copper(ii) ions possess a configuration, and you will recall that we expect such a configuration to exhibit a Jahn-Teller distortion - the six metal-ligand bonds in octahedral copper(ii) complexes are not all of equal strength. The typical pattern of Jahn-Teller distortions observed in copper(ii) complexes involves the formation of four short and two long metal-ligand bonds. 

V(CO)e generated by cocondensing presynthesized V(CO)6 with N2 at 10 K has been observed (44, 45). As suggested in a metal-atom study (125), the results indicated that a static, Jahn-Teller distortion is present. Matrix MCD also proved useful in confirming the predicted paramagnetism of Fe(CO)4 (45) (produced by photolysis of Fe(CO)5). In addition, matrix MCD was used to detect such paramagnetic species as MnOaCU in the presence of MnOsCl (45). 

The brass-colored PdTel consists of Jahn-Teller distorted PdTe2/2l4/4 octahedra, which are interconnected by common edges and corners to afford a loose, spatial network. The compound is considered to be ionic, containing Pd and Te , although the observed diamagnetism, electronic conduction, and color suggest some metallic character. 

In the present study, we focus on the effects of substituting one of the protons by a deuteron. While giving only one isomer of the unionized molecule, this produces two inequivalent isomers of the Jahn-Teller distorted ion one isomer where the deuteron occupies one of the two sites on the C2 symmetry axes (Hj or H4) and one where it occupies one of the four equivalent remaining sites (H2, H3, H5 or H6). The effects on the ESR spectrum will below be illuminated both theoretically and experimentally. 

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