Jahn-Teller octahedral distortion

Jahn-Teller Octahedral Distortion KCuF as an Example... 

In our analysis of the model Co(III) systems we shall assume strong octahedral parentage for the electronic states and for the C0L.6 vibrational modes. We shall further assume that the ground electronic state Ai(Aig) remains unaffected by vibronic interactions. Given these assumptions, the principal influences of the Q2(eg) and Q5(t2g) vibrational modes are to (1) cause Jahn-Teller (JT) and pseudo Jahn-Teller (PJT) distortions within the Tig, T2g, and Tiu excited states, and (2) induce mixing between the Tjg and T2g excited states. These effects will be manifested in the intensity distributions within the Ajg->-Ti and Aig->-T2g d d transitions, but they will not significantly alter the net (or total)... 

The 1-V step in the voltage profile of LF[Mn2]04 limits the capacity of this spinel to one LF per two Mn atoms at either 3.0 V or 4.0 V versus Lithium. The flat 3.0 V plateau reflects a cubic to tetragonal transition of the [Mn2]04 framework due to a cooperative Jahn-Teller site distortion where more than half of the 16 sites are occupied by Mn(III) ions. Octahedral-site, high-spin Mn(III) ions have a localized spin 5 = 2 with one electron occupying an orbitally twofold-degenerate pair of... 

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... 

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. 

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... 

Not even the slightest Jahn-Teller distortion and therefore no deviation from the ideal octahedral symmetry are to be expected when the t2g and eg orbitals are occupied evenly. This applies to the following electronic configurations ... 

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. 

The series of 3d elements from scandium to iron as well as nickel preferably form octahedral complexes in the oxidation states I, II, III, and IV. Octahedra and tetrahe-dra are known for cobalt, and tetrahedra for zinc and copper . Copper(II) (d9) forms Jahn-Teller distorted octahedra and tetrahedra. With higher oxidation states (= smaller ionic radii) and larger ligands the tendency to form tetrahedra increases. For vanadium(V), chromium(VI) and manganese(VII) almost only tetrahedral coordination is known (VF5 is an exception). Nickel(II) low-spin complexes (d8) can be either octahedral or square. 

State which of the following octahedral high-spin complexes should be Jahn-Teller distorted. 

KT1 does not have the NaTl structure because the K+ ions are too large to fit into the interstices of the diamond-like Tl- framework. It is a cluster compound K6T16 with distorted octahedral Tig- ions. A Tig- ion could be formulated as an electron precise octahedral cluster, with 24 skeleton electrons and four 2c2e bonds per octahedron vertex. The thallium atoms then would have no lone electron pairs, the outside of the octahedron would have nearly no valence electron density, and there would be no reason for the distortion of the octahedron. Taken as a closo cluster with one lone electron pair per T1 atom, it should have two more electrons. If we assume bonding as in the B6Hg- ion (Fig. 13.11), but occupy the t2g orbitals with only four instead of six electrons, we can understand the observed compression of the octahedra as a Jahn-Teller distortion. Clusters of this kind, that have less electrons than expected according to the Wade rules, are known with gallium, indium and thallium. They are called hypoelectronic clusters their skeleton electron numbers often are 2n or 2n — 4. 

The versatile binding modes of the Cu2+ ion with coordination number from four to six due to Jahn-Teller distortion is one of the important reasons for the diverse structures of the Cu-Ln amino acid complexes. In contrast, other transition metal ions prefer the octahedral mode. For the divalent ions Co2+, Ni2+, and Zn2+, only two distinct structures were observed one is a heptanuclear octahedral [LnM6] cluster compound, and the other is also heptanuclear but with a trigonal-prismatic structure. 

Would Jahn-Teller distortion be as significant for tetrahedral complexes as it is for octahedral complexes For which of the electron configurations would Jahn-Teller distortion occur ... 

Trans- complex is obtained only with Cu11 which is coordinated to four oxygen atoms of two hfac ions and two nitrogen atoms of two TTF—CH=CH py ligands. Cu11 lies on inversion center and therefore the TTF—CH=CH py ligands are in trans- conformation. The copper ion adopts a Jahn-Teller distorted octahedral... 

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