Copper Jahn-Teller distortion

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. 

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

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. 

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. 

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... 

Solvation of the divalent copper ion requires some special remarks. In solid state hexa-coordinate Cu2+ shows Jahn-Teller distortion the metal-ligand bonds of four ligands in the equatorial plane are shorter... 

It is well known that crystal and electronic structures are interdependent and define the reactivity of chemical substances. In Section 1.4.2, it was noted that copper-porphyrin complex gives cation-radicals with significant reactivity at the molecular periphery. This reactivity appears to be that of nucleophilic attack on this cation-radical, which belongs to n-type. The literature sources note, however, some differences in the reactivity of individual positions. A frequently observed feature in these n-cation derivatives is the appearance of an alternating bond distance pattern in the inner ring of porphyrin consistent with a localized structure rather than the delocalized structure usually ascribed to cation-radical. A pseudo Jahn-Teller distortion has been named as a possible cause of this alternation, and it was revealed by X-ray diffraction method (Scheidt 2001). 

The Cupric, Cu2+ or Cu(II) State, 3d9 The most important and stable oxidation state for copper is divalent. There is a well-defined aqueous chemistry of the Cu2+ ion, which generates the familiar blue solution when complexed with water. A large number of copper coordination compounds exist and these have been studied extensively. A strong Jahn-Teller distortion is associated with the 3d9 electronic configuration of this ion. This implies that a regular tetrahedron or octahedron about the Cu2+ ion is never observed, except in the rare occurrence of a dynamic Jahn-Teller effect. The tetragonal distortion about an octahedron can lead to a square-planar coordination which is often observed in Cu(II) oxides. 

The particular values and power dependence for the d-s mixing term are also not too critical although a certain threshold must be achieved. Tetragonally elongated Jahn-Teller distortions of d9 CuNe species (36) and the trigonal geometry of the oxidized copper center in Type 1 metalloproteins (37) can be achieved with an inverse sixth order power dependence and an associated a6 parameter of at least 300,000 kcal mol-1 A6. However, since eds also depends on symmetry—e.g., it makes no contribution for octahedral complexes—there are many systems where d-s mixing has a minimal effect. 

There is agreement over the gross structural features of these linear chain chromium(II) complexes (and the isomorphous copper(II) analogues), but different models have been used for structural refinement. Phase transitions associated with the Jahn-Teller distortion (or to fi to y as the temperature is lowered) complicate the structural studies. 

Jahn-Teller distortions cobalt and copper complexes, 91 hydrates, 308... 

Copper(II) has a 3d9 electronic configuration. In principle, pure octahedral and tetrahedral symmetries can never be observed because Jahn-Teller distortions (see Section 3.3.1) remove the orbital degeneracy of the ground state. The separation of the electronic energy levels depends on the coordination number and stereochemistry, as well as on the nature of the ligands. However, the ground state orbital is always well isolated from the excited states, and therefore the electronic relaxation mechanisms are relatively inefficient. Copperfll) complexes have thus relatively sharp EPR signals, and it is often possible to record these spectra at room temperature. 

An important condition for chiral matrices is that they need to form labile interactions with the substrate in order to facilitate both the recovery of the enantioselec-tively coordinated ligand and the recycling of the chiral matrix. Usually copper(II) complexes have been used[48]. Due to the problems involved in the modeling of Jahn-Teller distorted copper(II) complexes (see Chapter 11 for a detailed discussion on... 

A general approach for predicting Jahn-Teller distortions of copper(II) hexa-amines has recently been published, and it has the potential to be applied to donor atoms other than nitrogen, metal centers other than copper(II), and various types of coordination polyhedra11641. The method is based on a harmonic first-order model11651 where the Jahn-Teller stabilization energy is the result of the Qg distortion mode (Fig. 11.1, Eqs. 11.3, 11.4). 

Di- and tetranuclear Cu(II) complexes were obtained on reaction of 3 with two and four equivalents of Cu(II), respectively. The former complex has a similar structure to the dinuclear nickel complex mentioned above, although the presence of Jahn-Teller distortion is also evident in the copper complex. 

Transition metal difluorides are known mainly for first transition series elements, with palladium and silver difluorides from the second series, and no examples from the third. All these compounds have either the rutile structure, or, for chromium, copper, and silver, a distorted variant, which can be correlated with a Jahn-Teller distortion of the octahedral coordination of the ions. This rutile structure type is associated with smaller cations and, for comparison, although zinc difluoride has the same rutile structure, cadmium and mercury difluorides have the cubic fluorite structure with eight coordination of the cations (12). 

It has been suggested that the Jahn-Teller distortion is more marked in the silver than in the copper compound, and that this may... 

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